06.04.2017

Oncological diseases are common in our time; rejuvenation of pathology poses a priority treatment task for scientists.

Radiation therapy occupies a very important place in oncology and, despite numerous side effects, can bring great benefits to the patient and give a chance for success in defeating cancer.

Concept of radiation therapy

Radiation therapy for malignant tumors is a method of treatment using ionizing radiation. The point of this technique is the destructive effect of radioactive waves on the tumor, and accurate calculations of the dose, exposure distance and duration make it possible to ensure minimal radiation damage to surrounding organs and tissues.

The variety of forms of this method is so great that a separate medical specialty– radiation therapist, radiologist who deals exclusively with this area of ​​treatment. Any oncology clinic or other specialized in cancer diseases medical institution must have such a specialist.

Depending on the type of waves that are used, those used in medical practice, types of radiation:

• X-ray;
• α, β, γ;
• neutron;
• proton;
• π-meson.

Each of them has its own characteristics, its pros and cons, and is used for treatment in various cases.

Thus, X-rays can be used for the treatment of deep-lying tumors, α and β particles work well in contact irradiation methods, γ rays have significant energy and a long range in tissues, which gives an advantage when using this type of particles as a radiosurgical method (gamma knife).

The neutron flux is capable of imparting radioactive properties to any tissue (induced radioactivity), which can have an effect as a palliative treatment for advanced metastatic tumors.

Proton and π-meson radiation are among the most modern achievements of radiosurgery; their help can be used in neurosurgery and ophthalmology, due to its minimal damaging effect on the tissue surrounding the tumor.

Radiation for oncology makes sense various stages diseases, depending on the course of the disease and the patient’s condition, radiation treatment of cancer is carried out in various combinations with chemotherapy and surgical treatment, which are determined in advance by a whole council of doctors individually for each patient.

Indications and contraindications

On at the moment More than 50% of all cancer patients undergo radiation therapy. This technique is successfully used in the treatment of cancer of the cervix, brain, lungs, pancreas, stomach, prostate, skin, mammary glands and other organs.

It can be shown as initial stage therapy (before surgery, to reduce the tumor in volume), and after surgery to reduce the risk of metastasis and remove remnants of the affected tissue; chemoradiation treatment is more often used in case of unresectable tumor.

Contraindications for this type of treatment may include:

• blood changes in the form of lympho-, thrombocyto-, leukopenia or anemia;
• cachexia, an extremely serious condition of the patient;
• acute inflammatory processes accompanied by severe fever;
• severe cardiovascular, renal or respiratory failure;
• severe diseases of the central nervous system;
• skin damage in the area of ​​intended irradiation;

A history of tuberculosis and the presence of a focus of chronic infection in the tumor area can be considered a relative contraindication.

The final decision on the need to use radiation in a particular case can be made only on the basis of an assessment and comparison of all probable outcomes when using other methods, as well as natural course oncological process.

The balance of harm and benefit must always be assessed for each patient individually; no treatment should aggravate his condition.

Method of radiation treatment

Radiation therapy in oncology justifies some of its consequences by its high level of effectiveness. Such a destructive local effect on the tumor is possible only with its use and cannot be replaced by chemotherapy.

Radiotherapy is carried out using special devices or radioactive substances in various forms.

Depending on the method of directing the rays to the body, distant, contact and radionuclide radiotherapy are distinguished. Remote therapy involves positioning the patient at some distance from the radiation source, while the device can either be static or move in relation to the patient.

At contact method radiopharmaceuticals are applied using ointments, radiation sources are introduced into cavities and tissues, applied to the skin, and radionulide therapy involves the administration of a radiopharmaceutical intravenously. With this method of treatment, the patient must be isolated from other people for some time, since he himself becomes a source of radiation.

To take the course radiation therapy several stages must be completed: establishing accurate diagnosis and localization of the process, then at the consultation the role of radiotherapy in a particular case will be discussed and the radiologist will calculate the required dose and the number of sessions, and in the end it will be possible to begin the irradiation itself.

The classic course lasts from 6 to 8 weeks, during which the patient undergoes about 30-40 sessions. In some cases, hospitalization in a hospital is necessary for the duration of therapy, but most often it is well tolerated and is possible as a day hospital.

Side effects

The degree of severity and their localization depend on the stage of the disease and the location of the pathological focus. Radiation therapy for head and neck cancer can be complicated by side effects such as dizziness, a feeling of heaviness in the head, hair loss and hearing loss.

Irradiation of areas gastrointestinal tract provokes vomiting, nausea, loss of appetite, perversion of smell, weight loss. The skin may develop dermatitis, redness, pain, itching and peeling of the irradiated areas - a fairly common effect.

Almost everyone, regardless of the volume of the tumor and radiation exposure, notes weakness of varying intensity during the course of this type of treatment; this symptom can be associated both with intoxication due to the disintegration of the tumor, and with changes in the psycho-emotional state against the background of the constant need to attend radiotherapy sessions , be exposed various studies, procedures.

A feeling of fear of illness, death, or the treatment process can provoke psychosomatic disorders, which can often only be overcome with the support of relatives, friends or psychotherapists.

Recovery of the body after radiation therapy

In order to restore the body's energy and functional reserves, as well as reduce intoxication, throughout the course of radiotherapy it is necessary to adhere to certain recommendations that will not only increase the chances of recovery, but also significantly reduce the risk of side effects.

Rest is very important to replenish your strength. Such rest should not consist of endlessly reclining on the sofa in front of the TV, but involves adjusting your sleep-wake schedule, creating a complete daily routine with the obligatory inclusion of your favorite activities in this plan, as a way to receive positive emotions and a distraction.

A large period of time should be determined by hygiene procedures, which should be performed more often than usual to reduce the risk of infectious complications due to immunosuppression. Moderate physical activity also help the patient recover and has a beneficial effect on the cardiovascular, nervous and digestive systems.

In the event that general condition does not allow gymnastics, jogging or other physical exercises, walks become a mandatory component of the daily routine.

Nutrition can also significantly influence the course of the disease and the tolerability of radiotherapy. To eliminate or reduce discomfort from the gastrointestinal tract, recommended balanced diet, which should exclude alcohol, fatty foods and foods fried in large quantities of oil, and foods with strong odors.

You should not strictly adhere to diets; you can always find a place for dishes that the patient likes; the main condition is to eat at least something. Foods high in fiber, vitamins and microelements will have a beneficial effect on the body. The basic rule should be the principle fractional meals, in small portions, but often.

Restoration of water-electrolyte balance, excretion toxic substances breakdown and metabolites medicines can only occur with sufficient water intake. In addition to liquid food, tea and juices, you should drink more than one and a half liters if possible. clean water per day.

The glass of water at bedside should be filled. If you feel nauseous, you should not try to drink a lot of liquid at once, this can provoke vomiting; it is better to gradually, over the course of several hours, take one or several sips of water.

Giving up bad habits should not frighten the patient; this is no less necessary than the entire course of therapy, since smoking and drinking alcohol have a negative effect on the vascular and nervous systems and contributes to increased intoxication, which will already weaken health.

If any unpleasant sensations occur during or after irradiation, you should inform your attending physician, who will, together with the radiologist, adjust the treatment regimen.

If necessary, supplement drug treatment symptomatic means, such as antiemetics, painkillers, ointments, immunostimulants and others.

Oncology and radiation therapy are inseparable. This type of treatment allows you to achieve the desired result in the treatment of malignant tumors, and following doctors’ orders and being aware of the possible consequences helps to minimize its possible negative consequences and speed up recovery.

Cancer is the most unpleasant prognosis that a doctor can offer. There is still no medicine that guarantees a cure for this disease. The insidiousness of cancer is that it affects almost all known organs. In addition, cancer can spread its “tentacles” even into the body of domestic animals. Is there a way to fight this enemy? Radiation therapy in oncology is considered one of the most effective methods. But the point is that many refuse this prospect.

Let's go through the basics

What do we know about cancer? This disease is almost incurable. Moreover, the incidence is growing every year. The French are most often affected by the disease, which is explained by the aging population, since the disease often affects older people.

In essence, cancer is a disease of cells, during which they begin to continuously divide, forming new pathologies. By the way, cancer cells do not die, but simply transform into a new stage. This is the most dangerous moment. Our body a priori has a certain supply of cancer cells, but they can grow quantitatively due to external factors, such as bad habits, abuse fatty foods, stress or even heredity.

However, the tumor that is formed by these cells can be benign if it grows outside the organ. In such a situation, it can be cut out and thereby eliminate the problem. But if the tumor grows on the bone or it has grown through healthy tissue, then cutting it out is almost impossible. In any case, if the tumor is removed surgically, then radiation therapy is inevitable. This method is quite common in oncology. But more and more sick people are abandoning this practice due to fear of radiation exposure.

Types of treatment

If there is a disease, then it is worth considering the main methods of treatment. These include surgical removal of the tumor. By the way, it is always removed with a reserve to eliminate the risk of possible tumor growth into healthy tissue. In particular, for breast cancer, the entire gland is removed along with the axillary and subclavian lymph nodes. If you miss a certain part of the cancer cells, the growth of metastases accelerates and chemotherapy is required, which is effective method against rapidly dividing cells. Radiotherapy, which kills malignant cells, is also in use. In addition, they use cryo- and photodynamic therapy, immunotherapy, which provides assistance immune system in the fight against tumors. If the tumor is detected at an advanced stage, then a combination treatment or the use of narcotic drugs that relieve pain and depression may be prescribed.

Indications

So, when is radiation therapy needed in oncology? When talking with a sick person, the most important thing is to rationally explain the need for this method of treatment and clearly formulate the goal that you want to achieve in this way. If the tumor is malignant, then radiation therapy in oncology is used as the main method of treatment or in combination with surgery. The doctor expects the treatment to reduce the size of the tumor, temporarily stop growth, and relieve pain. For two thirds of cancer cases, radiation therapy is used in oncology. The consequences of this method are expressed in increased sensitivity of the diseased area. For some types of tumors, radiation therapy is more preferable than surgery, as it is less traumatic and has the best cosmetic result in open areas.

For epithelial tumors, combined radiation and surgical treatment is indicated, with radiation being the primary treatment, as it helps to shrink the tumor and suppress its growth. If the operation was not effective enough, then postoperative radiation is indicated.

For forms with distant metastases, a combination of radiation and chemotherapy is indicated.

Contraindications

When is radiation therapy clearly inappropriate in oncology? The consequences are not the most pleasant if there is lymphopenia, leukopenia, thrombocytopenia, anemia, as well as any diseases accompanied by high fever and feverish state. If the chest is to be irradiated, the risk factor will be cardiovascular or respiratory failure, as well as pneumonia.

Radiation therapy in oncology after surgery is indicated for those people who have excellent central nervous system health and genitourinary system. They shouldn't endure acute diseases, have pustules, allergic rashes or inflammation of the skin. There are also conditions, for example, anemia cannot be considered a contraindication if the bleeding is coming from a tumor. After all, after the first sessions of therapy, bleeding may stop.

Unexpected risk

Radiation therapy in oncology after surgery may be an unjustified risk if the patient's medical history contains a record of a tuberculosis process. The fact is that irradiation makes it likely that a dormant infection will worsen from latent foci. But at the same time, closed forms of tuberculosis will not be considered a contraindication, although they will require drug treatment during radiation therapy.

Accordingly, exacerbation will be possible subject to the existing inflammatory process, purulent foci, bacterial or viral infections.

Based on all of the above, it can be revealed that the use of radiation therapy is determined by specific circumstances based on a set of arguments. In particular, the criteria will be the expected time frame for the manifestation of results and the likely life expectancy of the patient.

Specific Goals

Tumor tissue is very sensitive to radioactive radiation. That is why radiation therapy has become widespread. Oncology treatment with radiation therapy is carried out with the aim of damaging cancer cells and their subsequent death. The impact is carried out on both the primary tumor and the isolated metastases. The goal may also be to limit aggressive cell growth with the possible transfer of the tumor to an operable state. Also, to prevent the occurrence of metastases in cells, radiation therapy in oncology may be recommended. The consequences, reviews and mood of sick people differ polarly, since, in essence, it involves irradiating the body in order to destroy damaged cells. How will this affect your health? Unfortunately, it is impossible to predict with accuracy, since everything depends on the individual characteristics of the organism.

Types of therapy

With an eye to the properties and sources of the beam beam, various types radiation therapy in oncology. These are alpha, beta, gamma therapies, as well as neutron, pi-meson and proton. There is also X-ray and electron therapy. For each type of cancer, radiation exposure has a unique effect, since the cells behave differently depending on the extent of the damage and the severity of the disease. With equal success, you can count on a complete cure or absolutely zero results.

When choosing the method of irradiation, the location of the tumor plays an important role, since it may be located near vital organs or blood vessels. Internal irradiation occurs when a radioactive substance is placed into the body through the alimentary tract, bronchi, bladder or vagina. The substance can also be injected into blood vessels or through contact during surgery.

But external radiation comes through the skin. It can be general or focused on a specific area. The source of exposure can be radioactive chemicals or special medical equipment. If external and internal irradiation is performed simultaneously, it is called combined radiotherapy. Based on the distance between the skin and the beam source, remote, close-focus and contact irradiation is distinguished.

Algorithm of actions

But how is radiation therapy done for oncology? Treatment begins with histological confirmation of the presence of a tumor. Already on the basis of this document, tissue affiliation, localization and clinical stage are established. The radiologist, based on these data, calculates the radiation dose and the number of sessions required for treatment. All calculations can now be done automatically, since there are appropriate computer programs. Available data also help determine whether radiation therapy should be given in combination with or without other modalities. If the treatment is combined, then irradiation can be carried out both before and after surgery. According to the standard, the duration of the course of radiation before surgery should be no more than three weeks. During this time, radiation therapy can significantly reduce the size of the tumor. In oncology, reviews of this method are very polar, since the effect remains unpredictable. It also happens that the body literally repels radiation or accepts it with healthy cells rather than diseased ones.

If radiation therapy is carried out after surgery, it can last from a month to two.

Side effects of the procedure

After starting a course of treatment, a sick person may experience weakness and chronic fatigue. His appetite decreases and his mood worsens. Accordingly, he can lose a lot of weight. Changes can be observed in tests - the number of red blood cells, platelets and leukocytes in the blood decreases. In some cases, the site of contact with the beam may become swollen and inflamed. This can cause ulcers to form.

Until recently, irradiation was carried out without taking into account the fact that healthy cells could also fall into the action zone. However, science is moving forward and intraoperative radiation therapy has appeared in breast oncology. The essence of the technique is that the irradiation process can be started at the surgical stage, that is, after excision, the beam can be directed to the intervention site. Promptness in this matter allows us to minimize the likelihood of residual tumor, as it is neutralized.

With a breast tumor, a woman always runs the risk of having to give up her breasts. This prospect is often even more frightening than a fatal disease. And breast restoration through intervention plastic surgeons too expensive for average residents. Therefore, women turn to radiation therapy as a means of salvation, since it can allow them to limit themselves to excision of the tumor itself, rather than removing the gland completely. Places of possible germination will be treated with rays.

The effect of radiation therapy directly depends on the patient’s health, his mood, existing side diseases and the depth of penetration of radiological rays. Often the effects of radiation appear in those patients who have undergone a long course of treatment. Minor pain may occur for a long time- these are the affected ones muscle tissue remind you of yourself.

The main problem of women

According to statistics, radiation therapy in uterine oncology is the most common treatment method. This pathology occurs in older women. It must be said that the uterus is a multi-layered organ, and cancer affects the walls, spreading to other organs and tissues. In recent years, uterine cancer has also occurred among young women, which doctors often explain early onset sexual activity and carelessness regarding contraception. If you “catch” the disease at an early stage, then it can be cured completely, but in the late period it will not be possible to achieve complete remission, but following the recommendations of the oncologist, you can prolong a person’s life.

Treatment for uterine cancer is based on surgery, radiation therapy and chemotherapy. The bonus is hormonal treatment, special diet and immunotherapy. If the cancer is actively progressing, then excision is not the right method. Better results can be achieved through irradiation. The procedure is prohibited in case of anemia, radiation sickness, multiple metastases and other ailments.

Radiotherapeutic techniques may vary in the distance between the source and the affected area. Contact radiotherapy is the mildest, since it involves internal exposure: a catheter is inserted into the vagina. Healthy tissues are practically not affected. In this case, can the cancer suffered be harmless? After radiation therapy, after removal of the uterus and other unpleasant procedures, the woman is weak and vulnerable, so she absolutely needs to reconsider her lifestyle and diet.

The uterus is removed if the tumor has grown greatly and affected the entire organ. Alas, in this situation, the possibility of further procreation is called into question. But this is not the time to regret, since so radical measures will extend the life of a sick woman. Now you need to reduce intoxication, which is done by drink plenty of fluids, reception plant food And vitamin complexes with the lion's share of antioxidants. Protein food should be introduced into the diet gradually, focusing on fish, chicken or rabbit meat. Bad habits need to be eliminated once and for all, and preventive visits to an oncologist made a rule.

It is worth including foods that have anti-cancer effects in your diet. These include potatoes, cabbage in all varieties, onions, herbs and various spices. You can focus on dishes made from cereals or whole grains. Soybeans, asparagus and peas are held in high esteem. Beans, beets, carrots and fresh fruits are also useful. It is still better to replace meat with fish and eat low-fat fermented milk products more often. But all alcoholic drinks, strong tea, smoked and salty foods, and marinades are prohibited. We'll have to say goodbye to chocolate, processed foods and fast food.

Radiation therapy is a treatment method in which the tumor is exposed to radiation. Typically, thanks to this impact, the growth of malignant cells stops, and the pain syndrome is noticeably reduced. Radiation irradiation in oncology is used as an independent method of therapy, but is more often performed in combination with other methods, for example, with surgery. A course of radiation therapy is prescribed by an oncologist for all types of malignant tumors, when the tumor is a compaction without cysts and fluid, as well as in the treatment of leukemia and lymphoma.

How is radiation used for oncology?

Irradiation in oncology is carried out using gamma rays or ionizing X-rays in a special chamber equipped with a linear particle accelerator. The principle of operation of the medical device is to use external radiotherapy to change the reproductive capabilities of cancer cells that stop dividing and growing. The final goal of the procedures performed is to help the body get rid of foreign formations through natural means.

A more progressive method is irradiation for oncology using a source of radioactive radiation introduced into the tumor through surgical needles, catheters or special conductors.

Consequences of radiation in oncology

The main problem with radiation therapy is that not only the tumor is exposed to radiation, but also neighboring healthy tissue. Consequences after the procedure occur after some time, and the degree of their severity depends on the size and type malignant formation and location of the tumor. For the sake of fairness, it should be noted that in any case, radiation has a significant impact on the general condition of the patient:

• loss of appetite;
• nausea and vomiting are observed;
• hair loss on the head and body hair, including eyelashes and eyebrows;
• irritability, fatigue, (or drowsiness) appear;
• the blood picture changes.

But in some cases, various complications are observed, even the most serious ones. The most common of them:

• skin damage in the area of ​​irradiation in the form of hyperemia, irritation, peeling, itching, rashes, blisters or blisters;
• violation of the integrity of the mucous membranes in oral cavity, esophagus, etc.;
• skin swelling, radiation ulcers;
• fever, cough;
• difficulty urinating and defecating in case of irradiation of the pelvic organs;
• inflammation of the periosteum, bone necrosis;
• formation of fistulas, atrophy of internal organs.

In all complicated cases, constant monitoring by a specialist is required, who prescribes appropriate drug treatment.

How to eliminate the effects of radiation?

For a patient who has undergone cancer, it is especially important to follow all the doctor’s recommendations. The most critical period is the first two years after a cycle of irradiation procedures. At this time, supportive and restorative therapy is carried out.

• Introduction
• External beam radiotherapy
• Electronic therapy
• Brachytherapy
• Open radiation sources
• Total body irradiation

Introduction

Radiation therapy is a method of treating malignant tumors with ionizing radiation. The most commonly used therapy is high-energy X-rays. This treatment method has been developed over the past 100 years and has been significantly improved. It is used in the treatment of more than 50% of cancer patients and plays the most important role among non-surgical methods treatment of malignant tumors.

A brief excursion into history

1896 Discovery of X-rays.

1898 Discovery of radium.

1899 Successful treatment of skin cancer with X-rays. 1915 Treatment of a neck tumor with a radium implant.

1922 Cure of laryngeal cancer using x-ray therapy. 1928 The X-ray was adopted as the unit of radioactive exposure. 1934 The principle of radiation dose fractionation is developed.

1950s. Teletherapy with radioactive cobalt (energy 1 MB).

1960s. Receiving megavolt x-ray radiation using linear accelerators.

1990s. Three-dimensional planning of radiation therapy. When X-rays pass through living tissue, the absorption of their energy is accompanied by the ionization of molecules and the appearance of fast electrons and free radicals. The most important biological effect of X-rays is DNA damage, in particular the breaking of bonds between two of its helical strands.

The biological effect of radiation therapy depends on the radiation dose and duration of therapy. Early clinical studies of the results of radiation therapy showed that daily irradiation with relatively small doses allows the use of a higher total dose, which, when applied simultaneously to tissues, turns out to be unsafe. Fractionation of the radiation dose can significantly reduce the radiation dose to normal tissues and achieve tumor cell death.

Fractionation is the division of the total dose during external beam radiation therapy into small (usually single) daily doses. It ensures the preservation of normal tissues and preferential damage to tumor cells and makes it possible to use a higher total dose without increasing the risk for the patient.

Radiobiology of normal tissue

The effects of radiation on tissue are usually mediated by one of the following two mechanisms:

• loss of mature functionally active cells as a result of apoptosis (programmed cell death, usually occurring within 24 hours after irradiation);
• loss of cell division ability

Typically, these effects depend on the radiation dose: the higher it is, the more cells is dying. However, the radiosensitivity of different cell types is not the same. Some types of cells respond to irradiation primarily by initiating apoptosis, these are hematopoietic cells and salivary gland cells. In most tissues or organs there is a significant reserve of functionally active cells, so the loss of even a significant part of these cells as a result of apoptosis is not clinically manifested. Typically, lost cells are replaced by proliferation of progenitor cells or stem cells. These may be cells that survived irradiation of the tissue or migrated into it from non-irradiated areas.

Radiosensitivity of normal tissues

• High: lymphocytes, germ cells
• Moderate: epithelial cells.
• Resistance, nerve cells, connective tissue cells.

In cases where a decrease in the number of cells occurs as a result of the loss of their ability to proliferate, the rate of cell renewal of the irradiated organ determines the time frame during which tissue damage manifests itself and can range from several days to a year after irradiation. This served as the basis for dividing the effects of radiation into early, or acute, and late. Changes that develop during radiation therapy up to 8 weeks are considered acute. This division should be considered arbitrary.

Acute changes during radiation therapy

Acute changes mainly affect the skin, mucous membrane and hematopoietic system. Although cell loss during irradiation initially occurs in part due to apoptosis, the main effect of irradiation is the loss of cell reproductive capacity and disruption of the process of replacing dead cells. Therefore, the earliest changes appear in tissues characterized by an almost normal process of cellular renewal.

The timing of the effects of radiation also depends on the intensity of radiation. After a single-stage irradiation of the abdomen at a dose of 10 Gy, death and desquamation of the intestinal epithelium occurs within several days, while when this dose is fractionated with 2 Gy administered daily, this process extends over several weeks.

The speed of recovery processes after acute changes depends on the degree of reduction in the number of stem cells.

Acute changes during radiation therapy:

• develop within weeks after the start of radiation therapy;
• skin suffers. Gastrointestinal tract, bone marrow;
• the severity of the changes depends on the total radiation dose and the duration of radiation therapy;
• therapeutic doses are selected in such a way as to achieve full recovery normal tissues.

Late changes after radiation therapy

Late changes occur primarily in, but are not limited to, tissues and organs whose cells are characterized by slow proliferation (eg, lung, kidney, heart, liver, and nerve cells). For example, in the skin, in addition to acute reaction epidermis, late changes may develop after a few years.

Distinguishing between acute and late changes important from a clinical point of view. Since acute changes also occur with traditional radiation therapy with dose fractionation (approximately 2 Gy per fraction 5 times a week), if necessary (development of an acute radiation reaction), the fractionation regimen can be changed, distributing the total dose over more long period in order to preserve more stem cells. The surviving stem cells, as a result of proliferation, will repopulate the tissue and restore its integrity. With relatively short-term radiation therapy, acute changes may appear after its completion. This does not allow the fractionation regimen to be adjusted based on the severity of the acute reaction. If intensive fractionation causes the number of surviving stem cells to decrease below the level required for effective recovery tissues, acute changes can become chronic.

According to the definition, late radiation reactions appear only a long time after irradiation, and acute changes do not always predict chronic reactions. Although the total radiation dose plays a leading role in the development of a late radiation reaction, the dose corresponding to one fraction also plays an important role.

Late changes after radiation therapy:

• lungs, kidneys, central nervous system(CNS), heart, connective tissue;
• the severity of the changes depends on the total radiation dose and the radiation dose corresponding to one fraction;
• recovery does not always occur.

Radiation changes in individual tissues and organs

Skin: acute changes.

• Erythema resembling sunburn: appears at 2-3 weeks; Patients note burning, itching, and soreness.
• Desquamation: First, dryness and desquamation of the epidermis are noted; later weeping appears and the dermis is exposed; Usually within 6 weeks after completion of radiation therapy, the skin heals, residual pigmentation fades within several months.
• When healing processes are inhibited, ulceration occurs.

Skin: late changes.

• Atrophy.
• Fibrosis.
• Telangiectasia.

Oral mucosa.

• Erythema.
• Painful ulcerations.
• Ulcers usually heal within 4 weeks after radiation therapy.
• Dryness may occur (depending on the radiation dose and the mass of salivary gland tissue exposed to radiation).

Gastrointestinal tract.

• Acute mucositis, manifested after 1-4 weeks by symptoms of damage to the gastrointestinal tract exposed to irradiation.
• Esophagitis.
• Nausea and vomiting (involvement of 5-HT 3 receptors) - with irradiation of the stomach or small intestine.
• Diarrhea - with irradiation of the colon and distal small intestine.
• Tenesmus, mucus secretion, bleeding - during irradiation of the rectum.
• Late changes - ulceration of the mucous membrane, fibrosis, intestinal obstruction, necrosis.

Central nervous system

• There is no acute radiation reaction.
• Late radiation reaction develops after 2-6 months and is manifested by symptoms caused by demyelination: brain - drowsiness; spinal cord- Lhermitte's syndrome (shooting pain in the spine, radiating to the legs, sometimes provoked by flexion of the spine).
• 1-2 years after radiation therapy, necrosis may develop, leading to irreversible neurological disorders.

Lungs.

• After simultaneous irradiation at a large dose (for example, 8 Gy), it is possible acute symptoms airway obstruction.
• After 2-6 months, radiation pneumonitis develops: cough, dyspnea, reversible changes on chest x-rays; improvement may occur with glucocorticoid therapy.
• After 6-12 months, irreversible fibrosis of the kidneys may develop.
• There is no acute radiation reaction.
• The kidneys are characterized by a significant functional reserve, so a late radiation reaction can develop after 10 years.
• Radiation nephropathy: proteinuria; arterial hypertension; renal failure.

Heart.

• Pericarditis - after 6-24 months.
• After 2 years or more, cardiomyopathy and conduction disturbances may develop.

Tolerance of normal tissues to repeated radiation therapy

Research recent years showed that some tissues and organs have a pronounced ability to recover after subclinical radiation damage, which makes it possible to carry out repeated radiation therapy if necessary. The significant regenerative capabilities inherent in the central nervous system make it possible to repeatedly irradiate the same areas of the brain and spinal cord and achieve clinical improvement in recurrent tumors localized in or near critical zones.

Carcinogenesis

DNA damage caused by radiation therapy can cause the development of a new malignant tumor. It can appear 5-30 years after irradiation. Leukemia usually develops after 6-8 years, solid tumors - after 10-30 years. Some organs are more susceptible to secondary cancer, especially if radiation therapy was performed in childhood or adolescence.

• Induction of secondary cancer is a rare but serious consequence of irradiation characterized by a long latent period.
• In cancer patients, the risk of induced cancer recurrence should always be weighed.

Repair of damaged DNA

Some DNA damage caused by radiation can be repaired. When administering more than one fractional dose per day to tissues, the interval between fractions must be at least 6-8 hours, otherwise massive damage to normal tissues is possible. There are a number of inherited defects in the DNA repair process, and some of them predispose to the development of cancer (for example, in ataxia-telangiectasia). Radiation therapy at normal doses used to treat tumors in these patients can cause severe reactions in normal tissues.

Hypoxia

Hypoxia increases the radiosensitivity of cells by 2-3 times, and in many malignant tumors there are areas of hypoxia associated with impaired blood supply. Anemia enhances the effect of hypoxia. With fractionated radiation therapy, the tumor's response to radiation may result in reoxygenation of areas of hypoxia, which can enhance its harmful effect on tumor cells.

Fractionated radiotherapy

Target

To optimize external radiation therapy, it is necessary to select the most favorable ratio of its parameters:

• total radiation dose (Gy) to achieve the desired therapeutic effect;
• the number of fractions into which the total dose is distributed;
• total duration of radiation therapy (determined by the number of fractions per week).

Linear-quadratic model

When exposed to doses taken in clinical practice, the number of dead cells in tumor tissue and tissues with rapidly dividing cells is linearly dependent on the dose of ionizing radiation (the so-called linear, or α-component of the radiation effect). In tissues with a minimal rate of cell turnover, the effect of radiation is largely proportional to the square of the dose delivered (the quadratic, or β-component of the radiation effect).

An important consequence follows from the linear-quadratic model: with fractionated irradiation of the affected organ with small doses, changes in tissues with a low rate of cell renewal (late responding tissues) will be minimal, in normal tissues with rapidly dividing cells the damage will be insignificant, and in tumor tissue it will be greatest .

Fractionation mode

Typically, tumor irradiation is carried out once a day from Monday to Friday. Fractionation is carried out mainly in two modes.

Short-term radiation therapy with large fractionated doses:

• Advantages: small number of irradiation sessions; saving resources; rapid tumor damage; lower likelihood of tumor cell repopulation during treatment;
• Flaws: limited opportunity increasing the safe total radiation dose; relatively high risk late damage in normal tissues; reduced possibility of reoxygenation of tumor tissue.

Long-term radiation therapy with small fractionated doses:

• Advantages: less pronounced acute radiation reactions (but longer treatment duration); lower frequency and severity of late damage in normal tissues; the possibility of maximizing the safe total dose; the possibility of maximum reoxygenation of tumor tissue;
• Disadvantages: great burden for the patient; a high probability of repopulation of rapidly growing tumor cells during the treatment period; long duration of acute radiation reaction.

Radiosensitivity of tumors

For radiation therapy of some tumors, in particular lymphoma and seminoma, a total dose of 30-40 Gy is sufficient, which is approximately 2 times less than the total dose required for the treatment of many other tumors (60-70 Gy). Some tumors, including gliomas and sarcomas, may be resistant to the highest doses that can be safely administered to them.

Tolerant doses for normal tissues

Some tissues are particularly sensitive to radiation, so the doses delivered to them must be relatively low to prevent late damage.

If the dose corresponding to one fraction is 2 Gy, then the tolerable doses for various organs will be as follows:

• testicles - 2 Gy;
• lens - 10 Gy;
• kidney - 20 Gy;
• lung - 20 Gy;
• spinal cord - 50 Gy;
• brain - 60 Gy.

At doses higher than specified, the risk of acute radiation damage increases sharply.

Intervals between fractions

After radiation therapy, some of the damage caused by it is irreversible, but some undergo reverse development. When irradiated with one fractional dose per day, the repair process is almost completely completed before irradiation with the next fractional dose. If more than one fractional dose per day is administered to the affected organ, then the interval between them should be at least 6 hours so that as much damaged normal tissue as possible can be restored.

Hyperfractionation

By delivering multiple fractionated doses of less than 2 Gy, the total radiation dose can be increased without increasing the risk of late damage to normal tissues. To avoid increasing the total duration of radiation therapy, weekend days should also be used or more than one fractional dose per day should be given.

According to one randomized controlled study conducted in patients with small cell lung cancer, the CHART (Continuous Hyperfractionated Accelerated Radiotherapy) regimen, in which a total dose of 54 Gy was administered in fractionated doses of 1.5 Gy 3 times a day for 12 consecutive days, turned out to be more effective compared to the traditional a radiation therapy regimen with a total dose of 60 Gy, divided into 30 fractions with a treatment duration of 6 weeks. There was no increase in the incidence of late lesions in normal tissues.

Optimal radiation therapy regimen

When choosing a radiation therapy regimen, one is guided by: clinical features diseases in each case. Radiation therapy is generally divided into radical and palliative.

Radical radiation therapy.

• Usually carried out at the maximum tolerated dose to completely destroy tumor cells.
• Lower doses are used to irradiate tumors that are highly radiosensitive and to kill microscopic residual tumor cells that are moderately radiosensitive.
• Hyperfractionation in a total daily dose of up to 2 Gy minimizes the risk of late radiation damage.
• Severe acute toxicity is acceptable given the expected increase in life expectancy.
• Typically, patients are able to undergo daily radiation for several weeks.

Palliative radiotherapy.

• The goal of such therapy is to quickly alleviate the patient's condition.
• Life expectancy does not change or increases slightly.
• The lowest doses and number of fractions are preferred to achieve the desired effect.
• Prolonged acute radiation damage to normal tissue should be avoided.
• Late radiation damage to normal tissues clinical significance don't have

External beam radiotherapy

Basic principles

Treatment with ionizing radiation generated external source, is known as external beam radiation therapy.

Superficially located tumors can be treated with low-voltage X-rays (80-300 kV). Electrons emitted by the heated cathode are accelerated in the X-ray tube and. hitting the tungsten anode, they cause X-ray bremsstrahlung. The dimensions of the radiation beam are selected using metal applicators of various sizes.

For deep-lying tumors, megavolt X-rays are used. One of the options for such radiation therapy involves the use of cobalt 60 Co as a radiation source that emits γ-rays with an average energy of 1.25 MeV. To obtain a sufficiently high dose, a radiation source with an activity of approximately 350 TBq is required

However, much more often, linear accelerators are used to produce megavolt X-rays; in their waveguide, electrons are accelerated to almost the speed of light and directed at a thin, permeable target. The energy of the X-ray radiation resulting from such bombardment ranges from 4-20 MB. Unlike 60 Co radiation, it is characterized by greater penetrating power, higher dose rate and is better collimated.

The design of some linear accelerators makes it possible to obtain beams of electrons of various energies (usually in the range of 4-20 MeV). With the help of X-ray radiation obtained in such installations, it is possible to uniformly influence the skin and tissues located underneath it to the desired depth (depending on the energy of the rays), beyond which the dose quickly decreases. Thus, the depth of exposure at an electron energy of 6 MeV is 1.5 cm, and at an energy of 20 MeV it reaches approximately 5.5 cm. Megavolt irradiation is an effective alternative to kilovolt irradiation in the treatment of superficial tumors.

The main disadvantages of low-voltage X-ray therapy:

• high dose of radiation to the skin;
• relatively rapid dose reduction as penetration deepens;
• higher dose absorbed by bones compared to soft tissues.

Features of megavoltage X-ray therapy:

• distribution of the maximum dose in the tissues located under the skin;
• relatively minor skin damage;
• exponential relationship between the decrease in absorbed dose and penetration depth;
• a sharp decrease in the absorbed dose beyond a given irradiation depth (penumbra zone, penumbra);
• the ability to change the beam shape using metal screens or multi-leaf collimators;
• the ability to create a dose gradient across the beam cross-section using wedge-shaped metal filters;
• possibility of irradiation in any direction;
• the possibility of delivering a larger dose to the tumor by cross-irradiation from 2-4 positions.

Radiotherapy planning

Preparation and conduct of external beam radiotherapy includes six main stages.

Beam dosimetry

Before clinical use of linear accelerators begins, their dose distribution should be established. Taking into account the peculiarities of absorption of high-energy radiation, dosimetry can be performed using small dosimeters with an ionization chamber placed in a tank of water. It is also important to measure calibration factors (known as output factors) that characterize the exposure time for a given absorption dose.

Computer planning

For simple planning, you can use tables and graphs based on beam dosimetry results. But in most cases, computers with special software. Calculations are based on beam dosimetry results, but also depend on algorithms that take into account the attenuation and scattering of X-rays in tissues of different densities. This tissue density data is often obtained using a CT scan performed with the patient in the same position as during radiation therapy.

Target Definition

The most important step in planning radiation therapy is identifying the target, i.e. volume of tissue to be irradiated. This volume includes tumor volume (determined visually by clinical examination or according to CT results) and the volume of adjacent tissues, which may contain microscopic inclusions of tumor tissue. Determining the optimal target boundary (planned target volume) is not easy, which is associated with changes in the patient’s position, movement of internal organs and the need, therefore, to recalibrate the device. It is also important to determine the position of critical bodies, i.e. organs characterized by low tolerance to radiation (for example, spinal cord, eyes, kidneys). All this information is entered into the computer along with CT scans that completely cover the affected area. In relatively uncomplicated cases, target volume and position of critical organs are determined clinically using plain radiographs.

Dose planning

The goal of dose planning is to achieve a uniform distribution of the effective radiation dose in the affected tissues so that the radiation dose to critical organs does not exceed their tolerable dose.

The parameters that can be changed during irradiation are as follows:

• beam dimensions;
• beam direction;
• number of bundles;
• relative dose per beam (“weight” of the beam);
• dose distribution;
• use of compensators.

Verification of treatment

It is important to direct the beam correctly and not cause damage to critical organs. For this purpose, radiography on a simulator is usually used before radiation therapy; it can also be performed during treatment with megavolt X-ray machines or electronic portal imaging devices.

Selecting a radiation therapy regimen

The oncologist determines the total radiation dose and creates a fractionation regimen. These parameters, together with the beam configuration parameters, fully characterize the planned radiation therapy. This information is entered into a computer verification system that controls the implementation of the treatment plan at the linear accelerator.

New in radiotherapy

3D planning

Perhaps the most significant development in the development of radiotherapy over the past 15 years has been direct application scanning research methods (most often CT) for topometry and radiation planning.

Computed tomography planning has a number of significant advantages:

• the ability to more accurately determine the location of the tumor and critical organs;
• more accurate dose calculation;
• True 3D planning capability to optimize treatment.

Conformal radiotherapy and multileaf collimators

The goal of radiation therapy has always been to deliver a high dose of radiation to a clinical target. For this purpose, beam irradiation was usually used rectangular shape with limited use of special blocks. Part of the normal tissue was inevitably irradiated with a high dose. By placing blocks of a certain shape, made of a special alloy, in the path of the beam and taking advantage of the capabilities of modern linear accelerators, which appeared thanks to the installation of multileaf collimators (MLC) on them. it is possible to achieve a more favorable distribution of the maximum radiation dose in the affected area, i.e. increase the level of conformity of radiation therapy.

The computer program provides such a sequence and amount of displacement of the blades in the collimator, which allows obtaining a beam of the desired configuration.

By minimizing the volume of normal tissue receiving a high dose of radiation, it is possible to achieve distribution of the high dose mainly in the tumor and avoid an increased risk of complications.

Dynamic and intensity modulated radiation therapy

By using standard method It is difficult for radiation therapy to effectively treat a target that has an irregular shape and is located near critical organs. In such cases, dynamic radiation therapy is used when the device rotates around the patient, continuously emitting X-rays, or modulates the intensity of the beams emitted from stationary points by changing the position of the collimator blades, or combines both methods.

Electronic therapy

Despite the fact that electronic radiation has a radiobiological effect on normal tissues and tumors that is equivalent to photon radiation, physical characteristics electron beams have some advantages over photon beams in the treatment of tumors located in certain anatomical areas. Unlike photons, electrons have a charge, so when they penetrate tissue they often interact with it and, losing energy, cause certain consequences. Irradiation of tissue below a certain level turns out to be negligible. This makes it possible to irradiate a volume of tissue to a depth of several centimeters from the surface of the skin without damaging critical structures located deeper.

Comparative features of electron and photon radiation therapy electron beam therapy:

• limited depth of penetration into tissue;
• the radiation dose outside the useful beam is negligible;
• especially indicated for superficial tumors;
• for example skin cancer, head and neck tumors, breast cancer;
• the dose absorbed by normal tissues (eg, spinal cord, lungs) underlying the target is negligible.

Photon radiation therapy:

• high penetrating ability of photon radiation, allowing to treat deep-seated tumors;
• minimal skin damage;
• Beam features make it possible to achieve greater compliance with the geometry of the irradiated volume and facilitate cross-irradiation.

Generation of electron beams

Most radiation therapy centers are equipped with high-energy linear accelerators capable of generating both X-rays and electron beams.

Since electrons are subject to significant scattering as they pass through air, a guide cone, or trimmer, is placed on the radiation head of the device to collimate the electron beam near the surface of the skin. Further adjustment of the electron beam configuration can be achieved by attaching a lead or cerrobend diaphragm to the end of the cone or by covering the normal skin around the affected area with leaded rubber.

Dosimetric characteristics of electron beams

The effect of electron beams on homogeneous tissue is described by the following dosimetric characteristics.

Dependence of dose on penetration depth

The dose gradually increases to a maximum value, after which it sharply decreases to almost zero at a depth equal to the normal penetration depth of electron radiation.

Absorbed dose and radiation flux energy

The typical penetration depth of an electron beam depends on the energy of the beam.

The surface dose, which is usually characterized as the dose at a depth of 0.5 mm, is significantly higher for the electron beam than for megavolt photon radiation, and ranges from 85% of the maximum dose at low energy levels (less than 10 MeV) to approximately 95% of the maximum dose at high energy level.

At accelerators capable of generating electron radiation, the radiation energy level ranges from 6 to 15 MeV.

Beam profile and penumbra zone

The penumbra zone of the electron beam turns out to be slightly larger than that of the photon beam. For an electron beam, the dose reduction to 90% of the central axial value occurs approximately 1 cm inward from the conventional geometric boundary of the irradiation field at the depth where the dose is maximum. For example, a beam with a cross section of 10x10 cm 2 has an effective irradiation field size of only Bx8 cmg. The corresponding distance for a photon beam is approximately only 0.5 cm. Therefore, to irradiate the same target in a clinical dose range, the electron beam must have a larger cross-section. This feature of electron beams makes coupling of photon and electron beams problematic, since dose uniformity at the boundary of irradiation fields at different depths cannot be ensured.

Brachytherapy

Brachytherapy is a type of radiation therapy in which the radiation source is located in the tumor itself (the radiation volume) or near it.

Indications

Brachytherapy is performed in cases where it is possible to accurately determine the boundaries of the tumor, since the irradiation field is often selected for a relatively small volume of tissue, and leaving part of the tumor outside the irradiation field carries a significant risk of relapse at the border of the irradiated volume.

Brachytherapy is applied to tumors whose localization is convenient both for the introduction and optimal positioning of radiation sources, and for its removal.

Advantages

Increasing the radiation dose increases the effectiveness of suppressing tumor growth, but at the same time increases the risk of damage to normal tissues. Brachytherapy allows you to deliver a high dose of radiation to a small volume, limited mainly by the tumor, and increase the effectiveness of its treatment.

Brachytherapy generally does not last long, usually 2-7 days. Continuous low-dose irradiation provides a difference in the rate of recovery and repopulation of normal and tumor tissues, and, consequently, a more pronounced destructive effect on tumor cells, which increases the effectiveness of treatment.

Cells that survive hypoxia are resistant to radiation therapy. Low-dose radiation during brachytherapy promotes tissue reoxygenation and increases the radiosensitivity of tumor cells that were previously in a state of hypoxia.

The radiation dose distribution in the tumor is often uneven. When planning radiation therapy, proceed in such a way that the tissues around the boundaries of the radiation volume receive the minimum dose. Tissue located near the radiation source at the center of the tumor often receives twice the dose. Hypoxic tumor cells are located in avascular zones, sometimes in foci of necrosis in the center of the tumor. Therefore, a higher dose of radiation to the central part of the tumor negates the radioresistance of the hypoxic cells located here.

At irregular shape tumor, rational positioning of radiation sources allows one to avoid damage to the normal critical structures and tissues located around it.

Flaws

Many radiation sources used in brachytherapy emit y-rays, and medical personnel are exposed to radiation. Although the radiation doses are small, this should be taken into account. Irradiation medical personnel can be reduced by using low activity radiation sources and their automated administration.

Patients with large tumors are not suitable for brachytherapy. however, it can be used as a helper method treatment after external beam radiation therapy or chemotherapy when the tumor size becomes smaller.

The dose of radiation emitted by the source decreases in proportion to the square of the distance from it. Therefore, to ensure that the intended volume of tissue is sufficiently irradiated, it is important to carefully calculate the position of the source. The spatial location of the radiation source depends on the type of applicator, the location of the tumor and what tissues surround it. Correct positioning of the source or applicators requires special skills and experience and is therefore not possible everywhere.

Structures surrounding the tumor, such as lymph nodes with obvious or microscopic metastases, are not subject to irradiation with radiation sources implanted or introduced into the cavity.

Types of brachytherapy

Intracavitary - a radioactive source is introduced into any cavity located inside the patient’s body.

Interstitial - a radioactive source is injected into the tissue containing the tumor focus.

Surface - the radioactive source is placed on the surface of the body in the affected area.

The indications are:

• skin cancer;
• eye tumors.

Radiation sources can be entered manually or automatically. Manual administration should be avoided whenever possible as it exposes medical personnel to radiation hazards. The source is administered through injection needles, catheters or applicators previously embedded in the tumor tissue. The installation of “cold” applicators is not associated with irradiation, so you can slowly select the optimal geometry of the irradiation source.

Automated introduction of radiation sources is carried out using devices, for example, Selectron, commonly used in the treatment of cervical and endometrial cancer. This method involves computerized delivery of stainless steel granules containing, for example, cesium in glasses, from a leaded container into applicators inserted into the uterine cavity or vagina. This completely eliminates exposure to radiation to the operating room and medical personnel.

Some automated injection devices work with sources of high-intensity radiation, for example, Microselectron (iridium) or Catetron (cobalt), the treatment procedure takes up to 40 minutes. With low-dose radiation brachytherapy, the radiation source must be left in the tissue for many hours.

In brachytherapy, most radiation sources are removed after the target dose has been achieved. However, there are also permanent sources; they are injected into the tumor in the form of granules and, after they are depleted, are no longer removed.

Radionuclides

Sources of y-radiation

Radium has been used for many years as a source of y-rays in brachytherapy. It has now fallen out of use. The main source of y-radiation is the gaseous daughter product of the decay of radium, radon. Radium tubes and needles must be sealed and subjected to frequent monitoring for a leak. The γ-rays they emit have relatively high energy (on average 830 keV), and a fairly thick lead shield is needed to protect against them. During the radioactive decay of cesium, no gaseous daughter products are formed, its half-life is 30 years, and the energy of y-radiation is 660 keV. Cesium has largely replaced radium, especially in gynecological oncology.

Iridium is produced in the form of soft wire. It has a number of advantages over traditional radium or cesium needles when performing interstitial brachytherapy. A thin wire (0.3 mm in diameter) can be inserted into a flexible nylon tube or hollow needle previously inserted into the tumor. Thicker hairpin-shaped wires can be inserted directly into the tumor using a suitable sheath. In the USA, iridium is also available for use in the form of granules enclosed in a thin plastic shell. Iridium emits γ-rays with an energy of 330 keV, and a 2 cm thick lead shield can reliably protect medical personnel from them. The main disadvantage of iridium is its relatively short half-life (74 days), which requires the use of a fresh implant in each case.

An isotope of iodine, which has a half-life of 59.6 days, is used as permanent implants for prostate cancer. The γ-rays emitted by it are of low energy and, since the radiation emanating from patients after implantation of this source is insignificant, patients can be discharged early.

β-Ray Sources

Plates emitting β-rays are mainly used in the treatment of patients with eye tumors. The plates are made of strontium or ruthenium, rhodium.

Dosimetry

Radioactive material is implanted into tissues in accordance with the radiation dose distribution law, depending on the system used. In Europe, the classic Parker-Paterson and Quimby implant systems have been largely replaced by the Paris system, particularly suitable for iridium wire implants. When dosimetric planning, a wire with the same linear radiation intensity is used, radiation sources are placed parallel, straight, on equidistant lines. To compensate for the “non-overlapping” ends of the wire, they take 20-30% longer than needed to treat the tumor. In a volumetric implant, the sources in the cross section are located at the vertices of equilateral triangles or squares.

The dose to be delivered to the tumor is calculated manually using graphs such as Oxford charts or on a computer. First, the base dose is calculated (the average value of the minimum doses of radiation sources). The therapeutic dose (for example, 65 Gy for 7 days) is selected based on the standard dose (85% of the baseline dose).

The normalization point when calculating the prescribed radiation dose for superficial and in some cases intracavitary brachytherapy is located at a distance of 0.5-1 cm from the applicator. However, intracavitary brachytherapy in patients with cervical or endometrial cancer has some peculiarities. Most often, when treating these patients, the Manchester technique is used, according to which the normalization point is located 2 cm above the internal os of the uterus and 2 cm away from the uterine cavity (the so-called point A) . The calculated dose at this point allows one to judge the risk of radiation damage to the ureter, bladder, rectum and other pelvic organs.

Development prospects

To calculate the doses delivered to the tumor and partially absorbed by normal tissues and critical organs, sophisticated three-dimensional dosimetric planning methods based on the use of CT or MRI are increasingly used. To characterize the radiation dose, use exclusively physical concepts, while the biological effect of radiation on various tissues is characterized by a biologically effective dose.

With fractionated administration of high activity sources in patients with cervical and uterine cancer, complications occur less frequently than with manual administration of low activity radiation sources. Instead of continuous irradiation with low activity implants, you can resort to intermittent irradiation with high activity implants and thereby optimize the radiation dose distribution, making it more uniform throughout the entire irradiation volume.

Intraoperative radiotherapy

The most important problem of radiation therapy is to deliver the highest possible dose of radiation to the tumor so as to avoid radiation damage to normal tissues. A number of approaches have been developed to address this problem, including intraoperative radiotherapy (IORT). It consists of surgical excision of tumor-affected tissue and a single remote irradiation with orthovoltage X-rays or electron beams. Intraoperative radiation therapy is characterized by a low complication rate.

However, it has a number of disadvantages:

• the need for additional equipment in the operating room;
• the need to comply with protective measures for medical personnel (since, unlike diagnostic x-ray examination the patient is irradiated in therapeutic doses);
• the need for a radiological oncologist to be present in the operating room;
• radiobiological effect of a single high dose of radiation on normal tissue adjacent to the tumor.

Although the long-term effects of IORT have not been well studied, results from animal experiments suggest that the risk of adverse long-term effects from a single dose of up to 30 Gy is negligible if normal tissues with high radiosensitivity (large nerve trunks, blood vessels, spinal cord, small intestine) from radiation exposure. The threshold dose for radiation damage to nerves is 20-25 Gy, and the latent period clinical manifestations after irradiation ranges from 6 to 9 months.

Another danger to consider is tumor induction. A number of studies conducted in dogs have shown a high incidence of sarcomas after IORT compared with other types of radiotherapy. In addition, planning IORT is difficult because the radiologist does not have accurate information regarding the volume of tissue to be irradiated before surgery.

The use of intraoperative radiation therapy for selected tumors

Rectal cancer. It may be appropriate for both primary and recurrent cancer.

Stomach and esophageal cancer. Doses up to 20 Gy appear to be safe.

Cancer bile ducts . Perhaps justified in cases of minimal residual disease, but in unresectable tumors it is not advisable.

Pancreatic cancer. Despite the use of IORT, its positive effect on treatment outcome has not been proven.

Head and neck tumors.

• According to individual centers, IORT is a safe method, well tolerated and produces encouraging results.
• IORT is warranted for minimal residual disease or recurrent tumor.

Brain tumors. The results are unsatisfactory.

Conclusion

Intraoperative radiotherapy and its use are limited by the unresolved nature of certain technical and logistical aspects. Further increase in the conformity of external beam radiotherapy neutralizes the advantages of IORT. In addition, conformal radiotherapy is more reproducible and does not have the disadvantages of IORT regarding dosimetric planning and fractionation. The use of IORT remains limited to a small number of specialized centers.

Open radiation sources

Achievements of nuclear medicine in oncology are used for the following purposes:

• clarification of the location of the primary tumor;
• detection of metastases;
• monitoring the effectiveness of treatment and identifying tumor relapses;
• conducting targeted radiation therapy.

Radioactive tags

Radiopharmaceuticals (RPs) consist of a ligand and an associated radionuclide that emits γ rays. The distribution of radiopharmaceuticals in oncological diseases may deviate from normal. Such biochemical and physiological changes tumors cannot be detected using CT or MRI. Scintigraphy is a method that allows you to monitor the distribution of radiopharmaceuticals in the body. Although it does not make it possible to judge anatomical details, nevertheless, all three methods complement each other.

Several radiopharmaceuticals are used for diagnostics and therapeutic purposes. For example, iodine radionuclides are selectively absorbed active tissue thyroid gland. Other examples of radiopharmaceuticals are thallium and gallium. There is no ideal radionuclide for scintigraphy, but technetium has many advantages over others.

Scintigraphy

A γ-camera is usually used to perform scintigraphy. Using a stationary γ-camera, plenary and whole-body images can be obtained within a few minutes.

Positron emission tomography

PET scans use radionuclides that emit positrons. This quantitative method, allowing you to obtain layer-by-layer images of organs. The use of fluorodeoxyglucose, labeled with 18 F, makes it possible to judge the utilization of glucose, and with the help of water, labeled with 15 O, it is possible to study cerebral blood flow. Positron emission tomography can differentiate primary tumors from metastases and assess tumor viability, tumor cell turnover, and metabolic changes in response to therapy.

Application in diagnostics and long-term period

Bone scintigraphy

Bone scintigraphy is usually performed 2-4 hours after injection of 550 MBq of 99 Tc-labeled methylene diphosphonate (99 Tc-medronate), or hydroxymethylene diphosphonate (99 Tc-oxidronate). It allows you to obtain multiplanar images of bones and an image of the entire skeleton. In the absence of a reactive increase in osteoblastic activity, a bone tumor on scintigrams may appear as a “cold” focus.

The sensitivity of bone scintigraphy is high (80-100%) in the diagnosis of metastases of breast cancer, prostate cancer, bronchogenic lung cancer, gastric cancer, osteogenic sarcoma, cervical cancer, Ewing's sarcoma, head and neck tumors, neuroblastoma and ovarian cancer. The sensitivity of this method is slightly lower (approximately 75%) for melanoma, small cell cancer lung, lymphogranulomatosis, kidney cancer, rhabdomyosarcoma, myeloma and bladder cancer.

Thyroid scintigraphy

Indications for thyroid scintigraphy in oncology are the following:

• study of a solitary or dominant node;
• control study in the long-term period after surgical resection of the thyroid gland for differentiated cancer.

Therapy with open radiation sources

Targeted radiation therapy using radiopharmaceuticals selectively absorbed by the tumor dates back about half a century. A ratiopharmaceutical used for targeted radiation therapy must have a high affinity for tumor tissue, a high focus/background ratio, and remain in the tumor tissue for a long time. The radiopharmaceutical radiation must have sufficiently high energy to provide a therapeutic effect, but be limited mainly to the boundaries of the tumor.

Treatment of differentiated thyroid cancer 131 I

This radionuclide allows you to destroy the thyroid tissue remaining after a total thyroidectomy. It is also used to treat recurrent and metastatic cancer of this organ.

Treatment of neural crest derivative tumors 131 I-MIBG

Meta-iodobenzylguanidine, labeled with 131 I (131 I-MIBG). successfully used in the treatment of neural crest derivative tumors. A week after the appointment of a radiopharmaceutical, a control scintigraphy can be performed. With pheochromocytoma, treatment gives a positive result in more than 50% of cases, with neuroblastoma - in 35%. Treatment with 131 I-MIBG also provides some effect in patients with paraganglioma and medullary thyroid cancer.

Radiopharmaceuticals that selectively accumulate in bones

The incidence of bone metastases in patients with breast, lung, or prostate cancer can be as high as 85%. Radiopharmaceuticals that selectively accumulate in bone have similar pharmacokinetics to calcium or phosphate.

The use of radionuclides that selectively accumulate in bones to eliminate pain in them began with 32 P-orthophosphate, which, although it turned out to be effective, was not found wide application due to toxic effects on the bone marrow. 89 Sr became the first patented radionuclide approved for systemic therapy bone metastases in prostate cancer. After intravenous administration 89 Sr in an amount equivalent to 150 MBq, it is selectively absorbed by skeletal areas affected by metastases. This is due to reactive changes in the bone tissue surrounding the metastasis and an increase in its metabolic activity. Suppression of bone marrow functions appears after approximately 6 weeks. After a single injection of 89 Sr, in 75-80% of patients, pain quickly subsides and the progression of metastases slows down. This effect lasts from 1 to 6 months.

Intracavitary therapy

The advantage of direct administration of radiopharmaceuticals into pleural cavity, pericardial cavity, abdominal cavity, bladder, cerebrospinal fluid or cystic tumors, there is a direct effect of radiopharmaceuticals on the tumor tissue and the absence of systemic complications. Typically, colloids and monoclonal antibodies are used for this purpose.

Monoclonal antibodies

When monoclonal antibodies were first used 20 years ago, many began to consider them a miracle cure for cancer. The goal was to obtain specific antibodies to active tumor cells that carry a radionuclide that destroys these cells. However, the development of radioimmunotherapy currently faces more challenges than successes, and its future appears uncertain.

Total body irradiation

To improve the results of treatment of tumors sensitive to chemotherapy or radiation therapy, and to eradicate the remaining stem cells in the bone marrow, increasing doses of chemotherapy drugs and high-dose radiation are used before transplanting donor stem cells.

Whole body irradiation goals

Destroying remaining tumor cells.

Destruction of residual bone marrow to allow engraftment of donor bone marrow or donor stem cells.

Providing immunosuppression (especially when the donor and recipient are HLA incompatible).

Indications for high-dose therapy

Other tumors

These include neuroblastoma.

Types of Bone Marrow Transplant

Autotransplantation - stem cells are transplanted from blood or cryopreserved bone marrow obtained before high-dose radiation.

Allotransplantation - HLA compatible or incompatible (but with one identical haplotype) bone marrow is transplanted, obtained from related or unrelated donors (bone marrow donor registries have been created to select unrelated donors).

Screening of patients

The disease must be in remission.

There must be no significant impairment of the kidneys, heart, liver, or lungs in order for the patient to cope with the toxic effects of chemotherapy and whole body radiation.

If the patient is receiving drugs that can cause toxic effects similar to those of whole body irradiation, the organs most susceptible to these effects should be especially examined:

• CNS - during treatment with asparaginase;
• kidneys - when treated with platinum drugs or ifosfamide;
• lungs - when treated with methotrexate or bleomycin;
• heart - when treated with cyclophosphamide or anthracyclines.

If necessary, prescribe additional treatment for the prevention or correction of dysfunction of organs that may be particularly affected by whole body irradiation (for example, the central nervous system, testes, mediastinal organs).

Preparation

An hour before irradiation, the patient takes antiemetics, including serotonin reuptake blockers, and is given intravenous dexamethasone. Phenobarbital or diazepam may be prescribed for additional sedation. In children younger age If necessary, general anesthesia with ketamine is used.

Methodology

The optimal energy level set on the linear accelerator is approximately 6 MB.

The patient lies on his back or on his side, or alternating the position on his back and on his side, under a screen made of organic glass (Perspex), which provides irradiation of the skin with a full dose.

Irradiation is carried out from two opposing fields with the same duration in each position.

The table together with the patient is placed at a distance greater than usual from the X-ray therapy machine so that the size of the irradiation field covers the entire body of the patient.

The dose distribution during irradiation of the whole body is uneven, which is due to the inequality of irradiation in the anteroposterior and posteroanterior directions along the entire body, as well as the unequal density of organs (especially the lungs compared to other organs and tissues). For a more uniform dose distribution, boluses are used or the lungs are shielded, but the irradiation regimen described below in doses not exceeding the tolerance of normal tissues makes these measures unnecessary. The organ at greatest risk is the lungs.

Dose calculation

Dose distribution is measured using lithium fluoride crystal dosimeters. The dosimeter is applied to the skin in the area of ​​the apex and base of the lungs, mediastinum, abdomen and pelvis. The dose absorbed by midline tissues is calculated as the average of dosimetry results on the anterior and posterior surfaces of the body, or a whole body CT scan is performed and the computer calculates the dose absorbed by a particular organ or tissue.

Irradiation mode

Adults. Optimal fractional doses are 13.2-14.4 Gy, depending on the prescribed dose at the point of rationing. It is preferable to focus on the maximum tolerated dose for the lungs (14.4 Gy) and not exceed it, since the lungs are dose-limiting organs.

Children. Children's tolerance to radiation is slightly higher than that of adults. According to the scheme recommended by the Medical Research Council (MRC - Medical Research Council), the total radiation dose is divided into 8 fractions of 1.8 Gy each with a treatment duration of 4 days. Other whole-body irradiation schemes are also used, which also give satisfactory results.

Toxic manifestations

Acute manifestations.

• Nausea and vomiting usually appear approximately 6 hours after irradiation with the first fractional dose.
• Parotid edema salivary gland- develops in the first 24 years and then goes away on its own, although patients still have dry mouth for several months after this.
• Arterial hypotension.
• Fever controlled by glucocorticoids.
• Diarrhea - appears on the 5th day due to radiation gastroenteritis (mucositis).

Delayed toxicity.

• Pneumonitis, manifested by shortness of breath and characteristic changes on chest x-rays.
• Drowsiness due to transient demyelination. Appears at 6-8 weeks, is accompanied by anorexia, and in some cases also nausea, and resolves within 7-10 days.

Late toxicity.

• Cataract, the frequency of which does not exceed 20%. Typically, the incidence of this complication increases between 2 and 6 years after irradiation, after which a plateau occurs.
• Hormonal changes leading to the development of azoospermia and amenorrhea, and subsequently sterility. Very rarely, fertility is preserved and a normal pregnancy is possible without an increase in the incidence of congenital anomalies in the offspring.
• Hypothyroidism, developing as a result of radiation damage to the thyroid gland in combination with damage to the pituitary gland or without it.
• In children, growth hormone secretion may be impaired, which, in combination with early closure of the epiphyseal growth plates associated with whole body irradiation, leads to growth arrest.
• Development secondary tumors. The risk of this complication after whole body irradiation increases 5 times.
• Long-term immunosuppression can lead to the development of malignant tumors of lymphoid tissue.

Radiation therapy is the effect on the patient’s body of ionizing radiation of chemical elements with pronounced radioactivity in order to cure tumors and tumor-like diseases. This research method is also called radiotherapy.

Why is radiation therapy needed?

The main principle that formed the basis of this section of clinical medicine was the pronounced sensitivity of tumor tissue, consisting of intensively multiplying young cells to radioactive radiation. Most Applications received radiation therapy for cancer (malignant tumors).

Goals of radiation therapy in oncology:

1. Damage, followed by death, of cancer cells when exposed to both the primary tumor and its metastases to internal organs.
2. Limiting and stopping the aggressive growth of cancer into surrounding tissues with the possible reduction of the tumor to an operable state.
3. Prevention of distant cell metastases.

Depending on the properties and sources of the radiation beam, the following types of radiation therapy are distinguished:

It is important to understand that a malignant disease is, first of all, a change in the behavior of various groups of cells and tissues of internal organs. Various variations in the relationship between these sources of tumor growth and the complexity, and often unpredictability, of cancer behavior.

Therefore, radiation therapy for each type of cancer gives a different effect: from complete cure without application additional methods treatment until there is absolutely no effect.

As a rule, radiation therapy is used in combination with surgical treatment and the use of cytostatics (chemotherapy). Only in this case can you count on a positive result and good prognosis for life expectancy in the future.

Depending on the location of the tumor in the human body, the location of vital organs and vascular lines near it, the choice of irradiation method occurs between internal and external.

• Internal irradiation is carried out when a radioactive substance is introduced into the body through the alimentary tract, bronchi, vagina, bladder, by introduction into blood vessels or by contact during surgical intervention(needling of soft tissues, spraying of the abdominal and pleural cavity).
• External irradiation is carried out through the skin and can be general (in very rare cases) or in the form of a focused beam on a specific area of ​​the body.

The source of radiation energy can be both radioactive isotopes of chemicals and special complex medical equipment in the form of linear and cyclic accelerators, betatrons, and gamma installations. A common X-ray unit used as a diagnostic equipment can also be used as healing method effects in some types of cancer.

The simultaneous use of internal and external irradiation methods in the treatment of a tumor is called combined radiotherapy.

Depending on the distance between the skin and the source of the radioactive beam, the following are distinguished:

• Remote irradiation (teletherapy) – distance from the skin 30-120 cm.
• Close-focus (short-focus) – 3-7 cm.
• Contact irradiation in the form of application to the skin, as well as external mucous membranes, of viscous substances containing radioactive drugs.

How is the treatment carried out?

Side effects and consequences

Side effects of radiation therapy can be general and local.

Common side effects of radiation therapy:

• Asthenic reaction in the form of deterioration in mood, the appearance of symptoms of chronic fatigue, decreased appetite with subsequent weight loss.
• Changes in general analysis blood in the form of a decrease in red blood cells, platelets and leukocytes.

Local side effects of radiation therapy include swelling and inflammation at the sites of contact of the beam or radioactive substance with the skin or mucous membrane. In some cases, the formation of ulcerative defects is possible.

Recovery and nutrition after radiation therapy

The main actions immediately after a course of radiation therapy should be aimed at reducing intoxication that can occur during the breakdown of cancer tissue - which is what the treatment was aimed at.

This is achieved using:

1. Drink plenty of water while maintaining the excretory functions of the kidneys.
2. Eating foods rich in plant fiber.
3. The use of vitamin complexes with sufficient amounts of antioxidants.

Reviews:

Irina K., 42 years old: Two years ago I underwent radiation after I was diagnosed with cervical cancer in the second clinical stage. For some time after treatment there was terrible fatigue and apathy. I forced myself to go to work earlier. The support of our women's team and work helped me get out of depression. The nagging pain in the pelvis stopped three weeks after the course.

Valentin Ivanovich, 62 years old: I underwent radiation after I was diagnosed with laryngeal cancer. I couldn’t talk for two weeks – I had no voice. Now, six months later, hoarseness remains. There is no pain. There is still a slight swelling on the right side of the throat, but the doctor says that this is acceptable. There was a slight anemia, but after taking pomegranate juice and vitamins, everything seemed to go away.