Classification of methods of radio therapy

I. Remote methods of long-focus radiotherapy:

• Shot-focus are carried out at distance of a source – a skin (RIC) from 1,5 up to 25 cm;

• Deep –focus are carried out at RIC from 30 cm up to 4 m.

Remote scale-therapy:

Static: the open fields, through a lead lattice, through lead wedge-shaped filter, through lead shielded blocks;

Mobile: rotational, pendular (sector), tangential or eccentrically, rotary-convergetive, rotational with operated speed.

Fig. 4.6. Schemes of a static and mobile remote radiation exposure.

1 - uniarial; 2 - polyarial; 3 - rotational; 4 - sector; 5 - tangential.

In a static radiation exposure the source of radiation during all time of an radiation exposure remains in the fixed position in relation to the patient. The mobile radiation exposure is characterized by moving of a source concerning the patient during the radiation exposure.

Advantages of a mobile radiation exposure in comparison with static: Greater accuracy, significant decrease and uniform distribution of radio loading to the skin. Lack of a mobile radiation exposure is the radiation exposure of significant volumes to the healthy tissues and the vital bodies which are located in a zone of radiation exposure.

1. Therapy by brake radiation of high energy:

Static: the open fields, through a lead lattice, through lead wedge-shaped filter, through lead shielding blocks

Mobile: rotational, pendular, tangential, rotational with operated speed

2. Fast electron therapy:

Static: the open fields, through a lead lattice, wedge-shaped filter, shielding blocks

Mobile: rotational, pendular, tangential

3. X-ray therapy (section see „X-ray therapy”).

Static: the open fields, through a lead lattice

Mobile: rotational, pendular, tangential

The listed methods of radio therapy can be used as independent methods of treatment of eradication(full treatment of the patient with cancers of skin, lip, cervix of uterus І - ІІ stages, etc.), palliative (the time termination of malignant Growth for improvement of the quality of life in inoperable cases) or symptomatic (reduction of a painful syndrome, the prevention of pathological crises of the bones with metastases, to stop bleedings when process is genralised, etc.)

II. Contact methods of an radiation exposure:

1. Introcavity

2. Interstitial method:

3. Radiosurgical.

4. Appliqual

III. Combined methods of radio therapy — a combination of one of methods of a remote and contact radiation exposure.

IV. The Combined methods of treatment of malignant tumours:

Radio therapy and surgical treatment — the combined method of treatment of malignant tumours, in which the preoperative radiation exposure (for radiation protectionof relapses and metastases of a tumour, translation of a tumour in an operable condition owing reduction of its sizes), a suboperational radiation exposure (it is spent during operative intervention for the prevention of development implantational metastases and destruction of the possible rests of a tumour) and a postoperative radiation exposure (for radiation protectionof relapses, destruction regional and the remote metastases spend in 3-4 weeks after operation) is carried out.

5. Complex methods of treatment of malignant tumoursRadio therapy + surgical intervention + chemise-and hormone-therapy.

Doses of radiations which use for treatment of malignant diseases

For treatment of malignant diseases use such sources of ionizing radiation which transfer a sufficient therapeutic dose to the tumour into necessary depth for its full destruction with the maximal preservation of surrounding healthy tissues, i.e. which is the basic principle radio therapy of malignant tumours.

Depending on histological structure of the tumour, its sizes and depth the arrangement use following total local doses (SCD) for all course of treatment:

• For destruction epithelial tumours SCD - 50-70 Gy;

• For adenocarcinomes - SCD 70-80 Gy;

• For sarcomas muscular and connectiv-tissual origins SCD - 80-90 Gy;

• For melanomes, osteogenetic sarcomas - SCD 100 - 120 and more Gy.

For the prevention of radio damage of tissues total doses of an radiation exposure divide into separate parts, i.e. fractions. Distinguish following concepts:

• Single basic dose (SORT) — dose which bring to the center for one session;

• Total skin (superficial) dose — a dose which bring on skin for all course of treatment;

• Single skin dose — a dose which bring on skin field for one session.

Ways of leading dose to the center and a rhythm of radiation exposure:

1. Unitary radiation exposure — the planned dose brings to a tumour for one session of an radiation exposure (a preoperative and suboperational radiation exposure).

2. Fractionation an radiation exposure — carry out fine fractions — 2-2,5 Gy every day, 5-6 sessions for a week, duration rate of radiation exposure 4-6 weeks, SCD 60-70 Gy; averages — 3,5-4 Gy, 2-3 sessions for a week (the week dose should not exceed 10 Gy), SCD 50-60 Gy; large fractions — 5-8-10 Gy for a session with an interval from several days about one week (use more often in the started cases with the palliative purpose).

3. The intensively-concentrated rate 5 and more Gy during 5-6 days every day, achievement of the total absorbed dose 30-40 Gy carried out by surgical intervention.

4. The split rate of radio therapy — is spent fine and average fractional doses for the increase of tolerance of normal tissues; occurrence of radio reaction after leading half prescribed dose temporarily for 2-4 weeks interrupt an radiation exposure and after that continue it. The split rate improves result and is not accompanied by the expressed biological effects of normal tissues. Owing to destruction of tumoural cells and improvement of blood circulation in a tumour it is marked reoxigenation cells which were in a condition of hypoxia’s and anoxia’s. Reoxygenation to a tumour promotes its increase radioaffection during the following after break of radiation exposure.

5. The continuous radiation exposure — is carried out incorporated RNP for treatment of plural metastases in a bone (radioactive phosphorus), a cancer of a thyroid gland (¹³¹ І), etc.

Calculation|computation| of deep focal doses.

Different sources|springs| and methods of radio therapy allow to expose to the rays pathological processes being on a different depth, in a necessary therapeutic dose. Penetrable ability|power| of ionizing radiations in the body of man depends on a kind|appearance| energy of radiation. At the controlled from distance radiation exposure choose a kind|appearance| and energy of radiation with such calculation|computation|, to provide|secures| the damage of the deeply located hearth at the minimum dose of radiation exposure of surrounding tissues. Relation of dose on the set depth to|by| the dose in a skin name|calls| a relative or percent|percentage| deep dose. Distributing of energy of different types of radiation in tissues see|q.v.|.4.7.

Distributing of deep energy of different types of radiations is represented|presented| as curves in every point of which the same percent of skinning|skin| dose. A line which connects points with the identical percent of deep doses is named|called| the isodose curve. The isodose| curves inflicted on transparent tape (isodose| line|ruler|) use in practice for determination|definition| of eaten up deep doses in the organism of man.

On the made schematic cut of body of patient with the place|seat| of location|disposition| of pathological hearth inflicted on him, radio internist together with a physicist-dosimetria plan|glides| the program of radiation exposure, determine the volume of area|zone| of radiation exposure. Choose the optimum volume of radiation exposure personally for every patient. It is necessary to choose the most rational location|disposition| of the dose| field at which a dose optimum was distributed in the hearth of defeat and was spread on the way of регионарного| limph-circulation|. Then elect a kind|appearance| radiations and method radiation exposures, sizes|dimensions| and form|shape| of the fields of radiation exposure, direction of cones of rays and inflict|drifts| them on a topography-anatomic sketch. After causing|applying| of the fields of radiation exposure through the centers of the set|planned| fields draw perpendicular lines which are crossed in the center of tumour|swelling| (see |q.v.|fig.4.8). In the direction of|in direction of| central cone of rays lay on isodose| lines|rulers| (see |q.v.|fig.4.7) and set|establishes| a percent|percentage| deep dose in the hearth of defeat from every field of radiation exposure.

Fig. 4.7. Distributing of energy of different types of radiations in tissues.

Fig. 4.8. Sketch of transversal section of body of patient and points| of the fields of radiation exposure. a|but|) sketch of transverse section of thorax: 1 center of tumour|swelling|; 2 contours of tumour|swelling|; б) the fields (1) of radiation exposure.

It should be remembered that at planning of radiation exposure it is necessary expressly to define the amount|quantity| of the skinning|skins| fields. For example, a tumour|swelling| is on a depth 10 см|, in obedience to dosimetria description of x-ray photography radiation (see |q.v.|fig.4.7) of depth 10 см| a 25% (1/4) skinning|skin| dose arrives at, for the gamma-radiation the percent of deep dose will make a 50% (1/2) skinning|skin| dose. If certain|definite| SD for this tumour|swelling| makes 75 Gр|, for tricking into of this dose on the indicated|specified| depth on a skin it is necessary totally to bring 75 Gy| of х 4 = 300 Gy| of x-ray or 75 Gy| of х 2 = 150 Gy| of gamma-radiation. Because tolerant skinning|skin| dose for the X-ray radiation makes 30 Gy|, that amount|quantity| of the skinning|skins| fields for X-ray therapy is determined by the division of total skinning|skin| dose on a tolerant skinning|skin| dose - 300:30 = 10 the fields; for the gamma-radiation a tolerant skinning|skin| dose makes 55Gy, therefore the amount|quantity| of the skinning|skins| fields will be 150:55 = 3 fields. It is visible from this example, that at the deeply located tumours|swelling| more rationally to use the gamma-radiation with the purpose of radiation exposure considerably less of the skinning|skins| fields and diminishing of general|common| and local biological effects.

Biological effects

In connection with the radiation, exposure of malignansy is carried out through skin by significant doses of ionizing radiation it is necessary to take measures for the prevention of radio damages of the skin.

Distinguish biological effects (reversible) and radio damages (irreversible).

Erytеma — reddening of skin, hypostasis, and painful sensitivity; arises due to fractional, radiation exposure of a skin field in doses: in children till 5 years – 1,5 Gy; in adults – 4-5 Gy; in persons of older age – 6-7 Gy. Erytema disappears in 10 days after the termination of radiation exposure.

Epidermitis— arises due to increase of dose on a skin field fine fractional radiation exposure up to 25 Gy — accrues erithema, the hypostasis, arises epilation and descvamation superficial cells, dry skin, pigmentational exfoliates epidermis.

Exudative (damp) radioepidermity — arises due to increase of dose on a skin field fine fractional X-ray radiation exposure up to 30 – 35 Gy, for scale-radiation up to 55 Gy. Epidermis descvamational, on edges surfaces there is a strip of new epithelia, which Gyadually for 2 – 3 weeks disseminate to the center of the amazed area of skin. Skin field is dry, non-uniformly migmented, atrophy of epidermis and epilation later.

Effect of radiation on cells

Radio damages-radio necrosis (the radio burn) — it independently does not heal, requires surgical treatment, can malignate. Therefore for radiation protection of damages of the skin with middle-fractional radio therapy use concept of tolerant skin dose of x-ray radiation 30-35 Gy, scale-radiation 55-60 Gy in which there are biological effects, i.e. return changes, but no radio damages.

Dose limits necessarily consider at scheduling radio treatment of patients for calculation of quantity of skin fields see below.