Radiotherapy

RADIOTHERAPY OF FEMALE GENITAL TRACT CANCERS PRESENTED BY DR K.N.GEORGEWILL

SYNOPSIS • INTRODUCTION • RADIATION PHYSICS • RADIOTHERAPY FOR INDIVIDUAL CANCERS • COMPLICATIONS

INTRODUCTION • Two important discoveries in the late 1800s led to future radiation treatment of human malignancies • 1895 Wilhelm Roentgen discovered x-rays & 1898 Curies in France isolated radium from uranium ore • Soon after, Robert Abbe of New York introduced radium for medical therapy. Howard kelly of Baltimore pioneered radium treatment of cervical cancer. • Since then radiation therapy has evolved to become a major modality in treatment of many cancers, particularly those of the female reproductive tract

RADIATION PHYSICS • Radiotherapy: Radiotherapy is the therapeutic use of ionizing radiation. It is used primarily for Rx malignant tumors, including Gynaecological cancers and in particular Ca cx. • Ionization: Ionization is the result of radiation energy emitting one or more electrons from an atom • Ionizing radiation: high-energy radiation capable of seperating electrons from their orbits in atoms & molecules. – They are composed of discrete units of radiant energy called photons – Have short wave length, high frequency, high penetrating power.

– Classified as Electromagnitic or particulate radiation – Conventional radiotherapy involves the use of Electromagnitic radiation – Electromagnitic radiation comprises: x-rays & gamma rays, both of which are generated from different sources but possess the same physical xteristics (lack mass & charge). – X-rays for Rx purposes are produced by a machine called a linear accelerator while gamma rays are emitted naturally by radioactive isotopes (such as cesium, cobalt, radium) as they decay to reach a stable form. – MOA: when absorbed in tissues produce photons which interact with cellular water in the cell, resulting in the formation of free radicals that then lead to cellular damage (ie damage DNA, hamparing effective replication & causing death of cells), hence their use in

Rx of cancer. Impt to note that Malignant cells are most sensitive to radiation during the mitotic phase of the cell cycle. Hypoxic cells are relatively resistant to radiation (molecular oxygen is required for radiation damage). – Particulate radiation: consists of atomic subparticles; electrons (-ve charges), protons (+ve charges), neutrons (no charges) & mesons ( -ve & have a mass 273x an electron). – At present only electrons are commonly used in radiotherapy, having been accelerated to high kinetic energy in a linear accelerator from which the tugsten target has been removed so that x-rays are not produced.

– Particulate radiation cause ionization directly while xrays & gamma rays cause ionization by giving up their energy (photons) to eject fast moving electrons from atoms. – Unit of measurement of radiation energy absorbed in tissue is the Gray (Gy): 1 Gy = 1 J/kg or 100 rads – Dose of radiotherapy:• Dose fractionation • Dose prescription – Dose fractionation; involves giving total radiation dose in fractions over a given period of time. Aim to avoid delivering too large a dose, preventing permanent damage to normal tissues by allowing for recovery since both normal & malignant cells are affected. Fractionated dose is usually given once dly 4-5 times per week.

– Dose prescription; involves total dose, total no of fractions, total time and the dose per fraction eg 50Gy in 25 fractions given 5 times wkly in 5wks at 2Gy per fraction. Prescription: 50Gy given 2Gy/fraction, 5x/wkly over 5wks – Radiation technique:• Brachytherapy • Teletherapy – Teletherapy; irradiation via radioactive source outside the body ie external beam irradiation used in Rx large volumes (tumor+parametrium+L’nodes). External beam therapy is normally given 1st b/c it shrinks the tumor mass, thus allowing a more satisfactory dose distribution. The radiotherapy apparatus used is most commonly a linear accelerator. A cobalt unit may be used. External beam therapy is normally given first b/c it shrinks the tumor mass, thus allowing a more satisfactory dose distribution from the intracavitary source

– Brachytherapy; irradiation via radioactive source within the body ie intracavitary irradiation. Involves placing isotopes in the uterine cavity & lateral vaginal fornices. • Utilizes the principle of the inverse square law: states that the intensity of radiation is inversely proportional to the square of the distance from the source (IR = 1/d2) • The procedure is carried out under GA. A pelvic exam, including cystoscopy & proctoscopy is performed. The bladder is catheterized, cx dilated & uterine length measured with a sound to ascertain the length of the uterine tube (applicator) required. The width of the vaginal vault is assessed to determine the size of vaginal applicator(s). The uterine applicator with the radioactive source is inserted 1st . • Applicators: Tandem, colpostat

– The afterloading system (Fletcher-Suit, most commonly used) allows the applicator to be positioned accurately b/4 the radioactive sources are inserted to avoid exposing theatre staff to unnecessary radiation. The sources may then be inserted either manually or remotely using automated device. Radioactive isotopes; 137Cs (caesium), 60Co. – Size of portal / field of radiation (external beam radiation): To spare normal structures within the pelvis, particularly bowel & bladder, a 4-field technique with both anterior-posterior & lateral portals is used. • Superior border of the ant-post field is usually the L4/L5 interspace (may extend more cephalad if the common iliac nodes are involved) • Inferior border of the ant-post field is the obturator foramen (may extend to the introitus if the vagina is involved)

• Lateral fields extend 1-2 cm lateral to the bony pelvis, includes the pubic symphysis antly & the sacral hollow postly – Calculating Dose of Radiotherapy: The dose of radiotherapy is expressed at representative points in the pelvis- A & B • Point A: defined as the point 2cm lateral to the central uterine canal and 2cm above the external cervical Os. This point is considered to lie in the paracervical region close to the point where the ureter crosses the uterine artery. This point is measured from the x-ray as 2cm lateral to the centre of the uterine radioactive source and 2cm superior to its inferior margin.

• Point B: defined as 5cm lateral to central uterine canal and 2cm above the external cervical Os. The dose to point B is approximately 1/3 dose to point A, owing to the rapid fall-off in dosage with intracavitary irradiations.

RADIOTHERAPY FOR INDIVIDUAL CANCERS – CARCINOMA OF CERVIX • Used in all stages of CA cervix: therapeutic / palliative purposes. • External irradiation: 45-50 Gy • Intracavitary irradiation: 20-25 GY to point A in a single insertion

• ENDOMETRIAL CA – Pre or post-op radiotherapy – Stage 1C (myometrial invasion >1/3): whole pelvis irradiation – Stage 11 (involvement of cervix): pre-op whole pelvis radiation (45-50 Gy), thereafter, intracavitary radiation (20-25 Gy) followed by surgery (extrafascial hysterectomy). – Stage 111 & 1V: whole abdominal radiation (25-30 Gy) + pelvic boost (45-50 Gy) = whole abdomino-pelvic radiation

• OVARIAN CA – Surgery & combination chemotherapy main stay Rx – Place of radiotherapy controversial. – Radiotherapy used as an adjunct in: • Pt with early stage dx • Minimal residual advanced ovarian Ca (Tumor debulked by chemotherapy) • Recurrent ovarian Ca (following failed chemotherapy) – Radiotherapy given as whole abdominal radiation (2530 Gy) with shielding of kidneys & liver, thereafter, whole pelvis radiation (45-50 Gy) = whole abdominopelvic radiation

• VAGINAL CA – Radiotherapy mainstay treatment – Whole pelvis irradiation followed by intracavitary & interstitial brachytherapy

• VULVAR CA – Surgery mainstay treatment – There are Reports that vulvar Ca is sensitive to radiation therapy, combined radiation therapy with surgery currently understudy.

COMPLICATIONS OF RADIOTHERAPY • • • • • • • • • •

Diarrhea Bowel damage Proctitis Cystitis Obstructive uropathy (strictures) Intestinal obstruction Fistula formation Ovarian failure Bone marrow damage Skin induration