16 Cervix Carcinoma

Cervix Cancer 347

For limited disease with known risk factors, postoperative external beam therapy is given: pelvic irradiation with central shielding adapted to the previous radiation therapy according to the dose delivered to the nodes by brachytherapy or external irradiation + brachytherapy performed 6 weeks before surgery (ranging from 30 - 40 Gy). In a series of 441 patients treated at IGR with preoperative brachytherapy, the mean TRAK was 4.6 cGy at 1 meter (ranging from 1.4 to 9.1), the mean dose rate 0.55 Gy per hour, the mean dose to the bladder 32 Gy (7.2 - 80), to the rectum 40 Gy (8.5 - 97), to the iliac external nodes 12 Gy (1.2 - 48), to the paraaortic nodes (0.2 - 21 Gy), to the pelvic wall 14 Gy (0.2 - 33) (39). 9.4.2 Definitive Brachytherapy and EBT in extended disease Tumour size less than 4 cm: external irradiation 45 Gy plus brachytherapy in one session with the reference isodose of 15 Gy (total dose 60 Gy). Irradiation must be radical, so the total dose to bladder and rectum is higher than in preoperative brachytherapy: bladder 65 - 70 Gy, rectum 60 - 65 Gy. Tumour size more than 4 cm: external irradiation with concomitant cisplatin based chemotherapy 45 Gy plus brachytherapy (one or two sessions) intracavitary +\- interstitial with a reference isodose of 15 Gy. Total dose to bladder is 70 - 75 Gy, to rectum 65 - 75 Gy. In these situations with a high dose delivered to the critical organs, the organ volume irradiated to a high dose must carefully be taken into account. The dose rate is the same as in limited disease: 0.3-0.6 Gy per hour. The TRAK is about 2 cGy at 1 meter. If there is nodal involvement with extended disease an external irradiation boost is applied adapted to the positive nodes with 5 - 15 Gy to an appropriate small volume. 9.5 Vienna method (HDR/PDR) 9.5.1 Definitive HDR Brachytherapy and EBT in limited disease (Vienna) (96) Intracavitary brachytherapy is given in 5 - 6 fractions of HDR-brachytherapy of 7 Gy in 5 - 15 minutes as the prescribed dose to the “PTV” at weekly intervals (to point A or close to point A). External beam therapy is given simultaneously four days a week with a linac with a four field box technique in 1.8 - 2 Gy fractions up to a total dose of 40 - 50 Gy at the ICRU-point (45 Gy with concomitant cis- platin chemotherapy). Central shielding outlined according to the 7 Gy isodose of the brachytherapy volume is inserted in a.p./p.a. portals from the beginning. The overall treatment time is 6 weeks. TRAK averages 2.8 cGy at 1 meter for 6 fractions in small tumours. The physical total dose at point A is 60-67 Gy in small tumours (5 - 6 fractions). The corresponding biologically weighted dose for conventional fractionated radiotherapy (analogous to LDR brachytherapy) calculated using the linear quadratic model (alpha beta value of 10) is 73 - 83 Gy. Dose per fraction at the pelvic side wall, and at the internal and common iliac lymph nodes are 1.35, 1.2, and 0.85 Gy, respectively (ICRU points) (range of medium dose rate). The treated volume by brachytherapy and EBT (isoeffective dose of 73 - 83 Gy) is 87 cm 3 ; the 60 Gy reference volume (taking the 4.7 Gy isodose as isoeffective (based on 25 Gy EBT dose)) is 180 cm 3 . The mean dose per fraction at the ICRU rectum reference point is 4 - 5 Gy, adding up to 24 - 30 Gy in 6 fractions and together with the dose from EBT (25x1Gy) to 49 - 55 Gy. The corresponding isoeffective dose (alpha beta value of 3, see above) is 56 - 68 Gy. Bladder