16 Cervix Carcinoma

332 Cervix Cancer

70 Gy for the rectum, corresponding to a total isoeffective dose for tolerance limits for small tumours of 56 - 68 Gy and for large tumours of 70 - 80 Gy . Analogous tolerance limits, although less strict, apply for the bladder. Doses at the vagina vary significantly (from 8 - 30 Gy per fraction), and also depend on the shielding of the ring (cap). Fig 14.13: Vienna Method (continued 1) B-D: Standard dose distributions showing 100%, 50%, 75% 150% and 200% isodose lines with a ring applicator of 26 (small: B), 30 (medium:C), and 34 mm (large:D) diameter (source to source distance) of the same intrauterine length. Transverse planes are given at the plane of the vaginal sources (ring) and at point A. The dimensions of the 60 and 85 Gy reference volume are shown in width, thickness and height. The 60/85 Gy isodose lines correspond within the standard radiochemotherapy dose schedule (45 Gy EBT plus 4 fractions of brachytherapy with 7 Gy per fraction) to the 3.4 (~50%) and 7 Gy (~100%)-isodose. The 100% isodose also corresponds to the volume of the isodose (computer calculated) going through point A (mean 101 cm 3 ). For TRAK values compare text. The mean standard 60 Gy volume (computer calculated) is 274 cm 3 (from 247 to 306).

Fig 14.13B: Standard dose distribution with a small size ring applicator (see above)