16 Cervix Carcinoma

334 Cervix Cancer

The treated volume is adapted to the GTV/PTV as far as possible using information from clinical examination and MRI. In any case, the entire cervix with some safety margin is included in the PTV. Adaptation leads to differences in the range of only a few millimeters. However, this difference is significant in terms of volumes. The larger treated volumes are about 90 to 155 cm 3 , the smaller volumes 46 - 90 cm 3 . A minimum dose per fraction of 7 Gy is prescribed to this volume (with isoeffective total doses from 73 - 90 Gy, see below). The dose is recorded at point A and varies from 6 - 8 Gy per fraction depending on the volume. The dose at other reference points averages about 8/4 Gy (PWP), 7/4 Gy at the external iliac and 5/3 Gy at the common iliac points for 6 and 3 fractions, respectively. The mean dimensions of the “point A volumes” (reference isodose for the brachytherapy volume going through point A) are about 7 - 10 cm in height, ~6.2 cm in width, and ~4 cm in thickness. For the 60 Gy reference volume, these dimensions average about 8.5 cm in height, Fig 14.13: Vienna Method (continued 3)

Fig 14.13E: Typical individual adaptation of the standard dose distribution for a large bilateral tumour in a favourable anatomical situation with a large individual vaginal packing. Increase of the dwell times in the intrauterine tube results in bilateral enlargement of the treated volume by ~ 2 mm each side at the level of point A and an appropriate adaptation for the PTV of brachytherapy. The encompassing isodose is 7 Gy per fraction. The dose at point A becomes 8 Gy per fraction. The overall total dose of brachytherapy for this PTV was nominally 28 Gy (4x7 Gy) and at point A 32 Gy (4x8) which is isoeffective to 40 and 48 Gy, respectively. The total dose of EBT (45 Gy) and BT (40 Gy) at the PTV encompassing isodose was 85 Gy and in point A right and left 93 Gy. Dimensions of the 60 Gy reference volume and the treated volume (85 Gy) (and the point A volume (93 Gy)) are indicated. The volumes were 350 cm 3 and 120 cm 3 (and 101 cm 3 ), respectively. TRAK was 2.3 cGy at 1 meter. Dose to rectum and bladder (2 cm 3 ) were mean 3.3 Gy and 5 Gy per fraction, resulting in an overall total isoeffective dose of 68 Gy and 90 Gy; dose at the respective ICRU points were mean 3 Gy per fraction for the rectum and 4 Gy for the bladder.