16 Cervix Carcinoma

346 Cervix Cancer

bladder complications, bladder dose and bladder dose rate, the decision rules are not so clear due to the small number of severe complications observed. However, the safe zone can be defined by reference bladder dose below about 70 Gy and bladder dose rate below about 50 cGy/h. 9.3.2 Definitive LDR brachytherapy + EBT in extended disease: According to Horiot (4,53,54) the indications are: * tumour size 3-6cm with or without proximal tumour extension: external radiotherapy 40 Gy + endocavitary brachytherapy: TRAK 4 - 4.5 cGy at 1 meter; 40 - 60 Gy to upper vagina. * tumour size >6cm +/- distal parametria +/- inferior vagina: external radiotherapy 40 - 50Gy + endocavitary +/- interstitial brachytherapy: TRAK 3.5-4.5 cGy at 1 meter; 50 - 70 Gy to upper vagina. If there are positive nodes the total dose delivered must be between 55 to 65/70Gy (65/70 Gy to a very limited volume). (In the classical Fletcher method, doses in mg.h radium (TRAK) have been correlated with doses to point A: if the anatomy is favourable, doses to point A are reported to be in the range of 85 - 95 Gy (73)). The mean HTW volumes for patients treated in the first period were 1061 cm 3 for stage IIIa and 990 cm 3 for stage IIIb. The mean HTW volumes for patients treated in the second period were 705 cm 3 for stage IIIa and 775 cm 3 for stage IIIb. The mean HTW volumes for patients treated in the third period were 474 cm 3 for stage IIIa and 528 cm 3 for stage IIIb (4,54). Dose and dose rate to critical organs are decided based on the risk of complications. This risk is estimated from the calculated HWT volume and the reference dose to critical organs. These parameters are correlated (according to the experience of the “group de neuf”) with a given probability of late side effects, in particular for the rectum and the bladder. The duration of application can be adapted as well as the radioactive length and/or the activity. The dose rate (0.8 - 1 Gy/h) at the surface of the applicator is kept constant by modifying the activity of the source as a function of colpostat size (4,54). For dose(rate) to the rectum and bladder see the studies presented above (9.3.1) 9.4 IGR-method (LDR) (37,38). 9.4.1 Preoperative radiotherapy in limited disease For limited stage IB and proximal IIA/B disease preoperative brachytherapy is adapted to tumour stage: Tumour size less than 4 cm (IB1/IIB): brachytherapy in one session, or in two sessions if the geometry of the implant is not perfectly adapted to the anatomy and/or to the topography of the tumour. The reference isodose is by definition 60 Gy and must encompass the target volume (upper third of the vagina, internal third of the the parametrium, upper third of the uterus). The maximum dose to the bladder and rectum is less than 50 Gy taking into consideration the volume of bladder and rectum irradiated. Dose rate is from 0.3 to 0.6 Gy per hour at the level of the reference isodose. Tumour size more than 4 cm (IB2/IIB): external irradiation 20 Gy plus brachytherapy. The reference isodose for brachytherapy is 40 Gy (60 Gy minus 20 Gy (dose of external irradiation)). For bladder and rectum the mean dose delivered by brachytherapy is 30 Gy. Dose rate is 0.3 to 0.6 Gy per hour at the level of the reference isodose. From 1999, in this clinical situation, treatment starts with concomitant chemoradiation up to 45 Gy followed by brachytherapy : the reference isodose is 15 Gy.