16 Cervix Carcinoma

Cervix Cancer 345

field box technique (10 - 12 cm length) is sometimes used applying 45 Gy by external therapy to treat the pelvis homogeneously and, in this situation 20 - 22.5 Gy is prescribed at point A in one insertion (62) (previously 2500cGy Radium). TRAK for the two brachytherapy schedules is 2.07 to 3.15 cGy for 32.5 Gy at point A and 1.44 to 2.07 cGy for 20-22.5 Gy at point A depending on the applicators used. 9.3 Modified Fletcher method (LDR) (54) 9.3.1 Definitive LDR brachytherapy +/- EBT in limited disease Amount of brachytherapy, external beam therapy, dose and fractionation are related to the tumour volume, the disease extension and the nodal status. According to Horiot (53,54) the indications are: * tumour size less than 1cm: two applications of brachytherapy: TRAK 7.2 cGy at 1 meter, 80 to 100 Gy to upper vagina. * tumour size 1-3cm +/- proximal extension: external radiotherapy (20 - 40 Gy) plus intracavitary brachytherapy: TRAK 4-4.5 cGy at 1 meter; 30-60 Gy to upper vagina. * tumour size 3-6cm +/- proximal extension: external radiotherapy 40 Gy plus intracavitary brachytherapy: TRAK 4-4.5 cGy at 1 meter; 40-60 Gy to upper vagina. 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. (54) In Dijon three time periods of treatment strategies can be defined. The first period between 1970 and 1978 with 289 patients, the second period between 1979 and 1984 with 199 patients and the third period between 1985 and 1994 with 154 patients (3,4). The mean HTW volumes for patients treated in the first period were 606 cm 3 for stage Ib, 711 cm 3 for stage IIa and 850 cm 3 for IIb. The mean HWT volumes for patients treated in the second period were 612 cm 3 for stage Ib, 630 cm 3 for stage IIa and 773 cm 3 for IIb. For patients treated in the third period mean HTW volumes were 498 cm 3 for stage Ib, 472 cm 3 for stage IIa, 511 cm 3 for IIb (3,4, 53). Pourquier et.al. (98) reported maximum bladder doses from intracavitary brachytherapy and cumulative bladder doses from both the intracavitary and external beam treatment for all 624 patients (stage I to IV, treated between 1970 - 1994): For an EBT dose of 20 Gy, the bladder doses were on average 24 Gy and 44 Gy, for EBT of 30 Gy the doses were on average 30.5 Gy and 60.5 Gy, for EBT of 40 Gy the doses were on average 24.8 to 30.6 Gy and 65.8 to 71.1 Gy and for EBT of 50 Gy the doses were on average 24.3 to 32.3 Gy and 74.3 to 82.5 Gy. Crook et.al. (19) reported data from 348 patients with stage Ia to IIIb treated between 1975 and 1983. For hwt volumes between about 100 cm 3 and 200 cm 3 the cumulative rectal doses (from both the intracavitary and external beam treatment) were between between 60 Gy and 90 Gy. They reported a correlation between the mean rectal dose from intracavitary brachytherapy alone and mean HWT volumes. For HWT volumes between about 500 cm 3 and 800 cm 3 the cumulative rectal doses were between about 60 Gy and 80 Gy. Barillot et.al. (4) reported for 624 patients (stage I to IV, treated between 1970 - 1994) new decision rules for rectal and bladder dose based on correlation curves. Only one G3/G4 rectal complication was demonstrated within the area delimited by HWT values below about 750 cm 3 and reference rectal dose rate below about 50 cGy/h. Keeping dosimetric parameters within this safe zone may avoid the occurrence of severe rectal complications. Although a correlation has been found between