16 Cervix Carcinoma

322 Cervix Cancer

Fig 14.10: Modern Manchester method (A1)

Fig 14.10 A1,2: Standard dose distributions showing 100%, 50% and 200% isodose lines with a standard Manchester applicator for ovoids with 20 mm (A1) and 30 mm (A2) in diameter. The position of the active pellets is indicated. Transverse planes are given at the plane of the ovoids (at 10 mm from the top of the ovoids) and at point A. The dimensions of the volume of the isodose going through point A are shown. The reference volume of the isodose going through point A is 267/312 cm 3 (HWT) for small and large ovoids, respectively, which corresponds roughly (divided by 2) to a computer calculated volume of 133/156 cm 3 (modified from isodose curves as provided by Wilkinson (116), with permission). In brachytherapy alone this isodose corresponds to a physical total dose of 65 Gy which is isoeffective to 75 Gy in classical dose rate (59,61,62). For combined treatment in advanced disease this nowadays corresponds to a physical dose of 40 Gy EBT and 32.5 Gy (isoeffective to 37.5 with 50 cGy/hour (57, 62)), which is a total isoeffective dose of 77.5 Gy. To aid understanding, the dimensions of the 60 Gy volume (60 Gy – 40 Gy EBT = 20 Gy) are also given, although these have never been used in the Manchester method. This becomes possible, as the 50% isodose which is indicated corresponds an isoeffective dose of ~ 19 Gy (37.5/2). The HWT volume for the small ovoids is then 11,6 cm in height x 8,7 cm in width x 7,2 cm in thickness, - 727 cm 3 , which corresponds roughly (divided by 2) to a computer calculated volume of 363 cm 3 . The HWT volume for the large ovoids is then 12.4 cm in height x 10.1 cm in width x 7.4 cm in thickness, which is 927 cm 3 . This corresponds roughly (divided by 2) to a computer calculated volume of 463 cm 3 .