6 Modern Imaging in Brachytherapy

Modern Imaging 145

As at present, little is known about the correlation between certain dose volume relationships based on 3D sectional imaging with regard to treatment outcome and treatment related morbidity, this data must be carefully collected for later correlation to clinical outcome. A

B C

Fig 5.15: MRI based 3D definitive treatment planning (A) for a combined intracavitary and interstitial gynaecological brachytherapy in a large III B cervix cancer with insufficient remission after 45 Gy pelvic EBT combined with cis-platin chemotherapy. Provisional treatment planning for needle placement was done based on the first intracavitary application with MRI and the ring applicator in place. At the time of brachytherapy the maximum latero-lateral dimension of the GTV was 6.5 cm, with 4.5 cm to the right from the uterine canal. Maximum thickness was 5 cm, maximum height 5 cm. Four round plastic needles were introduced through the vagina in template assisted free hand technique into the macroscopic tumour on the right side parallel to the intrauterine tube with the cervix ring applicator in place using a small template adapted to the ring. The treated volume (85 Gy (biologically weighted dose) corresponding to the “500 cGy-isodose”) is 140 cm 3 and encompasses the large GTV at the time of brachytherapy (60 cm 3 ) and the initial GTV (85 cm 3 ) tightly. The isodose indicating the 60 Gy reference volume is also shown (“280 cGy-isodose”). Maximum width is 9 cm, thickness 7.5 cm, height 9 cm (reference volume is 440 cm 3 ). No significant overdose at the rectum, sigma or bladder was observed: the 2/5cm 3 values for the rectum, bladder as calculated from DVH (B) were 50%/60%, 60%/70% of the prescribed dose for brachytherapy, which corresponds to a total biologically weighted dose of 60-70 Gy (level 3), DVH for the GTV is also shown (C).