Dose distribution and morbidity after high dose rate brachytherapy for prostate cancer: influence of V150 and V200 parameters.

The purpose of this study is to identify factors predicting morbidity in patients undergoing high dose rate (HDR) brachytherapy boost with external beam irradiation for prostate cancer. Acute and late morbidity data were collected for 104 prostate cancer patients treated with an HDR boost together with external beam radiotherapy. Significant urinary and rectal morbidity were correlated with urethral and rectal point doses, and the proportions of the target volume receiving 100%, 150% and 200% (V200) or more of the prescribed dose. Rectal or urethral point doses did not predict morbidity. By contrast, the V200 was significantly higher for patients experiencing either acute or late urinary morbidity. The cut-off V200 was 15% of the target volume. Although theoretically beneficial for tumour cell kill, the treatment of significant proportions of the prostate to high dose might be associated with increased morbidity, and should preferably be avoided.