Single-fraction high-dose-rate (HDR) brachytherapy boost and hypofractionated radiation for intermediate- and high-risk prostate cancer: A report of toxicity from a single center experience.

Abstract

112 Background: Single-fraction HDR brachytherapy offers a highly conformal approach to dose escalation for intermediate and high risk prostate cancer and exploits the apparent low α/β ratio of prostate cancer cells. The potential benefit of improving tumour control must be balanced against the heightened risk of toxicity. We assessed and compared toxicity among patients receiving either 12.5 Gy or 15 Gy as a single fraction HDR boost prior to conformal external beam radiotherapy (EBRT). Methods: Between July 2008 and February 2011, 177 patients received HDR brachytherapy prior to conformal EBRT (37.5 Gy in 15 fractions). 95 patients in the early cohort received 12.5 Gy and 82 patients in the later cohort received 15 Gy. The median patient age at presentation was 67 (range 57 – 77) with a median PSA of 16.0 (range 0.29 – 102), median Gleason score 7 (range 6 – 10), clinical stages T1c to T4 and median baseline IPSS was 8 (range 0 – 27). Prospective patient questionnaires - IPSS, LENT SOMA and EPIC QoL - were completed prior to treatment and at regular intervals following EBRT (6 weeks, 6 monthly thereafter). Results: Both treatment groups had similar median IPSS values at 6 weeks (12.5 Gy = 10, 15 Gy = 11); there was no significant difference in values throughout follow-up. Mean LENT SOMA scores for bladder/urethra toxicity peaked at 6 weeks (12.5 Gy = 0.6, 15 Gy = 0.72) with no trend towards greater reporting of maximum values of ≥ 2 in the 15 Gy cohort. Rectum/bowel mean LENT SOMA scores peaked at 6 weeks (12.5 Gy = 0.30, 15 Gy = 0.39). Although a greater proportion of 15 Gy patients reported a maximum score of ≥ 2 at 6 weeks and 6 months compared with the 12.5 Gy patients, this returned to pre-treatment levels at 12 months. Conclusions: We conclude that dose escalation from 12.5 Gy to 15 Gy delivered in a single HDR fraction is not associated with a clinically significant increase in toxicity. We believe that the reported toxicity is acceptable at this level of dose escalation (2 Gy equivalent = 112 Gy, assuming an α/β ratio of 1.5). Ongoing follow-up is required to ascertain tumour control.