Dosimetric and patient correlates of quality of life after prostate stereotactic ablative radiotherapy.

Abstract

Initial results of Stereotactic Ablative Body Radiotherapy (SABR) in the treatment of localized prostate cancer appear promising however long-term quality of life (QOL) outcomes and dosimetric correlates are necessary. A phase I/II study was performed where low risk prostate cancer patients received SABR 35 Gy in 5 fractions, once weekly. Patient self-reported QOL was measured using the Expanded Prostate Cancer Index Composite (EPIC) at baseline and q6 month up to 5 years. Urinary, bowel and sexual domains were analyzed. A minimally clinical important change (MCIC) was defined as 0.5∗standard deviation of the baseline. Univariate and multivariate logistic regression were used to identify dosimetric predictors of MCIC. 84 patients were included. The median follow-up was 50.8 months (interquartile range [IQR], 44.7-56.3). 17.9%, 26.2% and 37.5% of patients reported worse QOL on follow up in the urinary, bowel and sexual domains respectively. On univariate analysis Rectal V31.8>10%, D1cc>35 Gy were associated with bowel MCIC, penile bulb (PB) V35>4%, V20>40% with sexual MCIC. Of these factors only rectal D1cc and PB V35 were predictors of worse QOL on multivariate analysis. Long-term single-institution QOL outcomes are encouraging. Rigorous dosimetric constraints are needed to keep bothersome side effects low.