Virtual HDR SBRT for localized prostate carcinoma: Efficacy and quality-of-life assessment.

Abstract

45 Background: We designed a CyberKnife (CK) prostate Stereotactic Body Radiotherapy (SBRT) method to recapitulate HDR fractionation and target volume coverage (“Virtual HDR”). We report 4 year efficacy, toxicity and quality of life (QoL) outcomes. Methods: Eligible patients had low- (Gleason < 6, PSA < 10 ng/mL, < T2bN0) or intermediate-risk (Gleason < 6 with PSA 10.01 – 20 ng/mL or Gleason 7 with PSA < 10 ng/mL, < T2bN0) prostate cancer. A dose of 38 Gy/4 fractions was given to > 95% of the PTV; with “HDR-like” bladder, urethral and rectal dose constraints, and “HDR-like” dose escalation in the PTV. Toxicities were assessed using CTCAE3.0 criteria. QoL was assessed using the Expanded Prostate Cancer Index Composite (EPIC). Results: Since July 2006, 59 patients were treated. Two were lost to follow-up and 6 have been followed < 6 months, leaving 51 (32 low- and 19 intermediate-risk) patients for analysis. Median f/u is 42 months (range, 6-60). 4-year actuarial biochemical-disease free survival is 98% (ASTRO, Phoenix). Freedom from local and distant relapse is 100% and 98%. Median baseline PSA of 6.3 ng/mL (range 1.0 – 14.1) decreased to 0.1 ng/mL by 48 months. Acute grade 2 GU and GI toxicity rates were 22% and 4%, respectively (0% Grade 3+). Three (6%) late Grade 3 GU toxicities occurred at 18, 48 and 48 months. No grade 3+ GI toxicity occurred. Late grade 2 GU and GI toxicity rates were 18% and 2%, respectively. Only 2 patients (4%) had ongoing late > grade 2 GU toxicity at last follow-up (0% GI). Mean EPIC urinary and bowel scores decreased at 2 months, with subsequent improvement and stability to 48 months. Mean EPIC sexual scores gradually declined to 48 months. Of patients potent at baseline, 63% were potent at 3 years, including 100% < age 60, 64% age 61-70 and 60% > age 70. Conclusions: To 4 years, HDR-like CK SBRT for low- and intermediate-risk prostate cancer results in a very low PSA nadir and relapse rate, minimal toxicity and a favorable QoL outcome, with an age-dependent potency preservation rate. The occasional occurrence of late grade 3 urethral stricture can likely be reduced by better patient selection (caution re: patients with significant pre-existing uropathy). Acute and late grade 2 GU toxicity usually resolves with conservative management.