Frontiers in Oncology (Nov 2014)
Stereotactic Body Radiation Therapy for Prostate Cancer: Review of Experience of a Multicenter Phase I/II Dose Escalation Study
Abstract
Introduction: Stereotactic body radiation therapy (SBRT) is an area of active investigation for treatment of prostate cancer. In our phase I dose escalation study maximum tolerated dose was not reached, and subsequently phase II study has been completed. The purpose of this article is to review our experiences of dose escalated SBRT for localized prostate cancer. Methods and Materials: Patients enrolled to phase I/II study from 2006-2011 were reviewed. Prescription dose groups were 45, 47.5 and 50 Gray (Gy) in 5 fractions over 2.5 weeks. Toxicity and quality of life questionnaire data were collected and analyzed. Descriptive statistics were obtained in the form of means, medians, and ranges for the continuous variables, and frequencies and percentages for the categoric variables. Results: 91 patients were enrolled from five institutions. Median follow up for PSA evaluation was 42 months. PSA control remains at 99%. While the maximum tolerated dose was not reached in the phase I study, excess high grade rectal toxicity (10.6%) was noted in the phase II study. The 13 patients treated to 50 Gy in the phase I study that did not have high grade rectal toxicity, in retrospect met these parameters and have not had further events on longer follow up. Conclusion: PSA control rate, even for patients with intermediate risk, is thus far excellent at these dose levels. This study provides a platform for exploration of SBRT based clinical trials aimed at optimizing outcome for intermediate and high risk patients. High grade toxicities specifically related to the rectum were observed in a small but meaningful minority at the highest dose level. Dose constraints based on physiologic parameters have been defined to mitigate this risk, and strategies to minimize rectal exposure to such doses are being explored.
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