Phase II study of hypofractionated image-guided radiotherapy for localized prostate cancer: outcomes of 55 Gy in 16 fractions at 3.4 Gy per fraction.

Purpose: To estimate the late morbidity of a novel, hypofractionated external beam radiotherapy schedule of 55 Gy in 16 fractions (4 fractions/week, 3.4 Gy per fraction) for localized prostate cancer.
Methods and Materials: A multi-center phase 2 study enrolled seventy-three patients between September 2004 and June 2006. After insertion of fiducial gold markers, they were treated with image-guidance (IGRT) using conformal techniques with intensity-modulation, if necessary, and then followed every 6 months for toxicity rating and PSA. Patient reported outcomes were collected yearly. Median follow up was 4.6 years.
Results: At 4 years post-radiotherapy, the cumulative incidence of combined urinary and bowel grade 3 toxicity was 7% (95% CI 3-16%) and grade 2+ was 33% (95% CI 24-46%). All except two patients recovered from their grade 3 events. Patient-reported reduction of function was most pronounced at year two for urinary function (mean -7, SD 16), and at year one for bowel function (mean -7, SD 21). The cumulative incidence of biochemical (PSA nadir+2) or biopsy-proven relapse at 4 years was 9% (95% CI 4-18%).
Conclusions: Hypofractionated radiotherapy is clinically feasible and more convenient than conventional schedules for patients with localized prostate cancer. Phase 3 multicenter studies are on-going (NCT00126165).
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