Long-Term Outcomes of a Prospective Study on Highly Hypofractionated Intensity Modulated Radiation Therapy for Localized Prostate Cancer for 3 Weeks.

PURPOSE: Reports of radiation therapy for prostate cancer using dose fractions between moderate hypofractionation and ultrahypofractionation are limited. This pilot study involved the application of highly hypofractionated intensity modulated radiation therapy (IMRT) in 15 fractions for 3 weeks and the number of fractions was intermediate between the 2 previously mentioned dose fractions. The long-term outcomes are reported.

METHODS AND MATERIALS: From April 2014 to September 2015, patients with low- to intermediate-risk prostate cancer received 54 Gy in 15 fractions (3.6 Gy per fraction) for 3 weeks using IMRT without intraprostatic fiducial markers or a rectal hydrogel spacer. Neoadjuvant hormone therapy (HT) was administered for 4 to 8 months. Adjuvant HT was not administered to any patients. Rates of biochemical relapse-free survival, clinical relapse-free survival, overall survival, and the cumulative incidence of late grade ≥2 toxicities were analyzed.

RESULTS: Twenty-five patients were enrolled in this prospective study; 24 of them were treated with highly hypofractionated IMRT (17% had low-risk and 83% had intermediate-risk disease). The median neoadjuvant HT duration was 5.3 months. The median follow-up period was 77 months (range, 57-87 months). Biochemical relapse-free survival, clinical relapse-free survival, and overall survival rates were 91.7%, 95.8%, and 95.8% at 5 years, and 87.5%, 86.3%, and 95.8% at 7 years, respectively. Neither grade ≥2 late gastrointestinal toxicity nor grade ≥3 late genitourinary toxicity was observed. The cumulative incidence rates of grade 2 genitourinary toxicity were 8.5% and 18.3% at 5 and 7 years, respectively.

CONCLUSIONS: Highly hypofractionated IMRT delivering 54 Gy in 15 fractions for 3 weeks for prostate cancer without intraprostatic fiducial markers facilitated favorable oncological outcomes without severe complications. This treatment approach may be a possible alternative to moderate hypofractionation, but further validation is needed.