Moderately hypofractionated intensity-modulated radiation therapy for intermediate- or high-risk prostate cancer:...

Moderately hypofractionated radiotherapy has become a preferred option for localized prostate cancer based on multiple randomized trials demonstrating non‑inferiority to conventional fractionation. However, its adoption in Japan has been slower, partly due to limited domestic evidence. This study evaluated long‑term outcomes, toxicity, and dose-volume predictors of late gastrointestinal (GI) toxicity in patients treated with a uniform moderately hypofractionated regimen.

We retrospectively analyzed 486 consecutive patients treated with intensity‑modulated radiation therapy (IMRT) delivering 70 Gy in 28 fractions between 2010 and 2023. Biochemical relapse‑free survival (bRFS) was assessed using the Phoenix definition. Toxicities were graded using CTCAE v5.0. Dose-volume histogram (DVH) parameters were extracted for all patients, and associations with grade ≥ 2 late GI toxicity were examined using receiver‑operating characteristic (ROC) curves.

With a median follow‑up of 62 months, 5‑year bRFS rates were 100% for favorable intermediate‑risk, 98% for unfavorable intermediate‑risk, 97% for high‑risk, and 75% for very high‑risk disease. Acute grade ≥ 2 genitourinary (GU) and GI toxicities occurred in 29% and 3.1% of patients, while late grade ≥ 2 GU and GI toxicities occurred in 13% and 2.8%. Hydrogel spacers (used in 27% of patients) improved rectal DVH parameters and numerically reduced late GI toxicity. Rectal V40Gy, V50Gy, and V60Gy were strongly associated with late GI toxicity, and ROC analyses confirmed their predictive value.

Moderately hypofractionated IMRT using 70 Gy in 28 fractions provides excellent biochemical control with low toxicity in real‑world practice. These findings support the use of moderate hypofractionation in Japan.