TY - JOUR T1 - Long-term Outcomes of a Dose–reduction Trial to Decrease Late Gastrointestinal Toxicity in Patients with Prostate Cancer Receiving Soft Tissue-matched Image-guided Intensity-modulated Radiotherapy JF - Anticancer Research JO - Anticancer Res SP - 385 LP - 391 VL - 38 IS - 1 AU - NAOMI SASAKI AU - HIDEYA YAMAZAKI AU - DAISUKE SHIMIZU AU - GEN SUZUKI AU - KOJI MASUI AU - SATOAKI NAKAMURA AU - HARUUMI OKABE AU - TATSUYUKI NISHIKAWA AU - KEN YOSHIDA Y1 - 2018/01/01 UR - http://ar.iiarjournals.org/content/38/1/385.abstract N2 - Background/Aim: We experienced an unexpected high incidence of gastrointestinal (GI) toxicity in patients undergoing image-guided intensity-modulated radiotherapy (IG-IMRT) using helical tomotherapy in our initial 2.2 Gy/fraction schedule for prostate cancer; hence, a dose-reduction trial from 2.2 Gy to 2 Gy/fraction was conducted using modified planning target volume (PTV) contouring. Patients and Methods: We compared 130 patients treated using 2.2 Gy/fraction (Group A) and 144 treated using the 2 Gy/fraction (Group B) with modified PTV (excluding rectal volume) with a median follow-up period of 62 months. Prescribed dose was 72.6-74.8 Gy in 33-34 fractions (Group A) and 72-74 Gy in 36-37 fractions (Group B). Results: Patients in Group B had a reduced rectal and bladder V10-V70 and were irradiated at the maximal dose. Their cumulative incidence of grade ≤2 GI toxicity at 5 years improved from 10.1% [95% confidence interval (CI), 4.9-15.3%] to 1.4% (0-3.3%). Grade 2≤ urinary toxicity also decreased from 5.5% (1.5-9.4%) in Group A to 1.4% (0-3.3%, p=0.0167) in Group B. The biochemical failure-free 5-year survival rate was 89.1% (95%CI=83.6-95.4%) and 87.5% (82.0-92.9%, p=0.75) in groups A and B, respectively. Conclusion: The reduced dose fraction schedule decreased the incidence of late GI toxicity without compromising prostate-specific antigen control. Careful target volume definition and fraction size are important even for IG-IMRT. ER -