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.
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).
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.
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.
Anticancer research. 2018 Jan [Epub]
Naomi Sasaki, Hideya Yamazaki, Daisuke Shimizu, Gen Suzuki, Koji Masui, Satoaki Nakamura, Haruumi Okabe, Tatsuyuki Nishikawa, Ken Yoshida
Department of Radiology, Graduate School of Medical Science, Kyoto Prefectural University of Medicine, Kyoto, Japan., Department of Radiology, Graduate School of Medical Science, Kyoto Prefectural University of Medicine, Kyoto, Japan ., Department of Radiology, Ujitakeda Hospital, Uji, Japan., Department of Radiology, Osaka Medical College, Takatsuki, Japan.