Predictive factors of long-term rectal toxicity following permanent iodine-125 prostate brachytherapy with or without supplemental external beam radiation therapy in 2216 patients.

We analyzed factors associated with rectal toxicity after iodine-125 prostate brachytherapy (BT) with or without external beam radiation therapy (EBRT).

In total, 2216 prostate cancer patients underwent iodine-125 BT with or without EBRT between 2003 and 2013. The median followup was 6.9 years. Cox proportional hazards modeling was used for univariate and multivariate analyses to assess clinical and dosimetric factors associated with rectal toxicity. Dosimetric parameters from 1 day after implantation (Day 1) and 1 month after implantation (Day 30) were included in the analyses.

The 7-year cumulative incidence of Grade 2 or higher rectal toxicity was 5.7% in all patients. The multivariate analysis revealed that antiplatelet or anticoagulant therapy, neoadjuvant androgen deprivation therapy, treatment modality, Day 1 rectal volume receiving 100% of the prescribed dose (RV100), and the Day 30 minimal percent of the prescribed dose delivered to 30% of the rectum (RD30) were associated with rectal toxicity. Day 1 RV100 was a common predictor in both BT-alone and the BT + EBRT groups. The 5-year cumulative incidence of Grade 2 or higher rectal toxicity was 12.6%, 5.9%, and 1.7% for BT + 3-dimensional conformal radiation therapy, BT + intensity-modulated radiation therapy, and the BT-alone groups, respectively (p < 0.001).

Rectal dosimetric parameters in BT were associated with late rectal toxicity. Although the risk of rectal toxicity was higher when EBRT was combined with BT, with proper and achievable rectal dose constraints intensity-modulated radiation therapy yielded less toxicity than 3-dimensional conformal radiation therapy.

Brachytherapy. 2018 Jun 20 [Epub ahead of print]

Tomoki Tanaka, Atsunori Yorozu, Shinya Sutani, Yasuto Yagi, Toru Nishiyama, Yutaka Shiraishi, Toshio Ohashi, Takashi Hanada, Shiro Saito, Kazuhito Toya, Naoyuki Shigematsu

Department of Radiology, Tokyo Medical Center, National Hospital Organization, Meguro-ku, Tokyo, Japan; Department of Radiology, Keio University School of Medicine, Shinjuku-ku, Tokyo, Japan. Electronic address: ., Department of Radiology, Tokyo Medical Center, National Hospital Organization, Meguro-ku, Tokyo, Japan., Department of Urology, Tokyo Medical Center, National Hospital Organization, Meguro-ku, Tokyo, Japan., Department of Radiology, Keio University School of Medicine, Shinjuku-ku, Tokyo, Japan., Department of Radiology, Tokyo Medical Center, National Hospital Organization, Meguro-ku, Tokyo, Japan; Department of Radiology, International University of Health and Welfare Mita Hospital, Minato-ku, Tokyo, Japan.