Impact of changing rectal dose volume parameters over time on late rectal and urinary toxicity after high-dose intensity-modulated radiotherapy for prostate cancer: A 10-years single centre experience

Background. External beam radiotherapy is an excellent treatment for patients with prostate cancer (PC). Assessing long-term radiotherapy-induced toxicity is important. We evaluated the impact of implementing different rectal dose volume constraints (DVC) on late rectal and urinary toxicity.

Material and methods. Six hundred and thirty-seven PC patients were treated with high-dose intensity-modulated radiotherapy (IMRT) in the primary (median dose of 78 Gy to the prostate) or postoperative setting [median dose of 74 (adjuvant) and 76 Gy (salvage) to the prostatic bed]. Three groups were defined according to different DVC applied over time. The incidence of late rectal and urinary toxicity was evaluated. Three-year actuarial risk estimations of grade 2–3 rectal and urinary toxicity were calculated (Kaplan-Meier statistics).

Results. Median follow-up was five years. Overall, the incidence of late grade 3 and 2 rectal toxicity was 1% and 11%. The calculated three-year actuarial risk of developing late grade ≥ 2 rectal toxicity decreased from 16% to 7% and 5% for patients in Group 1, Group 2 and Group 3, respectively (p < 0.001). Respectively, 17 (4%) and 98 (24%) patients developed grade 3 and 2 late urinary toxicity in the primary setting. In the postoperative setting, 15 (6%) and 62 (26%) patients developed grade 3 and 2 urinary toxicity, respectively. The three-year actuarial risk of developing late ≥ grade 2 urinary toxicity in primary- and postoperative-treated patients was 22% and 23%, respectively. This was not significantly different between the three groups.

Conclusion. The majority of patients developed no or only moderate rectal toxicity after high-dose IMRT for PC. Implementing different rectal DVC resulted in a significant decrease of late rectal toxicity without affecting urinary toxicity.