Clinical Results Of Proton Boost Combined With Pelvic IMRT For Node-Positive Prostate Cancer: Dosimetric Analysis And Patient-Reported Outcomes

Abstract

Previous studies demonstrated the efficacy of radiation therapy for clinically node-positive prostate cancer. However, there are few reports on treatment strategies incorporating proton therapy. The purpose of this study was to evaluate the clinical outcome of pelvic IMRT combined with proton boost for node-positive prostate cancer, including toxicity and patient reported outcomes (PROs) of health-related quality of life (QOL), and to perform dosimetric comparison of boost plans between proton therapy and IMRT. From March 2013 to May 2016, 12 patients with node-positive prostate adenocarcinoma were treated by pelvic IMRT with 45 Gy/25 fr followed by proton boost with 34 GyE/17 fr to the prostate and seminal vesicles and 26 GyE/13 fr to positive lymph nodes. Biochemical failure was defined according to the Phoenix definition. Adverse effects were assessed using the National Cancer Institute Common Terminology Criteria for Adverse Events version 4.0. Dosimetric comparisons were carried out between proton therapy and IMRT regarding boost plans. The same CTVs, dose fractionation and target volume coverage, and OAR dose constraints were used. All 12 patients completed the Expanded Prostate Cancer Index Composite (EPIC) health-related QOL questionnaire before and at 1-36 months after treatment. The median follow-up period was 59 months (range, 42-80 months). The Gleason score was 7 in 1 patient, 8 in 3 patients, and 9 in 8 patients. The median PSA level before treatment was 38.8 ng/ml (range, 11-230). All patients underwent androgen deprivation therapy for a median duration of 48.5 months. Three patients had biochemical failure. Two of them experienced extrapelvic recurrence. There was no grade 3 or higher acute or late GI and GU toxicity. Planning target volume coverage by the prescription dose was similar between the proton and IMRT plans. In the proton plan, mean rectum V40Gy was significantly lower than in the IMRT plan (44.4% vs 59.3%). The dose to the small intestine for 1 cc and to the colon for 1 cc was 45.1 and 52.3 Gy, respectively, in the proton plans, and 47.0 and 55.7 Gy, respectively, in the IMRT plans, but there were no significant differences. Mean bowel bother score and bowel function score at 6-36 months were similar to or greater than the scores before treatment. Mean urinary summary QOL score was 86.2 before treatment and 82.0, 92.0, 86.7, and 89.8 at 1, 6, 12, and 36 months, respectively. Proton boost combined with pelvic IMRT was feasible and offered reductions in radiation doses to gastrointestinal organs at risk in patients with node-positive prostate cancer. No grade 3 AEs were observed after IMRT plus proton boost and no change was noted in PROS scores. Further studies are warranted for a larger population.