Prior Transurethral Resection Of The Prostate Does Not Predict For Grade 2+ Urinary Toxicity in Men Receiving Modest Dosing SBRT for Prostate Cancer

Abstract

the extent of prostate intrafraction translation and rotation has been previously investigated, the clinical impact of rotation independent of translation has not. Several series have characterized low rates of rectal toxicity when SBRT is used with different dose regimens. This study attempts to quantify the impact of intrafraction rotation on grade 2+ rectal toxicity for men diagnosed with prostate cancer treated with SBRT. Materials/Methods: Between April 11, 2006 and August 13, 2018, 1712 patients with prostate cancer were treated with robotic-based SBRT at an academic institution. 91.2% were treated with 3500cGy in 5 fractions while 8.8% received 3625cGy. 328 (19.7%) patients received ADT as a component of their treatment. By NCCN grouping, patients were treated for low risk (26.9%), intermediate risk (60.1%), and high risk (13.0%) disease. Each fraction employed real-time intrafraction translation correction. Due to prostate fiducial configuration or body habitus, 75 (4.4%) patients did not receive intrafraction rotation correction during treatment. Intrarectal amifostine was administered to patients prior to each SBRT fraction. Long-term rectal toxicity was scored by RTOG late toxicity scale. Freedom from grade 2+ proctitis was assessed using the Kaplan-Meier method and analyzed using Cox regression methods. Results: 13 patients developed grade 2 proctitis while 7 developed the grade 3 endpoint. 0.41% of all patients required hyperbaric oxygen or procedural intervention to manage toxicity. With a mean follow-up of 29 months (6-148), the 5-year freedom from grade 2+ proctitis was 97.8%. Rectal bleeding was more likely for patients older than age 75 (7.4% vs. 2.0%, pZ.003). In rare cases where intrafraction rotation was not corrected, a higher rate of patients experienced rectal bleeding (10.5% vs. 2.9%, pZ.03). Dosimetrically, a rectal V3600cGy <3cc predicted for decreased risk of bleeding (2.6% vs. 7.8%, pZ.006), as did Rectal V3400cGy<6cc's (1.9% vs. 4.3%, pZ.021). NCCN risk grouping, ADT, Race, and prescription dose (3500cGy vs. 3625cGy) were not significant. On multivariate analysis, the lone predictor of grade 2+ proctitis was intrafraction rotation non-correction (OR 4.033, CI 1.042-15.610, pZ.043). Conclusion: SBRT for prostate cancer is well tolerated with a low actuarial risk of grade 2+ proctitis. Prostate rotation independent of translation has the potential to modestly affect rectal toxicity. In patients treated on robotic platforms with pre-treatment administration of amifostine, intrafraction translation and rotation correction minimizes long-term rates of rectal bleeding.