Dosimetric impacts of endorectal balloon in CyberKnife stereotactic body radiation therapy (SBRT) for early-stage prostate cancer.

Hong F Xiang,Ricardo De Armas,Muhammad Mustafa Qureshi,Jason A Efstathiou,B Nicolas Bloch,Anthony L Zietman,Kathryn Harris,Hsiao‐Ming Lu,Ariel E Hirsch,Sean Keohan

doi:10.1002/acm2.12063

Abstract

PurposeIn SBRT for prostate cancer, higher fractional dose to the rectum is a major toxicity concern due to using smaller PTV margin and hypofractionation. We investigate the dosimetric impact on rectum using endorectal balloon (ERB) in prostate SBRT.Materials and MethodsTwenty prostate cancer patients were included in a retrospective study, ten with ERB and 10 without ERB. Optimized SBRT plans were generated on CyberKnife MultiPlan for 5 × 7.25 Gy to PTV under RTOG‐0938 protocol for early‐stage prostate cancer. For the rectum and the anterior half rectum, mean dose and percentage of volumes receiving 50%, 80%, 90%, and 100% prescription dose were compared.ResultsUsing ERB, mean dose to the rectum was 62 cGy (P = 0.001) lower per fraction, and 50 cGy (P = 0.024) lower per fraction for the anterior half rectum. The average V50%, V80%, V90%, and V100% were lower by 9.9% (P = 0.001), 5.3% (P = 0.0002), 3.4% (P = 0.0002), and 1.2% (P = 0.005) for the rectum, and lower by 10.4% (P = 0.009), 8.3% (P = 0.0004), 5.4% (P = 0.0003), and 2.1% (P = 0.003) for the anterior half rectum.ConclusionsSignificant reductions of dose to the rectum using ERB were observed. This may lead to improvement of the rectal toxicity profiles in prostate SBRT.

Highlights

Typical dose distributions of CyberKnife prostate stereotactic body radiation therapy (SBRT) plans for a case from the endorectal balloon (ERB) group and a case from the noERB group
Patel et al 30 first reported that using ERB in 3D-CRT of 38 9 2.0 Gy led to significant highdose rectal sparing comparable to that achieved by a highly conformal IMRT of 38 9 2.0 Gy
Rectum toxicity profiles at median follow-up of 3 yr for late grade 3 GI toxicities typically lies within the 1%–3% range, which is comparable to those seen in conventionally fractionated 3D-CRT, IMRT, or HDR

Summary

Introduction

In SBRT for prostate cancer, due to the much higher dose per fraction and use of smaller PTV margins (2–3 mm posterior, 3–5 mm in all other directions) than those in 3D-CRT or IMRT, it is critical to minimize the prostate motion and the exposure of rectum volumes to intermediate and high dose which are predictive factors for late rectal toxicity.[18,19,20] It has been shown that an air or water-filled endorectal balloon (ERB) can significantly reduce prostate motion[21,22,23] and displace the posterior portion of the rectal wall away from the intermediate-to-high dose regions in 3D-CRT and IMRT This displacement can lead to significant rectal wall sparing and reducing rectal toxicity from prostate or post-prostatectomy radiation treatment, potentially to allow for further dose escalation to the prostate.[24,25,26,27,28,29,30]

Methods

Results

Discussion

Conclusion