Dosimetric feasibility of neurovascular bundle-sparing stereotactic body radiotherapy with periprostatic hydrogel spacer for localized prostate cancer to preserve erectile function

Mark E Hwang,Catherine S Spina,Sven Wenske,Mark Mayeda,Israel Deutsch,Carl D Elliston,Hiram Shaish

doi:10.1259/bjr.20200433

Abstract

Objective:We aim to test the hypothesis that neurovascular bundle (NVB) displacement by rectal hydrogel spacer combined with NVB delineation as an organ at risk (OAR) is a feasible method for NVB-sparing stereotactic body radiotherapy.Methods:Thirty-five men with low- and intermediate-risk prostate cancer who underwent rectal hydrogel spacer placement and pre-, post-spacer prostate MRI studies were treated with prostate SBRT (36.25 Gy in five fractions). A prostate radiologist contoured the NVB on both the pre- and post-spacer T2W MRI sequences that were then registered to the CT simulation scan for NVB-sparing radiation treatment planning. Three SBRT treatment plans were developed for each patient: (1) no NVB sparing, (2) NVB-sparing using pre-spacer MRI, and (3) NVB-sparing using post-spacer MRI. NVB dose constraints include maximum dose 36.25 Gy (100%), V34.4 Gy (95% of dose) <60%, V32Gy <70%, V28Gy <90%.Results:Rectal hydrogel spacer placement shifted NVB contours an average of 3.1 ± 3.4 mm away from the prostate, resulting in a 10% decrease in NVB V34.4 Gy in non-NVB-sparing plans (p < 0.01). NVB-sparing treatment planning reduced the NVB V34.4 by 16% without the spacer (p < 0.01) and 25% with spacer (p < 0.001). NVB-sparing did not compromise PTV coverage and OAR endpoints.Conclusions:NVB-sparing SBRT with rectal hydrogel spacer significantly reduces the volume of NVB treated with high-dose radiation. Rectal spacer contributes to this effect through a dosimetrically meaningful displacement of the NVB that may significantly reduce RiED. These results suggest that NVB-sparing SBRT warrants further clinical evaluation.Advances in knowledge:This is a feasibility study showing that the periprostatic NVBs can be spared high doses of radiation during prostate SBRT using a hydrogel spacer and nerve-sparing treatment planning.

Highlights

Men undergoing all forms of definitive therapy for prostate cancer experience a decline in erectile function following treatment.[1,2,3] In the Monitoring, Surgery or Radiotherapy for Prostate Cancer (PROTECT) randomized trial,[1] approximately half of men developed radiation-induced erectile dysfunction (RiED).While our mechanistic understanding of post-radiotherapy rectal and urinary toxicity is well established, that of post-radiotherapy sexual dysfunction is less clear.[4]
Patient selection Men with low- and intermediate-risk prostate cancer treated with stereotactic body radiotherapy (SBRT) to 3625 cGy in five twice-weekly fractions after hydrogel spacer placement were included in this study
The results presented support the feasibility of neurovascular bundles (NVB)- sparing with prostate SBRT following placement of a perirectal hydrogel spacer in an effort to mitigate RiED

Summary

Introduction

Men undergoing all forms of definitive therapy for prostate cancer experience a decline in erectile function following treatment.[1,2,3] In the Monitoring, Surgery or Radiotherapy for Prostate Cancer (PROTECT) randomized trial,[1] approximately half of men developed radiation-induced erectile dysfunction (RiED).While our mechanistic understanding of post-radiotherapy rectal and urinary toxicity is well established, that of post-radiotherapy sexual dysfunction is less clear.[4]. Men undergoing all forms of definitive therapy for prostate cancer experience a decline in erectile function following treatment.[1,2,3] In the Monitoring, Surgery or Radiotherapy for Prostate Cancer (PROTECT) randomized trial,[1] approximately half of men developed radiation-induced erectile dysfunction (RiED). A range of doses was implicated in studies that showed a correlation between penile bulb dose and toxicity.[5,6,7] radiation to the penile bulb has not definitively been demonstrated as a cause of RiED.[4,5,8,9,10] A number of single and multi-institution series reported new onset erectile dysfunction after radiotherapy that was unexplained by dose-volume relationship analyses of the corpus spongiosum (penile bulb), corpora cavernosa, or crura.[9,11]

Methods

Results

Conclusion