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

• Published in: British journal of radiology Vol. 94; no. 1119; p. 20200433
• Main Authors: Hwang, Mark E, Mayeda, Mark, Shaish, Hiram, Elliston, Carl D, Spina, Catherine S, Wenske, Sven, Deutsch, Israel
• Format: Journal Article
• Language: English
• Published: England The British Institute of Radiology 01-03-2021
• Subjects: Aged; Erectile Dysfunction - prevention & control; Feasibility Studies; Humans; Hydrogels - therapeutic use; Magnetic Resonance Imaging - methods; Male; Organs at Risk - diagnostic imaging; Prostate - diagnostic imaging; Prostatic Neoplasms - diagnostic imaging; Prostatic Neoplasms - radiotherapy; Radiosurgery - methods; Radiotherapy Dosage; Radiotherapy Planning, Computer-Assisted - methods; Rectum - diagnostic imaging; Retrospective Studies
• ISSN: 0007-1285; 1748-880X
• DOI: 10.1259/bjr.20200433

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.
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%.
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 (
< 0.01). NVB-sparing treatment planning reduced the NVB V34.4 by 16% without the spacer (
< 0.01) and 25% with spacer (
< 0.001). NVB-sparing did not compromise PTV coverage and OAR endpoints.
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.
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.