Planning for Preservation: Feasibility of Erectile Tissue Sparing During Prostate Stereotactic Radiotherapy

An estimated one in six Australian men are diagnosed with prostate cancer (PC) by age 85. Cure and quality of life are the modern definitions of successful cancer treatment, and preservation of continence and sexual function relates closely to treatment outcome satisfaction. Erectile tissue sparing (ETS) is not generally standard practice for PC stereotactic body radiotherapy (SBRT). This retrospective planning study aimed to determine if erectile tissue (ET) could be spared whilst maintaining clinically acceptable doses to target volumes (TV) and critical organs during PC SBRT.

Imaging datasets of 30 PC patients treated at our centres were used. Patients underwent magnetic resonance imaging (MRI) scans, with the creation of a substitute CT (sCT) for planning. ET structures, including penile bulb (PB), internal pudendal arteries (IPA) and neurovascular bundles (NVB), were contoured on MRI. Two 40 Gy in five fraction plans were created for each patient, with and without ETS constraints. Plans were compared using Wilcoxon signed-rank tests.

Significant dose reduction was observed in bilateral IPAs and NVBs using ETS plans. No significant difference was seen in coverage of the clinical TVD_95%, rectum V_36Gy, urethra planning risk volume V_42Gy, bladder V_36Gy, or PB. Changes in coverage of the planning TVD_95% and bladder V_40Gy were deemed not clinically relevant.

Results indicate that ETS is feasible in conjunction with a planning MRI during SBRT for PC without compromise to TVs. Further prospective investigation is required to observe whether a decrease in ET dose correlates to a preservation in sexual function and/or improved treatment outcome satisfaction.