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Doses to Neurovascular Bundles and Internal Pudendal Artery Defined by Magnetic Resonance Imaging Correlate Significantly with Post-RT Sexual Function of Prostate Patients Who Received Stereotactic Body Radiotherapy
E Pryser*, J Lian , E Schreiber , S Das , R Chen , T Zhu , University of North Carolina, Chapel Hill, NC
Presentations
SU-E-FS4-2 (Sunday, July 30, 2017) 1:00 PM - 1:55 PM Room: Four Seasons 4
Purpose: SBRT is increasingly used for prostate cancer treatment, but dose effects correlating with sexual dysfunction is unknown. This is the focus of this study.
Methods: 21 patients were treated on a prospective clinical trial of SBRT without androgen deprivation therapy. The prescribed PTV dose of 38Gy (to 55%~60% isodose line) was given in 4 fractions, emulating HDR brachytherapy dosimetry. MRI/CT fusion was required for treatment planning of all patients. Sexual function was assessed prospectively using the validated questionnaire Sexual Health Inventory for Men (SHIM), at pre-RT, 1, 6, 12, 24 months post-RT. Structures related to sexual functions were contoured on MRI, including neurovascular bundles (NVB), lesser cavernosal nerve (LCN), internal pudendal artery (IPA), penile bulb (PB) and corpus cavernosum (CAV). Dosimetry was quantified by mean dose for IPA/PB/CAV and by max dose (as mean dose of top 5% in DVH) for NVB/LCN. For each follow-up, a stepwise linear regression was performed with SHIM as the response variable, age, utilization of sexual medication/device (a categorical co-variable), and dose values of abovementioned structures as predictors.
Results: Patients were stratified into three groups of poor (pre-RT SHIM<12, 6 patients), intermediate (12SHIM21, 8 patients) and good baseline performance (SHIM>21, 7 patients). Significant worsening in erectile functions was observed for intermediate and good groups as early as 6 months post-RT and was progressive longitudinally. At multiple follow-up after 6 months, severity of sexual dysfunction for patients with intermediate or good baseline correlated significantly with dose to NVB and IPA (R2 for model fit at 6/12/24 months were 0.65/0.55/0.67 respectively, p value for coefficients of NVB and IPA <0.05).
Conclusion: This is one of the first studies to demonstrate association between NVB and IPA dose with sexual dysfunction in prostate SBRT. This can help refine treatment planning in the future to minimize sexual side effects.
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