1003 - Dosimetric Analysis of Post-Radiotherapy Sexual Dysfunction in Patients Receiving Definitive Stereotactic Body Radiotherapy (SBRT) for Prostate Cancer: A Secondary Analysis of MIRAGE

08:20am - 08:25am PT

Room 307/308

Presenter(s)

Jonathan Massachi, MD, MS - University of California, Los Angeles, Los Angeles, CA

J. Massachi¹, T. Jiang², B. K. Neilsen¹, H. Wilhalme², D. Ruan¹, M. Casado¹, N. Chong¹, L. Zello¹, J. M. Lamb¹, T. M. M. Ma³, L. Valle¹, M. Cao⁴, M. L. Steinberg¹, and A. U. Kishan¹; ¹Department of Radiation Oncology, University of California, Los Angeles, Los Angeles, CA, ²University of California, Los Angeles, Los Angeles, CA, ³University of Washington, Seattle, WA, ⁴Department of Radiation Oncology, University of California San Francisco, San Francisco, CA

Purpose/Objective(s):

Preservation of sexual function following radiation therapy for prostate cancer remains a significant goal for many men choosing this treatment pathway. Aggressive margin reduction with MRI-guided radiotherapy has been shown to reduce toxicity in patients receiving stereotactic body radiotherapy (SBRT), but nearly 45% of men still experienced a significant decline in sexual function in the 2 years of treatment. We performed a secondary analysis of the MIRAGE phase III randomized trial, which compared CT-guided SBRT with MRI-guided SBRT, to evaluate potential predictors of sexual dysfunction.

Materials/Methods:

Sexual function was scored based on Expanded Prostate Cancer Index sexual function (EPIC-26 SF) domain, with a 24 point decline being considered clinically significant. The internal pudendal artery (IPA) and neurovascular bundle (NVB) were contoured on radiotherapy planning CT or low-field MRI scans using a rigid registration to a diagnostic MRI (MIM Software, Cleveland, OH). Dosimetric profiles were then extracted and statistical analysis was performed using non-parametric rank-sum and Chi square test of proportions to assess for differences between groups where appropriate.

Results:

A total of 127 patients had both EPIC-26 sexual function scores and analyzable dosimetry (CT: 61, MRI: 66). 65% of participants received ADT and 66% had recovered to a normal testosterone level by 24 months. 31% and 29% of patients in the CT and MRI groups experienced a significant decline in EPIC-26 SF at 2 years. In the CT group, bilateral NVB V20Gy and V36Gy were significantly higher than the MRI group. ADT use and duration, pelvic nodal radiation, and baseline EPIC-26 SF were significantly associated with a large decline in EPIC-26 SF by two years. However, there were no significant differences across multiple dosimetric measures (D0.035, V20Gy, V36Gy, D_mean) when comparing patients with significant versus non-significant declines in EPIC-26.

Conclusion:

Although a reduction in dose to the neurovascular bundles was achieved with aggressive margin reduction, the proportion of patients with a significant decline in EPIC-26 SF was similar between patients receiving CT versus MRI-guided SBRT. More advanced strategies such as vessel-sparing techniques may be needed to achieve adequate dose reduction and further improve sexual outcomes.