Genitourinary Cancer

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SU_29_2300 - Effects of Treatment Planning Factors, Patient & Disease Characteristics on Toxicity in Prostate SBRT

Sunday, October 21
1:15 PM - 2:45 PM
Location: Innovation Hub, Exhibit Hall 3

Effects of Treatment Planning Factors, Patient & Disease Characteristics on Toxicity in Prostate SBRT
M. E. May Jr1, J. Gaskins2, and M. A. Mezera3; 1University of Louisville School of Medicine, Louisville, KY, 2University of Louisville School of Public Health, Department of Bioinformatics & Biostatistics, Louisville, KY, 3University of Louisville, Louisville, KY

Purpose/Objective(s): Stereotactic Body Radiation Therapy (SBRT) is an emerging definitive treatment modality for carefully selected prostate cancer patients. We analyzed our single institution experience utilizing robotic stereotactic linear accelerator technology to assess relationships between treatment planning factors, patient/disease characteristics, and acute and long term toxicity.

Materials/Methods: We retrospectively analyzed 70 consecutive patients treated with robotic SBRT at our institution over a 5 year period. Treating physicians used varied methods, at their discretion, in the treatment planning process to improve setup reproducibility and attempt to minimize toxicity. Age, risk group, rectal balloon use, bladder filling, urethral and/or penile bulb sparing, MRI fusion, number of fiducials tracked, and PTV volumes were examined for effect on gastrointestinal (GI) and genitourinary (GU) toxicities. Toxicity was assessed with Common Terminology Criteria for Adverse Events (CTCAE) scoring and patient completed International Prostate Symptom Score (IPSS) and Sexual Health Inventory for Men (SHIM) questionnaires at end of treatment, first follow up (median 1.3 months), and periodically thereafter. Statistical analysis used Kendall’s tau coefficient and ordinal and linear regressions to characterize relationships between the above parameters and their effect on acute and long term toxicity.

Results: Average age at treatment was 67 years (range 48-84). 68 patients (97%) received 3625 cGy in 5 fractions. Median follow up was 13.6 months for 65 patients who returned after completion. 33% (n=23) experienced grade 1 and 27% (n=19) grade 2 acute GU toxicity. 21% (n=15) and 7% (n=5) experienced grade 1 and 2 acute GI toxicity, respectively. No grade ≥3 toxicity was observed. Regression analysis showed significant correlation between urethral sparing and GU toxicity at end of treatment, first follow up, and late follow up (p=.001 at 1 year). It was also associated significantly with IPSS, persisting on multivariate analysis at 1 year (p=.023), as was partial bladder filling (p=.033). At first follow up, IPSS was worse with larger PTV (p=.026) and ADT (p=.017) and improved with penile bulb sparing (p=.021); however, these associations did not persist at 1 year. SHIM correlated with MRI fusion in the short term (p=.001), but at 1 year only pre-treatment SHIM was significantly associated. No parameter correlated significantly with GI toxicity at any time point.

Conclusion: Multi-institutional registry data has shown SBRT for prostate cancer provides acceptable control rates and toxicity compared to conventionally fractionated radiation therapy, with long term data still accruing. Multiple techniques are used variably by physicians to improve toxicity profile. Our analysis demonstrates a benefit of urethral sparing on both physician- and patient-reported GU toxicity at 1 year.

Author Disclosure: M.E. May: None. J. Gaskins: None. M.A. Mezera: None.

Michael May, MD, MS

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