Genitourinary Cancer

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SU_20_2280 - Dosimetric Correlates and Patient-Reported Quality of Life Among Prostate Cancer Patients Treated with Stereotactic Body Radiation Therapy (SBRT)

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

Dosimetric Correlates and Patient-Reported Quality of Life Among Prostate Cancer Patients Treated with Stereotactic Body Radiation Therapy (SBRT)
N. A. Iarrobino1, R. Kalash2, B. S. Gill3, K. Holeva4, D. J. DAmbrosio5, and D. E. Heron3; 1University of Pittsburgh, Pittsburgh, PA, 2Department of Radiation Oncology, Hillman Cancer Center, University of Pittsburgh School of Medicine, Pittsburgh, PA, 3UPMC Hillman Cancer Center, Pittsburgh, PA, 4UPMC Hillman Cancer Center, Department of Radiation Oncology, Pittsburgh, PA, 5East Coast Radiation Oncology Associates, PA, Toms River, NJ

Purpose/Objective(s): While increasing data supports the use of stereotactic body radiation therapy (SBRT) for prostate cancer, limited evidence exists in regards to adequate dosimetry constraints and correlation with patient-reported outcomes. We present an interim analysis, specific to dosimetry and quality of life endpoints, for an ongoing, dual-institution phase II trial.

Materials/Methods: Patients with biopsy-proven low- (cT1b-T2a, Gleason 2-6, and PSA≤10) or intermediate- (cT2b, Gleason 2-6, and PSA≤10; cT1b-T2a, Gleason 2-6, and PSA 10-20; or cT1b-T2a, Gleason 7, and PSA≤10) risk prostate cancer, prostate volume ≤100 cc, and life expectancy ≥10 years were enrolled. Patients received 36.25 Gy in 5 non-consecutive fractions, with an integrated simultaneous boost of 40 Gy in 5 fractions to the prostate alone. None received androgen deprivation therapy. Various dosimetry constraints were established per protocol from extrapolation from existing non-SBRT treatment data. Expanded Prostate Cancer Index Composite (EPIC) scores were evaluated in relation to dosimetry. Minimally important difference (MID) were established using the anchor-based approach (urinary incontinence >5, urinary obstructive/irritative >6, bowel >4), and correlations made using Chi-square test.

Results: A total of 95 patients with ≥3 months of follow up (62 with ≥12 months) were analyzed with a median follow-up of 18.1 months (range 3.0-76.9 months). Post-treatment EPIC scores at 1, 6, 12 and 24 months were available for 89.5, 86.3, 67.4 and 37.9% of patients, respectively. EPIC scores in urinary obstructive/irritative domain at 1-month (-4.8, p=0.03) and bowel domain at 1-, 6-, and 12-months (-10.8, -6.1, -5.2) were significantly different from pre-treatment, with both returning to non-significant differences at 24 months. No significant, associations were seen with prostate volume or urethra dosimetry. Acute (1 month) two-fold MID urinary declines appeared more prevalent in patients prescribed to lower isodose lines (≤80%): incontinence 38.3 vs. 14.3% (p=0.03), obstructive/irritative 37.0 vs. 26.9% (p=0.39). Higher rectal D5% (>33 Gy) was associated with late bowel declines at 6 months (mean difference from baseline -8.9 vs. -3.6, p=0.09; two-fold MID 44.4 vs. 21.6%, p=0.04) and 12 months (mean difference -5.5 vs. -4.5, p=0.83; two-fold MID 26.9 vs. 22.2%, p=0.70).

Conclusion: In this prospective cohort of patients treated with prostate SBRT, patient-reported outcomes appeared favorable without significant differences from baseline at 2 years. Prolonged bowel symptoms were correlated with D5%. Despite concerns extrapolated from prostate brachytherapy literature, neither prostate volume nor urethral dosimetry correlated with urinary quality of life measures. In contrast, increased prostate dose heterogeneity may exacerbate urinary symptoms.

Author Disclosure: N.A. Iarrobino: None. R. Kalash: None. D.J. DAmbrosio: Partner; East Coast Radiation Oncology. D.E. Heron: No personal compensation; Accuray Exchange in Radiation Oncology. Partnership; Cancer Treatment Services International. Vice Chairman of Clinical Affairs; University of Pittsburgh School of Medicine. Director of Radiation Services; UPMC CancerCenter.

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