(Saturday, 4/7/2018)
Room: Foyer
Purpose: To determine the impact of reducing PTV margin on patient reported quality-of-life (QOL) for patients with low or low-intermediate risk prostate cancer with consideration of the actual delivered dose computed using deformable dose accumulation (DDA).
Methods: The IRB-approved prospective study included 20 patients; 9 planned using reduced margins (5 mm uniform with 4 mm at prostate/rectum interface), and 11 control patients planned using standard margins (10/6 mm). "Dose-of-the-day" was calculated using DDA, in which the daily CBCT dataset was deformed to the planning CT (PCT), and dose was computed on the resampled PCT using a parameter-optimized, B-spline algorithm (Elastix, ITK/VTK). Dose mapping was performed using the energy-mass congruence method. QOL data were collected via Expanded Prostate cancer Index Composite (EPIC-26) questionnaires pre- and post-treatment, and at 2,6,12,18,24,36 month time points. QOL data were standardized [range:0-100] and baseline-corrected. Mean differences between the margin-reduced group and control group (QOL_MR-QOL_control) were calculated. Bladder/PTV overlap and rectum/PTV overlap were dosimetrically assessed to evaluate OAR high dose regions.
Results: Differences between the delivered (cumulative, DDA-based) mean dose and planned mean dose were less than 2.2 Gy for targets and all OARs for both groups, and were not statistically significant (p=0.1). Standardized and baseline-corrected mean QOL_MR-QOL_control for EPIC domains categorized as “Urinary Incontinence�, “Urinary Irritative/Obstructive�, "Bowel�, “Sexual�, and “Hormonal� were 2.2, 12.5, 10.4, 13.5 and -1.1 at 36 months after radiation therapy (higher values better). The control group showed larger PTV/rectum and PTV/bladder intersection volumes (7.2±5.8, 18.2±8.1 cc) than the margin-reduced group (2.6±1.8, 12.5±8.3 cc), while the dose to these intersection volumes were not statistically different (p>0.1) between groups. PTV/rectum intersection volume correlated moderately (R=-0.5) with “Bowel� EPIC domain.
Conclusion: Margin-reduced prostate treatment exhibited clinically meaningful improvement of QOL without compromising the target dose coverage. Confirmation with more patients and longer follow-up is warranted.
Funding Support, Disclosures, and Conflict of Interest: This work was supported in part by a research grant from Varian Medical Systems, Palo Alto, CA
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