A Prospective Study of the Dosimetric Impact and Quality of Life from Margin Reduction for Patients with Localized Prostate Cancer

Abstract

To investigate the impact of reducing CTV to PTV margins on dosimetry and patient reported Quality of Life (QOL) for patients with localized prostate cancer. Twenty patients were included in a single institution IRB-approved prospective study. Nine were planned using reduced margins (5 mm uniformly except 4 mm at prostate/rectum boundary), and 11 were control patients with standard margins (10/6 mm). Cumulative delivered dose was calculated using deformable dose accumulation. Each daily CBCT dataset was deformed to the planning CT (pCT), dose was computed, and accumulated on the resampled pCT using a parameter-optimized, B-spline algorithm (Elastix, ITK/VTK). EPIC-26 based patient reported QOL data was collected pre-treatment, post-treatment, and at 2, 6, 12, 18, 24, 36, 48 and 60 months follow-up. Post-radiation therapy (RT) QOL scores were baseline corrected and standardized to a [0-100] scale using EPIC-26 methodology. QOL comparisons between the margin-reduced and the standard cohorts including the averages within each arm and the overall mean QOL differences between the groups (QOLM-R-QOLcontrol) were made at each time point. The median QOL follow-up length for the 20 patients was 48 months. Cumulative delivered dose and planned dose did not reach statistical significance (p>0.1) for targets and organs at risk, for both mean and maximum dose. At 4 years after RT, standardized and baseline-corrected mean QOLM-R-QOLcontrol were improved for “Urinary Incontinence”, “Urinary Irritative/Obstructive”, “Bowel”, and “Sexual” EPIC domains by 3.5, 14.8, 10.2, and 16.1, respectively (higher value is 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), though the dose to these intersection volumes did not reach statistical significance (p>0.1) between the groups. PTV/rectum intersection volume showed a moderate correlation (R = -0.6) to “Bowel” EPIC domain. Margin-reduced group exhibited clinically meaningful improvement of QOL without compromising the target dose coverage.Abstract 4152; TableTime PointUrinary IncontinenceUrinary Irritative/ObstructiveBowelSexualHormonalEnd of RT (N = 20)-6.413.46.36.6-2.62-month post RT (N = 20)3.18.26.68.3-3.26-month post RT (N = 19)-2.08.519.014.94.412-month post RT (N = 19)5.510.38.019.97.124-month post RT (N = 17)-1.59.515.614.6-13.036-month post RT (N = 16)5.616.59.020.2-13.848-month post RT (N = 13)-3.96.34.96.2-14.2Mean QOLM-R - QOLcontrol3.514.810.216.1-4.9Minimally important difference range [Skolarus et al. Urology 2015]6-95-74-610-124-6 Open table in a new tab