A Prospective Study of the Dosimetric Impact and Quality of Life from Margin Reduction for Patients with Localized Prostate Cancer
Kumarasiri AD, Brown SL, Elshaikh MA, Movsas B, and Chetty IJ. A Prospective Study of the Dosimetric Impact and Quality of Life from Margin Reduction for Patients with Localized Prostate Cancer. International Journal of Radiation Oncology Biology Physics 2020; 108(3):e925.
International Journal of Radiation Oncology Biology Physics
Purpose/Objective(s): 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.
Materials/Methods: 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.
Results: 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.
Conclusion: Margin-reduced group exhibited clinically meaningful improvement of QOL without compromising the target dose coverage. [Formula presented]