Are Auto-Generated Organ-at-Risk Contours Good Enough in Prostate Radiotherapy?

Purpose: Manual contouring of organs-at-risk (OARs) in radiotherapy planning is a time-consuming and labor-intensive task that is prone to inter- and intra-observer variabilities. Additionally, contours drawn prior to treatment may not accurately reflect the patient’s anatomy throughout the entire treatment course, meaning that doses planned based on pre-treatment contours may not correspond to the actual delivered doses. This study seeks to explore the impact of OAR contour accuracy on prostate radiotherapy outcomes. Methods: OARs (bladder and rectum) were manually delineated on planning CT and daily CBCT images for 20 patients. Atlas-based segmentation algorithms were used to automatically generate OAR contours on the planning CT scans. Both low-risk (LRP, CTV = Prostate) and intermediate-risk (IRP, CTV = Prostate+SV) patient groups were simulated. Treatment plans were created via a novel automated planning application that utilized a knowledge-based planning solution for both auto-generated OARs (aOAR-plan) and manual delineated OARs (mOAR-plan). Planned doses were transferred from CT to CBCTs based on clinical shifts, and contour-based deformable registrations were applied to calculate the cumulative doses. Cumulative dose differences for OARs were used to assess the agreement between aOAR- and mOAR-plans. Additionally, five patients were selected to compare the cumulative dose differences between the transferred and re-calculated doses on CBCT. Results: The Overlap index/Dice similarity coefficient between auto- and manual-contours was 0.89 ± 0.10/0.77 ± 0.11 for the bladder and 0.76 ± 0.15/0.70 ± 0.07 for the rectum. Both LRP and IRP groups demonstrated good dosimetric agreements between aOAR- and mOAR-plans. No significant OAR dose differences between the transferred and re-calculated doses were observed. Conclusion: Contours manually drawn prior to treatment are being used to represent patient anatomy that can fluctuate by several millimeters daily, which raises questions about the time and effort involved. Automated contouring tools enhance contour consistency and deliver acceptable doses, providing a more reliable alternative to manual contours in prostate radiotherapy.