Dosimetric Analysis of Radiation Treatment Plans Based on a Deep Learning Auto Contouring Model for Patients with Localized Prostate Cancer

Abstract

<h3>Purpose/Objective(s)</h3> To evaluate the feasibility and safety of creating radiation treatment plans based on a convolutional neural network auto-contouring (AC) model for patients receiving radiation for localized prostate cancer with a radio-opaque rectal spacer hydrogel. <h3>Materials/Methods</h3> The deep learning model produces ACs for target volumes (prostate, proximal seminal vesicle), OARs (rectum, bladder, penile bulb, femoral heads), and rectal hydrogel spacers. ACs were compared to manual contours (MC) by MDs for clinical use. Individual volumes and overall performance (composite score) were previously evaluated and reported, qualitatively using a 1 (minor discrepancy), 2 (moderate discrepancy), 3 (significant discrepancy), and 4 (rejected, gross error) scale and quantitatively using Dice Similarity Coefficient (DSC) and mean distance to agreement. VMAT treatment plans were created on unedited AC volumes from five composite 1 (C1) cases and five composite 2 (C2) cases and dose volume metrics were computed for the final MCs. Dosimetry comparison was performed to assess the safety of delivering a treatment plan created from unedited ACs. Cases were planned to 50.4 Gy in 28 fractions to the SVs, with a SIB of 70 Gy the prostate. PTV expansions were CTV+5 mm (CTV+4 mm posteriorly). <h3>Results</h3> Of 62 initial cases evaluated, 11 were scored as a C1, 28 were scored as a C2, and 23 received a C3. 10 cases were randomly selected for treatment planning. For prostate (CTV P) in selected C1 and C2 cases, mean score was 1 and 1.8 and mean DSC was 0.919 and 0.876, respectively. Clinical goals for planning and dosimetric data from treatment plans are shown in Table 1. The mean V70 Gy for prostate CTV/PTV was 99.83%/90.05% for C1 cases and 99.46%/89.15% for C2 cases. All clinical goals for OARs were met in both cohorts. <h3>Conclusion</h3> 63% of all cases evaluated received a C1 or C2 score. Our results indicate the treatment plans generated from unedited ACs on these cases respected all clinical goals for OARs. Although C1 plans produced better PTV coverage than C2, almost all plans had sub-optimal PTV coverage, indicating the need for MDs to edit target volumes before treatment planning.