ESTRO 2024 - Abstract Book

S3795

Physics - Image acquisition and processing

ESTRO 2024

anatomical fidelity, two OARs (bladder and rectum) were manually delineated. Dice similarity coefficient (DSC), average and 95 th percentile Hausdorff distance (HD) of the contours of sCTs were compared with CBCT FS .

Results:

Figure 1 illustrates CBCT cor and sCTs of a representative test patient and their corresponding HU differences. Comparing to the inputs, substantial image quality improvements and reduced difference to CBCT cor were observed for all sCTs. For sCTs of all dose levels, CUT, with an average MAE/SSIM/PSNR of ≤54/≥0.94/≥34, improved slightly better than the cycleGAN (≤59/≥0.94/≥33) from the low dose CBCTs (≤164/≥0.81/≥28). For target and OAR dose-volume histogram (DVH) parameter differences with respect to CBCT cor over all test patients in both models, deviations were within 2 Gy (total dose 74 Gy) for dose DVH parameters (D 2/50/98% ) and below 2% for volume DVH parameters (V 50/60/65Gy ). Particularly in the target DVH comparison, the mean differences of D 2/50/98% comparing all sCTs with respect to CBCTcor were ≤0.5% for the planning target volume (PTV). The average 2% DD pass-rates were higher than 98% for both models, indicating an excellent agreement of all sCTs to the reference CBCT cor .

Compared to CBCT FS -to-pCT, the mean absolute transformation differences in sCTs-to-pCT registrations were less than 0.30 mm / 0.30° for both models, demonstrating all sCTs have the potential to align patients accurately.

Figure 2 shows the contouring evaluation of sCTs. For all sCTs, cycleGAN with mean DSC for bladder/rectum of ≥0.85/≥0.81 performs better than the CUT (≥0.83/≥0.76). The same trend was observed for HDs. A clear drop of performance at 15% dose was identified, where cycleGAN model began to exhibit degraded accuracy in generating the organs, as observed from the significant differences appearing at 15% and 10% dose sCT compared to CBCT FS . For CUT, a significant performance decline at 15% dose for the bladder, and at 25% for the rectum was found.