Author: Laura Bennett, Matthew Charles, Greg Cooley, John M. Floberg, Ryan Hutten, Elissa Khoudary, Nicholas Lynch, Kaili Ranta, Jordan M. Slagowski, Trevor Wilson 👨🔬
Affiliation: University of Pennsylvania, Department of Human Oncology, University of Wisconsin School of Medicine and Public Health, Department of Human Oncology, University of Wisconsin-Madison, University of Wisconsin-Madison 🌍
Purpose: To evaluate the impact of an iterative cone beam CT with metal artifact reduction (iCBCT+MAR) reconstruction algorithm (HyperSight TrueBeam 4.1, Varian Medical Systems) on image quality and soft tissue visualization in prostate cancer patients with hip implants undergoing image-guided radiation therapy (IGRT).
Methods: Fifteen cone beam CT setup images, reconstructed using filtered backprojection (FBP), were acquired from six prostate patients with metal hip implants receiving IGRT; two were post-prostatectomy. For each acquisition, a retrospective reconstruction was performed using iCBCT+MAR. All images were presented in a blinded, randomized order to three radiation oncologists serving as qualified observers (QO). The QOs graded the images on a scale of 1-5 for overall image quality (OIQ), suitability for IGRT, and the ability to resolve prostate or prostate bed, rectum, seminal vesicles, and implanted fiducials (intact prostate patients only). Contrast was computed as the difference in target and rectum CT numbers. Statistical significance was assessed using paired one-sided Wilcoxon signed-rank tests.
Results: Mean image quality scores were significantly improved for iCBCT+MAR compared to FBP. OIQ improved from 2.7 (FBP) to 3.8 (iCBCT+MAR); suitability for IGRT was likewise improved (2.9 FBP, 4.0 iCBCT+MAR). Mean visualization of all ROIs was also improved across all acquisitions, including for the prostate/prostate bed (2.7 FBP, 3.5 iCBCT+MAR), rectum (3.1 FBP, 4.1 iCBCT+MAR), seminal vesicles (3.3 FBP, 3.4 iCBCT+MAR), and fiducials (3.7 FBP, 4.3 iCBCT+MAR). The improvement in observer scores was statistically significant for all ranked categories (p<0.05). Contrast between the target and rectum was improved by 36 HU on average with iCBCT+MAR.
Conclusion: The iCBCT+MAR algorithm significantly improved overall image quality and resulted in images considered more suitable for IGRT than standard FBP. Our findings demonstrate iCBCT+MAR improves visualization of target structures and adjacent normal tissues, including the rectal border, potentially improving setup accuracy and precision in prostate IGRT.