Dosimetric impact of different CT-to-RED curves on plans calculated using Eclipse TPS

Abstract Background The impact of using different computed tomography (CT) to relative electron density (RED) curves with various phantoms, such as CIRS and Catphan, as well as default CT-to-RED curves on treatment plans for brain, breast, and rectum sites is a crucial area of research in radiotherapy. This study aims to investigate how variations in these curves affect dose calculation accuracy for different treatment sites. Results A total of 45 volumetric modulated arc therapy plans for different clinical cases, including 15 brain, 15 breast, and 15 rectal patients, were recalculated using different CT-to-RED calibration curves for the two phantoms, in addition to the default curve implemented in the Eclipse Treatment Planning System. Dosimetric parameters were collected from dose-volume histograms, including planning target volume (PTV) coverage and organs-at-risk (OARs) were evaluated for each CT-to-RED calibration curve and each treatment site. Significant dosimetric differences for PTV and OARs parameters were observed between the CIRS and default CT-to-RED curves in the brain and rectum regions ( p < 0.05). Furthermore, significant differences were shown in the rectum cases between the Catphan and default curves, while no significant differences were found between the CIRS and Catphan curves ( p > 0.05). In the context of the brain region, the CIRS exhibited significant differences compared to the default curve, whereas the Catphan did not. Interestingly, no significant differences were observed in the PTV and OARs parameters of breast cancer cases across any of the CT-to-RED curves. Conclusion The study highlights the importance of choosing the appropriate CT-to-RED calibration curve, particularly in high-density regions, such as the brain and pelvis. The CIRS CT-to-RED calibration curve provided more accurate dose calculations than the default curve, particularly in the brain and rectum treatment sites. This suggests that the CIRS phantom is the most reliable for accurate calibration in these complex anatomical regions, leading to more precise treatment plans.