Evaluation of the impact of anatomical region-specific HU-RED conversion curves on VMAT treatment planning for head and neck cancer

Abstract Background The establishment of a precise correlation between Hounsfield units and electron densities is crucial for effectively correcting tissue inhomogeneities during radiation therapy treatment planning. This study aimed to investigate the benefits of personalizing the Hounsfield Unit—Relative Electron Density (HU-RED) conversion curve implemented in the treatment planning system (TPS) on the volumetric modulated arc therapy (VMAT) treatment plans quality for head and neck region cancer. Methods VMAT treatment plans for ten nasopharyngeal cancer patients were analysed using two conversion curves: the abdomen region curve, which is considered as the reference curve and the head and neck region curve. Both curves were obtained by scanning the entire Computerized Imaging Reference System (CIRS) model 062 for the abdomen region and its inner part for the head and neck region. Results Personalizing the conversion curve for the head and neck region has been shown to have no clear benefits on the radiation dose received by the key organs at risk in nasopharyngeal cancer, including the spinal cord, brainstem, right parotid, and left parotid, with P-values of 0.263, 0.401, 0.674, and 0.208, respectively. Additionally, there were no significant benefits on the dose coverage (D98%) of the planning target volumes PTV50 and PTV70, with P-values of 0.484 and 0.161, respectively. Conclusion Although these small changes between the two curves did not significantly impact treatment plans, it is crucial to continue evaluating, optimizing and personalizing the use of conversion curves to ensure that the more realistic treatment plans are delivered to the patients, offering them the best possible treatment outcomes.