Impact of Anatomical Position Errors on Dose Distribution in Head and Neck Radiotherapy and Robust Image Registration Against Anatomical Changes.

BACKGROUND/AIM: This study pursued two goals: Firstly, to search for anatomical structures strongly correlating with dose deterioration, and secondly to investigate the effectiveness of image registration focusing on critical anatomy by comparing it with a conventional method. The aim was to achieve robust image registration to correct for anatomical changes during treatment. PATIENTS AND METHODS: Twenty patients with head and neck cancer were enrolled, and 68 simulation computed tomography (CT) and rescan CT image sets were retrospectively analyzed. Forty volumetric-modulated arc therapy and intensity-modulated proton therapy plans were generated and recalculated according to the rescan CT to evaluate the dose effects of anatomical changes. Correlation coefficients were calculated for the relationships between the six-axis motion of the anatomy and the dose indices for the clinical target volume (CTV) and organs at risk. In the image registration, we compared a conventional method and target-based registration that limited the registration range to the CTV and vertebrae. RESULTS: The CTV coverage and spinal cord dose were correlated with the position error associated with the pitch and vertical position of the vertebrae, and the parotid gland and oral cavity dose were strongly correlated with the position error associated with the roll of the clivus and mandible. The target registration improved CTV coverage and suppressed the increase in dose to organs at risk compared with conventional methods. CONCLUSION: Monitoring vertebral alignment, the assessment and correction of positioning errors associated with the clivus and mandible position errors are important to ensure the quality of daily treatment. Target-based registration may allow for more robust image registration.