Improving treatment precision in head and neck BNCT: delineation of oral and pharyngeal mucosa based on an MRI Atlas for standardized applications

Abstract Background and purpose Boron neutron capture therapy (BNCT) has been routinely practiced for treatment of head and neck cancer in Japan. However, differences in contouring the oral and pharyngeal mucosa can lead to discrepancies in treatment. This study aimed to introduce a standardized approach using an MRI-based atlas, aiming to minimize inter-observer error and improve dose precision. Materials and Methods An MRI atlas of the head and neck mucosa was developed using water/fat-separated images from a healthy man. Using CT images from three patients, seven radiation oncologists performed contouring of the head and neck mucosa twice over a 3-week period. Contouring was first performed using CT alone, then later using fused T2-weighted images with the mucosal atlas for guidance. Contouring errors were assessed and their impacts on tumor dose were evaluated. Results The introduction of the MRI-based mucosal atlas significantly reduced inter-observer variation in mucosal volume (the coefficient of variation, abbreviated with COV, decreased from 0.61 with CT alone to 0.21 with the MRI atlas; p=0.003). Moreover, the atlas resulted in improved contour homology among observers and reduced variations in tumor dose. For all cases, COVs for maximum, mean, and minimum tumor doses were all below 5%. Conclusion Utilizing an MRI-based mucosal atlas in BNCT contouring can significantly reduce inter-observer variation, improve contour homology, and decrease variations in tumor dose. These findings suggest strong potential for standardizing and enhancing the quality of BNCT for head and neck cancer.