Impact of arc therapy in boron neutron capture therapy (BNCT) on dose uniformity and motion robustness

Monte Carlo simulations were conducted to evaluate the dose distribution characteristics and motion robustness of fixed-angle versus arc irradiation techniques in boron neutron capture therapy (BNCT), using a head phantom. For fixed-angle irradiation, an anterior-posterior (AP) beam was oriented towards the facial plane. In contrast, the arc technique involved a continuous 180° rotation, from the left to the right, around the central axis traversing the face. The target was located in the nasal cavity region. Results demonstrated the dosimetric superiority of the arc technique, which increased the mean tumor dose by 0.7 Gy-Eq and improved the dose homogeneity index from 0.67 to 0.74. For the head phantom in this study, the arc technique showed enhanced motion robustness, reducing dose deviations across five critical motion directions including anterior translation (AT), left translation (LT), right translation (RT), inferior rotation (IR), and superior rotation (SR). The maximum improvement was a 15.3 % reduction in the E2 % metric (dose error for the 2 % volume after motion-induced perturbations) at the RT direction. The largest average dose error reduction was achieved in the AT direction, reaching 8.2 %. These findings confirm that arc irradiation confers distinct advantages in BNCT cases affected by motion errors, owing to its superior dose conformity and stability.