Feasibility study of accelerator-based boron neutron capture therapy for thoracic tumors: treatment planning aspect.

This study discusses the feasibility of accelerator-based boron neutron capture therapy (AB-BNCT) for thoracic cancers. Fourteen patients were enrolled: six with breast cancer, five with lung cancer, and three with esophageal cancer. Although BNCT is performed with a single fraction from a single beam direction, two-fraction treatments with different beam angles were considered to improve the dose of gross tumor volume (GTV) in cases where the dose constraint of GTV was not achieved. Relative biological effectiveness (RBE)-weighted dose distributions were calculated based on computed tomography (CT) images via Monte Carlo simulation (PHITS) to evaluate the dose to GTV and organs-at-risk (OARs). One-field irradiation plans in six patients (breast: 1, lung: 4, esophageal: 1) did not achieve the dose constraint of GTV owing to deep-seated or large tumors, whereas those in the other patients did. Among these six patients, the two-field irradiation plan improved the achievement rate of the dose constraint of GTV from zero to five patients and that of heart from five to six patients. Moreover, the 2-field irradiation plan improved the homogeneity index of GTV. Changing the appropriate dose prescription and number of treatment fractions according to the patient's condition can enhance the safe delivery of BNCT for thoracic cancers while delivering a sufficient dose to the tumors.