Development of an Imaging Technique for Boron Neutron Capture Therapy

The development of 4-¹⁰B-borono-2-¹⁸F-fluoro-L-phenylalanine (¹⁸FBPA) for use in positron emission tomography (PET) has contributed to the progress of boron neutron capture therapy (BNCT). ¹⁸FBPA has shown similar pharmacokinetics and distribution to 4-¹⁰B-borono-L-phenylalanine (BPA) under various conditions in many animal studies. ¹⁸FBPA PET is useful for treatment indication. A higher ¹⁸FBPA accumulation ratio of the tumor to the surrounding normal tissue (T/N ratio) indicates that a superior treatment effect is expected. In clinical settings, a T/N ratio of higher than 2.5 or 3 is often used for patient selection. Moreover, ¹⁸FBPA PET is useful for predicting the ¹⁰B concentration delivered to the tumor and surrounding normal tissues, enabling high-precision treatment planning. Precise dose prediction using ¹⁸FBPA PET data has greatly improved the treatment accuracy of BNCT. However, the methodology used for the data analysis of ¹⁸FBPA PET findings varies; thus, data should be evaluated using a consistent methodology so as to be more reliable. In addition to PET applications, the development of ¹⁸FBPA as a contrast agent for magnetic resonance imaging that combines gadolinium and ¹⁰B is also in progress.