Assessment of 10B concentration in boron neutron capture therapy: potential of image-guided therapy using 18FBPA PET

In boron neutron capture therapy (BNCT) for cancer, the accurate estimation of B-10 tissue concentrations, especially in neighboring normal organs, is important to avoid adverse effects. The B-10 concentration in normal organs after loading with B-10, however, has not been established in humans. In this study, we performed 4-borono-2-[F-18]-fluoro-phenylalanine ((18)FBPA) PET in healthy volunteers and estimated the chronological changes in the B-10 concentrations of normal organs. In 6 healthy volunteers, whole-body (18)FBPA PET scans were repeated 7 times during 1 h, and the mean (18)FBPA distributions of 13 organs were measured. Based on the (18)FBPA PET data, we then estimated the changes in the B-10 concentrations of the organs when the injection of a therapeutic dose of (10)BPA-fructose complex ((10)BPA-fr; 30 g, 500 mg/kg body weight) was assumed. The maximum mean (18)FBPA concentrations were reached at 2-6 min after injection in all the organs except the brain and urinary bladder. The mean (18)FBPA concentration in normal brain plateaued at 24 min after injection. When the injection of a therapeutic dose of (10)BPA-fr was assumed, the estimated mean B-10 concentration in the kidney increased to 126.1 +/- 24.2 ppm at 3 min after injection and then rapidly decreased to 30.9 +/- 7.4 ppm at 53 min. The estimated mean B-10 concentration in the bladder gradually increased and reached 383.6 +/- 214.7 ppm at 51 min. The mean B-10 concentration in the brain was estimated to be 7.6 +/- 1.5 ppm at 57 min. (18)FBPA PET has a potential to estimate B-10 concentration of normal organs before neutron irradiation of BNCT when several assumptions are validated in the future studies.