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 ¹⁰B tissue concentrations, especially in neighboring normal organs, is important to avoid adverse effects. The ¹⁰B concentration in normal organs after loading with ¹⁰B, however, has not been established in humans. In this study, we performed 4-borono-2-[¹⁸F]-fluoro-phenylalanine (¹⁸FBPA) PET in healthy volunteers and estimated the chronological changes in the ¹⁰B concentrations of normal organs.

In 6 healthy volunteers, whole-body ¹⁸FBPA PET scans were repeated 7 times during 1 h, and the mean ¹⁸FBPA distributions of 13 organs were measured. Based on the ¹⁸FBPA PET data, we then estimated the changes in the ¹⁰B concentrations of the organs when the injection of a therapeutic dose of ¹⁰BPA-fructose complex (¹⁰BPA-fr; 30 g, 500 mg/kg body weight) was assumed.

The maximum mean ¹⁸FBPA concentrations were reached at 2-6 min after injection in all the organs except the brain and urinary bladder. The mean ¹⁸FBPA concentration in normal brain plateaued at 24 min after injection. When the injection of a therapeutic dose of ¹⁰BPA-fr was assumed, the estimated mean ¹⁰B 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 ¹⁰B concentration in the bladder gradually increased and reached 383.6 ± 214.7 ppm at 51 min. The mean ¹⁰B concentration in the brain was estimated to be 7.6 ± 1.5 ppm at 57 min.

¹⁸FBPA PET has a potential to estimate ¹⁰B concentration of normal organs before neutron irradiation of BNCT when several assumptions are validated in the future studies.