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

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

METHODS: 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 10 B 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.

RESULTS: 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 10 B 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 10 B concentration in the bladder gradually increased and reached 383.6 ± 214.7 ppm at 51 min. The mean 10 B concentration in the brain was estimated to be 7.6 ± 1.5 ppm at 57 min.

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