Non‐invasive estimation of 10B‐4‐borono‐L‐phenylalanine‐derived boron concentration in tumors by PET using 4‐borono‐2‐18F‐fluoro‐phenylalanine

In boron neutron capture therapy (BNCT), 10B‐4‐borono‐L‐phenylalanine (BPA) is commonly used as a 10B carrier. PET using 4‐borono‐2‐18F‐fluoro‐phenylalanine (18F‐FBPA PET) has been performed to estimate boron concentration and predict the therapeutic effects of BNCT; however, the association between tumor uptake of 18F‐FBPA and boron concentration in tumors remains unclear. The present study investigated the transport mechanism of 18F‐FBPA and BPA, and evaluated the utility of 18F‐FBPA PET in predicting boron concentration in tumors. The transporter assay revealed that 2‐aminobicyclo‐(2.2.1)‐heptane‐2‐carboxylic acid, an inhibitor of the L‐type amino acid transporter, significantly inhibited 18F‐FBPA and 14C‐4‐borono‐L‐phenylalanine (14C‐BPA) uptake in FaDu and LN‐229 human cancer cells. 18F‐FBPA uptake strongly correlated with 14C‐BPA uptake in 7 human tumor cell lines (r = .93; P < .01). PET experiments demonstrated that tumor uptake of 18F‐FBPA was independent of the administration method, and uptake of 18F‐FBPA by bolus injection correlated well with BPA uptake by continuous intravenous infusion. The results of this study revealed that evaluating tumor uptake of 18F‐FBPA by PET was useful for estimating 10B concentration in tumors. Tumor uptake of 18F‐FBPA was well correlated with that of BPA. Thefore, 18F‐FBPA PET would be a powerful tool to estimate 10B concentration in tumors and predict the therapeutic effects of BNCT.