Evaluation of the Key Advantages between Two Modalities of Boronophenylalanine Administration for Clinical Boron Neutron Capture Therapy Using an Animal Model

In clinical boron neutron capture therapy (BNCT), boronophenylalanine (BPA) administrations through one-step infusion (OSI) and two-step infusion (TSI) are the most widely used. This study compared the advantages of OSI and TSI using a human oral squamous cell carcinoma-bearing animal model. OSI was administered at a high-dose rate of 20 mg/kg/min for 20 min (total dose: 400 mg/kg) as the first step infusion. TSI was a prolonged infusion at a low-dose rate of 1.67 mg/kg/min for 15, 30, 45, and 60 min (total dose: 25, 50, 75, and 100 mg/kg) following the first step infusion. The sigmoid E(max) model was used to evaluate the boron accumulation effect in the tumor. The advantages of TSI were observed to be greater than those of OSI. The observed advantages of TSI were as follows: a stable level of boron concentration in blood; tumor to blood boron ratio (T/B); tumor to muscle boron ratio (T/M); and skin to blood boron ratio (S/B). The boron accumulation effect in tumors increased to 68.98%. Thus, effective boron concentration in these tumor cells was achieved to enhance the lethal damage in BNCT treatment. Boron concentration in the blood was equal to that in the skin. Therefore, the equivalent dose was accurately estimated for the skin.