Room: Davidson Ballroom A
Purpose: To investigate enhanced cell killing in the presence of boron for proton beam therapy through production of alpha particles using in vitro cell irradiations and contribution of B-10 and B-11 for the cell killing using a Monte Carlo (MC) simulation.
Methods: A non-small cell lung cancer line (H1299) was cultured in 35 mm dishes with different concentrations (0, 50, 75, 100, 200, 250, and 300 mg/L) of (L)-4-dihydroxy-borylphenylalanine (BPA) for 24 hours. The cells were irradiated at the center of a modulated proton beam (range: 15.0 g/cmÂ², modulation: 2.0 g/cmÂ², and a field size of 20Ã—20 cmÂ²) in a water tank and a dose of 6.0 Gy was delivered three times using Mevion S250 proton therapy system. Cell viability was evaluated by comparing the cell count for the irradiated specimen to that of the control group (the same BPA concentration without beam irradiation). To investigate the origin of cell killing, MC simulations were performed with 100% B-10, 100% B-11, natural boron (20% B-10+80% B-11), and water. A total of 1Ã—10â?¸ protons were delivered to 4-mm-thick layer targets at the similar depth of the cell line in water, and the number of alpha particles was counted.
Results: The average cell viability of the irradiated sample decreased from 93.1Â±1.2% at 0 mg/L to 49.5Â±1.2% at 300 mg/L as a function of BPA dose. The clinically used concentration of BPA (250 mg/L) enhanced the tumor cell killing almost twice compared to the conventional proton beam therapy (0 mg/L). The alpha particles produced in the MC simulations were 61,000 (B-10), 39,000 (B-11), 43,000 (natural boron), and 4,000 (water).
Conclusion: Boron effectively escalates therapeutic dose in proton beam therapy through the production of high-LET alpha particles. The MC simulations demonstrate that the alpha particles are produced by both B-10 (~30%) and B-11 (~70%).