Speaker
Description
In two-field BNCT for oral cavity cancer, blood boron concentration estimates are required before treatment to generate dose plans. Understanding how this parameter affects dose distribution and irradiation time is essential for robust planning and treatment-day calibration. This study quantified these effects at 30 versus 40 ppm in a two-field BNCT plan for a large-volume tumour. A retrospective planning study was conducted for oral cavity cancer with a 96.46 cc gross tumour volume and a tumour-to-normal tissue ratio of 2.18 at the 1.2 MW Tsing Hua Open-pool Reactor using TH-BNCTplan tratment planning. The two-field plan combined a right-lateral field F1 using collimator C09 and an anterior field F2. Both scenarios were normalised to a maximum oral mucosa dose of 15.00 Gy-w using compound biological effectiveness values of 3.8 for tumour, 2.5 for mucosa and skin, and 1.3 for other tissues. A validation calculation was performed at the measured blood boron concentration of 33.69 ppm. Increasing blood boron concentration from 30 to 40 ppm reduced the total irradiation time by 19.1%, dropping from 28.92 to 23.39 minutes. Specifically, F1 decreased by 18.0% to 12.47 minutes and F2 decreased by 20.4% to 10.92 minutes, reflecting the higher boron dose rate of F2. The dosimetric impact was negligible; the mean tumour dose changed by only 0.09 Gy-w from 22.13 to 22.22 Gy-w, and all organ-at-risk differences were less than 0.25 Gy-w. The final treatment at 33.69 ppm, requiring 24.12 minutes with a mean tumour dose of 22.69 Gy-w, was consistent with linear interpolation between scenarios. In mucosa-constrained two-field BNCT, blood boron concentration governs irradiation time with an approximate 19% to 21% reduction per 10 ppm increase but has negligible dosimetric impact, allowing for independent per-field calibration without dose re-optimisation.