Integrating measurement and simulation for evaluation of patient‐specific whole‐body dosimetry in clinical BNCT

BACKGROUND: Boron neutron capture therapy (BNCT) is a treatment modality that utilises high intensity neutron beam in combination with a boron drug to target cancer cells at the cellular level. Despite decades of research in this field, there are very few reports on out-of-field patient dose of BNCT. PURPOSE: To quantify patient whole-body out-of-field dose during clinical BNCT for recurrent head-and-neck cancer using an integrated measurement-simulation workflow. METHODS: The data of 271 patients that received BNCT for recurrent head and neck were analyzed for this study.First, the neutron and gamma ray doses were measured using activation foils and thermoluminescent dosimeters, respectively. The detectors were placed onto the surface of the patient at various locations and the reaction rate of the metal foils were measured. Second, PHITS Monte Carlo simulation was performed to evaluate the neutron energy spectrum at each location and the corresponding neutron equivalent dose was determined. The total dose was calculated by summing the neutron equivalent dose and the gamma ray dose. The results were compared with other radiotherapy modalities. RESULTS: The mean ± standard deviation of equivalent dose at neck, chest, abdomen, waist, knee, and ankle were calculated to be 1.93 ± 1.12, 0.71 ± 0.42, 0.23 ± 0.12, 0.11 ± 0.06, 0.05 ± 0.03, 0.02 ± 0.01 Gy-eq, respectively. Excluding the neck region, the gamma ray dose was dominant at all measurement points. From the abdomen below, dose from the primary gamma ray were dominant, indicating a potential for reducing the dose to these regions by installing additional lead shielding in the treatment room walls. In comparison to other radiotherapy modalities, out-of-field dose of BNCT was found to be similar. CONCLUSION: The whole-body dose for patients that received BNCT for recurrent head and neck cancer were estimated by scaling PHITS derived neutron dose using multifoil reaction rates and adding measured gamma dose. The results showed the out-of-field dose was comparable to other radiotherapy modalities and further added confidence that BNCT is a safe treatment modality.