Comparison of dose distribution with and without reflecting heterogeneous boron distribution using ¹⁸F-BPA positron...

This study investigated the dosimetric impact of implementing heterogeneous boron distribution into dose evaluations on tumors in BNCT. The study involved 27 patients who underwent ¹⁸F-BPA PET/CT scans. Dose evaluations were performed using various methods reflecting boron concentrations on CT images. The conventional dose evaluations, which reflected uniform boron concentration in blood of 25 ppm and a constant tumor-to-blood (T/B) ratio of 3.5, were compared with individual dose evaluations, which reflected the blood boron concentration and T/B ratio calculated from ¹⁸F-BPA in each patient. The heterogeneous tumoral dose distribution was also compared, revealing the dosimetric impact of the boron distribution calculated from each voxel of ¹⁸F-BPA. The spatial correspondence between ¹⁸F-BPA and dose distribution was compared using metabolic tumor volume (MTV) from ¹⁸F-BPA and isodose volume from the heterogeneous dose distribution. Results showed that the median blood boron concentration and T/B ratio calculated from ¹⁸F-BPA were 25.57 (23.90-27.84) ppm and 3.75 (2.54-4.59), respectively, comparable to those in the conventional dose evaluations. All dose indices in the heterogeneous tumoral dose evaluations were significantly lower than those in the conventional dose evaluations (p < 0.01). However, the spatial correspondence between the ¹⁸F-BPA and the dose distribution was not observed in the dice similarity coefficients of both MTV40-40% isodose volume and MTV50-50% isodose volume. In conclusion, the study confirmed the validity of applying the boron concentration calculated from ¹⁸F-BPA to the dose evaluation for a patient in BNCT. The differences might be associated with non-inter-patient variations of ¹⁸F-BPA, but the conventional dose evaluations mainly focused on the high boron concentration area within the tumor. Furthermore, the discrepancies in the patients were also observed between the ¹⁸F-BPA distribution and the heterogeneous dose distribution. Therefore, this study suggested that the indications for BNCT should consider not only ¹⁸F-BPA but also the dose distributions, which could reflect the heterogeneous tumoral boron distribution.