Analyzing spatial distribution between 18 F-fluorodeoxyglucose and 18 F-boronophenylalanine positron emission tomography to investigate selection indicators for boron neutron capture therapy

Background 18 F-FDG PET is often utilized to determine BNCT selection due to the limited availability of 18 F-BPA PET, which is performed by synthesizing 18 F into the boron drug used for BNCT, although the uptake mechanisms between those are different. Additionally, only a few non-spatial point parameters, such as maximum SUV (SUV max ), have reported a correlation between those in previous studies. This study aimed to investigate the spatial accumulation pattern between those PET images in tumors, which would be expected to either show higher uptake on 18 F-BPA PET or be utilized in clinical, to verify whether 18 F-FDG PET could be used as a selection indicator for BNCT. Methods A total of 27 patients with 30 lesions (11 squamous cell carcinoma, 9 melanoma, and 10 rhabdomyosarcoma) who received 18 F-FDG and 18 F-BPA PET within 2 weeks were enrolled in this study. The ratio of metabolic tumor volumes (MTVs) to GTV, histogram indices (skewness/kurtosis), and the correlation of total lesion activity (TLA) and non-spatial point parameters (SUV max , SUV peak , SUV min , maximum tumor-to-normal tissue ratio ( T max / N ), and T min / N ) were evaluated. After local rigid registration between those images, distances of locations at SUV max and the center of mass with MTVs on each image and similarity indices were also assessed along its coordinate. Results In addition to SUV max , SUV peak , and T max / N , significant correlations were found in TLA. The mean distance in SUV max was 25.2 ± 24.4 mm and significantly longer than that in the center of mass with MTVs. The ratio of MTVs to GTV, skewness, and kurtosis were not significantly different. However, the similarities of MTVs were considerably low. The similarity indices of Dice similarity coefficient, Jaccard coefficient, and mean distance to agreement for MTV40 were 0.65 ± 0.21 , 0.51 ± 0.21 , and 0.27 ± 0.30 cm, respectively. Furthermore, it was worse in MTV50. In addition, spatial accumulation patterns varied in cancer types. Conclusions Spatial accumulation patterns in tumors showed low similarity between 18 F-FDG and 18 F-BPA PET, although the various non-spatial point parameters were correlated. In addition, the spatial accumulation patterns were considerably different in cancer types. Therefore, the selection for BNCT using 18 F-FDG PET should be compared carefully with using 18 F-FBPA PET.