Objective: The tumor-to-normal tissue (T/N) boron ratio is determined in a patient prior to boron neutron capture therapy (BNCT) using 4-borono-2-18F-fluoro-l-phenylalanine (18F-FBPA) positron emission tomography (PET). The T/N ratio is used as a reference parameter to calculate BNCT dose and to evaluate treatment effects. The boronophenylalanine (BPA) dosage for BNCT treatment is higher than the 18F-FBPA dosage for PET diagnosis. Therefore, we aimed to determine whether the T/N ratios between diagnosis and treatment were correlated. Methods: In this study, SAS tongue cancer cells were used to develop an orthotopic nude mouse model. Micro-PET was performed after the mice were injected a dose of 3.7 ± 0.74 MBq of 18F-FBPA via the tail vein. The 18F radioactivity in the tumor, muscle, and heart blood pool was calculated using AMIND software. Organs and blood were collected for boron concentration analysis using inductively coupled plasma-atomic emission spectroscopy after the mice were injected with 400 mg/kg BPA at 15, 30, 45, and 60 min. Results: Pharmacokinetics of the tumor and muscle from 45 to 60 min after 18F-FBPA and BPA injections were slightly increased, whereas that of blood was slightly decreased. Median T/N ratios at 60 min after 18F-FBPA and BPA injections were 3.5 and 3.43, respectively. Median value of the T/N ratio between them was 3.49 at 60 min. The T/N ratio at 60 min after 18F-FBPA injection was similar to that after BPA injection. However, median tumor-to-blood (T/B) boron ratios of 18F-FBPA and BPA at 60 min were 1.63 and 3.35, respectively. Median value between them was 1.83 at 60 min. Conclusions: In this study, the T/B ratios demonstrate the spread of a distribution between 18F-FBPA and BPA injections. At 60 min, the T/N ratio of the 18F-FBPA injection was similar to that of the BPA injection. Boron concentration in normal tissue was almost equal to that in blood. Therefore, the representative T/N ratio could be obtained at 60 min after 18F-FBPA injection, and it was used as a reference parameter for calculating accurate radiation dose.