Quantification of Boron-10 concentration in normal rats after 4-borono-2-18F-fluoro-phenylalanine injection by PET/MRI

Objectives In the boron neutron capture therapy (BNCT), boron-10 (10B) concentration in tumor and normal tissue is critical. In order to deliver 10B specifically to tumor, Borono-phenylalanine-fructose complex (BPA-fr) is utilized. We aimed to quantify absolute boron-10 concentration in normal rats by 4-borono-2-18F-fluoro-phenylalanine (FBPA) PET/MRI.

Methods FBPA solution (10.23±0.50MBq) was injected into 6 male SD rats via the tail vein. Whole body scan by PET/MRI (Hitachi Metals / NEOMAX Company) was performed at 1 hour after injection of FBPA. Accumulation of FBPA as percentage of injected doze per gram (%ID/g) was estimated in the brain, lung, heart, liver, pancreas, kidney, and small intestine on PET images by referring MRI images. After PET/MRI imaging, variable doses of 10B BPA-fr (5, 10, 15 and 20mg) were injected intravenously. Rats were dissected at 1 hour after 10B BPA-fr injection. Absolute 10B concentration in autopsied tissue was measured by inductively coupled plasma optical emission spectrometry (ICP-OES).

Results The estimated 10B concentration by FBPA PET/MRI in the brain, lung, heart, liver, pancreas, kidney, and small intestine were 0.36±0.07, 0.41±0.07, 0.59±0.16, 0.74±0.10, 1.15±0.27, 2.62±0.54 and 0.46±0.07 %ID/g, respectively. The measured 10B concentration by ICP-OES were 0.40±0.11, 0.60±0.12, 0.62±0.12, 0.62±0.09, 2.62±0.37, 1.49±0.21 and 0.71±0.09 %ID/g, respectively. In the pancreas, the concentration by PET/MRI were underestimated more than 50% (p<0.01). On the other hand, in the kidney, the concentration was overestimated more than 40% (p<0.01).

Conclusions We demonstrated quantification of boron concentration in normal organs of rats by PET/MRI. This method and result can be extended to FBPA PET in candidate patients of BNCT.