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. 2016 Dec;6(1):75.
doi: 10.1186/s13550-016-0230-7. Epub 2016 Oct 18.

Comparison of the image-derived radioactivity and blood-sample radioactivity for estimating the clinical indicators of the efficacy of boron neutron capture therapy (BNCT): 4-borono-2-18F-fluoro-phenylalanine (FBPA) PET study

Kayako Isohashi  1 , Eku Shimosegawa  2   3 , Sadahiro Naka  2 , Yasukazu Kanai  2   3 , Genki Horitsugi  2 , Ikuko Mochida  2 , Keiko Matsunaga  2   3 , Tadashi Watabe  2 , Hiroki Kato  2 , Mitsuaki Tatsumi  4 , Jun Hatazawa  2   5
Affiliations

Comparison of the image-derived radioactivity and blood-sample radioactivity for estimating the clinical indicators of the efficacy of boron neutron capture therapy (BNCT): 4-borono-2-18F-fluoro-phenylalanine (FBPA) PET study

Kayako Isohashi et al. EJNMMI Res. 2016 Dec.

Abstract

Background: In boron neutron capture therapy (BNCT), positron emission tomography (PET) with 4-borono-2-18F-fluoro-phenylalanine (FBPA) is the only method to estimate an accumulation of 10B to target tumor and surrounding normal tissue after administering 10B carrier of L-paraboronophenylalanine and to search the indication of BNCT for individual patient. Absolute concentration of 10B in tumor has been estimated by multiplying 10B concentration in blood during BNCT by tumor to blood radioactivity (T/B) ratio derived from FBPA PET. However, the method to measure blood radioactivity either by blood sampling or image data has not been standardized. We compared image-derived blood radioactivity of FBPA with blood sampling data and studied appropriate timing and location for measuring image-derived blood counts.

Methods: We obtained 7 repeated whole-body PET scans in five healthy subjects. Arterialized venous blood samples were obtained from the antecubital vein, heated in a heating blanket. Time-activity curves (TACs) of image-derived blood radioactivity were obtained using volumes of interest (VOIs) over ascending aorta, aortic arch, pulmonary artery, left and right ventricles, inferior vena cava, and abdominal aorta. Image-derived blood radioactivity was compared with those measured by blood sampling data in each location.

Results: Both the TACs of blood sampling radioactivity in each subject, and the TACs of image-derived blood radioactivity showed a peak within 5 min after the tracer injection, and promptly decreased soon thereafter. Linear relationship was found between blood sampling radioactivity and image-derived blood radioactivity in all the VOIs at any timing of data sampling (p < 0.001). Image-derived radioactivity measured in the left and right ventricles 30 min after injection showed high correlation with blood radioactivity. Image-derived blood radioactivity was lower than blood sampling radioactivity data by 20 %. Reduction of blood radioactivity of FBPA in left ventricle after 30 min of FBPA injection was minimal.

Conclusion: We conclude that the image-derived T/B ratio can be reliably used by setting the VOI on the left ventricle at 30 min after FBPA administration and correcting for underestimation due to partial volume effect and reduction of FBPA blood radioactivity.

Keywords: BNCT; FBPA; PET; T/B ratio.

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Figures

Fig. 1
Fig. 1
Time–activity curves (TACs). TAC of blood sampling radioactivity in 5 healthy subjects (a) and TAC of PET image-derived blood radioactivity: average values from 5 healthy subjects (b). Both the TACs showed a peak within five min after the FBPA injection, gradually approaching a constant level at 20 min after the injection
Fig. 2
Fig. 2
Time-course of the PET image-derived blood radioactivity. Representative decay-corrected axial images of the left ventricle in a 56-year-old healthy woman after injection of FBPA. High accumulation in the left ventricle was observed soon after the FBPA injection, to promptly decrease soon thereafter and gradually approach a constant level at 20 min later after the tracer injection
Fig. 3
Fig. 3
Correlation between blood sampling radioactivity and image-derived radioactivity in each blood pool. The blood samplings radioactivity (BS) at 3, 20, 30 and 50 min after the tracer injection and the image-derived blood radioactivity (PET) at each site (ascending aorta, aortic arch, pulmonary artery, left and right ventricle, inferior vena cava and abdominal aorta) in mid-scan time at 3.8, 20.5, 28.8 and 53 min after the injection were compared. BS is plotted on the horizontal axis, and PET is plotted on the vertical axis. Both units are in cps/g. A linear relationship was found between blood sampling radioactivity and PET image-derived radioactivity in each blood pool (p < 0.001). Strong correlations were observed between these parameters at 20 min after FBPA administration. The image-derived radioactivity measured in the left ventricle and right ventricle 30 min after injection showed high correlation (0.97 and 0.99, respectively), slope close to be 1.0 (0.96 and 0.95, respectively), and intercept (-161 and -149) with blood radioactivity
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