Toward clinical application of prompt gamma spectroscopy for in vivo monitoring of boron uptake in boron neutron capture therapy

In boron neutron capture therapy (BNCT) the absorbed dose to the tumor cells and healthy tissues depends critically on the boron uptake. Pronounced individual variations in the uptake patterns have been observed for two boron compounds currently used in clinical trials. This implies a high uncertainty in the determination of the boron dose component. In the present work a technique known as prompt gamma spectroscopy (PGS) is studied that potentially can be used for in vivo and noninvasive boron concentration determination at the time of the treatment. The technique is based upon measurement of gamma rays promptly emitted in the 10B(n,alpha)7Li and 1H(n,gamma ) 2D reactions. The aim of this work is to prepare the present setup for clinical application as a monitor of boron uptake in BNCT patients. Therefore, a full calibration and a set of phantom experiments were performed in a clinical setting. Specifically, a nonuniform boron distribution was studied; a skin/dura, a larger blood vessel, and tumor within a head phantom was simulated. The results show that it is possible to determine a homogeneous boron concentration of 5 µg/g within ±3% (1 standard deviation). In the nonuniform case, this work shows that the boron concentration can be determined through a multistep measurement procedure, however, with a somewhat higher uncertainty (~10%). The present work forms the basis for a subsequent clinical application of the PGS setup aimed at in vivo monitoring of boron uptake.