Prompt gamma tomography during BNCT—a feasibility study

Abstract

The success of clinical boron neutron capture therapy (BNCT) lies in the ability to manage the radiobiological effect on the tumour and healthy tissue, and thus, accurate dosimetry measurements is pertinent for each individual patient. In the present work we investigate the possibility of performing online prompt gamma tomography (PGT) during BNCT. A prototype detector system was constructed, which is in principle a pin-hole collimator with a HPGe crystal to be mounted on a C-bow device, with shielding of lithium-plastic and lead. The detector system was used to measure on a phantom placed in an epithermal neutron beam and on a 137Cs-source. The possibility of tomographic reconstruction using the detector system was tested on a phantom filled with a 131I-solution with a smaller sphere inserted containing a higher specific activity (ratio 10:1). The detector system was possible to operate up to about 6 × 108 cm−2 s−1 thermal neutron fluence at the peak in the phantom, at which time it was saturated. A 478 keV boron-peak was visible in the measured spectra but the signal-to-noise-ratio was rather low. No post-irradiation damage or neutron activation was detectable. A tomographic reconstruction of the phantom filled with 131I-solutions was performed using an algorithm developed in house and based on the MLEM method. The image quality is fairly good and the results provide a clear indication that the detector system can be used to obtain data that enables tomographic reconstruction. A spatial resolution of the detector system of about 2 cm was obtained from both the measurement on the 137Cs-source and the 131I-phantom. In conclusion, the presented feasibility study on a prototype PGT system is encouraging further studies specifically directed at improving the signal-to-noise-ratio in measurements in epithermal neutron beams.