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 137 Cs-source. The possibility of tomographic reconstruction using the detector system was tested on a phantom filled with a 131 I-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 × 10 8 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-noiseratio was rather low. No post-irradiation damage or neutron activation was detectable. A tomographic reconstruction of the phantom filled with 131 I-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 137 Cs-source and the 131 I-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. KEYWORDS: Detector modelling and simulations I (interaction of radiation with matter, interaction of photons with matter, interaction of hadrons with matter, etc); Neutron sources; Dosimetry concepts and apparatus.

Experimentally determined vs. Monte Carlo simulated peak-to-valley ratios for a well-characterised n-type HPGe detector

“…The Monte-Carlo code utilised was MCNP5 v 1.40 (MCNP-A, 2003). This code was chosen since it was used in previous work by our group (Munck af Rosenschöld et al, 2006) utilising the same germanium detector as in this work. No peak shape modelling was deemed necessary in the simulations since the measurements were evaluated using gross ROI counts and no variation reduction technique or source bias was used in the simulations of photon and electron transport.…”

Boron neutron capture therapy (BNCT) in Finland: Technological and physical prospects after 20 years of experiences

“…Also, optimization of the collimator dimensions was studied, the results indicating that a 1 cm tumour could be detected using an array of detectors [146]. The germanium detector produces good signal and high quality single point measurements have been achieved [140,141,147], but the required space and cooling systems appear to be too extensive to be used in clinical setting. An Argentinean research group has designed and tested a LaBr 3 (Ce) detector system producing 1 cm 3 voxel images with 21 Â 21 voxels [148,149].…”

Accelerator technology and SPECT developments for BNCT

“…In addition, the tomographic principle gives access to three-dimensional information of the dose distribution. Other approaches have also been adopted for BNCT online dosimetry based on the 478 keV gamma ray detection, some of them were implemented in a BNCT facility [27] and others comprises conceptual studies or basic detector developments [28,29,30]. Despite the widespread application of SPECT in nuclear medicine, the use of such conventional diagnostic system for online BNCT dosimetry is not possible.…”