Development of a gamma ray telescope for online synovial dosimetry in boron neutron capture synovectomy

Abstract

Boron Neutron Capture Synovectomy (BNCS) is a novel application of the ¹⁰B(n,α) reaction for potential treatment of rheumatoid arthritis. During BNCS clinical trials, real-time knowledge of boron dose delivered to the synovium is necessary so that the remaining irradiation time can be determined. A 478 keV photon is emitted following 94% of boron neutron capture reactions, and detection of 478 keV photons emitted from the synovium provides a potential approach for online monitoring of the accumulated synovial boron dose. This thesis explores the feasibility of developing a telescope system for online determination of synovial boron dose for accelerator-based BNCS. The Monte Carlo code MCNP was used to design the telescope system. The neutron and photon background distributions in the radiation vault at the Laboratory for Accelerator Beam Applications (LABA) at MIT were explored via Monte Carlo simulations, and an optimum position for the photon detector was determined. Collimator and detector shields were designed, and significant reduction of neutron flux and background count at the detector location was observed. Sufficient boron photon counts from the synovium were predicted, and the feasibility of using a NaI detector instead of an HPGe detector was also confirmed. Next, a telescope system was built in the radiation vault at LABA. A background peak overlapping the energy region of 478 keV photons was observed in the measured spectrum by a 10.2 cm x 10.2 cm NaI(Tl) detector. Origin and direction of background particles entering the detector were explored, and further background reduction was achieved. The composition of the background peak was also analyzed.

(cont.) Experimental characterization of the telescope system was performed. It was confirmed that boron photons from the synovium could be detected in the presence of background counts. The count saturation became significant when the boron concentration was over 10,000 ppm, as predicted by simulations. Experimental results were compared with simulation results, and the overall agreement was within 10-20%. Reconstruction approaches for determination of the synovial boron dose based on the measured boron photon count and additional information such as anatomic configuration of the joint and boron compound distribution were generated.