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Measuring neutron spectra in radiotherapy using the nested neutron spectrometer

Published in: Journal of Medical Physics – November 2015
(Scientific journal of the American Association of Physicists in Medicine)

Authors: Robert Maglieri1, Angel Licea2, Michael Evans1, Jan Seuntjens1 and John Kildea1

1 McGill University, Montréal, Canada
2 Canadian Nuclear Safety Commission


This paper presents a new, fast and practical method for neutron spectra measurements in radiotherapy facilities. During radiotherapy treatments using medical linear accelerators, when high-energy beams are used, photoneutrons are produced in the head of the accelerator via photonuclear interactions. In this study, the investigators used the nested neutron spectrometer (NNS) to quantify neutron production in a radiotherapy facility. The NNS was developed by a Canadian company (DETEC, Gatineau, Quebec) and uses a novel design of nested, high-density polyethylene cylinders rather than the Bonner sphere systems (BSS) with activated foils traditionally used for this type of work. Its unique design makes the NNS more portable and less cumbersome to manipulate than the BSS. In addition, the NNS’s ability to operate in current mode solves the problem of pulse pile-up in high dose-rate environments. A radiotherapy bunker housing a Varian Clinac 21EX (Varian Medical Systems, Palo Alto, CA, USA) was used to verify the performance of the NNS in terms of reproducibility, linearity and dose rate effects. Neutron spectra obtained with the NNS were in reasonable agreement with results obtained with Monte Carlo simulations in a similar setup. The neutron equivalent doses obtained with the NNS agreed very well with doses recorded with bubble detectors (BTI Technologies, Chalk River, ON) in the treatment room.

The CNSC collaborated with DETEC through the Canadian Innovation Commercialization Program managed by Public Services and Procurement Canada. The program assists Canadian businesses with late-stage innovations by partnering them with federal departments that commit to testing and helping refine the innovation.

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