A convenient verification method of the entrance photo-neutron dose for an 18 MV medical linac using silicon p-i-n diodes

Authors

Vanja Gracanin, University of WollongongFollow
Susanna Guatelli, University of WollongongFollow
Dean L. Cutajar, University of WollongongFollow
Iwan Cornelius, University of WollongongFollow
Linh T. Tran, University of WollongongFollow
David Bolst, University of WollongongFollow
Rhys M. Preston, Commonwealth Scientific Industrial Research OrganisationFollow
Rashmi Gupta, St George Cancer Care Centre
Johnson Yuen, St George Cancer Care CentreFollow
Marco Petasecca, University of WollongongFollow
Michael L. F Lerch, University of WollongongFollow
Vladimir Perevertaylo, SPA BIT
Anatoly B. Rosenfeld, University of WollongongFollow

RIS ID

111915

Publication Details

Gracanin, V., Guatelli, S., Cutajar, D., Cornelius, I., Tran, L. T., Bolst, D., Preston, R., Gupta, R., Yuen, J., Petasecca, M., Lerch, M., Prevertaylo, V. & Rosenfeld, A. (2017). A convenient verification method of the entrance photo-neutron dose for an 18 MV medical linac using silicon p-i-n diodes. Radiation Measurements, 106 391-398.

Abstract

Electron Linear Accelerators (linacs) used in radiotherapy treatments produce undesired photo-neutrons when they are operated at energies above 10 MeV. (Neutron Contamination from Medial Electron Accelerators, 1984). These photo-neutrons contaminate the therapeutic beam and increase dose equivalent delivered to patients. In this work, the neutron entrance dose for an 18 MV Varian Medical linac was measured using passive silicon p-i-n diodes. These detectors were calibrated in separate photon, electron and neutron fields. The silicon p-i-n diode detectors have shown excellent discrimination between fast neutron and photon radiation, with sensitivity to fast neutrons being ≈4000 times higher than to photons from a ⁶⁰Co source in terms of absorbed dose to tissue. The neutron tissue absorbed dose was studied both on the surface and inside a cubic solid water phantom, both experimentally and also using Geant4 Monte Carlo simulations. The silicon p-i-n diodes were found to be useful for quick estimation of the fast neutron tissue dose and dose equivalent in pulsed, mixed radiation fields produced by a medical linac.