On the neutron radiation field and air activation around a medical electron linac

Abstract

In high-energy photon therapy, several radiation protection issues result from photonuclear reactions. In this study, the photoneutron radiation field around a Varian Clinac linear accelerator in 18 MV-X mode within two different radiotherapy bunkers was investigated by means of Monte Carlo simulations using the FLUKA code as well as ambient dose-equivalent measurements. Furthermore, the activation of the air inside the treatment room due to photonuclear reactions (13N and 15O) and the capture of photoneutrons moderated down within the bunker (41Ar) was studied by FLUKA simulations. From the simulation results, the annual effective dose to medical workers due to photoneutrons and activated air was estimated. The emission of radioactivity due to ventilation of the treatment room was found to be negligible.

Characterization of the Secondary Neutron Field Produced in a Thick Aluminum Shield by 1 GeV/u 56Fe Ions Using TLD-Based Ambient Dosimeters

“…All simulations have been performed with physics and transport parameters, including evaporation, coalescence, electromagnetic dissociation, and activation of the low-energy neutron optimized transport function. To compare with experimental values, the secondary neutron spectra have been scored in the detector volume, and the dosimeter response was then calculated by folding the simulated spectra with the energy-dependent response function of the GSI balls [41]. Additionally, the ambient dose equivalent calculated from ICRP74 [21] has been also scored in the volumes covered by the dosimeters.…”

“…However, as planned in the original IBER 17 project, secondary particle spectra were measured with ToF and energy loss measurements via E-E telescopes. Those spectra were then used as the source in another FLUKA simulation where the GSI ball geometry is irradiated with protons, which is similar to the simulations performed to obtain the neutron response function of the dosimeter [41]. After normalizing the simulation results to the calibration field ( 241 Am-Be neutrons) and subtracting the TLD600H signal contributions induced directly by the incident protons (these doses are also measured by the TLD700H chips), the neutron dose readings obtained during the measurements can be corrected for the influence of secondary protons.…”

Active Dosimetry with the Ability to Distinguish Pulsed and Non-Pulsed Dose Rate Contributions

“…Beyond this range, plastic scintillators underestimate the absorbed dose up to 2.5 times depending on energy. If one considers dosimetry behind the treatment room, then this behavior is completely satisfactory as the overwhelming part of the photon energy spectrum is in the energy region higher than 100 keV [7,8]. Regarding laser-induced X-rays, when the energy of incident photons is in the range of tens keV [9], such a simple correction does not work anymore, and the deconvolution of the spectrum can be required to restore the ratio of mass energy-absorption coefficients.…”

Measurement of neutron yield for a medical linear accelerator below 10 MV

“…Other studies have focused on calculations of photoneutron production, either through experiment and analytical analysis, 3,[7][8][9][10][11][12][13][14][15] or using Monte Carlo methods. [16][17][18][19][20] As well, Banaee and colleagues provided a useful review of the current state of knowledge for neutron production in medical linacs. 21 These studies of the clinical system are limited to photon beam energies above 10 MV.…”