Monte Carlo study of Siemens PRIMUS photoneutron production

Abstract

Neutron production in radiotherapy facilities has been studied from the early days of modern linacs. Detailed studies are now possible using photoneutron capabilities of general-purpose Monte Carlo codes at energies of interest in medical physics. The present work studies the effects of modelling different accelerator head and room geometries on the neutron fluence and spectra predicted via Monte Carlo. The results from the simulation of a 15 MV Siemens PRIMUS linac show an 80% increase in the fluence scored at the isocentre when, besides modelling the components necessary for electron/photon simulations, other massive accelerator head components are included. Neutron fluence dependence on inner treatment room volume is analysed showing that thermal neutrons have a 'gaseous' behaviour and then a 1/V dependence. Neutron fluence maps for three energy ranges, fast (E > 0.1 MeV), epithermal (1 eV < E < 0.1 MeV) and thermal (E < 1 eV), are also presented and the influence of the head components on them is discussed.

Secondary neutron spectra from modern Varian, Siemens, and Elekta linacs with multileaf collimators

“…Many studies have been performed to characterize the secondary neutrons from high-energy linacs, but most have investigated only one type of linac and the analytic techniques have varied widely. [6][7][8][9][10][11][12] A comprehensive study by…”

Neutron Dose Equivalent in Tissue Due to Linacs of Clinical Use

“…Furthermore it has been demonstrated in previous studies [23]; [34]; [22] that in fact, neutron production is defined by the material used and its respective threshold to the photonuclear reactions. For example, it is noted that Varian models used materials (see Table 93 Neutron Dose Equivalent in Tissue Due to Linacs of Clinical Use 1), with Z higher than those used by other models for the construction of the head.…”

“…Works like of the [23] established minimal differences in using of simplified geometries and complete for calculating photoneutrons. This has led most authors to use simplified geometries in their calculations [32]; [20]; [7]; [42]; [34]; [3]; [28]. Taking advantage that we have the complete geometry of the accelerator Varian Clinac 2100 C/D, we have studied the influence of the shielding cover in this study.…”

“…[41] calculated neutron ambient dose equivalent for different collimator configurations in a Varian Clinac 2300 C/D. [34] studied the effects of modeling different accelerator head and room geometries on the neutron fluence and spectra for a Siemens Primus Linac. [3] determined neutron doses to critical organs for a Siemens Mevatron KDS.…”

Calibration of a neutron detector based on single event upset of SRAM memories

“…In particular, delivery of modern Intensity Modulated Radiotherapy (IMRT) treatments with linac primary electron beams above 8e10 MeV, with a large total number of Monitor Units (MU), may lead to photo-neutron fluences in excess of 10 8 cm À2 at the isocenter (Pena et al, 2005). Neutron emission is essentially produced in high-Z materials (W, Pb, Fe, Cu, etc.)…”