Dosimetry and radioprotection evaluations of very high energy electron beams

Thongchai A M Masilela,Yolanda Prezado,Rachel Delorme

doi:10.1038/s41598-021-99645-7

Abstract

Very high energy electrons (VHEEs) represent a promising alternative for the treatment of deep-seated tumors over conventional radiotherapy (RT), owing to their favourable dosimetric characteristics. Given the high energy of the electrons, one of the concerns has been the production of photoneutrons. In this article we explore the consequence, in terms of neutron yield in a water phantom, of using a typical electron applicator in conjunction with a 2 GeV and 200 MeV VHEE beam. Additionally, we evaluate the resulting ambient neutron dose equivalent at various locations between the phantom and a concrete wall. Through Monte Carlo (MC) simulations it was found that an applicator acts to reduce the depth of the dose build-up region, giving rise to lower exit doses but higher entrance doses. Furthermore, neutrons are injected into the entrance region of the phantom. The highest dose equivalent found was approximately 1.7 mSv/Gy in the vicinity of the concrete wall. Nevertheless, we concluded that configurations of VHEEs studied in this article are similar to conventional proton therapy treatments in terms of their neutron yield and ambient dose equivalent. Therefore, a clinical implementation of VHEEs would likely not warrant additional radioprotection safeguards compared to conventional RT treatments.

Highlights

There has recently been a renewed interest in VHEEs due to the technological advancements of compact high-gradient RF-based accelerators and laser wakefield accelerators based on laser-plasma technology, which overcomes one of the limitations originally foreseen for VHEEs, namely the large size of the linear accelerator (LINAC) that would be needed for such high energy beams
Given that the FLASH effect can only be exploited under certain combinations of beam parameters[17], the flexibility of the modulation of beam parameters afforded by these types of accelerators makes FLASH-VHEE treatments an exciting prospect
One of the solutions to this problem was proposed by Kokurewicz et al, who showed that the use of a magnetic focusing lens placed around the patient enables highly localised dose deposition in a small volumetric element for electron beams of 200 MeV and 2 G eV22

Summary

Introduction

Wakefield accelerator technologies provide a compact, cost-efficient alternative for the production of electron b eams[14], but have been shown to be capable of producing dose distributions comparable to that of photon beams while exploiting the advantages linked with the delivery of electron beams, namely a more precise manipulation with fewer mechanical components and shorter, more intense electron b unches[15,16]. The space requirements of scanning dipoles and quadrupoles may pose a logistical challenge in terms of the space constraints of a clinical setting, diminishing the advantages of the otherwise comparative compactness of the technology Due to these aforementioned limitations, and given the fact that electron applicators are currently used in a clinical setting, we postulated that we might benefit from reduced beam penumbras with its use. This was valuable as the use of an electron applicator in conjunction with VHEEs could possibly correspond to the upper limit, and worse case scenario in terms of neutron production with a treatment room

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