Focused VHEE (very high energy electron) beams and dose delivery for radiotherapy applications

L Whitmore,R I Mackay,M Van Herk,J K Jones,R M Jones

doi:10.1038/s41598-021-93276-8

L Whitmore, R I Mackay + Show 3 more

Open Access

https://doi.org/10.1038/s41598-021-93276-8

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Journal: Scientific Reports	Publication Date: Jul 7, 2021
Citations: 26	License type: open-access

Affiliation: University of Manchester, Cockcroft Institute

Abstract

This paper presents the first demonstration of deeply penetrating dose delivery using focused very high energy electron (VHEE) beams using quadrupole magnets in Monte Carlo simulations. We show that the focal point is readily modified by linearly changing the quadrupole magnet strength only. We also present a weighted sum of focused electron beams to form a spread-out electron peak (SOEP) over a target region. This has a significantly reduced entrance dose compared to a proton-based spread-out Bragg peak (SOBP). Very high energy electron (VHEE) beams are an exciting prospect in external beam radiotherapy. VHEEs are less sensitive to inhomogeneities than proton and photon beams, have a deep dose reach and could potentially be used to deliver FLASH radiotherapy. The dose distributions of unfocused VHEE produce high entrance and exit doses compared to other radiotherapy modalities unless focusing is employed, and in this case the entrance dose is considerably improved over existing radiations. We have investigated both symmetric and asymmetric focusing as well as focusing with a range of beam energies.

Highlights

This paper presents the first demonstration of deeply penetrating dose delivery using focused very high energy electron (VHEE) beams using quadrupole magnets in Monte Carlo simulations
The on-axis dose distribution and transverse dose distributions show a significant reduction in entrance dose and similar exit dose compared to unfocused VHEE, and the use of the quadrupole magnets means the position of the maximum dose can be chosen by changing the quadrupole strengths
This study shows for the first time that combining multiple focused VHEE beams produced by changing the final quadrupole strength allows for a spread-out electron peak (SOEP) to be produced over a target region on-axis, with a lower entrance dose than the corresponding on-axis spread-out Bragg peak (SOBP), a low exit dose, and with a similar flatness to the SOBP

Summary

Introduction

This paper presents the first demonstration of deeply penetrating dose delivery using focused very high energy electron (VHEE) beams using quadrupole magnets in Monte Carlo simulations. We present a weighted sum of focused electron beams to form a spread-out electron peak (SOEP) over a target region This has a significantly reduced entrance dose compared to a proton-based spread-out Bragg peak (SOBP). The dose distributions of unfocused VHEE produce high entrance and exit doses compared to other radiotherapy modalities unless focusing is employed, and in this case the entrance dose is considerably improved over existing radiations. The entire tumour region can be covered using multiple proton beams of different energies weighted by intensity using for example the method shown in the 1984 paper by Bortfeld and Schlegel[7] in order to produce a spread-out Bragg Peak, this results in a significantly higher entrance dose (60–80%). Carbon-ion beams have a higher relative biological effectiveness (RBE) thereby causing more damage to the tumour, but with the disadvantage of requiring higher energy machines, which are more expensive and require significantly more space than proton radiotherapy m achines[11]

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