A focused very high energy electron beam for fractionated stereotactic radiotherapy

Kristoffer Svendsen,Anders Persson,Diego Guénot,Kristoffer Petersson,Jonas Björklund Svensson,Olle Lundh

doi:10.1038/s41598-021-85451-8

Abstract

An electron beam of very high energy (50–250 MeV) can potentially produce a more favourable radiotherapy dose distribution compared to a state-of-the-art photon based radiotherapy technique. To produce an electron beam of sufficiently high energy to allow for a long penetration depth (several cm), very large accelerating structures are needed when using conventional radio-frequency technology, which may not be possible due to economical or spatial constraints. In this paper, we show transport and focusing of laser wakefield accelerated electron beams with a maximum energy of 160 MeV using electromagnetic quadrupole magnets in a point-to-point imaging configuration, yielding a spatial uncertainty of less than 0.1 mm, a total charge variation below 1 % and a focal spot of 2.3 times 2.6;{text {mm}}^2. The electron beam was focused to control the depth dose distribution and to improve the dose conformality inside a phantom of cast acrylic slabs and radiochromic film. The phantom was irradiated from 36 different angles to obtain a dose distribution mimicking a stereotactic radiotherapy treatment, with a peak fractional dose of 2.72 Gy and a total maximum dose of 65 Gy. This was achieved with realistic constraints, including 23 cm of propagation through air before any dose deposition in the phantom.

Highlights

High intensity regions which creates a region void of electrons inside the plasma, trailing the laser pulse like a wake
We present our advancements towards making a LWFA source suitable for fractionated stereotactic very high energy electrons (VHEE) radiotherapy, i.e. the total dose is delivered in fractions where each fraction is delivered by irradiating the tumor over several different angles
This energy is close to the 100 MeV that has previously been shown to be superior to state-of-the-art volumetric modulated arc therapy treatment (VMAT) plans[6] and the pre-focused electron beam spectra peaks slightly at this energy, allowing for a focused electron beam with higher charge

Summary

Introduction

High intensity regions which creates a region void of electrons inside the plasma, trailing the laser pulse like a wake. Common to all injection mechanisms is that the electron beam charge and energy depends on the laser pulse characteristics and, in general, a higher laser power can produce electron beams of higher charge while a higher laser energy usually results in higher electron energy. In this experiment, ionization injection[26] was used which gives a large amount of charge (several tens to hundreds of pC), a very broad energy spectrum and an ultra short pulse duration of a few fs. By focusing the electron beam inside a phantom using the EMQs, a more deeply penetrating beam is achieved which is used to create a 3D dose distribution similar to a typical stereotactic radiotherapy treatment

Methods

Results

Discussion

Conclusion