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

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.

Single-fraction 34 Gy Lung Stereotactic Body Radiation Therapy Using Proton Transmission Beams: FLASH-dose Calculations and the Influence of Different Dose-rate Methods and Dose/Dose-rate Thresholds

“…Very high energy electron radiation therapy, achieving energies up to 250 Mev, can also be an interesting possibility for FLASH-RT, as similar dosimetry to that of TBs has been simulated and measured. 54 , 55 Because it is still uncertain what exactly leads to the FLASH-effect, multiple assumptions have had to be made in this analysis. The exact dose-rate and dose threshold are still unknown, 7 , 9 and we therefore decided to use multiple thresholds (40/100 Gy/s and 4/8 Gy).…”

FLASH radiotherapy treatment planning and models for electron beams

“…With current technology, small-sized VHEE beams can be readily produced and scanned at UHDR, and VHEE accelerators and gantries are more compact and cheaper than current proton beam technology [5,23,62,63]. While to date there are no clinical VHEE RT devices, interest in creating such devices has seen a resurgence [5,23,62,63], taking on the challenges of designing and building clinical UHDR VHEE RT devices for FLASH RT [64][65][66][67][68]. In the absence of existing VHEE RT devices, UHDR VHEE treatment planning and beam modelling was so far focused on predicting VHEE dose distributions and temporal beam delivery characteristics to assist the design and optimization of future VHEE devices and to compare them with standard-of-care RT.…”

“…Using magnetic quadrupole focussing, convergent VHEE beams can be obtained and were shown to result in strongly peaked PDD thereby allowing to cover small volumes (0.1-1 cm 3 ) at a selected depth with conformal dose distributions [98,99], see Figure 1, and a superposition of several of such focussed VHEE beams in depth was shown to create 'spread-out electron peaks' [68]. While this delivery concept is in principle appealing for treatment planning of small stereotactic targets, as it results for small volumes of a few cm 3 in depths-dose distributions with a conformity similar to the one achieved by particle therapy, it comes with some conceptual and technical challenges that may render it impractical when applying it to larger target volumes.…”

Back to the Future: Very High-Energy Electrons (VHEEs) and Their Potential Application in Radiation Therapy

“…The depth dose curves of these symmetrically focused electrons also show a depth peak and a more favorable dose distribution with reduced proximal and distal doses. Finally, the possibility to shape both the on-axis and transverse plane dose distributions of the beam, as well as to create weighted sums of focused electron beams to form spread-out electron peaks (SOEP) over a target region from focused beams, was demonstrated in a very recent study [53].…”