Very high-energy electron therapy as light-particle alternative to transmission proton FLASH therapy - An evaluation of dosimetric performances.

in Radiotherapy and oncology : journal of the European Society for Therapeutic Radiology and Oncology by Till Tobias Böhlen, Jean-François Germond, Laurent Desorgher, Izabella Veres, Andreas Bratel, Eric Landström, Erik Engwall, Fernanda G Herrera, Esat Mahmut Ozsahin, Jean Bourhis, François Bochud, Raphaël Moeckli

TLDR

  • This study is looking at whether using very high-energy electron beams (VHEE) instead of transmission proton beams (TP) for a type of radiation therapy called FLASH-RT can be just as effective in treating deep-seated tumors. The study found that VHEE beams can treat targets with roughly flat depth-dose distributions, and that the achievable dosimetric target conformity and adjacent organs-at-risk (OAR) sparing is driven for both modalities by their lateral beam penumbrae. The study suggests that VHEE-based FLASH-RT using sufficiently high beam energies may provide a lighter-particle alternative to TP-based FLASH-RT with comparable dosimetric plan quality. However, the study has limitations and further validation is needed in clinical settings. Future research should focus on larger patient cohorts and clinical validation of VHEE-based FLASH-RT to determine its safety and efficacy in treating deep-seated tumors. Additionally, future research should explore the use of VHEE beams at different energies and angles to further optimize the dosimetric plan quality and minimize the risk of radiation-induced side effects.

Abstract

Clinical translation of FLASH-radiotherapy (RT) to deep-seated tumours is still a technological challenge. One proposed solution consists of using ultra-high dose rate transmission proton (TP) beams of about 200-250 MeV to irradiate the tumour with the flat entrance of the proton depth-dose profile. This work evaluates the dosimetric performance of very high-energy electron (VHEE)-based RT (50-250 MeV) as a potential alternative to TP-based RT for the clinical transfer of the FLASH effect. Basic physics characteristics of VHEE and TP beams were compared utilizing Monte Carlo simulations in water. A VHEE-enabled research treatment planning system was used to evaluate the plan quality achievable with VHEE beams of different energies, compared to 250 MeV TP beams for a glioblastoma, an oesophagus, and a prostate cancer case. Like TP, VHEE above 100 MeV can treat targets with roughly flat (within ± 20 %) depth-dose distributions. The achievable dosimetric target conformity and adjacent organs-at-risk (OAR) sparing is consequently driven for both modalities by their lateral beam penumbrae. Electron beams of 400[500] MeV match the penumbra of 200[250] MeV TP beams and penumbra is increased for lower electron energies. For the investigated patient cases, VHEE plans with energies of 150 MeV and above achieved a dosimetric plan quality comparable to that of 250 MeV TP plans. For the glioblastoma and the oesophagus case, although having a decreased conformity, even 100 MeV VHEE plans provided a similar target coverage and OAR sparing compared to TP. VHEE-based FLASH-RT using sufficiently high beam energies may provide a lighter-particle alternative to TP-based FLASH-RT with comparable dosimetric plan quality.

Overview

  • The study evaluates the dosimetric performance of very high-energy electron (VHEE)-based radiotherapy (RT) as a potential alternative to transmission proton (TP)-based RT for the clinical transfer of the FLASH effect. The study compares the basic physics characteristics of VHEE and TP beams using Monte Carlo simulations in water and evaluates the plan quality achievable with VHEE beams of different energies, compared to 250 MeV TP beams for three patient cases. The primary objective of the study is to determine if VHEE-based FLASH-RT using sufficiently high beam energies can provide a lighter-particle alternative to TP-based FLASH-RT with comparable dosimetric plan quality.

Comparative Analysis & Findings

  • The study found that VHEE beams of 400[500] MeV match the penumbra of 200[250] MeV TP beams and penumbra is increased for lower electron energies. For the investigated patient cases, VHEE plans with energies of 150 MeV and above achieved a dosimetric plan quality comparable to that of 250 MeV TP plans. For the glioblastoma and the oesophagus case, although having a decreased conformity, even 100 MeV VHEE plans provided a similar target coverage and OAR sparing compared to TP. These findings suggest that VHEE-based FLASH-RT using sufficiently high beam energies may provide a lighter-particle alternative to TP-based FLASH-RT with comparable dosimetric plan quality.

Implications and Future Directions

  • The study's findings suggest that VHEE-based FLASH-RT using sufficiently high beam energies may provide a lighter-particle alternative to TP-based FLASH-RT with comparable dosimetric plan quality. However, the study has limitations, such as the small number of patient cases and the need for further validation in clinical settings. Future research should focus on larger patient cohorts and clinical validation of VHEE-based FLASH-RT to determine its safety and efficacy in treating deep-seated tumors. Additionally, future research should explore the use of VHEE beams at different energies and angles to further optimize the dosimetric plan quality and minimize the risk of radiation-induced side effects.
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