Hybrid ultra-high and conventional dose rate treatments with electrons and photons for the clinical transfer of FLASH-RT to deep-seated targets: A treatment planning study

Till Tobias Böhlen; Michele Zeverino; Jean-François Germond; Rémy Kinj; Luis Schiappacasse; François Bochud; Fernanda Herrera; Jean Bourhis; Raphaël Moeckli

doi:10.1016/j.radonc.2024.110576

Hybrid ultra-high and conventional dose rate treatments with electrons and photons for the clinical transfer of FLASH-RT to deep-seated targets: A treatment planning study

Radiother Oncol. 2024 Dec:201:110576. doi: 10.1016/j.radonc.2024.110576. Epub 2024 Oct 11.

Authors

Till Tobias Böhlen¹, Michele Zeverino¹, Jean-François Germond¹, Rémy Kinj², Luis Schiappacasse², François Bochud¹, Fernanda Herrera², Jean Bourhis², Raphaël Moeckli³

Affiliations

¹ Institute of Radiation Physics, Lausanne University Hospital and Lausanne University, Lausanne, Switzerland.
² Department of Radiation Oncology, Lausanne University Hospital and Lausanne University, Lausanne, Switzerland.
³ Institute of Radiation Physics, Lausanne University Hospital and Lausanne University, Lausanne, Switzerland. Electronic address: [email protected].

PMID: 39395673
DOI: 10.1016/j.radonc.2024.110576

Abstract

Purpose: This study explores the dosimetric feasibility and plan quality of hybrid ultra-high dose rate (UHDR) electron and conventional dose rate (CDR) photon (HUC) radiotherapy for treating deep-seated tumours with FLASH-RT.

Methods: HUC treatment planning was conducted optimizing a broad UHDR electron beam (between 20-250 MeV) combined with a CDR VMAT for a glioblastoma, a pancreatic cancer, and a prostate cancer case. HUC plans were based on clinical prescription and fractionation schemes and compared against clinically delivered plans. Considering a HUC boost treatment for the glioblastoma consisting of a 15-Gy-single-fraction UHDR electron boost supplemented with VMAT, two scenarios for FLASH sparing were assessed using FLASH-modifying-factor-weighted doses.

Results: For all three patient cases, HUC treatment plans demonstrated comparable dosimetric quality to clinical plans, with similar PTV coverage (V_95% within 0.5 %), homogeneity, and critical OAR-sparing. At the same time, HUC plans delivered a substantial portion of the dose to the PTV (D_median of 50-69 %) and surrounding tissues at UHDR. For the HUC boost treatment of the glioblastoma, the first FLASH sparing scenario showed a moderate FLASH sparing magnitude (10 % for D_2%,PTV) for the 15-Gy UHDR electron boost, while the second scenario indicated a more substantial sparing of brain tissues inside and outside the PTV (32 % for D_2%,PTV, 31 % for D_2%,Brain).

Conclusions: From a planning perspective, HUC treatments represent a feasible approach for delivering dosimetrically conformal UHDR treatments, potentially mitigating technical challenges associated with delivering conformal FLASH-RT for deep-seated tumours. While further research is needed to optimize HUC fractionation and delivery schemes for specific patient cohorts, HUC treatments offer a promising avenue for the clinical transfer of FLASH-RT.

Keywords: Electron; FLASH; Mixed beam radiotherapy; Ultra-high dose rates; VHEE.

MeSH terms

Brain Neoplasms / radiotherapy
Electrons* / therapeutic use
Feasibility Studies
Glioblastoma* / radiotherapy
Humans
Male
Pancreatic Neoplasms / radiotherapy
Photons* / therapeutic use
Prostatic Neoplasms* / radiotherapy
Radiotherapy Dosage*
Radiotherapy Planning, Computer-Assisted* / methods
Radiotherapy, Intensity-Modulated* / methods