A quantification of the electron return effect using Monte Carlo simulations and experimental measurements for the MRI-linac

Francesco Tortorelli; Cristian Borrazzo; Marica Masi; Maria Rago; Randa El Gawhary; Claudio Properzi; Domenico Marchesano; Gianmarco Grimaldi; Federico Bianciardi; Ivan Annessi; Annamaria Di Palma; Maria Valentino; Laura Verna; Giuseppina Chiarello; Plastino Wolfango; Piercarlo Gentile

doi:10.1088/2057-1976/ad8ce3

A quantification of the electron return effect using Monte Carlo simulations and experimental measurements for the MRI-linac

Biomed Phys Eng Express. 2024 Nov 13;11(1). doi: 10.1088/2057-1976/ad8ce3.

Authors

Francesco Tortorelli^{1

2}, Cristian Borrazzo², Marica Masi², Maria Rago², Randa El Gawhary², Claudio Properzi³, Domenico Marchesano², Gianmarco Grimaldi², Federico Bianciardi², Ivan Annessi², Annamaria Di Palma², Maria Valentino², Laura Verna², Giuseppina Chiarello², Plastino Wolfango⁴, Piercarlo Gentile²

Affiliations

¹ Department of Medical Physics, 'Tor Vergata' University of Rome, Rome, Italy.
² San Pietro Fatebenefratelli Hospital, Radiotherapy Department, Rome, Italy.
³ Radius s.r.l., Technology for life, Bologna, Italy.
⁴ Department of Industrial, Electronic and Mechanical engineering, 'Roma Tre' University of Rome, Rome, Italy.

PMID: 39476428
DOI: 10.1088/2057-1976/ad8ce3

Abstract

The integration of magnetic resonance (MR) imaging and linear accelerators into hybrid treatment systems has made MR-guided radiation therapy a clinical reality. This work aims to evaluate the influence of the Electron Return Effect (ERE) on the dose distributions. This study was conducted using MRIdian (ViewRay, Cleveland, Ohio) system. Monte-Carlo simulations (MCs) and experimental measurements with EBT3 Gafchromic films were performed to investigate the dose distribution in a slab water phantom with and without a 2-cm air gap. Plus, MCs took into account different field sizes and a lung gap. A gamma analysis compared calculated versus measured dose distributions. The MCs have shown an increase of the ERE with the radiation field size both in Percent Depth Dose (PDD) and crossline direction. As concerns to the PDD direction, the smallest field for which there was a significant dose accumulation was 4.15 × 4.15 cm²both for air-gap (13.5%) and lung-gap (3.3%). The largest field for which there was a significant dose accumulation was 24.07 × 24.07 cm²both for air-gap (39.7%) and lung-gap (4.9%). Instead for the crossline direction, the smallest field for which there was a significant dose accumulation was 2.49 × 2.49 cm²both for air-gap (8.6% ) and lung-gap (0.5%). The largest field for which there was a significant dose accumulation was 24.07 × 24.07 cm²both for air-gap (46.2%) and lung-gap (4.2%). PDD and crossline profiles showed good agreement with a gamma-passing rate higher than 91.15% for 2%/2 mm. The ERE can be adequately calculated by MC dose calculation platform available in the MRIdian Treatment Planning System. The MCs show an increase of the ERE directly proportional with the radiation field size. Good agreement was observed between the experimental measurements and calculated dose distributions.

Keywords: EBT3; MRgRT; Montecarlo simulation; electron return effect.

MeSH terms

Computer Simulation*
Electrons*
Humans
Lung / diagnostic imaging
Lung / radiation effects
Magnetic Resonance Imaging* / methods
Monte Carlo Method*
Particle Accelerators*
Phantoms, Imaging*
Radiotherapy Dosage*
Radiotherapy Planning, Computer-Assisted / methods
Radiotherapy, Image-Guided / methods