Study of the X-ray radiation interaction with a multislit collimator for the creation of microbeams in radiation therapy

Abstract

Microbeam radiation therapy (MRT) is a developing radiotherapy, based on the use of beams only a few tens of micrometres wide, generated by synchrotron X-ray sources. The spatial fractionation of the homogeneous beam into an array of microbeams is possible using a multislit collimator (MSC), i.e. a machined metal block with regular apertures. Dosimetry in MRT is challenging and previous works still show differences between calculated and experimental dose profiles of 10–30%, which are not acceptable for a clinical implementation of treatment. The interaction of the X-rays with the MSC may contribute to the observed discrepancies; the present study therefore investigates the dose contribution due to radiation interaction with the MSC inner walls and radiation leakage of the MSC. Dose distributions inside a water-equivalent phantom were evaluated for different field sizes and three typical spectra used for MRT studies at the European Synchrotron Biomedical beamline ID17. Film dosimetry was utilized to determine the contribution of radiation interaction with the MSC inner walls; Monte Carlo simulations were implemented to calculate the radiation leakage contribution. Both factors turned out to be relevant for the dose deposition, especially for small fields. Photons interacting with the MSC walls may bring up to 16% more dose in the valley regions, between the microbeams. Depending on the chosen spectrum, the radiation leakage close to the phantom surface can contribute up to 50% of the valley dose for a 5 mm × 5 mm field. The current study underlines that a detailed characterization of the MSC must be performed systematically and accurate MRT dosimetry protocols must include the contribution of radiation leakage and radiation interaction with the MSC in order to avoid significant errors in the dose evaluation at the micrometric scale.

A high‐resolution dose calculation engine for X‐ray microbeams radiation therapy

“…The source replication approach used in penMRT accelerates the simulations with the cost of neglecting the transmission, diffusion, and reflection through the MSC. In a recent study from Pellicioli et al 59 . the effect of the MSC on peak and valley doses has been investigated.…”

“…The source replication approach used in penMRT accelerates the simulations with the cost of neglecting the transmission, diffusion, and reflection through the MSC. In a recent study from Pellicioli et al 59 the effect of the MSC on peak and valley doses has been investigated. Based on this study, a perfect collimator assumption might cause an underestimation of the valley doses from 5% to 30% depending on the field size and the energy spectrum.The peak doses might be less affected with an underestimation of about 0.2%.…”

Non-Targeted Effects of Synchrotron Radiation: Lessons from Experiments at the Australian and European Synchrotrons

“…Typical photon energies in synchrotron beams dedicated to biomedical applications range from approximately 10 to 150 keV. Currently, many synchrotron facilities operate with an electron beam energy greater than or equal to 2.4 GeV and high electron-beam currents are achievable in the accelerator ring of third-and fourth-generation synchrotrons, which include the Australian Synchrotron (AS) in Melbourne, the National Synchrotron Light Source (NSLS) in Brookhaven, USA and the European Synchrotron Radiation Facility (ESRF) in Grenoble, France, [1][2][3]. A table summarizing third-and fourth-generation synchrotrons around the world housing beamlines capable of conducting radiobiological and clinical research is presented in Supplementary data (Section S1).…”

“…(i) the standard MRT configuration used for rodent experiments for many years has an average energy of 104.2 KeV and a peak energy of 87.7 keV, (ii) the preclinical MRT configuration developed for veterinary trials and has a mean energy of 119 KeV and a peak energy of 102.1 KeV, and/or (iii) the clinical MRT configuration for future clinical applications with a mean energy of 122.8 KeV and a peak energy of 108.2 KeV [3,13].…”

Synchrotron X-Ray Radiation-Induced Bystander Effect: An Impact of the Scattered Radiation, Distance From the Irradiated Site and p53 Cell Status

“…RIBE is thought to be transmitted via gap-junction intercellular communication (7), or extracellular soluble factors (8). X-ray beams produced by the third-generation synchrotron source such as Australian Synchrotron (AS) in Melbourne, Australia and the first fourthgeneration European Synchrotron Radiation Facility (ESRF) in Grenoble, France, have the advantage of delivering high radiation doses to a very small volume with low beam divergence (9,10). These features facilitate the study of in vitro and in vivo non-targeted effects.…”