Abstract
Successful transition of synchrotron-based microbeam radiation therapy (MRT) from pre-clinical animal studies to human trials is dependent upon ensuring that there are sufficient and adequate measures in place for quality assurance purposes. Transmission detectors provide researchers and clinicians with a real-time quality assurance and beam-monitoring instrument to ensure safe and accurate dose delivery. In this work, the effect of transmission detectors of different thicknesses (10 and 375 µm) upon the photon energy spectra and dose deposition of spatially fractionated synchrotron radiation is quantified experimentally and by means of a dedicated Geant4 simulation study. The simulation and experimental results confirm that the presence of the 375 µm thick transmission detector results in an approximately 1-6% decrease in broad-beam and microbeam peak dose. The capability to account for the reduction in dose and change to the peak-to-valley dose ratio justifies the use of transmission detectors as thick as 375 µm in MRT provided that treatment planning systems are able to account for their presence. The simulation and experimental results confirm that the presence of the 10 µm thick transmission detector shows a negligible impact (<0.5%) on the photon energy spectra, dose delivery and microbeam structure for both broad-beam and microbeam cases. Whilst the use of 375 µm thick detectors would certainly be appropriate, based upon the idea of best practice the authors recommend that 10 µm thick transmission detectors of this sort be utilized as a real-time quality assurance and beam-monitoring tool during MRT.
Highlights
Synchrotron X-ray microbeam radiation therapy (MRT) is a promising radiotherapy modality for the treatment of neurological disorders and inoperable brain tumours, those presenting in paediatric patients (Slatkin et al, 1992; Dilmanian et al, 2002; Laissue et al, 2007; Bouchet et al, 2010; Romanelli et al, 2011)
The synchrotron X-ray spectra simulated by the G4IMBL simulation were stored in a Phase space files (PSFs) situated before the water phantom in hutch 2B, after transport through the Imaging and Medical Beam-Line (IMBL)
Monte Carlo simulations and experimental measurements were performed to determine the effect of transmission detectors upon quality assurance (QA) for microbeam radiation therapy (MRT)
Summary
Synchrotron X-ray microbeam radiation therapy (MRT) is a promising radiotherapy modality for the treatment of neurological disorders and inoperable brain tumours, those presenting in paediatric patients (Slatkin et al, 1992; Dilmanian et al, 2002; Laissue et al, 2007; Bouchet et al, 2010; Romanelli et al, 2011). MRT makes use of highly collimated quasi-parallel X-ray microbeams, with typical widths ranging from 20 to 100 mm and pitch (i.e. centre-to-centre distance) ranging from 100 to 400 mm. This results in a dosimetric profile consisting of high dose rate ‘peaks’ which are separated by low dose rate ‘valleys’ formed primarily by scattered X-rays and secondary electrons generated within the ‘peak’ regions. The key advantage of MRT over traditional external beam radiotherapy techniques is the extraordinary radio-resistance demonstrated by normal tissue relative to cancerous tissue when irradiated by spatially fractionated micrometre-scale radiation fields (due to the dose–volume effect), allowing for a larger therapeutic dose delivery to the tumour site The key dosimetric parameters in MRT are related to the structure of the microbeam, such as the full width at half-maxiumum (FWHM) and the quality of the microbeam collimation, which can be evaluated by the peak-to-valley dose ratio (PVDR)
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