Highlights
- •A methodology has been developed for patient specific quality assurance in MRT.
- •The segmentation of peaks and valleys doses can be done on Gafchromic films for direct comparisons with MRT treatment plan.
- •Gamma-index tests performed on normalised dose distributions exhibit over 90% passing rate.
- •Some discrepancies remain on the absolute isocenter doses and require further investigation.
- •Despite these discrepancies, large animal MRT studies are starting at the ESRF based on valley doses prescription.
Abstract
Microbeam radiation therapy (MRT) uses synchrotron arrays of X-ray microbeams to take
advantage of the spatial fractionation effect for normal tissue sparing. In this study,
radiochromic film dosimetry was performed for a treatment where MRT is introduced
as a dose boost in a hypofractionated stereotactic radiotherapy (SRT) scheme. The
isocenter dose was measured using an ionization chamber and two dimensional dose distributions
were determined using radiochromic films. To compare the measured dose distribution
to the MRT treatment plan, peak and valley were displayed in separate dosemaps. The
measured and computed isocenter doses were compared and a two-dimensional 2%/2 mm
normalized -index analysis with a 90% passing rate criterion was computed. For SRT, a difference
of 2.6% was observed in the dose at the isocenter from the treatment plan and film
measurement, with a passing rate of 96% for the -index analysis. For MRT, peak and valley doses differences of 25.6% and 8.2% were
observed, respectively but passing rates of 96% and 90% respectively were obtained
from the normalized -index maps. The differences in isocenter doses measured in MRT should be further
investigated. We present the methodology of patient specific quality assurance (QA)
for studying MRT dose distributions and discuss ideas to improve absolute dosimetry.
This patient specific QA will be used for large animal trials quality assurance where
MRT will be administered as a dose boost in conventional SRT. The observed remaining
discrepancies should be studied against approximations in the TPS phantom materials,
beams characteristics or film read-out procedures.
Keywords
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Article info
Publication history
Published online: September 17, 2019
Accepted:
September 5,
2019
Received in revised form:
August 2,
2019
Received:
July 2,
2019
Identification
Copyright
© 2019 Associazione Italiana di Fisica Medica. Published by Elsevier Ltd. All rights reserved.
