Abstract
Synchrotron-generated microbeam radiotherapy holds great promise for future treatment, but the high dose gradients present conventional dosimetry with a challenge. Measuring the important peak-to-valley dose ratio (PVDR) of a microbeam-collimated synchrotron source requires both a dosimeter and an analysis method capable of exceptional spatial resolution. The PVDR is of great interest since it is the limiting factor for potential application of the microbeam radiation therapy technique clinically for its tissue-sparing properties (i.e. the valley dose should be below the tolerance of normal tissue). In this work a new method of measuring the dose response of PRESAGE dosimeters is introduced using the fluorescence from a 638 nm laser on a confocal laser-scanning microscope. This fluorescent microscopy method produces dosimetry data at a pixel size as low as 78 nm, giving a much better spatial resolution than optical computed tomography, which is normally used for scanning PRESAGE dosimeters. Using this technique the PVDR of the BL28B2 microbeam at the SPring-8 synchrotron in Japan is estimated to be approximately 52:1 at a depth of 2.5 mm. The PVDR was also estimated with EBT2 GAFchromic films as 30.5:1 at the surface in order to compare the PRESAGE fluorescent results with a more established dosimetry system. This estimation is in good agreement with previously measured ratios using other dosimeters and Monte Carlo simulations. This means that it is possible to use PRESAGE dosimeters with confocal microscopy for the determination of PVDR.
Highlights
Microbeam X-ray irradiation offers an innovative and promising modality for delivering high dose to well defined sections of tumour-bearing tissue whilst sparing the adjacent healthy tissue
Normal broad-beam radiotherapy has no need for pixel resolutions as high as those achieved here, but the high dose gradient inherent to microbeam collimation demands that the measurement technique be accurate down to the micrometre scale
It has shown that the dose recorded in a PRESAGE gel is capable of much better resolution than is used by current optical computed tomography (OCT) systems
Summary
Microbeam X-ray irradiation offers an innovative and promising modality for delivering high dose to well defined sections of tumour-bearing tissue whilst sparing the adjacent healthy tissue. This approach relies on the superior regenerative ability of healthy cells compared with tumourous cells when repopulating a depleted region (Dilmanian et al, 2007). Microbeam radiation therapy (MRT) requires a minimally divergent radiation source that passes through a collimator. For this purpose a synchrotron is used to generate highly collimated radiation. In order to assess the potential clinical usefulness of a MRT
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