High resolution optical calorimetry for synchrotron microbeam radiation therapy

We propose the application of optical calorimetry to measure the peak to valley ratio for synchrotron microbeam radiation therapy (MRT). We use a modified Schlieren approach known as reference image topography (RIT) which enables one to obtain a map of the rate of change of the refractive index in a water bath from which the absorbed dose can be determined with sufficient spatial accuracy to determine the peak to valley ratio. We modelled the calorimetric properties of X-rays using a heated wire in a water bath. Our RIT system comprised a light source, a textured reference object and a camera and lens combination. We measured temperature contours and showed a plume rising from the heated wire. The total temperature change in water was 12 degrees C, 500 times greater than the calculated change from a 1 ms exposure on a synchrotron. At 1.0 ms, thermal diffusion will be the major cause of uncertainty in determining the peak to valley ratio, and we calculate thermal diffusion will reduce the measured peak to valley ratio to 76% of its initial value, but the individual microbeams will still resolve. We demonstrate proof of concept for measuring X-ray dose using a modified RIT method.