Ponente
Descripción
Around 40 % of people surviving cancer do so because of radiotherapy. For improving this statistic, treatments based on hadron radiotherapy (HT) are allowing a better protection of the organs at risk by conforming the dose around the tumor target [1]. Nevertheless, some toxicities have recently been reported, being hypothesized that they can be due to the fact that hadrons deliver higher linear energy transfer (LET) that may generate collateral damages. Additionally, there is a rising interest in the medical-physics community in placing the enhanced LET of the beam within the tumour or removing it from the most sensitive normal structures around [2]. Thus, the experimental assessment of LET with high resolution would be a powerful tool to achieve optimized treatments. However, there are no radiation sensors capable of measuring the LET 2D-maps during treatments due to the technology complexity associated.
To face this challenge, we have created novel silicon 3D-cylindrical microdetectors (25 μm diameter, 20 μm depth, and 200 μm pitch) specifically designed for this purpose [3-5]. In particular, the present work shows four new multi-array configurations of these sensors (microdosimeters), first of its kind, enable of quantifying the LET 2D-maps in clinical conditions and covering a wide range of resolutions, namely: (i) a 11×11 array covering a 2 mm×2 mm radiation sensitive area [2] and (ii) a linear array of 3 × 3 microdetectors with a total surface of 0.4 mm×12 cm [3] (Fig. 1); (iii) a 5×25 pixel configuration covering an area of 1.9 cm × 0.1 cm and (iv) a 1×10 strip layout of 5.1 cm × 0.1 cm [4] (Fig. 2). To the best of our knowledge, these are the largest radiation sensitive surface covered with microdosimeters by now.
These systems have been tested in the the Accélérateur Linéaire et Tandem à Orsay facility (ALTO, France) by irradiating them with monoenergetic proton beams from 6 to 20 MeV at clinical-equivalent fluence rates to verify their potential application in the medical physics field (Figure 3). Likewise, we have irradiated some of these sensors in the the Orsay Proton Therapy Centre (CPO, France) with clinical fluence rates (~ 108 cm-2·s-1). The microdosimetry 2D-maps were obtained with a spatial resolution of 200 µm, the highest achieved so far at different positions of the Bragg curve by using a water-equivalent phantom (Figure 4) [5]. We will show the results of both sets of experiments. All the experimental results were crosschecked with Monte Carlo simulations and also compared to literature results (Figure 5).
We have demonstrated for first time that we may obtain microdosimetry distributions in two dimensions, which would be very useful for clinical conditions, e.g., close to organs-at-risk where we may have heterogeneous LET distributions, distal edges, for further voxel-by-voxel optimization treatments, etc. They can be used clinically as microdosimeters for measuring the LET distributions and, thus contributing to the optimization of HT treatments.
