A pCT approach to CT calibration in proton therapy treatment planning
Speaker: Mara Bruzzi
Abstract
Tomographic proton imaging is now increasingly being regarded by the international scientific community as a powerful and innovative tool for the direct measurement of Relative Stopping Power (RSP) maps to be used in proton therapy planning. Uncertainties in the conversion of X-rays Computed Tomography (CT) Hounsfield units of patient tissues into proton RSPs, determine the use of large proximal and distal margins for what concerns the management of the planned target volume. Proton CT (pCT) can potentially reduce these uncertainties either by directly measuring proton stopping power or through a detailed cross-calibration of the X-rays CT (X-CT) optimized using pCT data. This latter method would provide useful clinical information without the need to apply the pCT apparatus directly on patients. To this purpose, the pCT system developed by Istituto Nazionale di Fisica Nucleare (INFN), composed by a microstrip silicon tracker and a YaG:Ce calorimeter, has been tested at the Trento proton Therapy Center (Italy) using a set of stabilized, heterogeneous, biological phantoms. The obtained RSP maps are compared voxel-by-voxel with the corresponding X-CT images, in view to obtain a cross-calibrated X-CT vs. pCT calibration curve. Once validated, this procedure may represent a new and direct calibration method to be adopted in clinical treatment planning, that can be made available also to proton therapy centers not equipped with a pCT system.
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