Magdalena Garbacz1, Francesco Giuseppe Cordoni2, Marco Durante3, Jan Gajewski4, Kamil Kisielewicz5, Nils Krah6, Renata Kopeć4, Paweł Olko4, Vincenzo Patera7, Ilaria Rinaldi8, Marzena Rydygier4, Angelo Schiavi9, Emanuele Scifoni10, Tomasz Skóra5, Francesco Tommasino11, Antoni Rucinski4. 1. Institute of Nuclear Physics Polish Academy of Sciences, 31342 Krakow, Poland. Electronic address: magdalena.garbacz@ifj.edu.pl. 2. University of Verona, Department of Computer Science, Verona, Italy; Trento Institute for Fundamental Physics and Applications, TIFPA-INFN, Trento, Italy. 3. GSI Helmholtzzentrum fur Schwerionenforschung, Darmstadt, Germany; The Technical University of Darmstadt, Germany. 4. Institute of Nuclear Physics Polish Academy of Sciences, 31342 Krakow, Poland. 5. National Oncology Institute, National Research Institute, Krakow Branch, Krakow, Poland. 6. University of Lyon, CREATIS, CNRS UMR5220, Inserm U1044, INSA-Lyon, Université Lyon 1, Centre Léon Bérard, France; University of Lyon, Université Claude Bernard Lyon 1, CNRS/IN2P3, IP2I Lyon, UMR 5822, Villeurbanne, France. 7. INFN - Section of Rome, Italy; Department of Basic and Applied Sciences for Engineering, Sapienza University of Rome, Italy. 8. Department of Radiation Oncology (Maastro), GROW School for Oncology, Maastricht University Medical Centre+, Maastricht, The Netherlands. 9. Department of Basic and Applied Sciences for Engineering, Sapienza University of Rome, Italy. 10. Trento Institute for Fundamental Physics and Applications, TIFPA-INFN, Trento, Italy. 11. Trento Institute for Fundamental Physics and Applications, TIFPA-INFN, Trento, Italy; Department of Physics, University of Trento, Trento, Italy.
Abstract
PURPOSE: We investigated the relationship between RBE-weighted dose (DRBE) calculated with constant (cRBE) and variable RBE (vRBE), dose-averaged linear energy transfer (LETd) and the risk of radiographic changes in skull base patients treated with protons. METHODS: Clinical treatment plans of 45 patients were recalculated with Monte Carlo tool FRED. Radiographic changes (i.e. edema and/or necrosis) were identified by MRI. Dosimetric parameters for cRBE and vRBE were computed. Biological margin extension and voxel-based analysis were employed looking for association of DRBE(vRBE) and LETd with brain edema and/or necrosis. RESULTS: When using vRBE, Dmax in the brain was above the highest dose limits for 38% of patients, while such limit was never exceeded assuming cRBE. Similar values of Dmax were observed in necrotic regions, brain and temporal lobes. Most of the brain necrosis was in proximity to the PTV. The voxel-based analysis did not show evidence of an association with high LETd values. CONCLUSIONS: When looking at standard dosimetric parameters, the higher dose associated with vRBE seems to be responsible for an enhanced risk of radiographic changes. However, as revealed by a voxel-based analysis, the large inter-patient variability hinders the identification of a clear effect for high LETd.
PURPOSE: We investigated the relationship between RBE-weighted dose (DRBE) calculated with constant (cRBE) and variable RBE (vRBE), dose-averaged linear energy transfer (LETd) and the risk of radiographic changes in skull base patients treated with protons. METHODS: Clinical treatment plans of 45 patients were recalculated with Monte Carlo tool FRED. Radiographic changes (i.e. edema and/or necrosis) were identified by MRI. Dosimetric parameters for cRBE and vRBE were computed. Biological margin extension and voxel-based analysis were employed looking for association of DRBE(vRBE) and LETd with brain edema and/or necrosis. RESULTS: When using vRBE, Dmax in the brain was above the highest dose limits for 38% of patients, while such limit was never exceeded assuming cRBE. Similar values of Dmax were observed in necrotic regions, brain and temporal lobes. Most of the brain necrosis was in proximity to the PTV. The voxel-based analysis did not show evidence of an association with high LETd values. CONCLUSIONS: When looking at standard dosimetric parameters, the higher dose associated with vRBE seems to be responsible for an enhanced risk of radiographic changes. However, as revealed by a voxel-based analysis, the large inter-patient variability hinders the identification of a clear effect for high LETd.