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RESEARCH PRODUCT

Dosimetry for electron Intra-Operative RadioTherapy: Comparison of output factors obtained through alanine/EPR pellets, ionization chamber and Monte Carlo-GEANT4 simulations for IORT mobile dedicate accelerator

Maurizio Marrale ABAnna Longo ABGiorgio Russo CCarlo Casarino CGiuliana Candiano CSalvatore Gallo ABDAntonio Carlino EAMaria Brai AB

subject

Nuclear and High Energy PhysicsDosimeterPhysics::Instrumentation and DetectorsChemistryIORTSettore FIS/01 - Fisica SperimentalePhysics::Medical PhysicsMonte Carlo methodDetectorGeant4Dose profileElectronalanine dosimetry Monte Carlo Simulation Geant4Alanine dosimetrySettore FIS/07 - Fisica Applicata(Beni Culturali Ambientali Biol.e Medicin)Linear particle acceleratorMonte Carlo simulationsComputational physicsNuclear magnetic resonanceIonization chamberDosimetrySettore MED/36 - Diagnostica Per Immagini E RadioterapiaInstrumentation

description

Abstract In this work a comparison between the response of alanine and Markus ionization chamber was carried out for measurements of the output factors (OF) of electron beams produced by a linear accelerator used for Intra-Operative Radiation Therapy (IORT). Output factors (OF) for conventional high-energy electron beams are normally measured using ionization chamber according to international dosimetry protocols. However, the electron beams used in IORT have characteristics of dose per pulse, energy spectrum and angular distribution quite different from beams usually used in external radiotherapy, so the direct application of international dosimetry protocols may introduce additional uncertainties in dosimetric determinations. The high dose per pulse could lead to an inaccuracy in dose measurements with ionization chamber, due to overestimation of k s recombination factor. Furthermore, the electron fields obtained with IORT-dedicated applicators have a wider energy spectrum and a wider angular distribution than the conventional fields, due to the presence of electrons scattered by the applicator’s wall. For this reason, a dosimetry system should be characterized by a minimum dependence from the beam energy and from angle of incidence of electrons. This become particularly critical for small and bevelled applicators. All of these reasons lead to investigate the use of detectors different from the ionization chamber for measuring the OFs. Furthermore, the complete characterization of the radiation field could be accomplished also by the use of Monte Carlo simulations which allows to obtain detailed information on dose distributions. In this work we compare the output factors obtained by means of alanine dosimeters and Markus ionization chamber. The comparison is completed by the Monte Carlo calculations of OFs determined through the use of the Geant4 application ” iort _ therapy ” . The results are characterized by a good agreement of response of alanine pellets and Markus ionization chamber and Monte Carlo results (within about 3%) for both flat and bevelled applicators.

https://doi.org/10.1016/j.nimb.2015.05.022