Davide Cusumano1, Stefania Teodoli2, Francesca Greco2, Andrea Fidanzio3, Luca Boldrini4, Mariangela Massaccesi5, Francesco Cellini5, Vincenzo Valentini6, Luigi Azario7, Marco De Spirito3. 1. U.O.C. Fisica Sanitaria, Dipartimento di Diagnostica per immagini, Radioterapia Oncologica ed Ematologia, Fondazione Policlinico Universitario "A. Gemelli" IRCCS, Roma, Italy; Istituto di Radiologia, Università Cattolica del Sacro Cuore, Roma, Italy. 2. U.O.C. Fisica Sanitaria, Dipartimento di Diagnostica per immagini, Radioterapia Oncologica ed Ematologia, Fondazione Policlinico Universitario "A. Gemelli" IRCCS, Roma, Italy. 3. U.O.C. Fisica Sanitaria, Dipartimento di Diagnostica per immagini, Radioterapia Oncologica ed Ematologia, Fondazione Policlinico Universitario "A. Gemelli" IRCCS, Roma, Italy; Istituto di Fisica, Università Cattolica del Sacro Cuore, Roma, Italy. 4. Istituto di Radiologia, Università Cattolica del Sacro Cuore, Roma, Italy. 5. U.O.C. Radioterapia Oncologica, Dipartimento di Diagnostica per immagini, Radioterapia Oncologica ed Ematologia, Fondazione Policlinico Universitario "A. Gemelli" IRCCS, Roma, Italy. 6. Istituto di Radiologia, Università Cattolica del Sacro Cuore, Roma, Italy; U.O.C. Radioterapia Oncologica, Dipartimento di Diagnostica per immagini, Radioterapia Oncologica ed Ematologia, Fondazione Policlinico Universitario "A. Gemelli" IRCCS, Roma, Italy. 7. U.O.C. Fisica Sanitaria, Dipartimento di Diagnostica per immagini, Radioterapia Oncologica ed Ematologia, Fondazione Policlinico Universitario "A. Gemelli" IRCCS, Roma, Italy; Istituto di Fisica, Università Cattolica del Sacro Cuore, Roma, Italy. Electronic address: luigi.azario@unicatt.it.
Abstract
PURPOSE: Aim of this study is to experimental evaluate the impact of a 0.35 T transverse magnetic field on dose distribution in presence of tissue-air and tissue-lung interfaces. METHODS: The investigation was carried out using MRIdian (ViewRay, Cleveland, Ohio) and it consisted of comparing experimental measurements performed by Gafchromic EBT3 film dosimetry, to Montecarlo simulations, carried out in the presence and, as well as, the absence of the magnetic field. A preliminary dose calibration was planned on MRIdian, arranging 3 × 3 cm2 film pieces in a water slab phantom and exposing them at different beam-on times, in a dose range equal to 0.1-12.1 Gy. All experimental measurements were then carried out using the calibrated films and delivering one single beam orthogonally to three different phantoms: without inhomogeneity, with an air gap and with a lung inhomogeneity. The dose distributions measured by EBT3 films in presence of magnetic field were compared to those calculated in the presence and, as well as, the absence of the magnetic field, in terms of gamma analysis. A quantification of electron return effect (ERE) was also performed. RESULTS: All the tested plans considering the magnetic field show a gamma-passing rate higher than 98% for 3%/3 mm gamma analysis. In presence of tissue-air interface, the electron return effect causes an over-dosage of +31.9% at the first interface and an under-dosage of -33% at the second interface. The dosimetric variations in presence of tissue-lung interface results to be smaller (+0.8% first interface, -1.3% second interface). CONCLUSION: The impact of 0.35 T magnetic field is not negligible and it can be effectively modelled by the Montecarlo dose calculation platform available in the MRIdian TPS.
PURPOSE: Aim of this study is to experimental evaluate the impact of a 0.35 T transverse magnetic field on dose distribution in presence of tissue-air and tissue-lung interfaces. METHODS: The investigation was carried out using MRIdian (ViewRay, Cleveland, Ohio) and it consisted of comparing experimental measurements performed by Gafchromic EBT3 film dosimetry, to Montecarlo simulations, carried out in the presence and, as well as, the absence of the magnetic field. A preliminary dose calibration was planned on MRIdian, arranging 3 × 3 cm2 film pieces in a water slab phantom and exposing them at different beam-on times, in a dose range equal to 0.1-12.1 Gy. All experimental measurements were then carried out using the calibrated films and delivering one single beam orthogonally to three different phantoms: without inhomogeneity, with an air gap and with a lung inhomogeneity. The dose distributions measured by EBT3 films in presence of magnetic field were compared to those calculated in the presence and, as well as, the absence of the magnetic field, in terms of gamma analysis. A quantification of electron return effect (ERE) was also performed. RESULTS: All the tested plans considering the magnetic field show a gamma-passing rate higher than 98% for 3%/3 mm gamma analysis. In presence of tissue-air interface, the electron return effect causes an over-dosage of +31.9% at the first interface and an under-dosage of -33% at the second interface. The dosimetric variations in presence of tissue-lung interface results to be smaller (+0.8% first interface, -1.3% second interface). CONCLUSION: The impact of 0.35 T magnetic field is not negligible and it can be effectively modelled by the Montecarlo dose calculation platform available in the MRIdian TPS.
Authors: Shu-Hui Hsu; Zhaohui Han; Jonathan E Leeman; Yue-Houng Hu; Raymond H Mak; Atchar Sudhyadhom Journal: Front Oncol Date: 2022-09-23 Impact factor: 5.738