Monte Carlo simulation of electron beams generated by a 12 MeV dedicated mobile IORT accelerator

Abstract

The aim of this study was to investigate the dosimetric characteristics of the electron beams generated by the light intraoperative accelerator, Liac® (SORDINA, Italy), using Monte Carlo (MC) calculations. Moreover we investigated the possibility of characterizing the Liac® dosimetry with a minimal set of dosimetric data. In fact accelerator commissioning requires measurements of both percentage depth doses (PDDs) and off-axis profiles for all the possible combinations of energy, applicator diameter and bevelled angle. The Liac® geometry and water phantom were simulated in a typical measurement setup, using the MC code EGSnrc/BEAMnrc. A simulated annealing optimization algorithm was used in order to find the optimal non-monoenergetic spectrum of the initial electron beam that minimizes the differences between calculated and measured PDDs. We have concluded that, for each investigated nominal energy beam, only the PDDs of applicators with diameters of 30, 70 and 100 mm and the PDD without an applicator were needed to find the optimal spectra. Finally, the output factors of the entire set of applicator diameters/bevelled angles were calculated. The differences between calculated and experimental output factors were better than 2%, with the exception of the smallest applicator which gave differences between 3% and 4% for all energies. The code turned out to be useful for checking the experimental data from various Liac® beams and will be the basis for developing a tool based on MC simulation to support the medical physicist in the commissioning phase.

Use of parallel‐plate ionization chambers in reference dosimetry of NOVAC and LIAC® mobile electron linear accelerators for intraoperative radiotherapy: a multi‐center survey

“…Figure shows the electron beam PDD differences between a conventional linac and one of the machines studied here that have the same R 50 , and consequently the same z ref . This is consistent with previous studies . For the PDD measurements, 10 centers used IBA EFD 3G diodes.…”

“…NOVAC7 and LIAC have many similar features, due to the common intended use. Their structure and characteristics have been described elsewhere . Both devices consist of a mobile radiant unit and a control rack, connected by a cable that supplies the radiant unit with electrical power and transmits the treatment parameters.…”

“…The high number of monitor units increases the measurement time and, potentially, the required thickness of the shielding barriers. 15 Since 2003, many studies 14,16,22,23,26 have been published dealing with the dosimetric issues related to NOVAC and LIAC accelerators, hence it is worthwhile reconsidering the use of ionization chambers. In this respect, the aim of this study was to validate ionization chambers for the reference dosimetry of NOVAC and LIAC by comparison with ferrous sulfate dosimetry.…”

Dosimetric evaluation of Gafchromic EBT2 film for breast intraoperative electron radiotherapy verification

“…Diameter and base angle of these applicators can vary between 3 to 10 (3, 4, 5, 6, 7, 8 and 10) cm and 0 to 45 (0, 15, 30, and 45) degrees, respectively. The distance between scattering foil and end of IOERT applicator or SSD is equal to 71.3 cm [10].…”

Phase space determination from measured dose data for intraoperative electron radiation therapy

“…The distributions in energy, p and 8 for PHSP suitable to IOERT have been studied previously (Bjork et al 2002a, Iaccarino et al 2011. However, the angle 4> has received very scarce attention.…”