Dosimetric characteristics of electron beams produced by two mobile accelerators, Novac7 and Liac, for intraoperative radiation therapy through Monte Carlo simulation

Abstract

The Novac7 and Liac are linear accelerators (linacs) dedicated to intraoperative radiation therapy (IORT), which produce high energy, very high dose‐per‐pulse electron beams. The characteristics of the accelerators heads of the Novac7 and Liac are different compared to conventional electron accelerators. The aim of this work was to investigate the specific characteristics of the Novac7 and Liac electron beams using the Monte Carlo method. The Monte Carlo code BEAMnrc has been employed to model the head and simulate the electron beams. The Monte Carlo simulation was preliminarily validated by comparing the simulated dose distributions with those measured by means of EBT radiochromic film. Then, the energy spectra, mean energy profiles, fluence profiles, photon contamination, and angular distributions were obtained from the Monte Carlo simulation. The Spencer‐Attix water‐to‐air mass restricted collision stopping power ratios (normalsW,air) were also calculated. Moreover, the modifications of the percentage depth dose in water (backscatter effect) due to the presence of an attenuator plate composed of a sandwich of a 2 mm aluminum foil and a 4 mm lead foil, commonly used for breast treatments, were evaluated. The calculated normalsW,air values are in agreement with those tabulated in the IAEA TRS‐398 dosimetric code of practice within 0.2% and 0.4% at zref (reference depth in water) for the Novac7 and Liac, respectively. These differences are negligible for practical dosimetry. The attenuator plate is sufficient to completely absorb the electron beam for each energy of the Novac7 and Liac; moreover, the shape of the dose distribution in water strongly changes with the introduction of the attenuator plate. This variation depends on the energy of the beam, and it can give rise to an increase in the maximum dose in the range of 3%–9%.PACS number: 87.56.‐v

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.…”

Laser–plasma acceleration of electrons for radiobiology and radiation sources

“…One of the key aspects to be investigated is the very short bunch length, typical of LPA electron bunches, that leads to ultra-high instantaneous dose-rate, orders of magnitude higher than conventional sources. In view of this, preclinical studies are needed to address the radiobiological effectiveness of laser-driven electron sources compared to conventional linacs used in medical applications, with a particular attention to the intra-operatory radiation therapy (IORT) [7,8].…”

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

“…Although the energy range for IOERT with these conventional linacs may vary from 4 to 18MeV, more than 95% of IOERT treatments, including all treatments in conventional IOERT settings such as breast, performed by the Spanish hospitals considered in this project, employed beam energies in between 6 and 12MeV. In the case of IOERT dedicated accelerators (Righi et al 2013), a fixed value of SSD around 60cm and energies in the 4 to 12MeV range are typical. Therefore, in this work we have simulated two different applicators settings: one of a length of 100 cm, representative of the average length of the telescopic applicators used in IOERT when conventional linac systems are employed (Nevelsky et al 2010) and another one of 60 cm, typical for IOERT dedicated linacs.…”

“…We compare the dose delivered to the water phantom with the solution PHSP to the one of the reference PHSP for the same setup. Again, beveled applicators are very often used in IOERT (Bjork et al 2000, Nevelsky et al 2010, Righi et al 2013 and in particular in near half the clinical cases considered for this project. 45° is typically the maximum bevel angle employed.…”