Contents lists available at ScienceDirect Radiation Physics and Chemistry journal homepage: www.elsevier.com/locate/radphyschem Technical note: A new wedge-shaped ionization chamber component module for BEAMnrc to model the integral quality monitoring system® Oluwaseyi Michael Oderinde, FCP du Plessis ⁎ Department of Medical Physics, University of the Free State, PO Box 339, Bloemfontein 9300, South Africa ARTICLE INFO Keywords: Monte Carlo IQM Component Module BEAMnrc ABSTRACT The purpose of this study was to develop a new component module (CM) namely IQM to accurately model the integral quality monitoring (IQM) system® to be used in the BEAMnrc Monte Carlo (MC) code. The IQM is essentially a double wedge ionization chamber with the central electrode plate bisecting the wedge. The IQM CM allows the user to characterize the double wedge of this ionization chamber and BEAMnrc can then accurately calculate the dose in this CM including its enclosed air regions. This has been verified against measured data. The newly created CM was added into the standard BEAMnrc CMs, and it will be made available through the NRCC website. The BEAMnrc graphical user interface (GUI) and particle ray-tracing techniques were used to validate the IQM geometry. In subsequent MC simulations, the dose scored in the IQM was verified against measured data over a range of square fields ranging from 1 × 1–30 × 30 cm 2 . The IQM system is designed for the present day need for a device that could verify beam output in real-time during treatment. This CM is authentic, and it can serve as a basis for researchers that have an interest in real- time beam delivery checking using wedge-shaped ionization chamber based instruments like the IQM. 1. Introduction Advanced radiotherapy (RT) treatment techniques such as intensity modulated radiotherapy (IMRT) and volumetric modulated arc therapy (VMAT) have optimized radiation treatment and as well minimize the absorb dose received by critical organs at risk (OAR) (Mayles et al., 2007; Bucci et al., 2005; Roopashri and Baig, 2013; Ahmad et al., 2012; Nakamura et al., 2014). The quality assurance (QA) of these treatment techniques is quite complicated and time-consuming (Ishikura, 2008; Connell and Hellman, 2009; Thariat et al., 2013). A continuous effort has been made on image guidance radiotherapy (IGRT) to monitor the modern linear accelerator (linac) (Williamson et al., 2008). IGRT allows for online replanning of the dose and geometry. With this progress, there is still a dosimetric uncertainty in a modified treatment plan of IMRT and VMAT. Therefore, there is a huge interest in verifying and validating the treatment beams during real-time treatment. Few mon- itoring devices have been utilized in recent time for offline verification, but little has been achieved in online verification (Islam et al., 2009). The Integral quality monitoring (IQM) system (iRT Systems, Germany) is an independent real-time treatment verifying instrument that measures the beam output and compares it with expected values within a typically 2% dose margin. The aim is to validate the integrity and accuracy of the delivered beams on the treatment plan data calculated for the patient. This device has a large double wedge-shaped ionization chamber that is attached to the linac head in real-time radiotherapy (Islam et al., 2009; Chang et al., 2013; iRT Systems, 2014). The gradient of the wedge-shaped ionization chamber aligns with the MLC leaf movement. Monte Carlo (MC) codes have been utilized in several studies as dose calculation engines for clinical radiotherapy. It accurately calcu- lates the dose distribution in heterogeneous phantoms were physical measurement seems difficult (Chetty et al., 2007; Paganetti et al., 2004; Mesbahi, 2006; Michaeloderinde and Obed, 2015). The BEAMnrc MC user code was designed to accurately simulate electron/photon transport through all relevant components of a radio- therapy machine (Rogers et al., 2011, 1995; Chetty et al., 2007). To model a machine such as a linac radiation head, several component modules (CMs) would be arranged upstream. Hitherto, none of the existing CMs could model the IQM system that is essentially a double- wedge ionization chamber (Rogers et al., 2011). In this study, a new CM (IQM) was designed and added to the existing CMs for the BEAMnrc user code. The new CM was designed to simulate a wedge-shaped io- nization chamber that would calculate the dose distribution in its two enclosed air regions. The geometry of the IQM CM was validated by utilizing the ray-tracing technique. The ray-tracing method is used to test the geometry of a CM (Heath and Seuntjens, 2003). Macros http://dx.doi.org/10.1016/j.radphyschem.2017.08.005 Received 14 February 2017; Received in revised form 2 August 2017; Accepted 4 August 2017 ⁎ Corresponding author. E-mail address: DuPlessisFCP@ufs.ac.za (F. du Plessis). Radiation Physics and Chemistry 141 (2017) 346–351 Available online 12 August 2017 0969-806X/ © 2017 Elsevier Ltd. All rights reserved. MARK