The advent of dynamic treatment techniques in radiotherapy has required implementing quality assurance programs that include verifying each individual treatment plan. Growing patient numbers contribute to patient specific QA becoming more challenging and more time consuming. In addition, the trend toward multi-site centers and networks of centers encourages the introduction of beam matching across cancer clinics, elevating the logistical challenges of machine QA even more. The Integral Quality Monitor (IQM) System tackles these challenges with its virtualized and centralized network structure and a fully automated real-time patient QA workflow. Its core element, the IQM Detector, consists of a large-area wedge-shaped ion chamber which is flange-mounted at the collimator and measures a scalar, time-dependent dose-area-product per beam segment. During patient treatment, measurements are benchmarked in real-time against a predicted signal course which is pre-calculated by an independent, model-based, machine-specific algorithm, based on information in the DICOM-RT-Plan.
Extensive investigations concerning the dosimetric properties of the IQM Detector can be found in literature [1, 2]. Multiple studies have shown, that despite the IQM’s dramatic reduction of measurement data complexity, the error detection sensitivity and specificity of the IQM System is as least as high as observed for conventional QA tools [3, 4, 5, 6]. Further, the influence of the chamber on beam characteristics has been thoroughly investigated .
This study focuses on the applicability of one universal IQM calculation model for 4 matched machines across 4 different cancer centers. These 4 centers are part of a centralized QA network at GenesisCare Spain that consists of 16 IQM Systems in total. The following properties were compared between the matched machines: (i) area output factors, (ii) beam profiles and (iii) IQM Signal calculation performance for clinical VMAT treatment plans.
Kilian Michel, Thesi Roestel, Catherine Hamlin, Johannes Porzig, Jürgen Oellig