Linear accelerator multileaf collimator quality control methodologies in radiotherapy

Abstract

The multileaf collimator (MLC) system introduction into clinical linear accelerators (Linacs), facilitated computer-control and verification of complex treatment, and results in an increase in patient set up speed. An MLC system thus requires a re-evaluation of the quality assurance (QA) requirements for beam collimation. This study investigated, developed, performed and evaluated QA effors for conventional MLCs with the aim to evaluate the efficacy and reproducibility of the quality control (QC) procedures with different detectors. The performance of MLCs for an Elekta (Livingstone hospital) and siemens (Charlotte Maxeke Johannesburg academic hospital) linac were examined. The major QC procedures studied were leaf matching, leaf position accuracy, intraleaf leakage and transmission through abutting leaves. Three portal imaging devices (radiographic film, radiochromic film and an electronic portal imaging device) and a PTW LA48 linear array were used as detectors. Record and verify data management systems were used to set up and execute the procedures. The calibration of all the potal imaging devices was also performed. The calibration procedure of the portal imaging devices is linac specific in execution. The profiles obtained indicated consistency across device and time. A combined single execution procedure is viable and reproducible on all platforms. The results show tha the calibration of imaging devices is of great importance. The MLC design influences the range and extent of QC that can be performed. This may impact on the accuracy with advanced technologies requiring high conformity and reproducible leaf movement, can be deliverd. Imaging devices each have specific resource requirement issues affecting the efficacy of their use.