| Abstract [eng] |
Multileaf collimator quality assurance is crucial to effectiveness of intensity modulated radiotherapy procedures. American association of medical physicists as well as European society of radiotherapy and oncology highlights the importance of routine quality checks of multifeaf collimator positioning and travel speed accuracy. These procedures are not regulated in Lithuania and are not performed in any radiotherapy department. Positioning accuracy and travel speed stability of multileaf collimator leaves were evaluated. An evaluation was made in the Hospital of Lithuanian University of Health Sciences Kauno clinics Oncology and Haematology clinic, for linear accelerator Varian Clinac iX. „Garden fence“ and „speed“ tests were used. Images for these tests were acquired using Varian Electronic portal imaging device, Kodak dosimetric film and SunNuclear MAPCHECK dosimeter. Two image analysis programs were written using MATLAB software. Also DynaLog file analysis was made. Dependence of deviations on the gantry and collimator positions, and speed of leaves were estimated. Largest systematic leaf positioning error was 0,103 mm ± 0,035 mm , P=0,95. It is 10,3 % of the maximum permissible error. All other measured errors were smaller. A conclusion can be made that multileaf collimator meets the requirements for leaf positioning. The results got with electronic portal imaging device correlated with results got with Kodac dosimetric film. The conclusion was made that SunNuclear dosimeter does not provide sufficient resolution for the used methods. Significant dependence between systematic errors, gantry and collimator positions, and speed of leaves were were not discovered. Multileaf collimator also met the requirements for leaf travel speed stability because the measured deviations were of 10-2 order of percents. Used method was not accurate enough to determine systematic errors. The DynaLog file analysis confirmed that leaf travel speed stability meets the requirements. Dependence between deviations and gantry position were discovered. These results were confirmed by DynaLog file analysis as well as analysis of images made with electronic portal imaging device. Largest interleaf transmission value - 3,97 % was not larger than required 5,5 %. Also leaf positioning repeatability value - 0,038 was not larger than tolerated 1 mm. |
