الفهرس | Only 14 pages are availabe for public view |
Abstract Development of digital linear accelerators of moving multileaf collimator with arc mode has given a new dimension to radiation dose delivery. This technology is known as Dynamic Arc Therapy (DAT) and recently implemented in many of the clinical sites. The present proposed protocol describes a quality assurance (QA) tests on both static multileaf collimator (SMLC) and dynamic multileaf collimator (DMLC) for Dynamic Arc Therapy techniques. Visual and qualitative analyses of the leaf positioning accuracy according to the acceptable limits will be inspected. The stability of DMLC will be analyzed qualitatively and quantitatively using film dosimetry. The protocol will also summarize the systematic procedure and sequence of tests aiming to have a complete guide to the radiotherapy physicists for the QA of the DMLC with Dynamic Arc Therapy. The SMLC leaf positions were developed a robust, accurate and generic algorithm to measure the individual static MLC leaf positions. This was performed by extracting leaf tip locations from the radiographic film image and measuring their relative distance from a reference line on the film. The reference line was created with a selected set of MLC leaf sides. The film scaling was created and verified using the physical leaf width. The average measured distance corresponds to a leaf width of 10.0 mm was 9.95 ± 0.09 mm. The estimated reproducibility of the leaf tips location was ± 0.26 mm. The code accuracy was checked by intentionally positioning set of leaves with small errors (1.0 mm), and the detected deviations from the expected positions within the range from -0.25 mm to +0.32 mm. The algorithm includes two self testing functions in order to detect failures of leaf positioning due to poor film quality and to avoid the potential systematic errors attributable to the improper collimator setting. The code is promising to be more efficient with Gafchromic film and electronic portal image device (EPID). Abstract XIX In this study, assessment of the dynamic MLC performance was based on the evaluation of sliding gaps traveling across the field in different conditions in both gantry-fixed and arc modes which may affect the stability of MLC speed during gantry rotation. The sliding gap test was sensitive to small changes in leaf position and speed across the range of the leaf travel which could be affected by motor fatigue. In the present work the following QA of DMLC tests were performed: (1) Leaf speed stability test (multi-travel test) is performed to check the stability of the leaves motion with different speeds with a fixed gantry angle of zero as well as with arcs. The average of passed gamma values using 2%DD and 2.0 mm DTA criteria was above 98.80 % for all film irradiations except for the comparison between them and the absolute one (14×14 cm2) was 87.14%. (2) Oscillating sweeping gap test, different uniform MLC gap is moving repeatedly back and forth across the field at a constant speed during a fixed gantry angle of zero as well as full arcs. The average of passed gamma values using 2%DD and 2.0 mm DTA criteria was 90.93 % for all film irradiations. (3) Garden fence test, very small band moving across the field with stopping movement at defined positions during irradiation to create fences at fixed gantry angles (0°, 90°, 180°, and 270°) and arc mode. The average fraction of passed gamma values using 3%DD and 3.0 mm DTA criteria was above 96.74 % for all films except for the comparisons between gantry angle 0° with 270°, and 90° with 270° which yielded 91.15% and 90.12% respectively. Those new dynamic tests are better may be quick consistency test without comprehensive analysis. The elements which have been quantitatively investigated are: the accuracy and stability of MLC leaf gap width and their resulting; and the speed of each leaf over the whole range of its positions. The ultimate aim Abstract XX of this study is to develop and implement faster, easier, and more accurate QA techniques for MLC performance and helps in faster troubleshooting of MLC problems in both static and dynamic QA. The present QA applied protocol, based on the obtained results, had minimized both time taken during operations and money spend to buy expensive analysis software. Accordingly, static multileaf collimator (SMLC) and dynamic multileaf collimator (DMLC) for Dynamic Arc Therapy techniques have replaced as the standard quality assurance (QA) for linear accelerator machines in our department. These techniques were useful to be investigated by another material using Gafchromic and EPID |