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A. Meijers et al. / Medical Physics in the Baltic States 7 (2009) 56 - 59 4. Conclusions Developed tool is easy usable and appropriate for EQSQ calculation of irregularly shaped fields, which can be used for manual MU verification. It is easy adjustable for different machines and beam energies. Statistically it was determined that optimal number of vectors for EQSQ calculation is 24. Basic verification of tool showed that EQSQ can be determined with error 1.32 ± 0.52 %. Such EQSQ error would result in calculated MU error 0.042 ± 0.021 %. EQSQ values calculated by developed tool were compared with values calculated by TPS system with PBC dose calculation algorithm. Difference between both results was 1.83 ± 0.85 %. 59 To successfully implement this tool qualitative SMR data are necessary. If SMR are calculated from PDD data, it is suggested to measure PDD for 0 × 0 cm field. For further verification of the tool, it would be necessary to carry out measurements to determine whether actual PDD of square field as calculated by the tool is the same as for given irregularly shaped field. 5. References 1. Khan F. M., The Physics of Radiation Therapy, Lippincott Williams & Wilkins, Philadelphia, 2003. p. 511. 2. British Journal of Radiology, 1996, Supplement No. 25.
MEDICAL PHYSICS IN <strong>THE</strong> BALTIC STATES 7 (2009) Proceedings of the International Conference “Medical Physics 2009” 9 - 10 October 2009, Kaunas, Lithuania QUALITY ASSURANCE PROGRAMS FOR A LINEAR ACCELERATOR Carl MAGNUS NILSSON Medical Radiation Physics Malmö, Lund University, Malmö University Hospital, SE-205 02 Malmö, Sweden Abstract: Quality Assurance (QA) is a comprehensive method for evaluation of an accelerator’s performance. It involves tools aiming at getting a correct absorbed dose to the patient and a good uptime. Daily, weekly, monthly and yearly checks of an accelerator are needed for a good surveillance of the accelerator. An acceptance test is done to check that the accelerator at delivery is within specified limits. The parameters are later checked within different timeframes to see if the values keep within a specified limit, and if not then corrected. The QA and Quality Control (QC) of the accelerators at Malmö University Hospital are described. Keywords: Quality Assurance, Quality Control, Acceptance Test, Clinical Linear Accelerator 1. Introduction Linear accelerators has undergone a tremendous development since their introduction in the 1950s, and are now equipped with multiple interlocks, automatic change between photon and electron mode, multileaf collimators (MLC), moving collimators, etc. The QC has to check all parts of the system. It is the responsibility of a clinical physicist to coordinate the QC work. Some work can be delegated to e.g. radiographers since they are regular users of the accelerator. This paper will give an introduction to QA and QC at Malmö University Hospital and the following points will relate to different aspects of QC and the responsible personnel. 2. Quality Control Acceptance Test [1] During the installation of an accelerator the medical physicist must assure that the facility is properly prepared. This may include: (1) installing the proper warning signs, (2) assuring that the appropriate audio and video equipment is installed to monitor the patients, (3) assuring that the appropriate door interlocks are in place and connected properly and assuring that the emergency power failure illumination is installed or available (e.g. flashlights). As soon as the accelerator can deliver radiation, a beam safety tests should be the first thing on the agenda and to perform tests of the safety interlocks, determination of radiation exposure levels outside barriers and determination of exposure levels in the occupied areas during beam-on. Initial checking of mechanical and radiation systems is to commence after this. Alignment of collimator axis 60 and collimator jaws has to be made. The collimator axis, the light localizer axis and cross hairs must all be congruent and follow the same axis and this must be checked for all ranges of motions. When this is within the specified limits, the light field and radiation field congruence and coincidence must be verified. This can be done by exposing two films with collimators rotated 180 ◦ . Congruence and symmetry must be verified over the full range of both collimator and gantry positions. The mechanical and radiation isocenter location should then be determined to be within the specified limits. Other mechanical system tests must also be performed. The patient support system (couch) must be tested to assure that it’s flex, both with and without load is within the specified limits and that the couch is able to take the maximum weight, that the couch stops at the right positions and hold the position and the coordinates of the table are within specified limits. At commissioning of an accelerator it is necessary to establish that the beam profile conforms to the accelerator’s specifications. This should be done in a water phantom making measurements at least close to maximum and at 10 cm deep, and other specification depths at which the profile is specified. Variation of output with different field sizes is also a parameter that is required at commissioning. Depth doses and profiles are also measured for different field sizes. The manufacturers often have documents with tests to perform, and the documents should be reviewed to see which additional tests are needed. After the acceptance test, the commissioning can commence which includes beam data acquisition, entry
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2009 PROCEEDINGS OF THE 7 th INTERN
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Executive editor: D.Adlienė CONFER
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11.15-11.30 Daiva Leščiute, Valda
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MEDICAL PHYSICS IN THE BALTIC STATE
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