SU-GG-T-247: A New Method to Compensate Angular Dependency of MapCheck Device in Intensity Modulated Arc Therapy
2010; Wiley; Volume: 37; Issue: 6Part19 Linguagem: Inglês
10.1118/1.3468639
ISSN2473-4209
Autores Tópico(s)Advanced Radiotherapy Techniques
ResumoPurpose: To evaluate the performance of a new method to compensate angular dependency of QA devices in intensity modulated arc therapy. Methods and Materials: The QA phantom consisted of a MapCheck device sitting in an acrylic base, which is inserted between two 5-cm solid water pieces. Two-dimensional dose planes were measured by delivering one 10×10cm 6MV X-ray beam for per 15 degree beam angle. Two-dimensional doses at the diode detector plane were calculated in Eclipse using the AAA algorithm with inhomogeneity correction. Two types of halfpipe-shape boluses were added to the planning CT image. Bolus A has uniform thickness to attenuate the TPS dose to match the measured dose at the 180 degree beam angle. Bolus B has variable thickness to match the doses at every 15 degree beam angle. TPS doses were re-calculated using the modified CT images. Angular dependences were evaluated for the original phantom and with bolus A and B individually. Six patient QAs were performed to compare gamma analysis results. Results: Without compensation, the TPS dose was about 5% higher than the measured dose for most posterior angles (105 degree to 180 degree). It is probably due to angular dependence of diode detectors and CT metal artifacts. Bolus A slightly reduced the angular dependence for the posterior angles (RMS decreased from 4.0% to 3.4%). Bolus B reduced the dependence significantly (RMS=1.4%). The failure rate of gamma analysis was reduced by 39% and 41% in average. Conclusion: The new method has been shown to be able to compensate angular dependency for the MapCheck device.
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