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Analyzing the Performance of MapCHECK2 and Delta4 Quality Assurance Phantoms in IMRT and VMAT Plans

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S Lu

SH Lu*, YC Tsai , HT Lan , SY Wen , LH Chen , SH Kuo , CW Wang , National Taiwan University Hospital, Taipei City, Taiwan


SU-F-T-238 (Sunday, July 31, 2016) 3:00 PM - 6:00 PM Room: Exhibit Hall

Intensity-modulated radiotherapy (IMRT) and volumetric modulated arc therapy (VMAT) have been widely investigated for use in radiotherapy and found to have a highly conformal dose distribution. Delta⁴ is a novel cylindrical phantom consisting of 1069 p-type diodes with true treatments measured in the 3D target volume. The goal of this study was to compare the performance of a Delta⁴ diode array for IMRT and VMAT planning with ion chamber and MapCHECK2.

Fifty-four IMRT (n=9) and VMAT (n=45) plans were imported to Philips Pinnacle Planning System 9.2 for recalculation with a solid water phantom, MapCHECK2, and the Delta4 phantom. To evaluate the difference between the measured and calculated dose, we used MapCHECK2 and Delta⁴ for a dose-map comparison and an ion chamber (PTW 31010 Semiflex 0.125 cc) for a point-dose comparison.

All 54 plans met the criteria of <3% difference for the point dose (at least two points) by ion chamber. The mean difference was 0.784% with a standard deviation of 1.962%. With a criteria of 3 mm/3% in a gamma analysis, the average passing rates were 96.86%±2.19% and 98.42%±1.97% for MapCHECK2 and Delta⁴, respectively. The student t-test of MapCHECK2/Delta⁴, ion chamber/Delta⁴, and ion chamber/MapCHECK2 were 0.0008, 0.2944, and 0.0002, respectively. There was no significant difference in passing rates between MapCHECK2 and Delta⁴ for the IMRT plan (p = 0.25). However, a higher pass rate was observed in Delta⁴ (98.36%) as compared to MapCHECK2 (96.64%, p < 0.0001) for the VMAT plan.

The Pinnacle planning system can accurately calculate doses for VMAT and IMRT plans. The Delta⁴ shows a similar result when compared to ion chamber and MapCHECK2, and is an efficient tool for patient-specific quality assurance, especially for rotation therapy.

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