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Quality Assurance of Stereotactic Radiosurgery (SRS) and Stereotactic Body Radiation Therapy (SBRT) for Patient Specific Plans: A Comparison Between MATRIXX and Delta4 QA Devices

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Y Tsai

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


SU-F-T-587 (Sunday, July 31, 2016) 3:00 PM - 6:00 PM Room: Exhibit Hall

Patient-specific quality assurance (QA) is necessary to accurately deliver high dose radiation to the target, especially for stereotactic radiosurgery (SRS) and stereotactic body radiation therapy (SBRT). Unlike previous 2 dimensional (D) array QA devices, Delta⁴ can verify the dose delivery in 3D. In this study, the difference between calculated and measured dose distribution was compared with two QA devices (MATRIXX and Delta⁴) to evaluate the delivery accuracy.

Twenty-seven SRS/SBRT plans with VMAT were verified with point-dose and dose-map analysis. We use an ion chamber (A1SL, 0.053cc) for point-dose measurement. For verification of the dose map, the differences between the calculated and measured doses were analyzed with a gamma index using MATRIXX and Delta⁴ devices. The passing criteria for gamma evaluation were set at 3 mm for distance₋to₋agreement (DTA) and 3% for dose₋difference. A gamma index less than 1 was defined as the verification passing the criteria and satisfying at least 95% of the points.

The mean prescribed dose and fraction was 40 ± 14.41 Gy (range: 16₋60) and 10 ± 2.35 fractions (range: 1₋8), respectively. In point dose analysis, the differences between the calculated and measured doses were all less than 5% (mean: 2.12 ± 1.13%; range: ₋0.55% to 4.45%). In dose₋map analysis, the average passing rates were 99.38 ± 0.96% (range: 95.31₋100%) and 100 ± 0.12% (range: 99.5%₋100%) for MATRIXX and Delta⁴, respectively. Even using criteria of 2%/2 mm, the passing rate of Delta⁴ was still more than 95% (mean: 99 ± 1.08%; range: 95.6%₋100%).

Both MATRIXX and Delta⁴ offer accurate and efficient verification for SRS/SBRT plans. The results measured by MATRIXX and Delta⁴ dosimetry systems are similar for SRS/SBRT performed with the VMAT technique.

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