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Evaluation of Software Systems That Estimate Patient Dose Errors Based On Planar IMRT QA Measurements

M Bakhtiari*, A Parniani, F Lerma, S Reynolds, J Jordan, A Sedaghat, M Sarfaraz, J Rodgers, Radamerica II LLC, Baltimore, MD

SU-E-T-37 Sunday 3:00:00 PM - 6:00:00 PM Room: Exhibit Hall

Purpose: Although dose evaluation in IMRT QA may more closely depict patient dosimetry, measurements are in a surrogate phantom - not in the patient's anatomy. Techniques and software systems are commercially available which use individual field dosimetry measurements as input into algorithms that estimate 3D patient dose distributions. These dose distribution data when overlaid on CT scan derived target volumes and OARs, enables direct DVH analysis vs. TPS DVH. The purpose of this work is to present a systematic benchmarking technique for such kind of software systems.

Methods: A MapCheck2 diode array and 3DVH software from Sun Nuclear were used for this study. Benchmarking consists of taking IMRT beams created in actual patient treatment plans; re-computing these on a flat phantom using in the RTPS, and exporting these calculations to 3DVH as individual patient plans. Accuracy of the output of 3DVH is tested by comparing measured planar doses over a range of depths to the same planes reconstructed by 3DVH.

Results: The Gamma Index evaluation for comparing calculated 3D dose with measured 3D dose with 2% and 2mm DTA criteria returned a pass rate of > 90% for all patient cases calculated by the treatment planning system and it returned a pass rate of > 96% in 9 out of 10 cases calculated by 3DVH. Extracted computed dose planes with 3DVH software at different depths in the flat phantom passed all gamma evaluation analyses when compared to measured planes at different depths using MapCheck2.

Conclusions: It was shown that the 3D dose distribution predicted by the 3DVH software is both accurate and consistent. Accuracy is shown by the agreement of the calculations with measurements at different depths. Consistency is shown by using as inputs measured planar dose at different depths and comparing the results.

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