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Evaluation of the accuracy of 3DVH software estimates of dose to virtual ion chamber and film in composite IMRT QA

机译:评估3DVH软件估算复合IMRT QA中虚拟离子室和薄膜剂量的准确性

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Purpose: A novel patient-specific intensity modulated radiation therapy (IMRT) QA system, 3DVH software and mapcheck 2, purports to be able to use diode array-measured beam doses and the patient's DICOM RT plan, structure set, and dose files to predict the delivered 3D dose distribution in the patient for comparison to the treatment planning system (TPS) calculated doses. In this study, the composite dose to an ion chamber and film in phantom predicted by the 3DVH and mapcheck 2 system is compared to the actual measured chamber and film doses. If validated in this context, then 3DVH can be used to perform an equivalent dose analysis as that obtained with film dosimetry and ion chamber-based composite IMRT QA. This is important for those losing their ability to perform film dosimetry for true composite IMRT QA and provides a measure of confidence in the accuracy of 3DVH 3D dose calculations which may replace phantom-based IMRT QA. Methods: The dosimetric results from 15 consecutive patient-specific IMRT QA tests performed by composite field irradiation of ion chamber and EDR2 film in a solid water phantom were compared to the predicted doses for those virtual detectors based on the calculated 3D dose by the 3DVH software using mapcheck 2 measured doses of each beam within each plan. For each of the 15 cases, immediately after performing the ion chamber plus film measurements, the mapcheck 2 was used to measure the dose for each beam of the plan. The dose to the volume of the virtual ion chamber and the dose distribution in the plane of the virtual film calculated by the 3DVH software was extracted. The ratio of the measured to 3DVH or eclipse-predicted ion chamber doses was calculated. The same plane in the phantom measured using film and calculated with eclipse was exported from 3DVH and the 2D gamma metric was used to compare the relationship between the film doses and the eclipse or 3DVH predicted planar doses. Also, the 3D gamma value was calculated in the 3DVH software which compares the eclipse dose to the 3DVH predicted dose distribution. For the 2D and 3D gamma metrics, 2 dose and 2 mm distance to agreement (DTA) were used. In addition, a simple dose difference was performed using either a 2 or 3 dose difference tolerance. Results: The mean ratio±standard deviation of the measured vs 3DVH or vs ECLIPSE-predicted dose to the ion chamber was 1.013±0.015 and 1.003±0.012, respectively. For 3DVH vs ECLIPSE, the mean percentage of pixels failing the 3D gamma metric was 1.2%±1.4% while the failure rate for the 2D gamma metric was 1.1%±0.9%. When either 3DVH or ECLIPSE was compared to EDR2 film, the gamma failure rate was 2.3%±2.0% and 1.6%±1.7%, respectively. Mean dose difference failures were 9%27%±5%15% for 2 or 3% dose difference tolerances, depending on the combination of systems tested. No statistically significant differences were found for any of the planar dosimetric comparisons. Conclusions: 3DVH + mapcheck 2 predicts the same absolute dose, the percent of pixels failing the gamma metric, and the percent of pixels failing 2% or 3% dose difference tolerance tests as one would have obtained had one made measurements in solid water phantom using an ion chamber and coronal film instead of a diode array. This is also a necessary although not sufficient condition for validation of the accuracy of 3DVH predictions of the 3D dose using beam-by-beam measurements.
机译:目的:一种新颖的患者特定强度调制放射治疗(IMRT)质量保证系统,3DVH软件和mapcheck 2,据称能够使用二极管阵列测量的射线剂量以及患者的DICOM RT计划,结构集和剂量文件进行预测在患者体内传递的3D剂量分布,以便与治疗计划系统(TPS)计算的剂量进行比较。在这项研究中,将3DVH和mapcheck 2系统预测的幻影中离子室和膜的复合剂量与实际测量的室和膜剂量进行了比较。如果在这种情况下得到验证,则可以使用3DVH进行等效剂量分析,如通过薄膜剂量法和基于离子室的复合IMRT QA获得的剂量分析。这对于那些丧失了对真正的复合IMRT QA进行胶片剂量测定的能力的人来说非常重要,并为3DVH 3D剂量计算的准确性提供了一种置信度,可以取代基于幻影的IMRT QA。方法:将在固体水体模中对离子室和EDR2膜进行复合场辐照而进行的连续15次特定于患者的IMRT QA测试的剂量学结果,与基于3DVH软件计算的3D剂量的虚拟探测器的预期剂量进行比较使用mapcheck 2在每个计划中测量每个光束的剂量。对于这15种情况中的每一种,在执行离子室加膜测量之后,立即使用mapcheck 2来测量计划中每个光束的剂量。提取通过3DVH软件计算的虚拟离子室体积的剂量和虚拟膜平面中的剂量分布。计算测量值与3DVH或日食预测的离子室剂量之比。从3DVH输出使用胶片测量并用日食计算的体模中的同一平面,并使用2D伽马度量比较胶片剂量与日食或3DVH预测平面剂量之间的关系。同样,在3DVH软件中计算了3D伽玛值,该软件将日食剂量与3DVH预测剂量分布进行了比较。对于2D和3D伽玛度量,使用2剂量和2 mm一致距离(DTA)。此外,使用2或3个剂量差容限执行简单的剂量差。结果:测得的相对于3DVH或相对于ECLIPSE预测的离子室剂量的平均比率±标准偏差分别为1.013±0.015和1.003±0.012。对于3DVH与ECLIPSE,未通过3D伽玛度量的像素的平均百分比为1.2%±1.4%,而对于2D伽玛度量的失败率为1.1%±0.9%。当将3DVH或ECLIPSE与EDR2胶片进行比较时,伽马故障率分别为2.3%±2.0%和1.6%±1.7%。对于2或3%的剂量差异公差,平均剂量差异失败率为9%27%±5%15%,具体取决于所测试系统的组合。对于任何平面剂量比较,均未发现统计学上的显着差异。结论:3DVH + mapcheck 2预测相同的绝对剂量,通过伽玛度量的像素百分比以及通过2%或3%剂量差容限测试的像素百分比,因为使用固体水体模进行了一次测量,就可以得到相同的结果离子室和冠状膜,而不是二极管阵列。这也是必要的条件,尽管条件不足以使用逐束测量来验证3D剂量的3DVH预测的准确性。

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