An efficient protocol for radiochromic film dosimetry combining calibration and measurement in a single scan
An efficient protocol for radiochromic film dosimetry combining calibration and measurement in a single scan
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DOI：
10.1118/1.4754797
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发表时间：
2012-10-01
期刊：
影响因子：
3.8
通讯作者：
Chan, Maria F.
中科院分区：
文献类型：
--
作者：
Lewis, David;Micke, Andre;Chan, Maria F.
目的：辐射变色胶片提供了高空间分辨率的剂量测量，但由于易于使用的因素，通常不优选用于患者特异性调强放射治疗（IMRT）计划的常规评估。作者已经建立了一个有效的协议，结合校准和测量在一个单一的扫描，并使测量结果在不到30分钟内获得。这避免了并发症，由于辐射变色胶片，延迟测量的完成后，通常长达24小时，在常用的方法。此外，该协议解决了测量的准确性和完整性，通过消除环境和扫描间的变异性issues.Methods：作者收集的剂量反应数据，从6个生产批次的Gafchromic EBT 3电影和3个生产批次的EBT 2电影的剂量高达480 cGy。在这项工作中，作者使用了两种不同型号的7种不同的扫描仪-爱普生10000 XL和V700;扫描前30分钟到9天的扫描后时间;扫描的环境温度跨越11摄氏度;和两个胶片方向。扫描采用48位RGB格式，分辨率为72 dpi。使用三通道剂量测定法进行剂量评价。为了评价测量方案，患者特定的IMRT和体积调制式弧治疗（VMAT）计划暴露在瓦里安Trilogy直线加速器上的EBT 3胶片上。电影扫描完成后，在一些不同的条件下的协议和剂量图进行了分析，以证明结果的等效性。结果：结果表明，剂量-反应数据可以拟合一组相关的合理的功能，导致一个通用的校准曲线的描述。建立了一个简化的剂量测定方案，其中特定胶片批次、扫描仪和扫描条件的剂量响应数据可以从暴露于已知剂量的两个胶片中获得。在大多数情况下，只需要一次校准曝光，因为其中一张胶片的剂量可能为零。使用2%/2 mm的伽马测试标准来评估测量结果，从在各种条件下数字化的应用胶片中获得了所研究领域的约95%至99%的类似通过率，所有这些条件都不同于扫描校准胶片的条件。作者开发了一种简单有效的方案，仅使用患者胶片、一张校准胶片、一张未曝光胶片，以及应用单次扫描以获取用于计算和分析的数字图像。简化和节省时间提供了一个潜在的实际解决方案，使用辐射变色胶片的常规治疗计划的质量保证，而不牺牲空间分辨率的方便。(c)2012年美国医学物理学家协会。[http：//dx.doi.org/10.1118/1.4754797]
Purpose: Radiochromic film provides dose measurement at high spatial resolution, but often is not preferred for routine evaluation of patient-specific intensity modulated radiation therapy (IMRT) plans owing to ease-of-use factors. The authors have established an efficient protocol that combines calibration and measurement in a single scan and enables measurement results to be obtained in less than 30 min. This avoids complications due to postexposure changes in radiochromic film that delay the completion of a measurement, often for up to 24 h, in commonly used methods. In addition, the protocol addresses the accuracy and integrity of the measurement by eliminating environmental and interscan variability issues.Methods: The authors collected dose-response data from six production lots of Gafchromic EBT3 film and three production lots of EBT2 film at doses up to 480 cGy. In this work, the authors used seven different scanners of two different models-Epson 10000XL and V700; postexposure times before scanning from 30 min to 9 days; ambient temperatures for scanning spanning 11 degrees C; and two film orientations. Scanning was in 48-bit RGB format at 72 dpi resolution. Dose evaluation was conducted using a triple-channel dosimetry method. To evaluate the measurement protocol, patient specific IMRT and volumetric modulated arc therapy (VMAT) plans were exposed onto EBT3 films on a Varian Trilogy Linac. Film scanning was done following the protocol under a number of different conditions and the dose maps were analyzed to demonstrate the equivalence of results.Results: The results indicated that the dose-response data could be fit by a set of related rational functions leading to the description of a generic calibration curve. A simplified dosimetry protocol was established where dose response data for a specific film lot, scanner, and scanning conditions could be derived from two films exposed to known doses. In most cases only one calibrated exposure was required since the dose for one of the films could be zero. Using the Gamma test criterion of 2%/2 mm to evaluate the measurements, similar passing rates ranging between about 95% and 99% for the fields studied were obtained from application films digitized under a variety of conditions all of them different than the conditions under which the calibration films were scanned.Conclusions: The authors have developed a simplified and efficient protocol to measure doses delivered by an IMRT or VMAT plan using only the patient film, one calibration film, one unexposed film, and applying a single scan to acquire a digital image for calculation and analysis. The simplification and timesaving offer a potential practical solution for using radiochromic film for routine treatment plan quality assurance without sacrificing spatial resolution for convenience. (c) 2012 American Association of Physicists in Medicine. [http://dx.doi.org/10.1118/1.4754797]