Jacob Vesna, Kneschaurek Peter
Klinik für Radiotherapie und Radiologische Onkologie, Klinikum rechts der Isar, Technische Universität München, Ismaninger Strasse 22, 81675, München, Germany.
Strahlenther Onkol. 2009 Jan;185(1):34-40. doi: 10.1007/s00066-009-1879-x. Epub 2009 Feb 18.
: In one entire intensity-modulated radiation therapy (IMRT) plan, beams coming from different directions have different penetration depths in the phantom. Therefore, verifying an entire IMRT plan with a calibration curve for a single depth is error-prone. The aim of this study is to improve the quality of the dose verification of entire IMRT plans with film dosimetry.
: The dose response of the Kodak EDR2 film to 6-MV photon beams was investigated in a solid-water phantom for different field sizes and depths. A method is proposed for evaluating measurements of the optical density with a calibration curve that takes the response at different depths into account. The described method was tested for three entire IMRT plans. For this purpose, calculated and measured dose distributions were compared, where the measured dose distribution was evaluated using a calibration curve for one depth (5 cm) and a calibration curve derived according to the proposed method.
: All measurements suggest that the dose response significantly depends on the depth in the phantom, while dependencies on field size and off-axes distance are smaller. For tested plans, gamma index < 1 (using 3 mm distance and 3% dose as constrains) was reached for 81% and 91% of the points for one plan (prostate), 81% and 86% for the second plan (prostate), and 74% and 85% for the third plan (liver) when using two calibration curves, respectively.
: The method described here corrects for the change of the film response due to the variation of the scattered radiation with the penetration depth. This is achieved by a modified calibration curve, which can enhance the accuracy of the verification of entire IMRT plans.
在一个完整的调强放射治疗（IMRT）计划中，来自不同方向的射束在模体中的穿透深度不同。因此，用单一深度的校准曲线来验证整个IMRT计划容易出错。本研究的目的是通过胶片剂量测定法提高整个IMRT计划剂量验证的质量。
在固体水模体中研究了柯达EDR2胶片对6兆伏光子束在不同射野大小和深度下的剂量响应。提出了一种用校准曲线评估光学密度测量值的方法，该校准曲线考虑了不同深度的响应。用三个完整的IMRT计划对所描述的方法进行了测试。为此，比较了计算剂量分布和测量剂量分布，其中测量剂量分布使用一个深度（5厘米）的校准曲线和根据所提出的方法导出的校准曲线进行评估。
所有测量结果表明，剂量响应显著取决于模体中的深度，而对射野大小和离轴距离的依赖性较小。对于测试计划，使用两条校准曲线时，第一个计划（前列腺）的81%和91%的点、第二个计划（前列腺）的81%和86%的点以及第三个计划（肝脏）的74%和85%的点达到了伽马指数<1（使用3毫米距离和3%剂量作为约束条件）。
本文所述方法校正了由于散射辐射随穿透深度变化而导致的胶片响应变化。这是通过修改后的校准曲线实现的，该曲线可以提高整个IMRT计划验证的准确性。
