SU-E-T-118：EBT3 薄膜在光子束和质子束中的特性研究

Sorriaux J, Rossomme S, Kacperek A, Bertrand D, Vynckier S, Sterpin E

Molecular Imaging Radiotherapy & Oncology, Catholic University of Louvain, Belgium.

Douglas Cyclotron, Clatterbridge Center for Oncology, Wirral, UK.

Med Phys. 2012 Jun;39(6Part11):3730. doi: 10.1118/1.4735176.

PURPOSE

To measure the calibration curves of EBT3 dosimetry films in photon and proton beams and to quantify the related uncertainties from one beam type to another.

METHODS

EBT3 Gafchromic films have similar properties than EBT2 with a symmetric construction and a matte polyester substrate to prevent Newton's ring artefacts. Films from a same batch were exposed in three different beam qualities, an Elekta SL25 6 MV photon beam, a 100 MeV 5×5cm proton beam delivered by pencil-beam scanning dedicated system from IBA and a 60 MeV fixed proton beam (2.5cm in diameter) at Clatterbridge Center for Oncology (CCO), UK. The films were read using an EPSON 10000 XL/PRO scanner. Film calibration curves were acquired for all modalities within a range of 0.05 to 20 Gy. Influence of increasing linear-energy transfer (LET) on film response was investigated by comparing dose measured by EBT3 to a silicon diode detector in depth for a fully-modulated beam using the CCO beam line (homogeneous dose with distal end at 3.1cm in water). A comprehensive uncertainty budget (reproducibility, uniformity'¦) was estimated on films irradiated by Elekta SL25.

RESULTS

The main source of uncertainty was the non-uniformity of the scanner response. By placing all the irradiated films at the center of the scanner, the uncertainty could be reduced from 5.8% to 1.9% (1 sigma). For all beams and energies, the calibration curves were matched within uncertainties. Along the fully-modulated depth dose curve, diode and EBT3 measurement were in a 4% agreement point-to-point, indicating films weak dependence with LET.

CONCLUSIONS

The weak influence of LET, beam type and energy on film response as well as its small uncertainty make EBT3 suitable for relative dosimetry and a promising candidate for measuring correction factors (quality, recombination,'¦) for reference dosimetry with ion chambers of non-standard beams (e.g pencil-beam scanning proton-therapy). â€œThis work is supported by the Walloon Region under the project name InVivoIGT, convention number 1017266.â€.

目的

测量EBT3剂量测定薄膜在光子束和质子束中的校准曲线，并量化从一种束流类型到另一种束流类型的相关不确定性。

方法

EBT3变色薄膜与EBT2具有相似的特性，结构对称，采用磨砂聚酯基底以防止牛顿环伪影。同一批次的薄膜在三种不同的束流品质下进行照射，分别是医科达SL25 6MV光子束、由IBA的笔形束扫描专用系统提供的100MeV 5×5cm质子束，以及英国克拉特布里奇肿瘤中心（CCO）的60MeV固定质子束（直径2.5cm）。使用爱普生10000 XL/PRO扫描仪读取薄膜。在0.05至20Gy范围内获取所有模态的薄膜校准曲线。通过比较在使用CCO束流管线的完全调制束流深度处EBT3测量的剂量与硅二极管探测器测量的剂量，研究了线能量转移（LET）增加对薄膜响应的影响（水中远端3.1cm处的均匀剂量）。对医科达SL25照射的薄膜估计了一个综合不确定性预算（再现性、均匀性……）。