Trivedi Gaurav, Singh Pushpendra P, Oinam Arun S
Post Graduate Institute of Medical Education and Research, India.
Indian Institute of Technology, Ropar, India.
Biomed Phys Eng Express. 2023 Mar 1;9(3). doi: 10.1088/2057-1976/acbc80.
. Films and TLDs have been the common choices for passivedose measurement in radiotherapy. In the brachytherapy applications, it is very difficult to report and verify the dose at multiple localized high dose gradient regions and also the dose to organ at risk. This study was carried out to introduce a new and accurate calibration method for GafChromic EBT3 films irradiated using Ir-192 photon energy from miniature High Dose Rate (HDR) Brachytherapy source.. Film holder made of Styrofoam was used to hold the EBT3 film at its center. It was placed inside the mini water phantom and the films were irradiated by Ir-192 source of microSelectron HDR afterloading brachytherapy system. Two different setups: Single catheter-based film exposure and dual catheter-based film exposure were compared. The films scanned on a flatbed scanner were analysed in three different color channels: red, green, and blue using Image J software. The dose calibration graphs were generated using the third-order polynomial equations fitted on the data points from two different methods of calibration procedure. Maximum and mean dose difference between TPS calculated and measured was analyzed.. The measured dose difference from the TPS calculated doses were evaluated for the three groups of dose ranges (low, medium and high). In the high dose range, standard uncertainty of dose difference are ±2.3%, ±2.9%, and ±2.4% respectively for the red, green, and blue color channel when the TPS calculated dose was compared with single catheter based film calibration equation. Whereas it is observed as 1.3%, 1.4% and 3.1% for the red, green, and blue color channels respectively when compared with the dual catheter based film calibration equation. A test film was exposed to a TPS calculated dose of 666 cGy to validate the calibration equations, single catheter based film calibration equation estimated the dose difference as -9.2%, -7.8% and -3.6% respectively in the red, green, and blue color channels whereas the same were observed as 0.1%, 0.2% and 6.1% respectively when dual catheter based film calibration equation was applied.Source miniature size, reproducible positioning of the film and catheter system inside water medium are the major challenges in the film calibration with Ir-192 beam. To overcome these situations dual catheter-based film calibration was found more accurate and reproducible as compare to the single catheter based film calibration.
在放射治疗中，胶片和热释光剂量计一直是被动剂量测量的常用选择。在近距离放射治疗应用中，很难报告和验证多个局部高剂量梯度区域的剂量以及危及器官的剂量。本研究旨在介绍一种新的、准确的校准方法，用于校准使用微型高剂量率（HDR）近距离放射治疗源的铱-192光子能量照射的GafChromic EBT3胶片。由聚苯乙烯泡沫塑料制成的胶片夹用于将EBT3胶片固定在其中心。将其放置在微型水模体内部，胶片由microSelectron HDR后装近距离放射治疗系统的铱-192源进行照射。比较了两种不同的设置：基于单导管的胶片曝光和基于双导管的胶片曝光。在平板扫描仪上扫描的胶片使用Image J软件在三个不同的颜色通道（红色、绿色和蓝色）中进行分析。剂量校准图使用三阶多项式方程生成，该方程拟合自两种不同校准程序方法的数据点。分析了TPS计算剂量与测量剂量之间的最大和平均剂量差异。对三组剂量范围（低、中、高）评估了与TPS计算剂量相比的测量剂量差异。在高剂量范围内，如果将TPS计算剂量与基于单导管的胶片校准方程进行比较，红色、绿色和蓝色颜色通道的剂量差异标准不确定度分别为±2.3%、±2.9%和±2.4%。而当与基于双导管的胶片校准方程进行比较时，红色、绿色和蓝色颜色通道分别观察到为1.3%、1.4%和3.1%。一张测试胶片接受了TPS计算剂量为666 cGy的照射以验证校准方程，基于单导管的胶片校准方程在红色、绿色和蓝色颜色通道中估计的剂量差异分别为-9.2%、-7.8%和-3.6%，而当应用基于双导管的胶片校准方程时，相同颜色通道中的剂量差异分别观察到为0.1%、0.2%和6.1%。源的微型尺寸、胶片和导管系统在水介质中的可重复定位是使用铱-192束进行胶片校准时的主要挑战。为克服这些情况，发现基于双导管的胶片校准比基于单导管的胶片校准更准确且可重复。
