Kim Sangroh, Alaei Parham
Baylor Scott & White Health.
J Appl Clin Med Phys. 2016 Mar 8;17(2):153-164. doi: 10.1120/jacmp.v17i2.5988.
The purpose of this study was to implement full/half bowtie filter models in a com-mercial treatment planning system (TPS) to calculate kilovoltage (kV) cone-beam CT (CBCT) doses of Varian On-Board Imager (OBI) kV X-ray imaging system. The full/half bowtie filter models were created as compensators in Pinnacle TPS using MATLAB software. The physical profiles of both bowtie filters were imported and hard-coded in the MATLAB system. Pinnacle scripts were written to import bowtie filter models into Pinnacle treatment plans. Bowtie filter-free kV X-ray beam models were commissioned and the bowtie filter models were validated by analyzing the lateral and percent-depth-dose (PDD) profiles of anterior/posterior X-ray beams in water phantoms. A CT dose index (CTDI) phantom was employed to calculate CTDI and weighted CTDI values for pelvis and pelvis-spotlight CBCT protocols. A five-year-old pediatric anthropomorphic phantom was utilized to evaluate absorbed and effective doses (ED) for standard and low-dose head CBCT protocols. The CBCT dose calculation results were compared to ion chamber (IC) and Monte Carlo (MC) data for the CTDI phantom and MOSFET and MC results for the pediatric phantom, respectively. The differences of lateral and PDD profiles between TPS calculations and IC measurements were within 6%. The CTDI and weighted CTDI values of the TPS were respectively within 0.25 cGy and 0.08 cGy compared to IC measurements. The absorbed doses ranged from 0 to 7.22 cGy for the standard dose CBCT and 0 to 1.56 cGy for the low-dose CBCT. The ED values were found to be 36-38 mSv and 7-8 mSv for the standard and low-dose CBCT protocols, respectively. This study demonstrated that the established full/half bowtie filter beam models can produce reasonable dose calculation results. Further study is to be performed to evaluate the models in clinical situations.
本研究的目的是在商业治疗计划系统（TPS）中实现全/半蝴蝶结滤波器模型，以计算瓦里安机载成像仪（OBI）千伏（kV）锥形束CT（CBCT）的千伏X射线成像系统剂量。全/半蝴蝶结滤波器模型是使用MATLAB软件在Pinnacle TPS中作为补偿器创建的。两种蝴蝶结滤波器的物理轮廓被导入并硬编码到MATLAB系统中。编写了Pinnacle脚本，将蝴蝶结滤波器模型导入Pinnacle治疗计划中。对无蝴蝶结滤波器的kV X射线束模型进行了调试，并通过分析水模中前后X射线束的横向和百分深度剂量（PDD）轮廓对蝴蝶结滤波器模型进行了验证。使用CT剂量指数（CTDI）模体计算骨盆和骨盆聚焦CBCT协议的CTDI和加权CTDI值。使用一个五岁儿童的人体模型评估标准和低剂量头部CBCT协议的吸收剂量和有效剂量（ED）。将CBCT剂量计算结果分别与CTDI模体的电离室（IC）和蒙特卡罗（MC）数据以及儿童模体的MOSFET和MC结果进行比较。TPS计算结果与IC测量结果之间的横向和PDD轮廓差异在6%以内。与IC测量结果相比，TPS的CTDI和加权CTDI值分别在0.25 cGy和0.08 cGy以内。标准剂量CBCT的吸收剂量范围为0至7.22 cGy，低剂量CBCT的吸收剂量范围为0至1.56 cGy。标准和低剂量CBCT协议的ED值分别为36 - 38 mSv和7 - 8 mSv。本研究表明，所建立的全/半蝴蝶结滤波器束模型能够产生合理的剂量计算结果。有待进一步开展研究以评估这些模型在临床情况下的表现。
