Arjunan Manikandan, Sekaran Sureka Chandra, Sarkar Biplab, Manavalan Saran Kumar
Department of Medical Physics, Bharathiar University, Coimbatore, Tamil Nadu, India.
Department of Radiation Oncology, Manipal Hospital, Delhi, India.
J Med Phys. 2019 Jul-Sep;44(3):176-184. doi: 10.4103/jmp.JMP_42_19.
This study aimed at evaluating the efficacy of treatment planning system (TPS)-based heterogeneity correction for two- and three-dimensional (2D and 3D) electronic portal imaging device (EPID)-based pretreatment dose verification. An experiment was conducted on the EPID back-projection technique and intensity-modulated radiotherapy (IMRT).
Treatment plans were delivered in EPID without a patient to obtain the fluence pattern (F). A heterogeneity correction plane (F) for an open beam of 30 cm × 30 cm was extracted from the TPS. The heterogeneity-corrected measured fluence is developed by matrix element multiplication (F = F × F). Further planes were summed to develop a 3D dose distribution and exported to the TPS. Dose verifications for 2D and 3D were carried out with the corresponding TPS values using 2D gamma analysis (ɣ) and dose volume histogram (DVH) comparison, respectively. Totally, 33 patients (17 head-neck and 16 thorax cases) were evaluated in this study.
The head-neck and thorax plans show a 3-mm-distance to agreement (DTA) 3% DD gamma passing of 96.3% ± 2.0% and 95.4% ± 1.8% points, respectively, between F and F. The comparison of the uncorrected measured fluence (F) with F reveals a gamma passing of 82.2% ± 7.3% and 80.4% ± 8.6% for head-neck and thorax cases, respectively. A total of 87 out of the 102 head-neck and thorax beams exhibit a planner gamma passing of 97.6% ± 2.1%. In the 3D-DVH comparison of thorax and head-neck cases, D5% for planning target volume were -0.5% ± 2.2% and -2.1% ± 3.5%, respectively; D95% varies as 1.0% ± 2.7% and 1.4% ± 1.1% between TPS calculated and heterogeneity-corrected-EPID-based dose reconstruction.
The novel TPS-based heterogeneity correction can improve the 2D and 3D EPID-based back projection technique. Structures with large heterogeneities can also be handled using the proposed technique.
本研究旨在评估基于治疗计划系统（TPS）的不均匀性校正对基于二维和三维（2D和3D）电子射野影像装置（EPID）的预处理剂量验证的有效性。对EPID反投影技术和调强放射治疗（IMRT）进行了一项实验。
在没有患者的情况下在EPID中实施治疗计划以获得注量分布（F）。从TPS中提取30 cm×30 cm开放射野的不均匀性校正平面（F）。通过矩阵元素相乘（F = F×F）得出经不均匀性校正的测量注量。对更多平面求和以生成三维剂量分布并导出到TPS。分别使用二维伽马分析（ɣ）和剂量体积直方图（DVH）比较，根据相应的TPS值对2D和3D进行剂量验证。本研究共评估了33例患者（17例头颈病例和16例胸部病例）。
头颈和胸部计划在F与F之间显示3毫米距离一致性（DTA）3%剂量差异伽马通过率分别为96.3%±2.0%和95.4%±1.8%。未经校正的测量注量（F）与F的比较显示，头颈和胸部病例的伽马通过率分别为82.2%±7.3%和80.4%±8.6%。102例头颈和胸部射野中共有87例显示计划者伽马通过率为97.6%±2.1%。在胸部和头颈病例的三维DVH比较中，计划靶体积的D5%分别为-0.5%±2.2%和-2.1%±3.5%；在TPS计算值与基于不均匀性校正的EPID剂量重建之间，D95%分别为1.0%±2.7%和1.4%±1.1%。
基于TPS的新型不均匀性校正可改善基于2D和3D EPID的反投影技术。使用所提出的技术也可以处理具有大不均匀性的结构。
