Fotina Irina, Zourari Kyveli, Lahanas Vasileios, Pantelis Evaggelos, Papagiannis Panagiotis
Eckert & Ziegler BEBIG GmbH, Berlin, Germany, currently at: Department of Radiation Oncology, King Hamad University Hospital, Kingdom of Bahrein.
Medical Physics Laboratory, Medical School, National and Kapodistrian University of Athens, Greece.
J Contemp Brachytherapy. 2018 Feb;10(1):73-84. doi: 10.5114/jcb.2018.74327. Epub 2018 Feb 28.
To perform a comparative study of heterogeneities and finite patient dimension effects in Co and Ir high-dose-rate (HDR) brachytherapy.
Clinically equivalent plans were prepared for 19 cases (8 breast, 5 esophagus, 6 gynecologic) using the Ir2.A85-2 and the Co0.A86 HDR sources, with a TG-43 based treatment planning system (TPS). Phase space files were obtained for the two source designs using MCNP6, and validated through comparison to a single source dosimetry results in the literature. Dose to water, taking into account the patient specific anatomy and materials (D), was calculated for all plans using MCNP6, with input files prepared using the BrachyGuide software tool to analyze information from DICOM RT plan exports.
A general TG-43 dose overestimation was observed, except for the lungs, with a greater magnitude for Ir. The distribution of percentage differences between TG-43 and Monte Carlo (MC) in dose volume histogram (DVH) indices for the planning target volume (PTV) presented small median values (about 2%) for both Co and Ir, with a greater dispersion for Ir. Regarding the organs at risk (OARs), median percentage differences for breast V were 3% (5%) for Co (Ir). Differences in median skin D were found comparable, with a larger dispersion for Ir, and the same applied to the lung D and the aorta D. TG-43 overestimates D for the rectum and the sigmoid, with median differences from MC within 2% and a greater dispersion for Ir. For the bladder, the median of the difference is greater for Co (2%) than for Ir (0.75%), demonstrating however a greater dispersion again for Ir.
The magnitude of differences observed between TG-43 based and MC dosimetry and their smaller dispersion relative to Ir, suggest that Co HDR sources are more amenable to the TG-43 assumptions in clinical treatment planning dosimetry.
对钴和铱高剂量率（HDR）近距离放射治疗中的不均匀性和有限患者尺寸效应进行比较研究。
使用Ir2.A85 - 2和Co0.A86 HDR源，基于TG - 43的治疗计划系统（TPS）为19例患者（8例乳腺癌、5例食管癌、6例妇科疾病）制定临床等效计划。使用MCNP6获取两种源设计的相空间文件，并通过与文献中单个源剂量测定结果进行比较来验证。考虑患者特定解剖结构和材料的水吸收剂量（D），使用MCNP6为所有计划进行计算，输入文件使用BrachyGuide软件工具准备，以分析来自DICOM RT计划导出的信息。
观察到除肺部外，基于TG - 43的剂量普遍高估，铱的高估幅度更大。计划靶体积（PTV）的剂量体积直方图（DVH）指数中，TG - 43与蒙特卡罗（MC）之间百分比差异的分布显示，钴和铱的中位数均较小（约2%），但铱的离散度更大。对于危及器官（OARs），钴（铱）的乳腺V中位数百分比差异为3%（5%）。发现皮肤D中位数差异相当，铱的离散度更大，肺部D和主动脉D也是如此。TG - 43高估了直肠和乙状结肠的D，与MC的中位数差异在2%以内，铱的离散度更大。对于膀胱，钴（2%）的差异中位数大于铱（0.75%），不过铱的离散度再次更大。
基于TG - 43的剂量测定与MC剂量测定之间观察到的差异幅度以及相对于铱较小的离散度表明，在临床治疗计划剂量测定中，钴HDR源更符合TG - 43假设。
