Karius Andre, Shariff Maya, Schaller Sabrina, Lotter Michael, Strnad Vratislav, Lackner Niklas, Fietkau Rainer, Bert Christoph, Merten Ricarda, Schweizer Claudia
Department of Radiation Oncology, Universitätsklinikum Erlangen, Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), Universitätsstraße 27, 91054, Erlangen, Germany.
Comprehensive Cancer Center Erlangen-EMN (CCC ER-EMN), Erlangen, Germany.
Strahlenther Onkol. 2025 Jan;201(1):57-70. doi: 10.1007/s00066-024-02318-3. Epub 2024 Nov 27.
Model-based dose calculation considering tissue compositions is increasingly being investigated in brachytherapy. The aim of this study was to assess the suitability of modern cone-beam computed tomography (CBCT) imaging compared to conventional computed tomography (CT) scans for this purpose.
By means of a phantom study, we evaluated the CT numbers and electron densities measured using a modern CBCT device as well as a conventional CT scanner for various materials. Based on this, we compared dose calculations (using the TG-43 formalism as well as model-based collapsed cone calculations assuming uniform materials [ACE] and considering CT numbers [ACE]) on planning CTs and control CBCTs for patients with cervical and breast cancer as well as phantom-simulated skin cancer cases. Assessing dosimetric deviations between the planning CTs and control CBCTs acquired during the treatment course served to estimate interfractional implant variations.
The comparison of ACE-ACE deviations between planning CTs and control CBCTs revealed no statistically significant difference for almost all examined dose parameters. Dosimetric deviations between model-based dose calculations and TG-43 were partly significant but of small magnitude (< 10 cGy per fraction). Interfractional dosimetric variations were substantially larger than the dosimetric differences found between the various dose calculation procedures.
Model-based dose calculation based on modern CBCT imaging was suitable. However, the found differences between these calculations and the TG-43 formalism should be investigated in dose-outcome analyses. The observed interfractional dosimetric variations revealed the importance of performing treatment quality assurance.
在近距离放射治疗中，越来越多地研究考虑组织成分的基于模型的剂量计算。本研究的目的是评估与传统计算机断层扫描（CT）扫描相比，现代锥形束计算机断层扫描（CBCT）成像用于此目的的适用性。
通过体模研究，我们评估了使用现代CBCT设备以及传统CT扫描仪对各种材料测量的CT值和电子密度。基于此，我们比较了宫颈癌、乳腺癌患者以及体模模拟皮肤癌病例在计划CT和对照CBCT上的剂量计算（使用TG-43形式主义以及基于模型的坍缩锥计算，假设材料均匀[ACE]并考虑CT值[ACE]）。评估治疗过程中获取的计划CT和对照CBCT之间的剂量偏差，以估计分次间植入物的变化。
计划CT和对照CBCT之间ACE-ACE偏差的比较显示，几乎所有检查的剂量参数在统计学上均无显著差异。基于模型的剂量计算与TG-43之间的剂量偏差部分显著，但幅度较小（每分次<10 cGy）。分次间剂量变化远大于不同剂量计算程序之间的剂量差异。
基于现代CBCT成像的基于模型的剂量计算是合适的。然而，这些计算与TG-43形式主义之间发现的差异应在剂量-结果分析中进行研究。观察到的分次间剂量变化揭示了进行治疗质量保证的重要性。
