Scherf Christian, Licher Jörg, Mletzko Christina, Trommel Martin, Tselis Nikolaos, Chatzikonstantinou Georgios, Diefenhardt Markus, Rödel Claus, Köhn Janett, Ramm Ulla
Department of Radiation Oncology, University Hospital, Goethe University, Frankfurt, Germany.
J Contemp Brachytherapy. 2021 Apr;13(2):179-187. doi: 10.5114/jcb.2021.105286. Epub 2021 Apr 14.
Dosimetric treatment planning evaluations concerning patient-adapted moulds for iridium-192 high-dose-rate brachytherapy are presented in this report.
Six patients with perinasal skin tumors were treated with individual moulds made of biocompatible epithetic materials with embedded plastic applicators. Treatment plans were optimized with regard to clinical requirements, and dose was calculated using standard water-based TG-43 formalism. In addition, retrospective material-dependent collapsed cone calculations according to TG-186 protocol were evaluated to quantify the limitations of TG-43 protocol for this superficial brachytherapy technique.
The dose-volume parameters D, V, and V of the planning target volumes (PTVs) for TG-43 dose calculations yielded 92.2% to 102.5%, 75.1% to 93.1%, and 7.4% to 41.7% of the prescribed dose, respectively. The max- imum overall dose to the ipsilateral eyeball as the most affected organ at risk (OAR) varied between 8.9 and 36.4 Gy. TG-186 calculations with Hounsfield unit-based density allocation resulted in down by -6.4%, -16.7%, and -30.0% lower average D, V, and V of the PTVs, with respect to the TG-43 data. The corresponding calculated OAR doses were also lower. The model-based TG-186 dose calculations have considered reduced backscattering due to environmental air as well as the dose-to-medium influenced by the mould materials and tissue composition. The median PTV dose was robust within 0.5% for simulated variations of mould material densities in the range of 1.0 g/cm to 1.26 g/cm up to 7 mm total mould thickness.
HDR contact BT with individual moulds is a safe modality for routine treatment of perinasal skin tumors. The technique provides good target coverage and OARs' protection, while being robust against small variances in mould material density. Model-based dose calculations (TG-186) should complement TG-43 dose calculations for verification purpose and quality improvement.
本报告介绍了关于铱 - 192高剂量率近距离放射治疗中患者适配模具的剂量学治疗计划评估。
6例鼻周皮肤肿瘤患者接受了由生物相容性上皮材料制成并嵌入塑料施源器的个体化模具治疗。根据临床需求优化治疗计划，并使用基于标准水模体的TG - 43形式计算剂量。此外，根据TG - 186协议进行了回顾性材料依赖性坍缩锥计算，以量化TG - 43协议在此浅表近距离放射治疗技术中的局限性。
对于TG - 43剂量计算，计划靶体积（PTV）的剂量体积参数D、V和V分别产生规定剂量的92.2%至102.5%、75.1%至93.1%和7.4%至41.7%。作为最受影响的危险器官（OAR），同侧眼球的最大总剂量在8.9至36.4 Gy之间变化。基于Hounsfield单位密度分配的TG - 186计算结果显示，与TG - 43数据相比，PTV的平均D、V和V分别降低了 - 6.4%、 - 16.7%和 - 30.0%。相应计算的OAR剂量也较低。基于模型的TG - 186剂量计算考虑了环境空气导致的反向散射减少以及模具材料和组织成分对介质剂量的影响。对于总模具厚度达7 mm、模具材料密度在1.0 g/cm³至1.26 g/cm³范围内的模拟变化，PTV的中位剂量在0.5%范围内具有稳健性。
使用个体化模具的高剂量率近距离接触放疗是鼻周皮肤肿瘤常规治疗的一种安全方式。该技术能提供良好的靶区覆盖和对OAR的保护，同时对模具材料密度的小变化具有稳健性。基于模型的剂量计算（TG - 186）应作为TG - 43剂量计算的补充，用于验证目的和质量改进。
