Introduction
Dosimetric treatment planning evaluations concerning patient-adapted moulds for iridium-192 high-dose-rate brachytherapy are presented in this report.

Material and methods
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.

Results
The dose-volume parameters D90, V100, and V150 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 maximum 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 D90, V100, and V150 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/cm³ to 1.26 g/cm³ up to 7 mm total mould thickness.

Conclusions
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.



中文翻译：

---

用于鼻周皮肤肿瘤的个体化基于模具的高剂量率近距离放射治疗：从剂量学的角度进行技术评估

简介
本报告介绍了有关适用于患者的 Iridium-192 高剂量率近距离放射治疗模具的剂量学治疗计划评估。

材料和方法
六名患有鼻周皮肤肿瘤的患者接受了由生物相容性上皮材料制成的单个模具和嵌入式塑料涂药器的治疗。根据临床要求优化治疗计划，并使用标准的水基 TG-43 形式计算剂量。此外，对根据 TG-186 协议的回顾性材料相关塌陷锥计算进行了评估，以量化 TG-43 协议对这种表面近距离放射治疗技术的局限性。

结果
用于 TG-43 剂量计算的计划目标体积 (PTV) 的剂量体积参数 D90、V100 和 V150 分别为规定剂量的 92.2% 至 102.5%、75.1% 至 93.1% 和 7.4% 至 41.7% . 作为受影响最大的风险器官 (OAR)，同侧眼球的最大总剂量在 8.9 到 36.4 Gy 之间变化。与 TG-43 数据相比，使用基于 Hounsfield 单元的密度分配的 TG-186 计算导致 PTV 的平均 D90、V100 和 V150 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 剂量计算考虑了由于环境空气以及受模具材料和组织成分影响的剂量对介质的影响而减少的反向散射。中位 PTV 剂量在 0 范围内稳健。

结论
HDR 接触 BT 与单个模具是常规治疗鼻周皮肤肿瘤的安全方式。该技术提供了良好的目标覆盖和 OAR 保护，同时对模具材料密度的微小变化具有鲁棒性。基于模型的剂量计算 (TG-186) 应补充 TG-43 剂量计算，以用于验证目的和质量改进。