PURPOSE

In this paper we present a further step in the implementation of a physical phantom designed to generate sets of “true” independent reference data as requested by TG-186, intending to address and mitigate the scarcity of experimental studies on brachytherapy (BT) validation in heterogeneous media. To achieve this, we incorporated well-known heterogeneous materials into the phantom in order to perform measurements of ¹²⁵I dose distribution. The work aims to experimentally validate Monte Carlo (MC) calculations based on MBDCA and determine the conversion factors from LiF response to absorbed dose in different media, using cavity theory.

METHODS AND MATERIALS

The physical phantom was adjusted to incorporate tissue equivalent materials, such as: adipose tissue, bone, breast and lung with varying thickness. MC calculations were performed using MCNP6.2 code to calculate the absorbed dose in the LiF and the dose conversion factors (DCF).

RESULTS

The proposed heterogeneous phantom associated with the experimental procedure carried out in this work yielded accurate dose data that enabled the conversion of the LiF responses into absorbed dose to medium. The results showed a maximum uncertainty of 6.92 % (k = 1), which may be considered excellent for dosimetry with low-energy BT sources.

CONCLUSIONS

The presented heterogeneous phantom achieves the required precision in dose evaluations due to its easy reproducibility in the experimental setup. The obtained results support the dose conversion methodology for all evaluated media. The experimental validation of the DCF in different media holds great significance for clinical procedures, as it can be applied to other tissues, including water, which remains a widely utilized reference medium in clinical practice.

中文翻译：

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用于 I-125 剂量测量和介质剂量确定的异质物理体模

目的

在本文中，我们提出了实施物理体模的进一步步骤，该物理体模旨在根据 TG-186 的要求生成“真实”独立参考数据集，旨在解决和缓解近距离放射治疗 (BT) 验证实验研究的匮乏问题。异构媒体。为了实现这一目标，我们将众所周知的异质材料合并到模型中，以便执行¹²⁵ I 剂量分布的测量。这项工作旨在通过实验验证基于 MBDCA 的蒙特卡罗 (MC) 计算，并利用空腔理论确定不同介质中 LiF 响应到吸收剂量的转换因子。

方法和材料

物理模型经过调整以纳入组织等效材料，例如：不同厚度的脂肪组织、骨骼、乳房和肺部。使用 MCNP6.2 代码进行 MC 计算，以计算 LiF 中的吸收剂量和剂量转换因子 (DCF)。

结果

所提出的与本工作中进行的实验程序相关的异质模型产生了准确的剂量数据，使 LiF 响应能够转换为介质的吸收剂量。结果显示最大不确定度为 6.92% ( k  = 1)，这对于低能量 BT 源的剂量测定来说可能被认为是极好的。

结论

由于其在实验设置中易于再现，所提出的异质体模实现了剂量评估所需的精度。获得的结果支持所有评估介质的剂量转换方法。DCF 在不同介质中的实验验证对于临床操作具有重要意义，因为它可以应用于其他组织，包括水，水仍然是临床实践中广泛使用的参考介质。