The main aim of this study was to investigate the dosimetric characteristics of the INTRABEAM ® system in the presence of air gaps between the surface of applicators (APs) and tumor bed. Additionally, the effect of tissue heterogeneities was another focus. Investigating the dosimetric characteristics of the INTRABEAM® system is essential to deliver the required dose to the tumor bed correctly and reduce the delivered dose to the ribs and lung. Choosing the correct AP size and fitting it to the lumpectomy cavity is essential to remove the effect of air gaps and avoid inaccurate dose delivery. Consequently, the Geant4 toolkit was used to simulate the INTRABEAM ® system with spherical APs of various sizes. The wall effect of the ion chamber (IC) PTW 34013 used in the present study was checked. The simulations were validated in comparison with measurements, and then used to calculate any inaccuracies in dose delivery in the presence of 4- and 10-mm air gaps between the surface of the APs and the tumor bed. Also, the doses received due to tissue heterogeneities were characterized. It turned out that measurements and simulations were approximately in agreement (± 2%) for all sizes of APs. The perturbation factor introduced by the IC due to differences in graphite-coated polyethylene and air as compared to the phantom material was approximately equal to one for all AP. The greatest relative dose delivery difference was observed for an AP with a diameter of 1.5 cm, i.e., 44% and 70% in the presence of 4- and 10-mm air gaps, respectively. In contrast, the lowest relative dose delivery difference was observed for an AP with a diameter of 5 cm, i.e., 24% and 42% in the presence of 4- and 10-mm air gaps, respectively. Increasing APs size showed a decrease in relative dose delivery difference due to the presence of air gaps. In addition, the undesired dose received by the ribs turned out to be higher when a treatment site closer to the ribs was assumed. The undesired dose received by the ribs increased as the AP size increased. The lung dose turned out to be decreased due to the shielding effect of the ribs, small lung density, and long separation distance from the AP surface.

中文翻译：

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在存在气隙和组织异质性的情况下，采用球形涂药器的INTRABEAM®系统的剂量特性。

这项研究的主要目的是研究在涂抹器表面（APs）与肿瘤床之间存在气隙的情况下INTRABEAM®系统的剂量特性。另外，组织异质性的影响是另一个焦点。研究INTRABEAM®系统的剂量特性对于将所需剂量正确地输送到肿瘤床并减少向肋骨和肺部的输送剂量至关重要。选择正确的AP尺寸并将其安装在肿块切除术腔中对于消除气隙的影响并避免不正确的剂量输送至关重要。因此，使用Geant4工具包来模拟具有各种尺寸的球形AP的INTRABEAM®系统。检查了本研究中使用的离子室（IC）PTW 34013的壁效应。通过与测量结果进行比较，对模拟进行了验证，然后将其用于计算在AP表面与肿瘤床之间存在4毫米和10毫米气隙的情况下剂量输送中的任何不准确之处。而且，表征了由于组织异质性而接受的剂量。事实证明，所有尺寸的AP的测量和模拟结果基本一致（±2％）。与幻影材料相比，由于石墨涂层的聚乙烯和空气的差异，IC引入的扰动因子大约等于所有AP的扰动因子。对于直径为1.5 cm的AP，在存在4 mm和10 mm气隙的情况下，观察到最大相对剂量输送差异。相反，对于直径为5 cm的AP，观察到最低的相对剂量输送差异，即在存在4毫米和10毫米气隙的情况下分别为24％和42％。由于空气间隙的存在，增加的AP尺寸显示相对剂量输送差异的减小。另外，当假设更靠近肋骨的治疗部位时，肋骨不希望的剂量更高。肋骨接受的不希望的剂量随着AP尺寸的增加而增加。事实证明，由于肋骨的屏蔽作用，较小的肺密度以及与AP表面的距离较长，肺剂量降低了。肋骨接受的不希望的剂量随着AP尺寸的增加而增加。事实证明，由于肋骨的屏蔽作用，较小的肺密度以及与AP表面的距离较长，肺剂量降低了。肋骨接受的不希望的剂量随着AP尺寸的增加而增加。事实证明，由于肋骨的屏蔽作用，较小的肺密度以及与AP表面的距离较长，肺剂量降低了。