Saatchian Erfan, Nasseri Shahrokh, Hosseini Sare, Gholamhosseinian Hamid
Department of Medical Physics, Mashhad University of Medical Sciences, Mashhad, Iran.
Medical Physics Research Center, Mashhad University of Medical Sciences, Mashhad, Iran.
Discov Oncol. 2024 Sep 27;15(1):494. doi: 10.1007/s12672-024-01383-5.
The utilization of metal shields in intensity-modulated brachytherapy (IMBT) enables the modulation of the dose, resulting in improved conformance to the tumor while simultaneously reducing the doses to organs at risk (OARs). Utilizing higher-energy sources like Co in IMBT for cervical and vaginal cancers has consistently posed challenges. This study evaluates the dosimetric aspects of modified applicators designed for IMBT using Co and Ir sources.
GATE, a Geant4-based simulation code, was utilized to model and simulate four distinct applicators. The clinical applicators were redesigned to place the structure of the source tube and the shield while keeping the general characteristics unchanged. These shields were evaluated by calculating transmission factors (TFs) and the dose homogeneities were also determined.
Transmission factors for the IMBT technique in redesigned intrauterine applicators and tungsten shields for iridium and cobalt sources were at least 12.8 and 65.4%, and these values were obtained for the intravaginal applicator at 0.2 and 7.0%, respectively. The dose homogeneities for all combinations of radionuclide-shield were within a 15% range of the non-IMBT applicators.
This study has quantitatively evaluated the dosimetric effect of tungsten shields in the IMBT technique for cervical and vaginal cancer using cobalt sources. Ir compared to Co resulted in higher effectiveness for the designed intrauterine and intravaginal shields. while implementing tungsten shields in the redesigned applicators against the Co source may not offer complete protection, it does show promising results in reducing the dose to organs at risk.
在调强近距离放射治疗（IMBT）中使用金属屏蔽可实现剂量调制，从而在提高肿瘤适形性的同时，降低危及器官（OARs）的剂量。在宫颈癌和阴道癌的IMBT中使用钴等高能量源一直存在挑战。本研究评估了为使用钴源和铱源的IMBT设计的改良施源器的剂量学方面。
使用基于Geant4的模拟代码GATE对四种不同的施源器进行建模和模拟。对临床施源器进行重新设计，以放置源管和屏蔽的结构，同时保持一般特性不变。通过计算传输因子（TFs）对这些屏蔽进行评估，并确定剂量均匀性。
重新设计的子宫内施源器和用于铱源和钴源的钨屏蔽的IMBT技术的传输因子分别至少为12.8%和65.4%，而阴道内施源器的相应值分别为0.2%和7.0%。所有放射性核素 - 屏蔽组合的剂量均匀性在非IMBT施源器的15%范围内。
本研究定量评估了在宫颈癌和阴道癌的IMBT技术中使用钴源时钨屏蔽的剂量学效果。与钴相比，铱在设计的子宫内和阴道内屏蔽方面具有更高的有效性。虽然在重新设计的针对钴源的施源器中实施钨屏蔽可能无法提供完全保护，但它在降低危及器官的剂量方面确实显示出有希望的结果。
