Physics in Medicine & Biology ( IF 3.5 ) Pub Date : 2021-06-07 , DOI: 10.1088/1361-6560/ac02d6 Justine M Dupere 1 , John J Munro 2 , David C Medich 1
Purpose. We propose an approach for treating ocular melanoma using a new type of brachytherapy treatment device. This device couples Yb-169, a middle-energy high dose rate (HDR) brachytherapy source, with a gold shielded ring applicator to better conform radiation exposures to the tumor. In this study, we computationally test the dosimetric output of our proposed shielded ring applicator design using MCNP6 and validate it against an I-125 COMS plaque. Methods. The proposed Yb-169 ring applicator consists of an assembly of discrete sources delivered into an applicator with a conical collimated opening; this opening is tangent to the outside of the source tube. Using MCNP6, we simulated the dosimetric output of a ring of Yb-169 pellets placed within the collimator at various conical diameters and angles to demonstrate the dosimetric distribution for various prescription dose depths and target sizes using static intensity modulation. Results. Using various angles of collimation, the prescription dose was delivered to target apex depths of 3.5–8.0 mm into the eye covering target sizes ranging from 10 to 15 mm in diameter. This proposed device reduced the maximum absorbed dose to critical structures relative to I-125 by 5.2% to the posterior lens, 9.3% to the iris, 13.8% to the optic nerve, and 1.3% to the sclera. Conclusions. This proposed eye plaque design provides a more conformal dose distribution to the ocular tumor while minimizes dose to healthy ocular structures. In addition, the use of a middle-energy HDR brachytherapy source allows the use of a remote afterloader to expose the tumor after the plaque is sutured in place. This system is inherently safer and eliminates dose to the surgeon’s hands.
中文翻译:
使用 Yb-169 的屏蔽高剂量率眼部近距离放射治疗
目的。我们提出了一种使用新型近距离放射治疗设备治疗眼部黑色素瘤的方法。该设备将 Yb-169(一种中等能量高剂量率 (HDR) 近距离放射治疗源)与一个金屏蔽环施放器相结合,以更好地使辐射暴露与肿瘤相符。在这项研究中,我们使用 MCNP6 计算测试了我们提出的屏蔽环施药器设计的剂量学输出,并针对 I-125 COMS 斑块对其进行了验证。方法。提议的 Yb-169 环形施加器由一组离散源组成,这些源被输送到一个带有锥形准直开口的施加器中;该开口与源管的外部相切。使用 MCNP6,我们模拟了以各种锥形直径和角度放置在准直器内的 Yb-169 颗粒环的剂量学输出,以展示使用静态强度调制的各种处方剂量深度和目标尺寸的剂量学分布。结果。使用各种准直角度,将处方剂量递送至目标顶点深度为 3.5-8.0 毫米的眼睛覆盖目标尺寸,直径范围为 10 至 15 毫米。与 I-125 相比,此提议的装置将关键结构的最大吸收剂量降低了 5.2%,对后晶状体降低了 9.3%,对虹膜降低了 9.3%,对视神经降低了 13.8%,对巩膜降低了 1.3%。结论。这种建议的眼斑设计为眼部肿瘤提供了更适形的剂量分布,同时最大限度地减少了对健康眼部结构的剂量。此外,使用中能 HDR 近距离放射治疗源允许使用远程后装器在斑块缝合到位后暴露肿瘤。该系统本质上更安全并且消除了外科医生手的剂量。