A Monte Carlo study comparing dead-time losses of a gamma camera between tungsten functional paper and lead sheet for dosimetry in targeted radionuclide therapy with Lu-177.

IF 2.5 4区 医学 Q2 RADIOLOGY, NUCLEAR MEDICINE & MEDICAL IMAGING
Kohei Nakanishi, Naotoshi Fujita, Haruna Iwanaga, Yuki Asano, Shinji Abe, Ryuichi Nishii, Katsuhiko Kato
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引用次数: 0

Abstract

Objective: Dead-time loss is reported to be non-negligible for some patients with a high tumor burden in Lu-177 radionuclide therapy, even if the administered activity is 7.4 GBq. Hence, we proposed a simple method to shorten the apparent dead time and reduce dead-time loss using a thin lead sheet in previous work. The collimator surface of the gamma camera was covered with a lead sheet in our proposed method. While allowing the detection of 208-keV gamma photons of Lu-177 that penetrate the sheet, photons with energies lower than 208 keV, which cause dead-time loss, were shielded. In this study, we evaluated the usefulness of tungsten functional paper (TFP) for the proposed method using Monte Carlo simulation.

Methods: The count rates in imaging of Lu-177 administered to patients were simulated with the International Commission on Radiological Protection (ICRP) 110 phantom using the GATE Monte Carlo simulation toolkit. The simulated gamma cameras with a 0.5-mm lead sheet, 1.2-mm TFP, or no filter were positioned closely on the anterior and posterior sides of the phantom. The apparent dead times and dead-time losses at 24 h after administration were calculated for an energy window of 208 keV ± 10%. Moreover, the dead-time losses at 24-120 h were analytically assessed using activity excretion data of Lu-177-DOTATATE.

Results: The dead-time loss without a filter was 5% even 120 h after administration in patients with a high tumor burden and slow excretion, while those with a lead sheet and TFP were 0.22 and 0.58 times less than those with no filter, respectively. The count rates with the TFP were 1.3 times higher than those with the lead sheet, and the TFP could maintain primary count rates at 91-94% of those without a filter.

Conclusions: Although the apparent dead time and dead-time loss with the lead sheet were shorter and less than those with TFP, those with TFP were superior to those without a filter. The advantage of TFP over the lead sheet is that the decrease in primary count rates was less.

蒙特卡洛研究:比较钨功能纸和铅板在用 Lu-177 进行放射性核素靶向治疗时伽马相机的死时损失。
目的:据报道,对于一些肿瘤负荷较高的患者,在进行 Lu-177 放射性核素治疗时,即使给药活度为 7.4 GBq,死区时间损失也不可忽略。因此,我们在之前的工作中提出了一种利用薄铅片缩短表观死区时间和减少死区时间损失的简单方法。在我们提出的方法中,伽马相机的准直器表面覆盖了一层铅片。在探测穿透铅板的 208 千伏伽马光子的同时,能量低于 208 千伏的光子也被屏蔽了,而这些光子会造成死区时间损失。在这项研究中,我们利用蒙特卡洛模拟评估了钨功能纸(TFP)在拟议方法中的实用性:方法:使用 GATE 蒙特卡洛模拟工具包,用国际放射防护委员会(ICRP)的 110 个模型模拟了给病人注射 Lu-177 时的成像计数率。模拟伽马相机分别安装了 0.5 毫米铅片、1.2 毫米 TFP 或无滤光片,并紧贴模型的前后两侧。在208keV±10%的能量窗口中,计算了给药后24小时的表观死区时间和死区时间损失。此外,还利用 Lu-177-DOTATATE 的活性排泄数据分析评估了 24-120 h 的死亡时间损失:结果:对于肿瘤负荷高、排泄缓慢的患者,即使在给药后 120 小时,无过滤器的死亡时间损失也达到了 5%,而使用铅板和 TFP 的死亡时间损失分别是无过滤器患者的 0.22 倍和 0.58 倍。使用TFP的计数率是使用铅片的1.3倍,TFP可将初级计数率维持在无过滤器计数率的91-94%:结论:虽然使用铅片的表观死区时间和死区时间损失比使用 TFP 的短和少,但使用 TFP 的效果优于不使用过滤器的效果。与铅片相比,TFP 的优势在于初级计数率的下降幅度较小。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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来源期刊
Annals of Nuclear Medicine
Annals of Nuclear Medicine 医学-核医学
CiteScore
4.90
自引率
7.70%
发文量
111
审稿时长
4-8 weeks
期刊介绍: Annals of Nuclear Medicine is an official journal of the Japanese Society of Nuclear Medicine. It develops the appropriate application of radioactive substances and stable nuclides in the field of medicine. The journal promotes the exchange of ideas and information and research in nuclear medicine and includes the medical application of radionuclides and related subjects. It presents original articles, short communications, reviews and letters to the editor.
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