Department of Nuclear Medicine, Asan Medical Center, University of Ulsan College of Medicine, Seoul, Korea.
Department of Nuclear Medicine, Nowon Eulji Medical Center, Eulji University School of Medicine, Seoul, Korea.
PLoS One. 2021 May 21;16(5):e0251627. doi: 10.1371/journal.pone.0251627. eCollection 2021.
Retained radioactivity of 131I after ablation therapy largely differs in each patient according to factors including the amount of remnant thyroid tissue, renal function, and use of recombinant human thyroid-stimulating hormone. To reduce unnecessary restriction of patient's daily life after inpatient 131I ablation therapy, we propose a practical individualized method for radiation precaution based on dose rate at release time.
We evaluated 215 patients with differentiated thyroid cancer who underwent inpatient 131I ablation therapy following total thyroidectomy. Effective dose equivalent rates at 1-m distance were measured upon release (EDRR) on day 2 and during delayed whole-body scan (EDRD) visits on day 6‒8 after 131I administration. The biexponential model was designed to estimate total effective dose equivalent to others. To assess conservativeness of our model, EDRD estimated by our model was compared with measured EDRD. EDRR-based periods of precaution not to receiving 1 mSv of radiation exposure were estimated and compared with those based on administered radioactivities on American Thyroid Association (ATA) recommendations.
The EDRR ranged from 1.0-48.9 μSv/hr. The measured EDRD were equal to or lower than estimated EDRD in all patients, except for one, indicating that our model is sufficiently conservative. According to our model, no subjects needed additional daytime restriction after release. The maximum permissible times for public transportation use were longer in all patients compared with those based on administered radioactivities. Nighttime restriction periods were significantly shorter than those based on administered radioactivity; median periods requiring sleeping apart were 0 (range, 0‒5), 4 (range, 1‒14), and 3 (range, 2‒13) days after release in patients treated with radioactivity doses of 2.96, 5.50, and 7.40 GBq, respectively, needing 8, 16, and 19 additional days, respectively, based on administered radioactivity.
Radiation safety instructions using proposed method based on EDRR of individual patient could safely reduce the burden of radiation precaution.
根据残余甲状腺组织量、肾功能和重组人促甲状腺激素的使用等因素，131I 消融治疗后患者的放射性残留差异很大。为了减少住院 131I 消融治疗后患者日常生活的不必要限制，我们提出了一种基于释放时剂量率的实用个体化辐射防护方法。
我们评估了 215 例接受全甲状腺切除术后住院 131I 消融治疗的分化型甲状腺癌患者。在 131I 给药后第 2 天（释放日）和第 6-8 天（延迟全身扫描日）测量 1 米距离处的有效剂量当量率（EDRR）。设计双指数模型来估计对他人的总有效剂量当量。为了评估我们模型的保守性，将我们模型估计的 EDRD 与实测 EDRD 进行比较。根据美国甲状腺协会（ATA）建议，基于 EDRR 估计的避免接受 1mSv 辐射暴露的防护期，并与基于放射性活度的防护期进行比较。
EDRR 范围为 1.0-48.9μSv/hr。除 1 例外，所有患者的实测 EDRD 均等于或低于估计的 EDRD，表明我们的模型足够保守。根据我们的模型，释放后无需额外限制白天活动。与基于放射性活度的结果相比，所有患者可使用公共交通工具的最长时间都更长。夜间限制期明显短于基于放射性活度的结果；释放后，分别接受 2.96、5.50 和 7.40GBq 放射性活度治疗的患者，需要分开睡觉的中位时间分别为 0（范围 0-5）、4（范围 1-14）和 3（范围 2-13）天，分别需要额外的 8、16 和 19 天，基于放射性活度。
使用基于个体患者 EDRR 的建议方法进行辐射安全指导，可以安全地减轻辐射防护负担。
