방사선의학 웹진

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Abstract
Introduction: 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.

Methods: 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.

Results: 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.

Conclusions: Radiation safety instructions using proposed method based on EDRR of individual patient could safely reduce the burden of radiation precaution.

그림1. 퇴원선량 기반 (본 연구) 모델과 치료용량 기반 모델의 격리기간 비교.

그림2. 퇴원선량 기반 (본 연구) 모델로 예측선량과 실제 측정선량의 비교. 본 연구 모델이 충분히 보수적이고 안전함을 시사함.

Affiliations

Sangwon Han  1 , Soyoung Jin  2 , Seon Hee Yoo  1 , Hyo Sang Lee  3 , Suk Hyun Lee  4 , Min Ji Jeon  5 , Jin-Sook Ryu  1
1 Department of Nuclear Medicine, Asan Medical Center, University of Ulsan College of Medicine, Seoul, Korea.
2 Department of Nuclear Medicine, Nowon Eulji Medical Center, Eulji University School of Medicine, Seoul, Korea.
3 Department of Nuclear Medicine, Gangneung Asan Hospital, University of Ulsan College of Medicine, Gangneung, Korea.
4 Division of Nuclear Medicine, Department of Radiology, Kangnam Sacred Heart Hospital, Hallym University College of Medicine, Seoul, Korea.
5 Department of Endocrinology, Asan Medical Center, University of Ulsan College of Medicine, Seoul, Korea.