5mCi pretreatment scanning does not cause stunning when the ablative dose is administered within 72 hours

Abstract

Objective: To determine the stunning effect of a tracer dose of 5mCi iodine-131. Patients and Methods: We retrospectively analyzed 145 patients who received the first ablative treatment at our service. Patients were divided according to disease status determined upon post-treatment scanning (101 patients with thyroid remnants and 44 with pulmonary metastases) and whole-body scanning before ablation (performed on 69 individuals). All patients with thyroid remnants were treated with an ablative dose of 100mCi and those with metastases received 200mCi. Results: In patients with remnants only (n= 41) or metastases (n= 28) submitted to diagnostic scanning, uptake was found to be apparently increased in most patientscases (71 and 73%, respectively) 7 days after therapy, while reduced uptake (visual) was not observed in any patient. The efficacy of ablation was similar in the groups submitted or not to diagnostic scanning: 71 and 80% in patients without metastases (p= 0.28), respectively, and 43 and 50% in those with pulmonary involvement (p= 0.64). Conclusion: The present results indicate that diagnostic scanning using a 5mCi iodine-131 dose does not interfere with uptake of the ablative dose or with treatment efficacy when ablation is performed within 72h. Objetivo: Determinar a interferência de uma dose traçadora de 5mCi de 131 I. Pacientes e Método: Nós analisamos retrospectivamente 145 pacientes que receberam o primeiro tratamento ablativo em nosso serviço. Eles foram divididos de acordo com o estadio da doença determinado pelo rastreamento pós-terapêutico (101 pacientes com remanescentes tireoidianos e 44 com metástases pulmonares) e scanning de corpo inteiro antes da ablação (realizada em 69 indivíduos). Todos os pacientes com remanescentes tireoidianos foram tratados com uma dose ablativa de 100mCi e aqueles com metástases receberam 200mCi. Resultados: Nos pacientes com remanescentes apenas (n= 41) ou metastases (n= 28) submetidos ao scanning diagnóstico, a captação encontrava-se aparentemente aumentada na maioria dos patientscasos (71 e 73%, respectivamente) 7 dias após a terapia, enquanto captação reduzida (visual) não foi observada em nenhum paciente. A eficácia da ablação foi similar nos grupos submetidos ou não ao rastreamento diagnóstico: 71 e 80% em pacientes sem metástases (p= 0,28), respectivamente, e 43 e 50% naqueles com envolvimento pulmonar (p= 0,64). Conclusão: Esses resultados indicam que o rastreamento diagnóstico usando uma dose de 5mCi de 131 I não interefere com a captação da dose ablativa ou com a eficácia do tratamento quando a ablação é realizada dentro de 72h.

The Effect of Diagnostic Absorbed Doses from 131I on Human Thyrocytes in Vitro

“…However, since those authors reduced diagnostic activity to the 37–74 MBq, they have not observed obvious stunning effect in WBS [ 16 ]. Furthermore, in several studies the increased reduction in 131 I uptake between DxWBS and RxWBS was not present when the diagnostic activity of 131 I was equal to 185 MBq or less [ 6 , 31 , 32 , 33 , 34 ].…”

Thyroid nodules and differentiated thyroid cancer: update on the Brazilian consensus

“…To avoid stunning, diagnostic WBS must be performed with 123 I, 2 mCi of 131 I (148), or tracer activity of 5 mCi of 131 I, provided that the 131 I therapy (whenever necessary) is performed 3 to 5 days later (149).…”

Appropriate Use Criteria for Nuclear Medicine in the Evaluation and Treatment of Differentiated Thyroid Cancer

“…Although 123 I is adequate for imaging of residual thyroid tissue in the neck, comparison of diagnostic 123 I and 131 I scans performed sequentially in the same patients demonstrated that 123 I is less sensitive than 131 I for detection of thyroid cancer metastases (41). In addition to these factors, the absence of evidence for stunning with low (1-2 mCi) diagnostic 131 I activities and when 131 I therapy is administered within 72 h of the diagnostic 131 I dose contributed to more widespread use of 131 I for diagnostic preablation scintigraphy (42)(43)(44)(45)(46). The decision about which radioisotope to use for diagnostic imaging should also include consideration of the timing between administration of the diagnostic tracer and the therapeutic tracer.…”