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Radiation Exposure of the Members of the Public from Patients Treated with 3.7 GBq and 1.85 GBq of 131I—May We Simply Divide by 2?

dos Santos, João António Miranda*†‡; Antunes, Vera Catarina Marques*†; da Silva Trindade Duarte, Luís Hugo§

doi: 10.1097/HP.0000000000000329
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In this work, the dose to the members of the public from two different 131I thyroid ablation patient groups (1.85 GBq and 3.7 GBq), whose a priori programmed hospitalization time is 48 h, is compared. The possibility of allocating half of the hospitalization time (24 h) for patients treated with 1.85 GBq is evaluated, having in mind the dose to the family members after patient release. The maximum dose rate at 1 m from the patient was measured at approximately 20 min, and 24, 48, and 192 h after administration of 3.7 GBq to 70 patients and 1.85 GBq to 55 patients. A triple exponential biological decay combined with physical decay was considered. Different weighting coefficients were applied to the squared residuals, allowing improved fitting and optimization of the calculation of the effective dose received by the public, E, by integration from 24 h or 48 h to infinite. Effective dose at 1 m from patients with 3.7 GBq after being released at 48 h is similar to the case of patients treated with 1.85 GBq after being released at 24 h. The average release dose rate at 24 h due to those patients is slightly higher than those administered with 3.7 GBq released at 48 h. However, no direct correspondence in the calculated dose to the members of the public was found, indicating that different dose rate release limits could be considered in both cases. These results show that it is safe, under the latest ICRP dose limits, to schedule a 24‐h hospitalization time for patients administered with 1.85 GBq.

*Centro de Investigação do Instituto Português de Oncologia do Porto Francisco Gentil, EPE, Rua Dr. António Bernardino de Almeida, 4200‐072 Porto, Portugal; †Serviço de Física Médica do Instituto Português de Oncologia do Porto Francisco Gentil, EPE, Rua Dr. António Bernardino de Almeida, 4200‐072 Porto, Portugal; ‡Instituto de Ciências Biomédicas Abel Salazar da Universidade do Porto, Rua de Jorge Viterbo Ferreira, 228, 4050‐313, Porto, Portugal; §Serviço de Medicina Nuclear do Instituto Português de Oncologia do Porto Francisco Gentil, EPE, Rua Dr. António Bernardino de Almeida, 4200‐072 Porto, Portugal.

The authors declare no conflicts of interest.

For correspondence contact: João António Miranda dos Santos, Serviço de Física Médica do Instituto Português de Oncologia do Porto Francisco Gentil, EPE, Rua Dr. António Bernardino de Almeida, 4200‐072 Porto, Portugal, or email at joao.santos@ipoporto.min-saude.pt.

(Manuscript accepted 5 May 2015)

© 2015 by the Health Physics Society