A comparison of thyroid blockade strategies in paediatric 123I-meta-iodobenzylguanidine scanning: a dual centre study.

Objective The aim of this study was to evaluate three thyroid blockade regimes to determine which protocol provides the optimal level of thyroidal protection for paediatric 123-I-meta-iodobenzylguanidine (mIBG) imaging and estimate the relative radiation dose inferred from unbound radioiodine. Methods A total of 231 patients were retrospectively evaluated for thyroid uptake and categorised into five subgroups depending upon the protocol of thyroid blockade received. Efficacy of thyroid blockade was established by visual scoring and image quantitation with comparison against a control group. Results Visual Likert scale responses were subjected to the Mann-Whitney U and Kruskal-Wallis tests, respectively. Statistical significance was reached for observed thyroid uptake in potassium perchlorate recipients (U = 1107, P = 0.001). No statistically significant difference was observed in thyroid uptake for iohexol blockade (U = 176, P = 0.71) or potassium iodate blockade despite variations in iodate dosage and duration (chi(2)(2) = 0.203, P = 0.93). The analyses were repeated for the image quantitation data. A statistically significantly higher absorbed thyroid dose was observed using potassium perchlorate blockade compared with the control group (U = 719, P = 0.001). The Mann-Whitney U did not reach statistical significance in absorbed thyroid dose for iohexol blockade (U = 126, P = 0.209, r = -0.13). The Kruskal-Wallis test, conducted across the potassium iodate groups, did not reach statistical significance (chi(2)(2) = 0.513, P = 0.774). The median absorbed thyroid dose across the iodate groups ranged from 3.58 to 3.91 mGy indicating comparable blockade effectiveness for single-dose potassium iodate. Conclusion Potassium iodate blockade is more efficacious compared with potassium perchlorate within the cohort observed. Both visual and quantitative data indicate that potassium iodate given at 30-60 min before I-123-mIBG injection provides comparable blockade effectiveness to lengthier administrations, suggesting that a single dose is well tolerated and practical.