A simple and accurate dosimetry protocol to estimate activity for hyperthyroidism treatment

BACKGROUND: Aim of the study was to evaluate accuracy of different dosimetry protocols in estimating the required 131I activity to treat hyperthyroid patients. MATERIALS AND METHODS: Forty consecutive patients were analysed: twenty-eight Graves’ disease; twelve autonomous thyroid nodule (ATN). Maximum-uptake, effective half-time and residence-time were estimated from Radioiodine Uptake Test. Residence-time was estimated using a bi-compartmental model. For 131I activity calculation, algorithms laid down in European Association of Nuclear Medicine (EANM) guidelines, ICRP 53 approach and a mono-exponential formula (ME), were compared with OLINDA/EXM results. RESULTS: Based on EANM guidelines, activities to be administered were 3% higher in Graves’ disease (p = 0.001) and 3% higher in ATN (p = 0.046). Calculated activities using ICRP 53 approach were significantly lower compared to OLINDA/EXM: 33% in Graves’ disease; 17% in ATN. Activities recommended by ME, were significantly higher: in Graves’ disease 20%; 42% in ATN. CONCLUSIONS: Only EANM algorithm predict quite well, compared to OLINDA/EXM, the required activity to treat hyperthyroid patients.