I-124 pre-therapy dosimetry for the treatment of differentiated thyroid cancer: A single center experience

Introduction: The maximum tolerable activity (MTA) of I-131 in radioiodine therapy is an established surrogate quantity to ensure that the therapeutic activity does not produce severe damages to the bone marrow and lung. The aim of this study was to estimate the MTAs for high-risk patients using I-124 pre-therapy dosimetry and to compare the results with published literature. Methods: A total of 15 thyroid cancer patients, who received I-124 pre-therapy dosimetry procedure, had underwent serial blood sampling and whole-body external measurements at approximately 1–2, 4, 24, 48, and 96 h or longer after I-124 administration. The blood sampling and whole-body external measurements were used to calculate the MTA for each individual using published dosimetry procedures. Results: The estimated MTAs ranged from 14 to 34 GBq. The range of blood residence and whole-body residence times were 2.6 h and 22.4 h, respectively; the 48-h whole-body retention value ranged from 2% - 14%. An overall good MTA agreement can be found between our centre and the results of the well-established centre (Essen, Germany) that included 108 patients. Conclusion: I-124 pre-therapy dosimetry provides toxicity levels similar to published values. Further prospective studies are warranted to assess the benefits of I-124 pre-therapy dosimetry for the individual patient and, in particular, the patient outcome.