Background: High risk patients with differentiated thyroid cancer (DTC) undergoing radioiodine (I-131) treatment can be prepared by thyroid hormone withdrawal (THW) or with parenteral recombinant TSH (rhTSH). We compared two centres predominantly using THW or rhTSH to study the impact on radioiodine retention and length of hospital stay (LoHS).
Methods: We retrospectively compared radioactivity at discharge following high dose I-131 therapy (35 GBq administered activity) between THW (Centre-A) and rhTSH (Centre-B). Baseline characteristics (in a euthyroid state) were obtained from pre-operative records. The creatinine value prior to I-131 therapy was taken for GFR calculation (Pre-radioiodine GFR). The outcome parameters compared were radiation dose emission rate at 1 metre before discharge and LoHS.
Results: We included 57 and 87 patients in THW and rhTSH arm respectively (Table 1). Data are mean (±S.D.) unless otherwise stated. The mean age of the study population was 53 ±17 and 50 ± 15 years in Centre-A and B respectively. Only the important findings are presented here.
|Centre-A (THW N=57)||Centre-B (rhTSH N=87)||P-value|
|T1 and T2||29%||35%|
|T3 and T4||71%||65%|
|Baseline eGFR (ml/min)||96.57±18.61||96.15±15.60||0.420|
|Pre-radioiodine eGFR (ml/min)||74.63±19.74||95.60±16.14||0.0001|
|Percentage meeting target dose rate at discharge (<30 uSv/hour @ 1metre)||98.6%||95.4%||0.247|
Conclusion: There was a significant reduction in eGFR between euthyroid and hypothyroid state in THW arm (P<0.05) when compared with rhTSH arm (who remain euthyroid during the I-131 therapy). This impairment of renal function in THW arm caused increased I-131 retention and contributed to an increased LOHS (4 days rather than 2). The impact on renal function and LoHS should also be a factor when considering use of rhTSH with shorter LoHS and scope to relax radiation protection guidance earlier.