Introduction: In our institution the post high-dose RAI whole body scan (WBS) report includes a measurement of quantitative percentage uptake of the dose of RAI administered although this may not be standard practice elsewhere. We aimed to ascertain whether this was associated with the extent of unresected thyroid tissue or residual thyroid cancer following total thyroidectomy and neck dissection represented by the post-surgery TSH-stimulated thyroglobulin concentrations. Methods Case note review was undertaken for 32 patients (44% male) who received high dose RAI (mean dose 3810 Mbq) for thyroid cancer (Papillary 66%, Follicular 25%, Hurthle cell 9%). Patients were included only if they proceeded to high-dose RAI within 6 months (3.7±1.5) following total thyroidectomy and if they underwent a post high-dose RAI WBS within 5 days (4.1±0.4) of treatment. Linear regression analysis was used to look for a correlation between quantitative RAI uptake on the post-therapy WBS and the pre-therapy TSH-stimulated thyroglobulin concentrations relating to the first dose of RAI.
Results: Patients were appropriately hypothyroid before proceeding to high-dose RAI (mean TSH 77.0±32.2 mU/l). Mean TSH-stimulated thyroglobulin prior to high-dose RAI was 17.4±26.7 mcg/l. Mean quantitative percentage RAI uptake on the post-therapy WBS was 0.79±1.0%. Linear regression analysis showed no correlation between percentage RAI uptake on the post-therapy whole body scan and the pre-therapy TSH-stimulated thyroglobulin concentrations (R2=0.103, P=0.09).
Conclusions: Although small, this study indicates that, following total thyroidectomy and neck dissection for thyroid cancer, there is no relationship between quantitative RAI uptake on the post high-dose RAI WBS and the pre-therapy TSH stimulated thyroglobulin concentrations. This suggests that quantitative RAI uptake on the post therapy scan does not provide useful information regarding the extent of unresected thyroid tissue or residual disease following surgery and should not be used to inform decisions regarding prognosis or management.
Declaration of interest: There is no conflict of interest that could be perceived as prejudicing the impartiality of the research reported.
Funding: No specific grant from any funding agency in the public, commercial or not-for-profit sector.