Optimization of the timing of the whole body diagnostic scintigraphy with 131I in patients with differentiated thyroid cancers

Summary

Introduction: Diagnostic whole-body scintigraphy with ¹³¹I (dxWBS) in patients with differentiated thyroid cancers (DTC) is an important procedure to verify radioiodine avidity of the DTC tissue before planning ¹³¹I therapy. Guidelines of the scientific societies (EANM, SNMMI, DGN) do not mention the exact time of dxWBS acquisition, 48 or 72 hours after ¹³¹I application are mostly recommended. The goal of our limited study was to assess which time interval after ¹³¹I application is the best for the detection of accumulating foci on dxWBS

Metod: We assessed 16 patients both 48 and 72 hours after application of 185 MBq of ¹³¹I during postablation dxWBS check-up. Planar scintigrams were acquired for 10 minutes at 48 hours and for 20 minutes at 72 hours post application. Images were performed  with the gamma camera using HEGP collimator. Comparison of early and late scintigrams was performed visually, by calculation of foci contrast (T-B/B) and signal to noise ratio (SNR), respectively. Wilcoxon pair test was used to compare T-B/B and SNR in both acquisition times.

Results: Focal accumulation of ¹³¹I in the neck was detected in 10 patients; it was definitely evident only on late scintigrams in 4 patients. Average value of T-B/B increased from 0,219 on early to 0,592 on late scintigrams (p = 0,005); average value of SNR increased from 0,457 to 0,841 equally (p = 0,005).

Conclusion: We believe that dxWBS performed 72 hours after injection of ¹³¹I is diagnostically more effective even if the acquisition time is significantly longer.

Keywords:

therapy – differentiated thyroid cancers – 131I – diagnostic whole-body scintigraphy