Clinical value of planar and tomographic dual-isotope scintigraphy using 99mTc-methylene diphosphonate and 131I in patients with thyroid cancer.

Purpose: (131)I whole-body scintigraphy is a highly sensitive method for the detection of differentiated thyroid tumours and metastases. However, a lack of anatomical landmarks and the physiological excretion of the tracer complicates the evaluation of the images. Therefore, we determined whether additional bone scintigraphy in combination with (131)I scintigraphy, simultaneously acquired via planar and tomographic techniques, positively contributes to the treatment plan in patients with non-conclusive (131)I images.

Methods: Twenty-one patients with differentiated thyroid cancer and known metastases or unclear findings in the (131)I whole-body scan underwent dual-isotope scintigraphy (DIS) within 2-7 days after application of 5000-8000 MBq (131)I. Dual-energy planar and tomographic data were acquired simultaneously and the results compared with other imaging modalities.

Results: In 48% of the cases (10 of 21), DIS supplied important additional information that either altered the treatment plan or staging of the patients. In 28% (six of 21), DIS provided new information that was not known before, but did not change the staging of the patients. In five cases (24%), DIS did not add any new data regarding the extent of the disease.

Conclusions: The simultaneous acquisition of (131)I and (99m)Tc-methylene diphosphonate provides clear landmarks and facilitates the localization of functioning metastases from differentiated thyroid cancer as well as improves the fusion with morphological images. It can be performed easily and also transferred to other isotope combinations.