The value of simultaneous co-registration of 99mTc- MDP and 131Iodine in metastatic differentiated thyroid carcinoma.
BACKGROUND
The lack of anatomical details in standard (131)Iodine whole body scanning ((131)I WBS) interferes with the proper localization of metastatic differentiated thyroid carcinoma (DTC) lesions. In addition, nearby or overlapping variable physiological distribution of (131)I may affect the specificity of (131)I uptake, giving indeterminate results. The aim of this study was to demonstrate the clinical usefulness of simultaneous co-registration of (99m)Tc MDP bone scanning as an anatomical landmark with (131)I scanning in the evaluation of metastatic DTC.


METHODS
Twenty-five patients (16 females and 9 males, mean age +/- SD = 52 +/- 13 years) with metastatic DTC (17 papillary, 8 follicular), were included. Whole body scanning using a 256 x 1024 matrix and an 8 cm/min scan rate were obtained 48 hours after oral administration of 185-370 MBq 131I and 2 hours after IV administration of 185-370 MBq (99m)Tc MDP using a dual head gamma camera equipped with high energy parallel hole collimators. Occasionally, additional simultaneous co-registration of localised detailed images was also performed using a 256 x 256 matrix size. The two planar images were fused with optional fusion of SPECT images. The data from standard (131)I scanning and fused (131)I/ (99m)Tc-MDP scanning were separately assessed by two nuclear medicine physicians. Fusion images were considered to improve image interpretation in comparison with standard (131)I scanning when they provided better localization of lesions.


RESULTS
All lesions in the present study were validated by radiological images and clinical follow up for at least 12 months. Forty-eight metastatic lesions were confirmed as follows: 2 in the skull, 10 in the neck, 20 in the thorax, 12 in the pelvic-abdominal region and 4 in the extremities. Standard (131)I WBS showed 54 extra-thyroidal foci with 8 false positive lesions of which 2 were located in the scalp and 6 in the pelvic-abdominal region extra-skeleton (i.e. sensitivity 100%, specificity 86%). Out of the 48 validated lesions, 16 were indeterminately localized: 10 in the thorax (3 mediastinal nodal lesions, 5 vertebral lesions and 2 ribs) and 6 in the pelvic-abdominal region (2 upper sacral, 2 sacroiliac region and 2 ischial bone). Fusion images confirmed the precise localization of the pathological uptake in the validated 48 lesions (sensitivity 100%, specificity 100%). There were 2 (4%) indeterminate lesions in fused planar imaging that were clearly localized via fused SPECT images.


CONCLUSIONS
Fusion images using simultaneous co-registration of (131)I and (99m)Tc MDP scanning is a simple and feasible technique that improves the anatomically limited interpretation of scintigraphy using (131)I alone in patients with metastatic differentiated thyroid carcinoma. The diagnostic advantage of this technique seems to be more apparent in the thoracic and pelvic- abdominal regions in contrast to the neck and extremities.
Kotb
Magdy H
MH
Department of Nuclear Medicine, National Cancer Institute, Cairo University, Egypt.
Omar
Walid
W
El-Maghraby
Tariq
T
El-Bedwihy
Marwa
M
El-Tawdy
Magdy
M
Mustafa
Hosna
H
Al-Nahhas
Adil
A
D002277:Carcinoma / Q000000981:diagnostic imaging* / Q000556:secondary*; D005260:Female; D006801:Humans; D007089:Image Enhancement / Q000379:methods*; D007457:Iodine Radioisotopes; D008297:Male; D008875:Middle Aged; D011877:Radionuclide Imaging; D019275:Radiopharmaceuticals; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013382:Subtraction Technique; D013669:Technetium Tc 99m Medronate; D013964:Thyroid Neoplasms / Q000000981:diagnostic imaging*; D051598:Whole Body Imaging / Q000379:methods*
D007457:Iodine Radioisotopes; D019275:Radiopharmaceuticals; D013669:Technetium Tc 99m Medronate