A comparison between diagnostic I-123 and posttherapy I-131 scans in the detection of remnant and locoregional thyroid disease.
OBJECTIVE
The aim of this study was to compare pretherapy diagnostic I-123 scans with 7-day posttherapy I-131 scans days in detecting remnant thyroid disease as well as locoregional metastases in patients who had undergone thyroidectomy for differentiated thyroid cancer.


METHODS
The I-123 and I-131 scans from 53 patients were reviewed. The number of lesions identified on each scan was compared as well as the relative intensity of each lesion on the I-123 and I-131 scans using region-of-interest-derived lesion to background ratios. For the I-123 diagnostic scans, 1.0 to 1.6 mCi of activity was administered orally 24 hours before scan acquisition. Patients received therapeutic doses of I-131 ranging from 30.7 to 362.2 mCi orally, on the same day but after acquisition of the I-123 scan. All posttherapy I-131 scans were performed 7 days after radioablative therapy with I-131.


RESULTS
Of the 53 patients, 14 had concordant scans, with an equal number of lesions detected by both scans. Thirty-nine I-123/I-131 scan pairs showed discordance, with 27 patients demonstrating more lesions on the I-123 scans. Of the 142 total lesions, 35% were detected only by I-123 pretherapy images compared with 15% detected only on posttherapy images. In a subgroup of 42 patients I-123 scans showed 56 lesions (out of a total of 116) that demonstrated either a better lesion to background ratio than I-131 or were seen exclusively by I-123.


CONCLUSIONS
The use of diagnostic I-123 pretherapy scintigraphy seems to be superior in many patients to posttherapy I-131 imaging obtained at 7 days in detecting locoregional metastases or remnant in postsurgical patients. This is likely due to the fact that 1 week is too long to wait to perform posttherapy imaging.
Department of Radiology, Division of Nuclear Medicine, University of Iowa Hospitals and Clinics, Iowa city, IA, USA. damita-thomas@uiowa.edu
Damita L
DL
Thomas
Yusuf
Y
Menda
David
D
Bushnell
D000328:Adult; D000368:Aged; D005260:Female; D006801:Humans; D007457:Iodine Radioisotopes; D008297:Male; D008875:Middle Aged; D018365:Neoplasm, Residual / Q000000981:diagnostic imaging* / Q000628:therapy; D011877:Radionuclide Imaging; D013964:Thyroid Neoplasms / Q000000981:diagnostic imaging* / Q000628:therapy*; D055815:Young Adult
D007457:Iodine Radioisotopes