Comparison between radioiodine therapeutic and diagnostic whole body scans in postoperative differentiated thyroid carcinoma patients correlation with serum thyroglobulin levels

Abstract FRE

It has been reported that high image quality and high sensitivity can be achieved by the I-131 posttherapy scan.

We aim to demonstrate through our clinical experience the efficacy of I-131 therapeutic whole body scans (WBSs) compared to diagnostic scans in detecting lesions and to appraise whether the differentiated thyroid carcinoma patient has to undergo postoperative radioiodine therapy based on the diagnostic scan and/or thyroglobulin level.

Method : 263 patients (193 females, 70 males, 19-67 years old) with welldifferentiated thyroid carcinoma (208 papillary, 55 follicular) underwent postoperative diagnostic radioiodine scan.

All patients (263) were imaged 48 hours after receiving a diagnostic I-131 dose of 111-185 MBq (3-5 mCi).

Two hundred seven (207) with a postoperative thyroid ablation and I-131 uptake above 2% received an 1110-4440 MBq (30-120 mCi) therapeutic I-131 dose and were imaged 72 hours thereafter.

Images from both scans, diagnostic and therapeutic, were compared for the presence and the intensity of thyroid cancer lesions (recurrences and metastases) and correlated to the serum thyroglobulin level.

Results : Compared to negative diagnostic WBSs (25 patients) and those with high serum thyroglobulin level (110 patients), therapeutic scans revealed positive lesions in 19/25 patients (76%).

Almost all lesions (104/ 110) were detected and more clearly defined in the therapeutic scan than the diagnostic scan.

Sensitivity was calculated to be 96% for therapeutic WBS and 88% for diagnostic WBS, respectively.

Only 7/207 patients (3.4%) who received a high therapeutic dose (4440 MBq) showed a greater lesion uptake in the diagnostic scan than the therapeutic scan.

Conclusion : The findings indicate that therapeutic scans are more effective than diagnostic scans for follow-up studies in differentiated thyroid carcinoma patients undergoing postoperative radioiodine treatment.

Despite recording a negative diagnostic scan, postoperative radioiodine therapy still had to be performed for those patients with high serum thyroglobulin levels.-