Prediction of treatment response to ¹³¹I therapy by diffuse hepatic uptake intensity on post-therapy whole-body scan in patients with distant metastases of differentiated thyroid cancer

Radioiodine whole body scan pitfalls in differentiated thyroid cancer

PURPOSE

whole body scan (WBS) performed following diagnostic or therapeutic administration of I-131 is useful in patients with differentiated thyroid carcinoma. However, it can be falsely positive in various circumstances. We aimed to report a series of pitfalls in a clinical perspective.

METHODS

A search in the database PubMed utilizing the following terms: "false radioiodine uptake" and "false positive iodine 131 scan" has been made in January 2023. Among the 346 studies screened, 230 were included in this review, with a total of 370 cases collected. Physiological uptakes were excluded. For each patient, sex, age, dose of I-131 administered, region and specific organ of uptake and cause of false uptake were evaluated.

RESULTS

370 cases of false radioiodine uptake were reported, 19.1% in the head-neck region, 34.2% in the chest, 14.8% in the abdomen, 20.8% in the pelvis, and 11.1% in the soft tissues and skeletal system. The origin of false radioiodine uptake was referred to non-tumoral diseases in 205/370 cases (55.1%), benign tumors in 108/370 cases (29.5%), malignant tumors in 25/370 cases (6.7%), and other causes in 32/370 cases (8.7%).

CONCLUSIONS

WBS is useful in the follow-up of patients with differentiated thyroid carcinoma, however it can be falsely positive in various circumstances. For this reason, it is critically important to correlate the scintigraphic result with patient's medical history, serum thyroglobulin levels, additional imaging studies and cytologic and/or histologic result.

Semi-quantitative assessment of diffuse hepatic uptake seen in I-131 scans - an indicator of functioning thyroid tissue and disease burden in differentiated thyroid cancer

BACKGROUND

To semi-quantitatively analyze liver uptake of I-131 in diagnostic and post-therapy scans by calculating hepatic to thigh ratios (HTR) and evaluate its clinical significance in management of differentiated thyroid cancer.

METHOD

Two hundred forty-nine patients were included in the study. Hepatic to thigh ratio (HTR) of counts were calculated for 249 diagnostic and 104 post-therapy scans. Patients were divided into six study groups based on their disease status:1-Serum thyroglobulin (serum Tg) negative (serum Tg ≤ 4 ng/dl) and scan negative; 2-Thyroid remnant only; 3-Thyroid remnant and lymph node metastasis; 4- Tg positive (serum Tg > 4 ng/dl) and scan negative; 5-Bone or/and lung metastasis, and 6-Only lymph node metastasis. Comparison of HTR between these groups was done using one-way ANOVA test. Correlation of HTR with serum Tg, serum thyroid stimulating hormone (TSH), anti-thyroglobulin antibody (ATg) titer and therapeutic dose of I-131 was also assessed.

RESULTS

Comparison of HTR between different study groups (1 to 6) showed significant difference in HTR (p = .001). Study group 5 (bone or/and lung metastasis) showed significantly higher mean HTR compared to other groups (p = 0.001). There was only a weak correlation between serum Tg and HTR (r = 0.395). Dose of I-131 administered also had a weak correlation with HTR (r = 0.207).

CONCLUSION

HTR has good correlation with functional status of tumor cells, while it has weak correlation to therapeutic dose of I-131 administered and serum Tg. Increased HTR predicts significant disease burden in the form of distant bone and lung metastasis and may potentially be used as a second prognostic factor apart from serum Tg.

A Quantitative Evaluation of Hepatic Uptake on I-131 Whole-Body Scintigraphy for Postablative Therapy of Thyroid Carcinoma

This study aimed to determine clinical association between quantitative hepatic uptake on postablative whole-body scan (WBS) with differentiated thyroid cancer (DTC) prognosis. We analyzed 541 scans of 216 DTC patients who were divided into 3 groups based on radioactive iodine (I-131) WBS uptake and clinical follow-up: group 1 (completion of ablation), group 2 (abnormal uptake in the cervical region), and group 3 (abnormal uptake with distant metastases). For each group, we calculated the ratio of I-131 WBS hepatic uptake (H) to cranial uptake as background (B); this ratio was defined as H/B. Furthermore, we made a distinction between group 1, as having completed radioactive iodine therapy (RIT) (CR), and group 2 and 3, as requiring subsequent RIT (RR). The average H/B scores were 1.34 (median, 1.36; range 1.00-2.1) for group 1; 1.89 (median, 1.75; range 1.41-4.20) for group 2; and 2.09 (median, 1.90; range 1.50-4.32) for group 3. Bonferroni multiple comparisons revealed significant differences in H/B among these groups. The H/B of group 1 was significantly smaller than that of other 2 groups (P < 0.0001). The precise cutoff value of H/B for therapeutic effect was ≤1.5. Moreover, 159 of 160 scans in the CR and 375 of 381 patients in the RR were correctly diagnosed using this cutoff value in the final outcome of RIT, yielding a sensitivity, specificity, positive predictive value, and negative predictive value of 99.4%, 98.4%, 99.7%, and 96.3%, respectively. Increased hepatic uptake of I-131 on WBS may predict disease-related progression.