Salivary gland side effects (SSEs) can be a source of significant morbidity in thyroid cancer patients receiving radioactive iodine (RAI) for remnant ablation or therapy. However, the incidence, time course, and ultimate resolution of SSEs that develop in the first few months after a single administered activity of RAI for remnant ablation has not be adequately defined. Methods: We retrospectively reviewed the clinical records of patients after RAI remnant ablation (RRA) to determine the incidence of salivary gland–related side effects reported within the first year of RRA, the dose-response relationship between administered activity and specific SSEs, and the incidence of specific SSEs based on the method of preparation for remnant ablation (recombinant human thyroid-stimulating hormone [rhTSH] vs. traditional thyroid hormone withdrawal [THW]). Results: SSEs were reported within the first year of RAI ablation in 39% of a cohort of 262 patients (66% women, 93% papillary thyroid cancer; median dose, 5,217 MBq [141 mCi]). Persistent side effects were noted after a median of 7 y in 5% or less of the entire cohort. However, when side effects developed in patients during the first year, the incidence of persistence of the symptom at last follow-up ranged from 5% to 13%. A statistically significant dose response was seen between administered activity of RAI and development of salivary gland swelling (P = 0.001, logistic dose-response curve) but not with dry mouth (P = 0.63), altered taste (P = 0.27), or salivary gland pain (P = 0.152). SSEs developed in 14% of patients receiving administered activities of 1,110 MBq (30 mCi); administered activities of 2,775 MBq (75 mCi) or more were associated with symptoms in 40% of patients (P = 0.046). Despite receiving a statistically higher administered activity (5,661 ± 2,997 MBq [153 ± 81 mCi] for THW vs. 4,958 ± 2,294 MBq [134 ± 62 mCi] for rhTSH), THW was associated with a lower rate of salivary gland swelling than the rhTSH preparation (20% vs. 10%; P = 0.017), without differences in the development of dry mouth, altered taste, or salivary gland pain. Conclusion: Although SSEs occurred in 39% of patients after routine RRA, they were usually transient, so that the overall incidence of persistent side effects at a median follow-up of 7 y was only 5%. Even though the risk for persistent side effects is rather small, these data do emphasize the need to select patients carefully for RRA who are thought to be at moderate to high risk for recurrence and to use the minimally effective dose of RAI activity, in an attempt to maximize the potential benefit while minimizing the risk for adverse events for an individual patient.

The objective of this study was to determine whether posttherapy ¹³¹I SPECT/CT changed the need for additional cross-sectional imaging or modified the American Thyroid Association risk of recurrence classification. We performed planar imaging and SPECT/CT in a consecutive series of patients after ¹³¹I therapy. Methods: Planar imaging and SPECT/CT were performed on 148 consecutive patients with thyroid carcinoma (125 papillary, 2 follicular, 8 Hürthle cell, and 13 poorly differentiated) approximately 5 d after the therapeutic administration of 1,739–8,066 MBq (47–218 mCi) of ¹³¹I. The indication for treatment was postsurgical ablation (n = 109) or recurrent or metastatic disease with rising thyroglobulin levels (n = 39). SPECT/CT scans were obtained for all subjects for 1 bed position (38 cm), which included the neck and upper chest. Additional SPECT/CT scans of the abdomen or pelvis were acquired if suggestive findings were noted on planar images. All patients were treated in real time, according to the standard of care in our practice. At that time, clinical decisions regarding thyroid tumor classification were made by our multidisciplinary group based on all data, including operative findings, pathology, imaging, and thyroglobulin levels. In a retrospective analysis, planar and SPECT/CT images were interpreted independently, and sites of uptake were categorized as likely benign, malignant, or equivocal. An experienced thyroid endocrinologist used a combination of surgical histopathology and scan findings to determine whether additional cross-sectional imaging was required and determined if the imaging findings changed the patient's risk category. Results: In 29 patients, 61 additional cross-sectional imaging studies were avoided using SPECT/CT, compared with medical decision making based on the planar images alone. In 7 of 109 postsurgical patients, SPECT/CT findings changed the initial American Thyroid Association risk of recurrence classification. The sensitivity of planar imaging and SPECT/CT for identification of focal ¹³¹I uptake in the thyroid bed was similar in the postsurgical and recurrence cohorts. For metastatic disease in the neck, characterization of ¹³¹I uptake by SPECT/CT in the postsurgical group was significantly better than that by planar scanning (P < 0.01). Among the 109 postsurgical patients, the characterization of iodine uptake in the lung, liver, and bone was also more accurate using SPECT/CT than planar scanning (P < 0.01). The CT portion of SPECT/CT demonstrated non–iodine-avid lesions in 32 of 148 patients. Conclusion: SPECT/CT data provided information that reduced the need for additional cross-sectional imaging in 29 patients (20%) and significantly altered the initial risk of recurrence estimates in 7 of 109 patients (6.4%), thereby altering patient management recommendations with regard to frequency and intensity of follow-up studies.

The incidence of thyroid cancer has been increasing. After total thyroidectomy of well-differentiated thyroid tumors with intermediate- or high-risk features on pathology, radioiodine remains one of the mainstays of therapy for both thyroid remnant ablation as well as for treatment of metastatic disease. SPECT/CT, a relatively new modality, has been shown to play a pivotal role predominantly in the post-therapy setting by changing the risk stratification of patients with thyroid cancer. In the case of radioiodine treatment failure, FDG-PET/CT may provide prognostic information based on extent and intensity of metabolically active metastatic sites as well as serve as an important imaging test for response assessment in patients treated with chemotherapy, targeted therapies, or radiotherapy, thereby affecting patient management in multiple ways. The role of newer redifferentiation drugs has been evaluated with the use of I-124 PET/CT.