(1) Background: The study aimed to investigate the association between radioactive iodine (RAI) treatment and long-term gastrointestinal disorders including ulcers, atrophic gastritis, and secondary malignant neoplasm of the stomach in patients with thyroid cancer. (2) Methods: The data of the study were extracted from the National Health Insurance Database (NHIRD) of Taiwan between 2000 to 2015. Patients of ages older than 20 with thyroid cancer after thyroidectomy were included and divided into groups with RAI (study cohort) and without RAI (comparison cohort). Multivariate Cox proportional hazards regression analysis and the Kaplan–Meier method were used for statistical analysis. (3) Results: A total of 7250 (with RAI: 5800, without RAI: 1450) patients were included. The Kaplan-Meier analysis revealed a significantly higher cumulative risk for overall gastrointestinal disorders in the group with RAI (log-rank p = 0.034). The risk for gastrointestinal disorders was higher when receiving a cumulative RAI dose higher than 1.11 GBq in the Cox regression analysis. In the subgroup analysis, the risks of gastric and duodenal ulcers are significantly higher in the group with RAI treatment. (4) Conclusions: This study revealed that RAI was associated with an increased risk for long-term gastrointestinal disorders, specifically gastric and duodenal ulcers, in thyroid cancer, especially when the cumulative dose exceeds 1.11 GBq.

Chemotherapy-induced cognitive impairment (CICI) is a frequently reported complication in lung cancer patients, yet the underlying cerebral metabolic changes remain poorly characterized. This study aimed to evaluate chemotherapy-related alterations in brain glucose metabolism in patients with non-small cell lung cancer (NSCLC) using a longitudinal, within-subject voxel-based ¹⁸F-FDG PET approach. Forty NSCLC patients who underwent both pre- and post-chemotherapy FDG PET imaging were retrospectively enrolled. Voxel-wise comparisons were performed using SPM12 to identify regional metabolic changes. Patients were stratified based on chemotherapy intensity (standard: ≥4 cycles; short-course: 1-3 cycles) and recovery interval (short: <6 months; long: ≥6 months), with subgroup and interaction analyses conducted accordingly. Compared with baseline, post-treatment scans revealed regional metabolic reductions, predominantly in the right thalamus, left frontal lobe, and bilateral temporal regions. Patients receiving standard chemotherapy exhibited more extensive metabolic reductions than those receiving short-course treatment, particularly in the bilateral temporal and cingulate regions. Furthermore, patients scanned within six months post-chemotherapy showed more pronounced reductions than those with longer recovery intervals, suggesting a potential trend of metabolic recovery over time. In contrast, patients with limited initial metabolic changes (i.e., short-course group) exhibited minimal changes across intervals. This within-subject FDG PET study provides longitudinal evidence that chemotherapy independently contributes to brain metabolic alterations in NSCLC patients, predominantly involving the frontal, temporal, and limbic regions. These findings highlight vulnerable neural substrates and underscore the clinical value of functional neuroimaging in cancer survivorship research.