| Abstract |
Purpose: Planar scintigraphic imaging (PS) with radioactive Ι131 remains the gold standard in monitoring patients after initial surgery. After total thyroidectomy, diagnostic and post therapeutic Ι131 scan is performed to detect residual thyroid tissue, lymph node and distant metastases. Interpretation of radioiodine uptake on planar imaging remains difficult, as it shows findings that can be misinterpreted leading to false positive results. Furthermore, radioiodine uptake in normal structures and tissues makes it even more difficult to distinguish normal uptake from metastatic disease. Hybrid scintigraphic imaging systems (SPECT/CT) with integrated low-dose CT, provide additionally to functional also anatomical information with higher diagnostic value compared to planar imaging. It improves the accuracy of disease staging and subsequent patient diagnostic and therapeutic management.
This postgraduate thesis aims to highlight the additional diagnostic value of post-treatment SPECT/CT WBS in terms of assessing recurrence in patients with well differentiated thyroid cancer. We first evaluate the use of SPECT/CT WBS in the detection of residual thyroid tissue, lymph node and distant metastases. Specifically, we studied the incremental diagnostic value (positive predictive value) of SPECT/CT WBS in the recurrence of patients with well differentiated thyroid cancer. It is shown that SPECT/CT WBS is superior to PS in terms of improved interpretation of radiopharmaceutical uptake lesions as well as in distinguishing malignant lesions from normal findings. Finally, the overall impact of SPECT/CT WBS on the diagnosis and follow-up of patients with DTC is evaluated.
Material and Methods: This study is a retrospective data search study of patients with well differentiated thyroid cancer who underwent SPECT/CT WBS with radioactive iodine Ι131 at the Nuclear Medicine department of the University General Hospital of Heraklion. The examinations studied were those of post-treatment hybrid SPECT/CT imaging with 131I. The sample consisted of 205 patients who underwent PS imaging followed by SPECT/CT in the areas where findings were detected. The findings of the two methods were recorded and followed by statistical analysis to compare the findings of the two methods.
Results: The study showed that for all patients undergoing, SPECT/CT WBS detected all foci (N=261, 100%) of iodine uptake which were detected during the PS, while it revealed 82 and identified 82 (23.9%) more foci of radioiodine uptake. SPECT/CT WBS shows higher diagnostic value in terms of interpretation of findings, as they classified 94 suspicious findings on PS, that through better anatomical localization were attributed to normal iodine uptake and identified as foci of normal or benign uptake on SPECT/CT WBS, thus avoiding additional procedures to clarify doubtful images and led to a change in the risk stratification. The incremental diagnostic value of metastases is also undisputed, as 29 suspected distant foci detected by planar were identified and classified. Overall, SPECT/CT WBS classified 1 equivocal PS, confirmed 3 negative scintigraphic studies, detected and confirmed PS findings by improving anatomic localization of sites of radioiodine uptake observed on planar WBS in 98 patients, reclassified abnormal findings on planar imaging by attributing them to normal uptake in 44 patients, while in 11 patients with positive planar scintigraphy, SPECT/CT was negative. Finally, in 27 scans the hybrid method detected more foci of abnormal uptake, while in 21 patients it detected more foci of abnormal and benign uptake.
Conclusions: SPECT/CT WBS improved the diagnostic performance as it highlighted more pathological foci, while at the same time reducing false-positive results. In post-ablation scans, SPECT–CT WBS has demonstrated incremental value over PS WBS, as it correctly characterized all of equivocal sites of radioiodine uptake observed on planar WBS as normal or metastatic. Μoreover, SPECT/CT detected unexpected sites of either neck lymph node or distant metastases. Finally, SPECT/CT WBS clarified the presence of residual thyroid tissue, thyroglossal duct remnants and the existence of a thymus gland. In conclusion, for patients with DTC, PS in combination with SPECT/CT is a powerful diagnostic tool for detection and classification of regional and distant metastases as it provides more accurate identification, anatomical localization and interpretation of radioiodine uptake foci.
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