Abstract
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Introduction: Radioactive Iodine treatment (RAI) is the cornerstone of differentiated thyroid cancer (DTC) treatment. The single-photon emission computed tomography with integrated computed tomography (SPECT/CT) scan following RAI theoretically allows for precise lesions’ localization and characterization, and thus, better initial staging of the disease. Our aim was to evaluate the necessity of associated neck planar imaging (at least 10 minutes acquisition) when cervical SPECT/CT is performed during the first treatment course (15 minutes acquisition).
Methods: We retrospectively reviewed all consecutive patients treated by RAI in our institution from January 2020 to November 2021. Inclusion criteria were a histologically confirmed well-differentiated thyroid carcinoma and the absence of known metastatic lesions before Iodine therapy. For each patient, we collected the number and most probable location of abnormal foci of radioiodine uptake first on planar whole body + centered cervico-thoracic static planar images, and then on cervico-thoracic SPECT-CT acquisition. We then compared the total number of lesions between the two imaging techniques: SPECT/CT was deemed better if more lesions were identified, and vice versa. In case one modality showed a greater number of iodine avid foci, we reviewed images for qualitative analysis of discordance.
Results: 179 patients out of 203 screened were included (47 men/132women). 56 patients received 1100 MBq, the remaining 123 patients received 3700 MBq. SPECT/CT and planar imaging were equivalent 75% of the time (135/179 - IC95 [68-81]). SPECT/CT showed an increase number of lesions in 20% of the cases (36/179 - IC95 [15-27]), while planar imaging showed more lesions in 4% of the cases (8/179 - IC95 [2-9]). For the later ones, qualitative analysis of corresponding SPECT/CT imaging showed that most of the uptake foci were false positives. Well-known salivary uptake in the esophagus was the most frequent false positive uptake (5/8).
Conclusions: Planar static centered cervico-thoracic imaging is at best redundant, at worst less sensitive and specific than SPECT/CT imaging for abnormal foci uptake identification and characterization after a first RAI treatment. Removing static planar imaging, when SPETC/CT is performed, can reduce up to a 25% of the time examination time without any loss of diagnostic performance, allowing better optimization of gamma-camera exams schedule.
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