Adding SPECT/CT to whole-body scintigraphy with iodine 131 ( 131I)provided incremental diagnostic value compared with scintigraphy alone after radioiodine therapy in patients with well-differentiated thyroid cancer, according to a study published online Sept. 25 in Radiology.
Patients with differentiated thyroid cancer often have a favorable prognosis. However, prognosis hinges on multiple factors, including the presence or absence of distant metastases. Previous research has suggested that the presence or absence of 131I radioiodine uptake in distant metastasis may correlate with outcomes in patients with well-differentiated disease.
However, the current imaging protocol to evaluate uptake— 131I scintigraphy planar imaging—results in noisy, low-resolution images. SPECT/CT has been employed in an adjunctive role; however, its value has not yet been determined.
Yasuhiro Maruoka, MD, of the department of clinical radiology at Kyushu University in Fukouka, Japan, and colleagues undertook a retrospective analysis to determine the incremental diagnostic value of SPECT/CT in this patient population.
Two nuclear medicine physicians retrospectively reviewed whole-body scintigraphy and SPECT/CT images of 147 patients with well-differentiated thyroid cancer.
The researchers recorded results as positive or equivocal in terms of the thyroid bed, lymph node and distant metastasis uptake. Histopathological diagnosis, additional imaging and/or clinical follow-up for 13 to 23 months served as the reference standard.
The physicians located 120 foci in the thyroid bed in 78 patients using both modalities. After SPECT/CT they revised scintigraphic findings in seven patients.
They identified 105 foci as potential lymph node metastases on whole-body scintigraphic images, with 85 believed to be clearly positive for uptake and 20 equivocal. SPECT/CT results confirmed 84 of the positive foci and corrected scintigraphic results in 24 radioactive foci in 20 patients.
Whole-body scintigraphic images suggested 52 areas of distant metastases, with 32 classified as positive and 20 as equivocal. SPECT/CT altered the interpretation of 21 radioactive foci in 17 patients.
The researchers emphasized the utility of SPECT/CT and wrote, “A SPECT image … is a tomographic image that reduces summation artifacts and more clearly defines the spatial localization of hot spots.”
In this study, the addition of SPECT/CT changed the interpretation of radioactive foci at scintigraphy in 40 of 147 patients. Clinical staging according to tumor-node-metastasis classification and therapeutic planning were changed in nine and three patients, respectively.
The researchers concluded by recommending the routine use of SPECT/CT with 131I scintigraphy after 131I radioiodine therapy for reliable management of patients with high-risk well-differentiated thyroid cancer.