I-131 SPECT/CT aids thyroid cancer management
The combination of functional and anatomic information from SPECT/CT increased diagnostic accuracy as well as modified therapeutic strategies in nearly three-quarters of patients with differentiated thyroid carcinoma (DTC), according to a group of researchers from Shanghai Chest Hospital in China.

DTC is the most common form of thyroid cancer and one of the success stories in the war on cancer. Since the advent of radioiodine therapy, it has been considered one of the more curable cancers. In 2009, about 37,340 new cases of thyroid cancer will be diagnosed in the United States. Of the new cases, about 28,410 will occur in women, and 8,930 in men, according to the American Cancer Society.

Currently, patients with DTC who have had their thyroid removed are treated with radioactive iodine, which effectively zeros in on and kills any remaining cancerous thyroid cells. Radioiodine, I-131, is taken up by any thyroid tissue not removed by surgery, including cancerous cells spreading to other body parts, such as lymph nodes. In addition to emitting electrons that destroy the tissue harboring the radionuclide, radioactive iodine emits photons suitable for imaging.

A 43-year-old woman (patient 6) who had undergone nearly total thyroidectomy for follicular thyroid carcinoma was referred for 131-I therapy because of lung metastases. Left, CT; middle, SPECT; right, 131-I SPECT/CT) revealed prestyloid parapharyngeal space metastasis and thyroid remnant. In this patient, final diagnosis of metastasis from follicular thyroid carcinoma was based on findings of fine-needle aspiration biopsy. Image and caption courtesy of SNM.
“Because of high sensitivity and specificity, thyroglobulin measurement combined with I-131 whole-body scintigraphy (WBS) currently remains indispensable for the management of patients with DTC,” wrote the authors of the study published in the December 2008 issue of the Journal of Nuclear Medicine.

“However, a lack of anatomic landmarks and the physiologic or other pathologic uptake of the tracer somewhat complicate interpretation of the images,” they noted.

The prospective study, conducted by the departments of radiology and nuclear medicine, was designed to evaluate the value of 131-I SPECT/CT over planar WBS in the management of DTC patients after the oral administration of a therapeutic dose of I-131. The scientists enrolled 66 consecutive DTC patients who were considered to have locally advance or metastatic disease after total or near-total thyroidectomy. Planar WBS imaging and SPECT/CT imaging were acquired on a GE Healthcare Hawkeye SPECT/CT system.

The planar images were assessed by two nuclear medicine physicians who were aware of the medical history of the patients. The I-131 SPECT/CT findings were compared with the findings of planar imaging obtained on a dedicated workstation and was interpreted by one of the nuclear medicine physicians and an experienced radiologist. The SPECT/CT findings were confirmed by pathologic follow-up, other imaging modalities, and by correlation with clinical follow-up of at least 12 months.

“In our series, the hybrid imaging device provided a significant contribution in up to 73.9 percent of patients whose I-131WBS findings were inconclusive, thus having a substantial impact on the clinical management of DTC patients referred for radioiodine therapy,” the authors wrote. “This ability is of particular importance because the therapeutic approaches to different metastatic DTC lesions are completely different.”

The researchers noted that newer generation SPECT/CT systems are available with higher slice CT capabilities than are present on the system used for their study. As such, they said that these modalities may be of even greater benefit to patients and clinicians because they can provide a contrast-enhanced high-resolution diagnostic CT scan to evaluate the extent of disease and the relationship of lesions to vascular structures for surgical candidates.

“As SPECT/CT techniques emerge, I-131 SPECT/CT may demonstrate higher value than WBS in the management of DTC,” they observed.