98 Thyroid Cancer 1

Clinical Presentation

A 34-year-old woman presents with a lump in her neck (Figs. 98.1).

Fig. 98.1

Fig. 98.2

Technique

• ^99mTc-pertechnetate, 10 mCi (370 MBq) intravenously. Planar imaging of the neck with a pinhole collimator 20 minutes later (Fig. 98.1B).

• ¹³¹I, 2 mCi (74 MBq) orally. Planar imaging with a high-energy collimator 2 days later (Fig. 98.2A, C).

• ¹³¹I, 100 mCi (3700 MBq) orally (therapy dose). Planar imaging with a high-energy collimator 7 days later (Fig. 98.2B).

Image Interpretation

Coronal image from thyroid ultrasound (Fig. 98.1A) reveals a 3.5-cm mildly heterogeneous nodule (arrowheads) in the right lobe. ^99mTC scan (Fig. 98.1B) demonstrates very little uptake in the nodule (“cold” nodule). The incidence of malignancy in cold nodules is 15 to 20%, so a fine-needle aspiration biopsy is performed, diagnosing papillary thyroid cancer. The patient undergoes thyroidectomy and is referred to nuclear medicine for therapy with ¹³¹I. A pre-therapy scan is performed (Fig. 98.2A) 2 days following the oral administration of ¹³¹I, 2 mCi. As expected, there is intense uptake in the thyroid remnant, resulting in some star artifact as a result of collimator penetration. There is physiologic uptake in the liver, bowel, and bladder, with no evidence of iodine-avid metastases. A rectangular area of activity to the right of the head is within a standard of known activity placed next to the patient for calculation purposes.

Therapy

A 100 mCi oral dose of ¹³¹I was administered for therapy purposes without incident. The patient returned 1 week later for a post-therapy scan with the on-board therapy dose of ¹³¹I (Fig. 98.2B). This confirmed the absence of metastases. A follow-up diagnostic scan (2 mCi) 6 months later (Fig. 98.2C) demonstrates successful ablation of the thyroid remnants and no metastases; there is physiologic up-take in the colon, bladder, and (mild uptake) in salivary glands.

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