Some patients want their doctors to use PET-CT, “the most advanced tumor screening tool available today,” so let’s talk about whether and when they need PET-CT.
What is PET-CT?
What is PET-CT?
PET-CT is actually a combination of PET (positron emission computed tomography) and a regular CT scan.
PET involves injecting a contrast agent into the body that is similar to glucose, labeled with a radioactive substance, and will appear when organs and lesions with high metabolism (including malignancies) take up more glucose.
CT, on the other hand, “cuts” the body from top to bottom into layers of cross-sections that are clearly visible to the doctor, each layer only a few millimeters long.
Fusing the two allows you to see the location, size, shape, and relationship of the lesion to the surrounding tissue, as well as the nature of the lesion through glucose uptake.
PET-CT is not a routine test for thyroid cancer
PET-CT does not specifically target tumors, but only shows organs and lesions that are more metabolically active. Therefore, not all malignant nodules may be “positive,” while some benign nodules may be “positive.
PET-CT alone does not accurately determine the benignity of thyroid nodules. In fact, ultrasound and fine-needle biopsy are currently the most reliable tools for identifying benign and malignant nodules.
In patients with a definite diagnosis of thyroid cancer requiring surgery, PET-CT is also inferior to B ultrasound, CT, and magnetic resonance imaging (MRI) for preoperative evaluation of lesions and metastases in the neck lymph nodes. Given its high price and radiation damage, it is not currently a routine test for thyroid cancer.
What conditions require PET-CT?
But there are specific situations in which PET-CT is useful, including the following categories:
- After applying other tests (ultrasound, CT, fine-needle aspiration, etc.), the doctor may try to make a secondary diagnosis with PET-CT if the diagnosis is still not clear.
- After a diagnosis of thyroid cancer has been made and the surgeon determines that the malignancy is high, preoperative PET-CT may be used to identify systemic metastases such as mediastinal lymph nodes, lung, bone, etc. This can have an important impact on the surgeon’s treatment plan.
- Sometimes a nodule in the thyroid does not originate in the thyroid, but is metastatic from a malignancy elsewhere, and PET-CT can help identify the primary lesion.
- Evaluation and monitoring after treatment of thyroid cancer to identify recurrent or residual lesions. For example, patients with medullary thyroid cancer presenting with elevated blood calcitonin after surgery (suggestive of recurrence) may be considered for evaluation of recurrence and metastases with PET-CT; and then for localizing systemic metastases in iodine-refractory differentiated thyroid cancer.
PET-CT is not currently recommended for routine follow-up of thyroid cancer.
In summary, patients with thyroid nodules generally do not need PET-CT, even if thyroid cancer has been diagnosed, in most cases. Your physician will determine whether PET-CT is needed on a case-by-case basis after evaluating your condition.
Co-written by Dr. Yiming Cao, Cancer Hospital, Fudan University