Senior Faculty, Icahn School of Medicine
Mount Sinai Hospital
Vice Chair of Education Professor of Radiology and Nuclear Medicine
Medical University of South Carolina
Don C. Yoo
Professor of Diagnostic Imaging, Clinician Educator, Warren Alpert Medical School of Brown University
Director of Nuclear Medicine, Miriam Hospital
Associate Professor of Radiology, Chief of Division of Nuclear Medicine
George Washington University Medical Center
Departments of Medicine and Radiology
Theranostics is an exciting, emerging field where imaging and therapy are intimately tied together, as the same chemical molecule is used for imaging and therapy with a different radionuclide. Theranostics is a relatively new word, but radioiodine ablation with Iodine-131 (I-131) for imaging and treatment of thyroid cancer is one of the earliest examples of theranostics. Although radioactive iodine (RAI) has been used in clinical practice since the second world war, advances in imaging, therapeutic agents, and our understanding of the molecular basis of disease has slowly led to change. Developing a standardized approach to the management of thyroid cancer has been challenging and controversial. The American Thyroid Association (ATA) and the National Comprehensive Cancer Network (NCCN) guidelines for the management of thyroid cancer have undergone several iterations, some of which have been controversial, as conclusive data on the use of imaging and management strategies is often limited. Recently, however, discussion has led to the publication of the Martinique principles—setting the stage for increased interdisciplinary communication in an attempt to establish a set of recommendations based on the existing data and our wealth of accumulated experience.
Today, when a patient is diagnosed with thyroid cancer, they are assessed clinically and stratified as low, intermediate, or high risk. This is commonly done using the ATA or NCCN risk stratification system for recurrence, and the American Joint Committee on Cancer staging system predictions for long-term outcomes. Based on the risk stratification, a management plan is devised. Often, this includes pre-therapy imaging, therapy, and post-therapy imaging. There is a host of imaging that may be performed before and after therapy. Most commonly, ultrasound, CT, and planar imaging using RAI are performed with a gamma camera; however, SPECT and SPECT combined with CT may improve the sensitivity and specificity for the detection of disease compared with planar imaging alone. PET either with CT or MRI has a role for patients suspected of having thyroid cancer recurrence with rising thyroglobulin and negative diagnostic thyroid scans. There are several radioactive agents to choose from for imaging purposes. Although I-131 is typically less expensive and may be used for both imaging and therapy, Iodine-123 (I-123) has better imaging characteristics and is often used for diagnostic scans, especially in low- or intermediate-risk patients; however, I-123 cannot be used for therapy. Additionally, I-124 (although not routinely clinically used) and 18F-FDG may be helpful in certain situations, but they require access to PET.
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There are several controversies regarding imaging and therapy of patients with thyroid cancer. For example, there is significant debate about the need for imaging before and after therapy using radioactive iodine vs other modalities, such as ultrasound and CT. Also, whereas RAI therapy has been a mainstay in thyroid cancer treatment for years, there have been recent changes in how this therapy is done. Historically, the amount of RAI to give for the purposes of therapy was based on disease extent, so those patients with distant metastases received a higher empiric amount of RAI than those with localized disease. Furthermore, pediatric patients were treated similarly to adults. Recently, however, we have tried to lower the amount of RAI administered based on the patient’s risk stratification and age to improve long term outcome and minimize radiation exposure, where possible. There is also a recognition that pediatric patients have some different clinical issues; thus, their approach to RAI has some key differences compared to adults.
While the use of and approach to theranostics in thyroid cancer is evolving, a few constants remain. Specifi cally, the experience and expertise of the multidisciplinary care team, as well as the desires of the patient, all need to be considered when making decisions about how to proceed. Imagers must recognize which information they can glean from their scans will best assist in determining the optimal course for treatment. When deciding on therapy, the amount and type of therapy to be given is based not only on pathology, but also on the medical team and patient’s wishes for short- and long-term follow up. Ultimately, as physicians who are intimately involved with both imaging and therapy, our insight can offer a lot to the overall care of the patient with thyroid cancer.
The opinions expressed in InPractice magazine are those of the author(s); they do not necessarily reflect the viewpoint or position of the editors, reviewers, or publisher.