Day: July 25, 2011

What Are the Indications for PET and PET/CT?

Patient Presentation
A pediatrician overheard one of her residents trying to arrange sedation for a toddler with cancer for a positron emission tomography test (PET). To her it seemed like PET had come up several times during clinical care recently. She commented that she didn’t know the indications for PET since it wasn’t something she would order. A search of the literature found several articles mainly for oncological indications. She reviewed the articles and learned more about the pros, cons and limitations of PET.

Discussion
Positron emission tomography test (PET) and PET/CT that combines PET with computed tomography (CT) was first begun in the 1950s. In 2000 it was the TIME magazine invention of the year. PET gives functional, metabolic data about the human body. When combined with CT’s anatomical, structural data, PET/CT can give both data types concurrently.

PET uses radioactive tracers linked to metabolites. One of the most common tracers is 18F-fluorodeoxyglucose (FDG), a glucose metabolite. Since FDG contains glucose, there will be background tracer uptake particularly in the skeletal muscle, brain, thymus, brown fat, heart, and gastrointestinal track. The tracer is excreted by the kidneys but not reabsorbed, so increased background may be seen in the urinary system. Increasing filtration along with bladder emptying helps to minimize this problem.

The primary indications for PET and PET/CT in pediatrics are for malignancies (see below), but PET and PET/CT are not specific for cancer. PET resolution for malignant lesions is about 10 mm, and PET/CT is about 5 mm. Smaller, slow-growing and well-differentiated tumors have less tracer uptake which can cause a false-negative reading. Other physical problems such as increased test background, increased normal muscle activity, inflammation and infection, may lead to false-positive PET readings too.

Learning Point
PET and PET/CT in adults is mainly used in malignanicies, especially lymphoma, but other indications such as pulmonary infections, rheumatological disorders, and neurosurgical planning for epilepsy treatment have been explored.

Indications and use for PET and PET/CT for pediatric malignancies includes:

  • Bone tumors – staging, prognosis, and treatment response
  • Brain tumors – prognosis, recurrent disease detection, and planning surgical interventions
  • Endocrine tumors – staging
  • Hepatoblastoma – prognosis, recurrent disease detection
  • Lymphomas – staging, restaging, treatment response and recurrent disease detection
  • Sarcomas of the soft-tissue – staging, treatment response, recurrent disease detection
  • Neuroblastoma – staging

One review in 2009 summarized its findings by saying “In paediatric oncology patients, clinical applications of PET/CT including staging, monitoring therapy and therapy planning in lymphomas, soft-tissue and osseous sarcomas, and neuroblastoma. In other entities, PET/CT may be of diagnostic value but the literature is limited.”
Another review in 2010 said, “PET and PET/CT appear to be excellent noninvasive imaging modalities for the management of most of the pediatric cancers except leukemia.” They go on to state that due to their high radiation exposure, PET/CT should be limited to certain applications mainly in lymphoma and certain sarcomas.

Questions for Further Discussion
1. Is PET and PET/CT available in your country??
2. What other nuclear medicine tests are used for malignancy management and what are their indications?

Related Cases

To Learn More
To view pediatric review articles on this topic from the past year check PubMed.

Evidence-based medicine information on this topic can be found at SearchingPediatrics.com, the National Guideline Clearinghouse and the Cochrane Database of Systematic Reviews.

Information prescriptions for patients can be found at MedlinePlus for these topics: Nuclear Scans and Cancer in Children.

To view current news articles on this topic check Google News.

To view images related to this topic check Google Images.

Brody AS, Frush DP, Huda W, Brent RL. Radiation Risk to Children From Computed Tomography. Pediatrics 2007;120;677.
Kumar R, Shandal V, Shamim SA, Halanaik D, Malhotra A. Clinical applications of PET and PET/CT in pediatric malignancies. Expert Rev Anticancer Ther. 2010 May;10(5):755-68.

Franzius C, Juergens KU. PET/CT in paediatric oncology: indications and pitfalls. Pediatr Radiol. 2009 Jun;39 Suppl 3:446-9.

Andersen JB, Mortensen J, Bech BH, Hojgaard L, Borgwardt L. First experiences from Copenhagen with paediatric single photon emission computed tomography/computed tomography. Nucl Med Commun. 2011 May;32(5):356-62.

Wikipedia. Positron emission tomography. http://pediatrics.aappublications.org/cgi/reprint/120/3/677.pdf. (rev. 5/12/2011, cited 5/16/2011)

ACGME Competencies Highlighted by Case

  • Medical Knowledge
    10. An investigatory and analytic thinking approach to the clinical situation is demonstrated.

  • Practice Based Learning and Improvement
    12. Evidence from scientific studies related to the patients’ health problems is located, appraised and assimilated.
    13. Information about other populations of patients, especially the larger population from which this patient is drawn, is obtained and used.
    14. Knowledge of study designs and statistical methods to appraisal clinical studies and other information on diagnostic and therapeutic effectiveness is applied.
    15. Information technology to manage information, access on-line medical information and support the healthcare professional’s own education is used.

    Author

    Donna M. D’Alessandro, MD
    Professor of Pediatrics, University of Iowa Children’s Hospital