PET/CT has varied applications for oncologic imaging

Jun 3, 2006

SAN DIEGO - PET/CT is a soup to nuts modality in oncology, offering useful clinical information before, during, and after treatment, according to a presentation Saturday at the Society of Nuclear Medicine (SNM) meeting.

Dr. Lale Kostakoglu of New York-Presbyterian Hospital in New York City reviewed some general scenarios for when PET/CT can be deployed in three types of cancer: head and neck (including thyroid), non-small cell lung cancer (NSCLC), and breast cancer.

Kostakoglu, who also serves with the SNM's PET Center of Excellence, outlined the pros and cons of oncologic PET/CT.

Head and neck

FDG-PET in this cancer subtype offers several advantages over anatomic imaging, including detecting unknown primaries as well as post-therapeutic residual disease, Kostakoglu said. The modality's sensitivity and specificity are on par with MRI and CT.

But PET/CT can go one better than contrast-enhanced CT or MRI, supplanting those modalities, she said. Contrast-enhanced PET/CT can spot locally advanced disease and confirm distant metastases.

For cancer recurrence, PET/CT is the superior imaging choice, although Kostakoglu did suggest performing a whole-body scan to increase sensitivity.

However, PET/CT may not be the right modality for the job in some circumstances, she explained. In node-negative disease, for example, PET/CT has not proved superior and cannot be used as a basis for surgical management, most likely elective neck dissection, she said.

In addition, cost is a sticking point with PET/CT in cancer response. At this juncture, the exam is not fully reimbursed, although it has shown a 95% negative predictive value, Kostakoglu said. In locally advanced disease, its utility as a monitoring technique remains unclear and may simply not be cost-effective, she added.

In thyroid cancer, iodine-131 whole-body imaging remains the scan of choice, Kostakoglu said, although PET/CT may have a role in defining papillary, follicular, and medullary disease. However, she pointed out that PET and CT image fusion is better than side-by-side PET and CT interpretation.

NSCLC

For non-small cell lung cancer, pulmonary nodules remain a challenge, Kostakoglu said. PET/CT combined with diagnostic chest CT has shown a sensitivity of 97% and a specificity of 78%. But she warned that this is not an easy exam as it may require full inhalation on CT.

For preoperative lung cancer staging, PET has shown 15% to 30% higher sensitivity than CT alone, especially for evaluating the extent of lymph node involvement. But a CT scan will still be necessary for anatomic markers, she said.

In distant metastases, contrast-enhanced PET/CT has the potential to increase the accuracy of staging and pinpoint distant metastases. The presence or absence of the latter is important for deciding if a patient must undergo invasive mediastinoscopy or can be treated with neoadjuvant therapy, Kostakoglu explained.

For NSCLC recurrence, FDG-PET has been valuable in selecting patients who would benefit from repeat surgery. Again, PET/CT with diagnostic chest CT can offer useful information about disease recurrence, but cannot take the place of histologic diagnosis, she emphasized.

Breast cancer

In this setting, PET/CT is adept at finding small-volume axillary metastases. However, sentinel lymph node biopsy is still superior to PET/CT and most likely more cost-effective, Kostakoglu said.

For locally advanced breast cancer, PET/CT can reveal unsuspected distant metastases, especially bone metastases. In recurrence, PET/CT has turned in 93% sensitivity and can alter clinical management, she explained. The modality has shown the ability to separate treatment responders from nonresponders, which can result in a change in therapeutic regimen.

Kostakoglu pointed out that as PET/CT continues to gain ground in oncology imaging, the following issues will need to considered:

Risk to patient from exposure to imaging test
Validity of test based on disease prevalence
Cost-effectiveness
Reproducibility of test results
Access to equipment
Effect of test on survival and cure rates

Finally, she posed the question of whether PET/CT results will change patient management and, if so, does an effective intervention method exist to justify the imaging exam.

By Shalmali Pal
AuntMinnie.com staff writer
June 4, 2006

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