The Utility of Dedicated Chest or Neck CT at Time of PET-CT for Lymphoma Patients

1. The Utility of Dedicated Chest or Neck CT at Time of PET-CT for Lymphoma Patients presented by Guy J. Amir, M.D., MPH

2. PURPOSE • Lymphoma patients at the University of Iowa are initially evaluated with PET/CT primarily for staging and to assess response to therapy. • Our center includes a 40 slice Siemens Biograph PET/CT which permits diagnostic quality chest and neck CTs to be performed. Lymphoma patients are currently evaluated with both PET/CT and chest/neck contrast CT(s), which is done on the same system immediately after the PET/CT scan. • We have observed there seems to be little added utility of the dedicated CT. This study was designed to review the utility, if any, of obtaining a dedicated chest/neck CT at the time of the PET/CT.

3. INTRODUCTION • “Ionizing radiation exposure skyrockets since 1980s” • “Over the past quarter century, exposure to ionizing radiation from medical procedures in the U.S. has grown sevenfold, according to the National Council on Radiation Protection and Measurements. CT is a major source.”

6. INTRODUCTION • MORE CONCERNS • complications from administration of IV contrast • expense to the patient • poor use of clinical manpower

7. INTRODUCTION • Recent literature suggests PET/CT has greater accuracy for nodal diagnosis than CT alone • more sensitive (58-93%) and more specific (74-98%) than CT for the detection of nodal disease, with greater accuracy reported for mediastinal lymphadenopathy.

8. INTRODUCTION • Radiologic examinations for lymphoma • Chest radiographs • Computed tomography • Magnetic resonance imaging • Ultrasonography and echocardiography • Bone scanning • Positron emission tomography

9. METHOD AND MATERIALS • We performed a retrospective chart review of 200 lymphoma patients, who had concurrent PET-CT imaging with dedicated chest and/or neck CT within the period 1/1/2004 to 6/1/2008. • Initially, comparison was made between the PET-CT report and the concurrent CT chest/neck report(s). If there was a CT finding with the impression of malignancy (i.e. "consistent" or "suspicious" for malignancy) that was not matched to an identical PET-CT reported malignancy, a discrepancy was identified and further chart investigation was undertaken to determine change in management, defined as therapy. • Further chart review was done to determine if the change in management had significant impact on patient outcome.

10. PET/CT protocol • NPO • Fasting blood glucose within 60-200 mg/dl • Oral contrast dose of 250-550 mL • F-18 FDG dose of 8-15 mCi • Scout CT image obtained followed by whole-body low dose CT (used for attenuation correction and co-registration with PET) • PET acquisition begins no sooner than 81 min after FDG injection (90 min +/- 10%) • CT of IV contrast-enhanced CT images acquired

12. RESULTS

13. RESULTS • In 45/47 discordances, the treating physician chose to act on the PET-CT information. • In 2/7 discordances, additional diagnostic management was taken, but further follow-up did not document any change in treatment or outcome for 2.5 and 3+ years!

14. CONCLUSION • Our results suggest that, in follow-up of lymphoma patients after treatment, obtaining CT of the chest and/or neck at the time of the FDG-PET exam offers no additional information which would alter therapy for the patient. • Concurrent CT examination of the chest and/or neck adds to the already high cost of the PET-CT scan, increases radiation exposure and the risk of contrast complications. Since there is no advantage of do such CT studies, they should not be done.

15. CLINICAL RELEVANCE/APPLICATION • This study has the potential to impact the ordering behavior of oncologists treating lymphoma, specifically the clinically unnecessary and expensive adjunct imaging ordered with PET-CT.

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