18F-FDG PET/CT and 99mTc-MDP Imaging of Non–Small Cell Lung Carcinoma Osseous Metastases

Maria Komissarova; Ka Kit Wong; Lorraine M. Fig

doi:10.2967/jnmt.111.101956

A 74-y-old male smoker presented with hemoptysis and was diagnosed with non–small cell lung cancer causing postobstructive pneumonia. He complained of lower back pain. A PET/CT scan was ordered to stage his disease. Sixty minutes after intravenous administration of 595.7 MBq (16.1 mCi) of ¹⁸F-FDG, sequential unenhanced CT and then PET images were acquired:

QUESTION 1

Based on the ¹⁸F-FDG PET/CT images, which of the following statements best describes the findings in the skeleton:

A. Multiple traumatic fractures.
B. Multiple metabolically active osseous metastases.
C. Lesions that cannot be characterized and are most likely degenerative disease.
D. Bone marrow stimulation.

One week later, a bone scan was performed to evaluate if ⁸⁹Sr could be used to manage the patient’s intractable lower back pain. A whole-body bone scan was obtained 2 h after intravenous injection of 925 MBq (25 mCi) of ^99mTc-methyldiphosphonate (^99mTc-MDP):

QUESTION 2

Based on the anterior and posterior whole-body bone scan images, and considering the prior PET/CT scans, which of the following statements is true (Note: there is a history of trauma to the right ankle):

A. The bone scan appearance is expected because ¹⁸F-FDG PET is more sensitive than bone scanning for detection of osteoblastic metastases.
B. The discrepancy between the bone scan and ¹⁸F-FDG findings is most consistent with a benign process.
C. ¹⁸F-FDG PET allows earlier detection of metabolically active metastases in marrow that may not yet have generated an osseous response.
D. Bone scintigraphy is generally an insensitive modality for staging lung cancer skeletal metastases.

CASE DISCUSSION

In this patient with non–small cell lung cancer, ¹⁸F-FDG PET and ^99mTc-MDP bone scintigraphy were strikingly discrepant for visualization of skeletal metastases. Although the literature shows varying results, the consensus is that ¹⁸F-FDG PET and ^99mTc-MDP bone scintigraphy have equivalent sensitivity (∼90%), with ¹⁸F-FDG PET having the higher specificity (98% vs. 61% in 1 study).

The 2 agents show different sensitivities in osteoblastic versus osteolytic skeletal metastases, based on the mechanisms of tracer localization. ¹⁸F-FDG uptake represents increased glucose metabolism in malignant cells, whereas diphosphonate uptake reflects the remodeling response surrounding the metastatic deposits, which may take longer to develop. ¹⁸F-FDG PET thus potentially has an advantage for detection of early bone disease. Several authors have shown that ¹⁸F-FDG PET is more sensitive in detecting osteolytic metastases than bone scintigraphy, whereas bone scintigraphy is more sensitive in detecting osteoblastic metastases. This suggests a complementary role for ¹⁸F-FDG PET and bone scintigraphy depending on the predominate type of bone metastases expected.