NaF18 PET/CT bone scans: Examining the value PSA=10ng/ml as a cutoff for predicting metastatic bone disease

Objectives NaF18 PET/CT bone scan is considered to be more sensitive than Tc99m-MDP bone scan in detecting osseous metastasis. Previous studies have suggested that for newly diagnosed prostate cancer patients with PSA(prostate specific antigen) value of <10ng/ml, a Tc99m-MDP bone scan is unnecessary due to low likelihood of finding bone metastasis. The goal of this study is to assess if PSA= 10ng/ml is a good cutoff value to predict metastatic bone disease in newly diagnosed prostate cancer patients imaged with NaF18 PET/CT.

Methods From the NaF18 PET/CT bone scans ordered to evaluate for prostate cancer metastasis between January 2010 and April 2011 (n=91), newly diagnosed cases before treatment were chosen (n=28). The PET/CT bone scans were independently reviewed by two Nuclear Medicine physicians with full agreement. The sample was divided into two groups: group I (bone metastasis, n=4) and group II (no bone metastasis, n=24). PSA value at the time of imaging was reviewed.

Results Group I had (mean PSA 121ng/ml, range 27.15-297.55ng/ml) and group II had (mean PSA 27.43ng/ml, range 0.05- 348.68ng/ml). In our small sample, 25% of patients from group I with PSA<10ng/ml had bone metastasis and 46% of patients from group II with PSA>10ng/ml had no bone metastasis. PSA cutoff value of 10ng/ml has a negative predictive value of 92.86% (odds ratio=3.55, 95% confidence interval 0.32 to 39.14, Z=1.03, P=0.30).

Conclusions For our study with veterans, there is no statistical significance between PSA value of less than 10ng/ml and negative bone metastasis in newly diagnosed prostate cancer cases. This is evidenced by the fact that 1 in 4 patients with PSA<10ng/ml from group I had bone metastasis. More studies involving multiple institutions and larger sample sizes are needed to further confirm the association between PSA value alone and bone metastasis

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