Article

New Types of PET/CT Scans May Be Helpful in Evaluating Bone Metastases in Prostate Cancer Patients

Nuclear medicine physicians showed high accuracy and consistency when reading sodium fluoride (NaF) PET/CT scans of patients with prostate cancer metastases in a new study published in the Journal of Nuclear Medicine.1

Prostate cancer is one of the most common cancers and causes of cancer death in men in the United States, according to the Centers for Disease Control and Prevention.2 Despite a positive initial response to chemotherapy and/or surgery, many patients become resistant, and have recurrence or progression of cancer, and a subgroup of patients will develop bone metastases.3 Current guidelines from both the National Comprehensive Cancer Network and the European Association of Urology recommend the use of bone scintigraphy to assess bone metastases in prostate cancer.1 As PET/CT imaging has become more accessible, many imaging centers are shifting from bone scintigraphy to PET/CT, namely, 18F-sodium fluoride (NaF) PET/CT, for the assessment of bone metastases.1

Bone scintigraphy versus NaF PET/CT

NaF PET/CT offers several advantages to bone scintigraphy. Compared to methylene diphosphonate, commonly used for bone scintigraphy, it has more favorable pharmacokinetic properties and a better target-background ratio. Previous studies have suggested that NaF PET/CT offers improved diagnostic accuracy as well. But imaging’s weak point is always evaluation, which introduces subjectivity. Thus, some debate remains over the efficacy of NaF PET/CT for diagnosing metastases from prostate cancer.1

NaF PET/CT study shows near-perfect interobserver agreement

A new study published in the Journal of Nuclear Medicine evaluated interobserver agreement when using NaF PET/CT in the detection of bone metastases. Danish researchers used two very experienced observers, board-certified nuclear medicine physicians, who blindly evaluated the images and sorted them according to presence or absence of bone metastases. They found “almost perfect agreement in their assessment” with over 90 percent agreement on the number of lesions and their location. Images comprised a range of stages of prostate cancer and the sample size was 219 patients. The pair achieved near-identical results in regard to sensitivity, specificity, positive predictive value, and negative predictive value, with only a handful of relatively minor disagreements.1

These findings are similar to those found in interobserver agreement studies of planar whole-body bone scintigraphy as well as in studies of other radioactive tracers used in PET/CT, such as the tracer 68Ga-prostate specific membrane antigen (PSMA). The diagnostic accuracy for NaF PET/CT in this study was comparable to similar studies that looked at PSMA PET/CT as well.1

New tool for the assessment of bone metastases

The near-perfect agreement between observers in this study, the NaF PET/CT agreement on a lesion level, and its good diagnostic accuracy led the authors to conclude that this imaging modality is a “robust tool for the assessment of bone metastases” in prostate cancer. There is still a lack of studies focused on patient-related outcomes when NaF PET/CT is used compared to bone scintigraphy, and future studies to assess this would perhaps bolster its use.1

A meta-analysis published in the Annals of Nuclear Medicine in May 2019 compared NaF PET/CT to other imaging techniques including bone scintigraphy, SPECT, and DWI-MRI, for the detection of bone metastases in prostate cancer patients. The researchers analyzed fourteen studies and found that NaF PET/CT has “excellent diagnostic performance” in detecting bone metastases, rendering it superior to bone scintigraphy and SPECT and comparable to DWI-MRI.4

Sources

1. Observer Agreement and Accuracy of 18F‐Sodium‐Fluoride PET/CT in the Diagnosis of Bone Metastases in Prostate Cancer. Journal of Nuclear Medicine. http://jnm.snmjournals.org/content/early/2019/08/29/jnumed.119.232686 Last Accessed October 3, 2019.

2. Prostate Cancer Statistics. Centers for Disease Control and Prevention. https://www.cdc.gov/cancer/prostate/statistics/index.htm Last Accessed October 3, 2019.

3. Prospective Study Evaluating Na18F-Positron Emission Tomography/Computed Tomography (NaF-PET/CT) in Predicting Clinical Outcomes and Survival in Advanced Prostate Cancer. Journal of Nuclear Medicine. http://jnm.snmjournals.org/content/57/6/886 Last Accessed October 3, 2019.

4. 18F-NaF-PET/CT for the Detection of Bone Metastasis in Prostate Cancer: A Meta-Analysis of Diagnostic Accuracy Studies. Annals of Nuclear Medicine. https://www.ncbi.nlm.nih.gov/pubmed/30877561 Last Accessed October 3, 2019.