Observer agreement and accuracy in the evaluation of bone scans in newly diagnosed prostate cancer

OBJECTIVE: The aim of the study was to assess the agreement in the interpretation of bone scintigraphy (BS) in a newly diagnosed prostate cancer.

MATERIALS AND METHODS: A total of 635 consecutive patients had their planar whole-body BS independently reviewed by three nuclear medicine physicians and classified by two grading systems: (a) a four-category scale (1: benign; 2: equivocal; 3: most likely malignant; and 4: multiple metastases) and (b) a dichotomous scale (bone metastasis present or absent).

RESULTS: Agreement in the same category, or with one or two categories of differences, was found in 66, 34, and 1.3% of the readings, respectively. Average κ-values were 0.59, 0.72, and 0.83 for unweighted, linear, and quadratic weighted variants, respectively. Very high agreement was observed (96% of the readings) with the dichotomous scale (average κ=0.87); a comparison with a final imaging diagnosis with additional CT or MRI showed a sensitivity of 83% and a specificity of 98%. BS categories 1, 3, and 4 were consistent with the final imaging diagnosis in 96-99% of cases. The prevalence of metastasis was 10% in category 2. To optimize the diagnostic characteristics, category 2 should be regarded as a separate option.

CONCLUSION: Close agreement was found among trained observers for the evaluation of BS in prostate cancer. The high level of agreement with a dichotomous scale was hampered by diagnostic misclassification. A scale with equivocal findings on planar BS is considered important to allow for additional imaging and correct staging at the bone level of BS in a population with newly diagnosed prostate cancer.