Reproducibility and clinical correlations of post-treatment changes on CT of prostate cancer bone metastases treated with chemotherapy

Abstract

Objectives: The objective of this study was to determine whether, in patients with prostate cancer (PCa) bone metastases receiving chemotherapy, early post-treatment changes on CT are reproducible and associated with clinical outcomes.

Methods: Blinded to outcomes, two radiologists with 1 year and 5 years of experience independently reviewed CTs obtained before and 3 months after chemotherapy initiation in 38 patients with bone metastases from castration-resistant PCa, recording the size, matrix and attenuation of ≤5 lesions; presence of new lesions, extraosseous components, periosteal reactions and cortical thickening; and overall CT assessment (improved, no change or worse). Kappa statistics were used to assess inter-reader agreement; the Kruskal-Wallis test and Cox regression model were used to evaluate associations.

Results: Inter-reader agreement was low/fair for size change (concordance correlation coefficient=0.013), overall assessment and extraosseous involvement (κ=0.3), moderate for periosteal reaction and cortical thickening (κ=0.4-0.5), and substantial for CT attenuation (κ=0.7). Most metastases were blastic (Reader 1, 58%; Reader 2, 67%) or mixed lytic-blastic (Reader 1, 42%; Reader 2, 34%). No individual CT features correlated with survival. Readers 1 and 2 called the disease improved in 26% and 5% of patients, unchanged in 11% and 21%, and worse in 63% and 74%, respectively, with 64% interreader agreement. Overall CT assessment did not correlate with percentage change in prostate-specific antigen level. For the more experienced reader (Reader 2), patients with improved or unchanged disease had significantly longer median survival (p=0.036).

Conclusions: In PCa bone metastases, interreader agreement is low in overall CT post-treatment assessment and varies widely for individual CT features. Improved or stable disease identified by an experienced reader is statistically associated with longer survival.

Figure 1

Examples of predominant types of bone metastases on baseline CT scans. (a) Blastic metastases in a 67-year-old male. Axial CT image of the pelvis shows multiple blastic metastases in L5 (arrow) and iliac bones (arrowheads). (b) Mixed lytic and blastic metastases in an 81-year-old male. Axial CT image of the chest shows lytic metastases in the right humeral head and T2 vertebral body (arrows). There were blastic metastases at other sites (not shown) in this patient.

Figure 2

Example of periosteal reaction of bone metastasis in an 82-year-old male. Axial CT image of the pelvis at baseline shows periosteal reaction (arrow) in the left medial acetabular wall. There is an osteoblastic metastasis in the left posterior acetabulum (arrowhead).

Figure 3

Example of extraosseous mass of bone metastasis in an 82-year-old male. Axial CT image of the pelvis at baseline shows an extraosseous mass (arrow) of a subtle blastic metastasis (arrowhead) in the right acetabulum.

Figure 4

Changes in tumour size measured in millimetres for patients deemed to have improved bone disease, no change or worse bone disease by (a) Reader 1 and (b) Reader 2. Note that for both readers, the range of size changes is widest in the “worse” assessment category. The interreader concordance correlation coefficient is low (0.013).

Figure 5

(a) Overall survival for patients with a post-treatment decline in prostate-specific antigen (PSA) and those with a post-treatment rise in PSA. (b, c) Overall survival for patients deemed to have improved bone disease, no change or worse bone disease on CT by Reader 1 (b) and Reader 2 (c).