Quantitative contrast-enhanced CT attenuation evaluation of osseous metastases following chemotherapy

Abstract

Purpose: Osseous metastases often undergo an osteoblastic response following chemotherapy also known as the “flare” phenomenon. The purpose of our study was to demonstrate the quantitative CT changes in density of osseous metastases before and after chemotherapy. Materials and Methods: Our study was IRB approved and HIPAA compliant. Our cohort consisted of 48 consecutive cancer patients with studies both before chemotherapy/at the time of diagnosis of osseous metastases and 14 ± 3 (12-20) months after the initiation of treatment 60 ±10 (range: 37-80) years, 26 F, 22 M). CT density of all lesions was measured by two fellowship trained MSK radiologists. The largest possible region of interest was selected to measure the average and maximum densities in Hounsfield Units (HU). If multiple lesions were present, the largest lesion was evaluated. Treatment effects were assessed using paired t-tests, using P < 0.05 as statistically significant. Intraclass correlation coefficient (ICC) was calculated for the two readers. Results: The distribution of primary tumors was as follows: breast (20/48, 42%), lung (10/48, 21%), prostate (5/48, 10%), pancreatic (5/48, 10%), renal (2/48, 4%), and other (6/48, 13%). The measured lesions were in the following locations: spine/sacrum (35/48, 73%), pelvis (10/48, 21%), sternum (3/48, 6%). The distribution of lesion types were as follows: lytic (14/48, 29%), blastic (25/48, 52%), and mixed lytic-blastic (9/48, 19%). Mean and maximum CT densities (Reader 1) of all metastases before chemotherapy treatment were 328 ± 206 HU and 580 ± 391 HU, respectively and after chemotherapy treatment were 511 ± 263 HU and 789 ± 439 HU, respectively. There was a significant increase in mean and maximum CT densities of metastases following chemotherapy for all lesions collectively but also when separated into lytic, blastic, and mixed lytic-blastic lesions (P < 0.05). ICC was almost perfect for average density and moderate to substantial for maximum density. Conclusion: Quantitative assessment of osseous metastatic disease using CT density measurements confirms a statistically significant increase in density 12-20 months after initiation of chemotherapy. Clinical Application: Measuring changes in CT density of osseous metastases may have a significant role in evaluating chemotherapy effect.