Is whole body low dose CT still necessary in the era of 18F-FDG PET/CT for the assessment of bone disease in multiple myeloma patients?

Objective: Whole body low dose computed tomography (WBLDCT) is the first-choice imaging modality to identify bone involvement in multiple myeloma (MM). Because the unenhanced LDCT co-registered to positron emission tomography (PET) (LDCT/PET) has similar technical characteristics to WBLDCT, we aimed to assess its reliability in the detection of bone disease, for employing fluorine-18-fluorodeoxyglucose (F-18-FDG) PET/CT as unique multimodality imaging method in MM patients. Subjects and Methods: Thirty three consecutive MM patients were prospectively enrolled and evaluated with WBLDCT to assess bone involvement. In addition, patients underwent F-18-FDG PET/CT using a disease-tailored optimized LDCT protocol. To compare both methods, skeletal anatomical regions were identified and a per-region and per-patient analysis were performed using Cohen's k test. Low dose computed tomography/PET sensitivity, specificity and accuracy were also calculated. Results: The two imaging modalities resulted highly concordant considering both patient-based (k=0.841) and region-based analysis; some discrepancies were observed in dorsal spine (k=0.809) and thorax (k=0.756). Low dose computed tomography/PET sensitivity, specificity and accuracy were 89.4%, 98.3% and 93.5%, respectively. Conclusion: Low dose computed tomography co-registered PET has comparable performance to WBLDCT. If confirmed on a lager sample, these encouraging results suggest the possibility to use this multimodal hybrid imaging as the only method for MM evaluation, rather than both exams, providing both morphologic and metabolic information in one session with impact on patient compliance, health care spending and especially radiation exposure.