Whole-body low-dose multidetector row-CT in the diagnosis of multiple myeloma: an alternative to conventional radiography

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Abstract

Objective: The goal of this study was to establish the feasibility of a low-dose whole-body multidetector row-CT (MDCT) protocol in the diagnosis of multiple myeloma (MM), as an alternative to conventional X-ray imaging, which is currently still state-of-the-art in these patients, with emphasis on the comparison of image resolution on axial and multiplanar reformatted (MPR) scans and reduction of radiation dose. Material and methods: 100 patients with known MM, or monoclonal gammopathy of unknown significance (MGUS) underwent unenhanced whole-body MDCT on a 16-slice scanner in a randomised fashion, using a 16 × 1.5 mm collimation and four different energy parameters (40, 50, 60 and 70 mAs). Three different reconstruction algorithms were used in every patient (B40f, B50f and B60f kernel). CT scans were reviewed independently by two radiologists, with regard to correct classification into one of the three known MM stages, and recognition of fracture risk. Thereafter, axial and MPR images were evaluated in consensus by both readers, with respect to image resolution. Diagnosis of osteolytic lesions was performed on the basis of axial and multiplanar reformatted images, whereas the assessment of spinal misalignment and fracture was done only on MPR images. The distribution of image resolution categories (very good, good, sufficient, insufficient for diagnosis) was evaluated depending on following parameters: current time product, patient’s weight, bone density and reconstruction algorithm. The effective radiation dose was determined with the aid of an anthropomorphic Alderson Rando-Phantom, using a tube current time product of 40 mAs, and then extrapolating it on all current time products applied in this study on a commercially available software program WinDose (Institute of Medical Physics, Erlangen, Germany). Results: In all 100 patients, image resolution was diagnostic, regardless of scanning parameters, enabling correct classification of multiple myeloma patients. Image quality of MPR images was either equal or inferior to correspondent axial images in the delineation of smaller lytic lesions, because of the use of non-isotropic voxel size. However, they proved accurate in diagnosing fracture and spine misalignment. A strong dependency of image resolution on bone density was observed, with reduced quality in patients with either diffuse skeleton infiltration or concurrent osteoporosis. Spatial resolution was also dependent on the reconstruction algorithm and energy level (mAs) used, as well as on patient’s weight, but their influence was low within the given ranges. A middle-frequency reconstruction algorithm (B50f kernel) proved beneficial for all energy protocols. The interobserver agreement was excellent (kappa = 0.95) for classification of MM-patients. Effective radiation dose of MDCT calculated at a tube current time product of 40 mAs was 1.7-fold higher than the mean radiation dose of conventional X-ray (4.1 mSv versus 2.4 mSv). Discussion: Our study shows that whole-body low-dose MDCT investigational protocols are appropriate for the diagnosis of lytic bone changes and for assessment of fracture risk in multiple myeloma patients, representing a serious alternative to current standards.

Introduction

Multiple myeloma (MM) is a malignancy of plasma cells showing variable degrees of differentiation [1]. Typically, it involves the bone marrow and is usually multicentric. Durie and Salmon [2] showed that lytic bone lesions, hemoglobin, serum calcium and the monoclonal component blood levels significantly correlate with tumor mass and patient eventual survival. Their staging system is the most widely used for untreated multiple myeloma patients, based on the size of the tumor mass and M-gradient (M-protein level), respectively. According to this classification system, the task of the radiologist is to bring roentgenographic evidence of typical punched-out lytic bone lesions in order to categorize the stage of multiple myeloma. Patients with more than two unequivocal lytic lesions are classified as stage III, for which immediate treatment is indicated [3]. The diagnosis must yet finally be confirmed by a bone marrow aspirate or biopsy [4]. Bone marrow infiltration exceeding a certain degree leads in most cases to typical imaging findings on conventional X-ray and CT, including osteolysis, osteopenia and seldom osteosclerosis (e.g. “ivory vertebra”) [5]. Bone lesions in the appendicular skeleton are mostly well recognized, both by conventional X-ray, and CT. Lesions of multiple myeloma involving the axial skeleton, the thoracic cage and the skull, however, are better recognized by CT because of lacking add-up effects of interposed, different radioopaque soft tissue and bony structures, as on planar conventional X-ray images, sometimes missing even centimeter-large lytic lesions. Thus, the superiority of CT over conventional X-ray diagnosis in imaging skeletal lesions is a methodical one and must not be questioned. One main impediment in replacing conventional X-ray staging by CT represents the much higher radiation exposure associated with standard CT, in comparison with conventional radiographs. The effective dose, following radiological diagnosis, plays in stage III multiple myeloma patients, admittedly, a subordinate role, because of reduced life expectancy. However, monoclonal gammopathy of unknown significance (MGUS) patients suspected of multiple myeloma should not be unnecessarily overexposed to radiation. Therefore, establishing a low-dose CT-protocol, with a radiation exposure in a range comparable to that of conventional roentgenography, could represent a superior alternative in the imaging approach of this disease.

The aim of this study was to establish an optimised whole-body low-dose multidetector row-CT (MDCT) investigation protocol for staging and follow up of multiple myeloma, able to replace whole-body conventional radiography, and also appropriately deliver supplementary data about unexpected findings outside the skeleton, for instance in the lung, abdominal or pelvic viscera.

Section snippets

Patients

Between September 2002 and April 2003, a number of 100 consecutive patients (67 male and 33 female) with a mean age of 63.5 years (range 50–81 years) with diagnosed multiple myeloma (n = 86), or MGUS (n = 14), were included in this prospective study. There were two major requests of the clinician to the CT: correct classification of the patient into one of the three classical MM-stages, according to Laroche, and diagnosis of extramedullary plasmacytoma. A whole-body low-dose MDCT was performed

Results

Seventy patients showed multiple osteolysis, five had solitary manifestations, whereas in 25 patients CT revealed no bone lesions. Twenty-eight patients had no prior therapy. Thirty-five (35%) (n = 10) of them showed reduced bone density, while the rest demonstrated normal bone density. From the group of patients with pre-therapy (chemotherapy, radiation or biphosphonate) only 21% (n = 15) showed reduced bone density.

  • 1.

    Axial image resolution was rated better or equal to MPR in all 100 cases. The

Discussion

Since the introduction of the multiple myeloma classification system by Durie and Salmon, conventional radiographs are considered state-of-the-art in the diagnosis of multiple myeloma bone lesions. It is, however, known that the whole-body radiographic survey is inadequate for depiction of small lytic bone lesions, particularly in the axial skeleton, and therefore, inaccurate for staging this patient category. Underestimation of bone lesions by conventional radiography could lead to

Conclusion

We recommend the implementation of low-dose whole-body multidetector-CT in the staging and monitoring of multiple myeloma patients, as a precise and quick diagnostic tool, with high acceptance among patients and medical personal, which also enables acquisition of precious, complementary data concerning other organs. On the basis of our data, we perform whole-body low-dose CT in thin patients using a tube current of 40 mAs, increasing the dose up to 60 mAs in overweighed patients, or patients with

Acknowledgements

We thank Mr. Markus Buchgeister from the Department of Medical Physics of the University of Tübingen for his support in establishing the radiation dose for all energy levels chosen, using an anthropomorphic Alderson Rando Phantom, as well as Mr. Klaus Herz from the Department for Radiation Protection of UKT for guiding in the calculation of the effective dose in the conventional radiological diagnosis.

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