Is there any complimentary role of F-18 NaF PET/CT in detecting of osseous involvement of multiple myeloma? A comparative study for F-18 FDG PET/CT and F-18 FDG NaF PET/CT

Diagnostic Innovations: Advances in imaging techniques for diagnosis and follow-up of multiple myeloma

Introduction

The International Myeloma Working Group (IMWG) defines myeloma related bone disease (MBD) as a diagnostic criterion for symptomatic multiple myeloma (MM) as the presence of osteolytic lesions ≥ 5 mm or more than one focal lesion (FL) ≥ 5 mm by magnetic resonance imaging (MRI). Whole-body low-dose CT (WBLDCT) is recommended as the first-choice imaging technique for the diagnosis of MBD with 18F-fluorodeoxyglucose-positron emission tomography/CT (18F-FDG-PET/CT) being considered a possible alternative at staging, whereas use of MRI studies is recommended in cases without myeloma-defining events (MDEs) in order to exclude the presence of FLs. Furthermore, use of 18F-FDG-PET/CT is recommended in response assessment, to be integrated with hematologic response and bone marrow minimal residual disease (MRD).

Areas covered

In this paper, we review novel functional imaging techniques in MM, particularly focusing on their advantages, limits, applications and comparisons with 18F-FDG-PET/CT or other standardized imaging techniques.

Conclusions

Combining both morphological and functional imaging, 18F-FDG-PET/CT is currently considered a standard imaging technique in MM for staging (despite false positive or negative results) and response assessment. The introduction of novel functional imaging techniques, as whole-body diffusion-weighted magnetic resonance imaging (WB-DWI-MRI), or novel PET tracers might be useful in overcoming these limits. Future studies will give more information on the complementarity of these imaging techniques or whether one of them might become a new gold standard in MM.

The role of conventional and novel PET radiotracers in assessment of myeloma bone disease

Over 80 % of patients with multiple myeloma (MM) experience osteolytic bone lesions, primarily due to an imbalanced interaction between osteoclasts and osteoblasts. This imbalance can lead to several adverse outcomes such as pain, fractures, limited mobility, and neurological impairments. Myeloma bone disease (MBD) raises the expense of management in addition to being a major source of disability and morbidity in myeloma patients. Whole-body x-ray radiography was the gold standard imaging modality for detecting lytic lesions. Osteolytic lesions are difficult to identify at an earlier stage on X-ray since the lesions do not manifest themselves on conventional radiographs until at least 30 % to 50 % of the bone mass has been destroyed. Hence, early diagnosis of osteolytic lesions necessitates the utilization of more complex and advanced imaging modalities, such as PET. One of the PET radiotracers that has been frequently investigated in MM is 18F-FDG, which has demonstrated a high level of sensitivity and specificity in detecting myeloma lesions. However, 18F-FDG PET/CT has several restrictions, and therefore the novel PET tracers that can overcome the limitations of 18F-FDG PET/CT should be further examined in assessment of MBD. The objective of this review article is to thoroughly examine the significance of both conventional and novel PET radiotracers in the assessment of MBD. The intention is to present the information in a manner that would be easily understood by healthcare professionals from diverse backgrounds, while minimizing the use of complex nuclear medicine terminology.

18F-FDG Versus Non-FDG PET Tracers in Multiple Myeloma

Multiple myeloma (MM) accounts for 0.9% of cancer diagnoses, and incidence and mortality rate have increased in previous years. 18F-fluorodeoxyglucose (FDG) PET-computed tomography (CT) is an established modality for MM evaluation. MR imaging is helpful where 18F-FDG PET-CT is lacking. To standardize PET reporting, methods like Italian Myeloma Criteria for PET Use and Deauville criteria have been studied. Tracers like 11C-acetate and 11C-choline/18F-fluoromethylcholine (FCH) have shown higher sensitivity and detected more focal lesions and diffuse involvement than 18F-FDG PET-CT. 18F-FCH showed higher maximum standardized uptake value than 18FDG. 11C-methionine appears to be the best radiopharmaceutical, apart from 18F-FDG, for evaluating MM.

Multiple Myeloma Associated Bone Disease

The lytic bone disease is a hallmark of multiple myeloma, being present in about 80% of patients with newly diagnosed MM, and in more during the disease course. The myeloma associated bone disease (MBD) severely affects the morbidity and quality of life of the patients. MBD defines treatment demanding MM. In recent years, knowledge of the underlying pathophysiology has increased, and novel imaging technologies, medical and non-pharmaceutical treatments have improved. In this review, we highlight the major achievements in understanding, diagnosing and treating MBD. For diagnosing MBD, low-dose whole-body CT is now recommended over conventional skeletal survey, but also more advanced functional imaging modalities, such as diffusion-weighted MRI and PET/CT are increasingly important in the assessment and monitoring of MBD. Bisphosphonates have, for many years, played a key role in management of MBD, but denosumab is now an alternative to bisphosphonates, especially in patients with renal impairment. Radiotherapy is used for uncontrolled pain, for impeding fractures and in treatment of impeding or symptomatic spinal cord compression. Cement augmentation has been shown to reduce pain from vertebral compression fractures. Cautious exercise programs are safe and feasible and may have the potential to improve the status of patients with MM.

Can 18F-NaF PET/CT before Autologous Stem Cell Transplantation Predict Survival in Multiple Myeloma?

There is an unmet need for positron emission tomography (PET) radiotracers that can image bone disease in multiple myeloma (MM) in a more sensitive and specific way than the widely used ¹⁸F-fluorodeoxyglucose (¹⁸F-FDG). Sodium fluoride (¹⁸F-NaF) is a highly sensitive tracer of bone reconstruction, evolving as an important imaging agent for the assessment of malignant bone diseases. We attempted to investigate for the first time the prognostic significance of ¹⁸F-NaF PET/CT in newly diagnosed, symptomatic MM patients planned for autologous stem cell transplantation (ASCT). Forty-seven patients underwent dynamic and static PET/CT with ¹⁸F-NaF before treatment. After correlation with the respective findings on CT and ¹⁸F-FDG PET/CT that served as reference, the ¹⁸F-NaF PET findings were compared with established factors of high-risk disease, like cytogenetic abnormalities as well as bone marrow plasma cell infiltration rate. Furthermore, the impact of ¹⁸F-NaF PET/CT on progression-free survival (PFS) was analyzed. Correlation analysis revealed a moderate, significant correlation of the ¹⁸F-NaF parameters SUV_average and K₁ in reference tissue with bone marrow plasma cell infiltration rate. However, no significant correlation was observed regarding all other ¹⁸F-NaF PET parameters. Survival analysis revealed that patients with a pathologic ¹⁸F-NaF PET/CT have a shorter PFS (median = 36.2 months) than those with a physiologic scan (median = 55.6 months) (p = 0.02). Nevertheless, no quantitative ¹⁸F-NaF parameter could be shown to adversely affect PFS. In contrast, the respective analysis for quantitative dynamic ¹⁸F-FDG PET/CT revealed that the parameters SUV_max, fractional blood volume (V_B), k₃ and influx from reference tissue as well as SUV_average from MM lesions had a significant negative impact on patient survival. The herein presented findings highlight the rather limited role of ¹⁸F-NaF PET/CT as a single PET approach in MM.

Positron Emission Tomography (PET) Radiopharmaceuticals in Multiple Myeloma

Multiple myeloma (MM) is a plasma cell disorder, characterized by clonal proliferation of malignant plasma cells in the bone marrow. Bone disease is the most frequent feature and an end-organ defining indicator of MM. In this context, imaging plays a pivotal role in the management of the malignancy. For several decades whole-body X-ray survey (WBXR) has been applied for the diagnosis and staging of bone disease in MM. However, the serious drawbacks of WBXR have led to its gradual replacement from novel imaging modalities, such as computed tomography (CT), magnetic resonance imaging (MRI) and positron emission tomography/computed tomography (PET/CT). PET/CT, with the tracer ¹⁸F-fluorodeoxyglucose (¹⁸F-FDG), is now considered a powerful diagnostic tool for the detection of medullary and extramedullary disease at the time of diagnosis, a reliable predictor of survival as well as the most robust modality for treatment response evaluation in MM. On the other hand, ¹⁸F-FDG carries its own limitations as a radiopharmaceutical, including a rather poor sensitivity for the detection of diffuse bone marrow infiltration, a relatively low specificity, and the lack of widely applied, established criteria for image interpretation. This has led to the development of several alternative PET tracers, some of which with promising results regarding MM detection. The aim of this review article is to outline the major applications of PET/CT with different radiopharmaceuticals in the clinical practice of MM.

18F-fluoro-ethyl-tyrosine (18F-FET) PET/CT as a potential new diagnostic tool in multiple myeloma: a preliminary study

Aim of the study

The aim of this study was to analyse the diagnostic accuracy of ^“18F-fluoro-ethyl-tyrosine (¹⁸F-FET) PET/CT tracer in multiple myeloma.

Material and methods

The analysed group included: patients with newly diagnosed active myeloma (eight patients); in very good partial remission or complete remission (VGPR or CR) after treatment (nine patients); and with active disease after relapse (15 patients).

Results

In patients with newly diagnosed myeloma, 64 lesions were found using CT and 83 lesions using ¹⁸F-FET. In six patients, the number of lesions using CT and ¹⁸F-FET was the same, and two had more lesions with the ¹⁸F-FET than with the CT. Patients in VGPR or CR had no FET-positive lesions. Fourteen out of 15 patients with active relapsed myeloma had 47 FET-positive lesions, CT assessment of the same group showed 282 lesions. In one patient with relapse soft tissue mass was found with ¹⁸F-FET but not with CT.

Conclusions

¹⁸F-FET can be a promising alternative to ¹⁸F-FDG PET/CT for myeloma-related bone disease diagnosis.

Dual-tracer PET/CT scan after injection of combined [18 F]NaF and [18 F]FDG outperforms MRI in the detection of myeloma lesions

The detection rates of whole-body combined [¹⁸ F]NaF/[¹⁸ F]FDG positron emission tomography combined with computed tomography (PET/CT), CT alone, whole-body magnetic resonance imaging (WB-MRI), and X-ray were prospectively studied in patients with treatment-requiring plasma cell disorders The detection rates of imaging techniques were compared, and focal lesions were classified according to their anatomic location. Twenty-six out of 30 initially included patients were assessable. The number of focal lesions detected in newly diagnosed patients (n = 13) and in relapsed patients (n = 13) were 296 and 234, respectively. The detection rate of PET/CT was significantly higher than those of WB-MRI (P < 0.05) and CT (P < 0.0001) both in patients with newly diagnosed and in those with relapsed multiple myeloma (MM). The X-ray detection rate was significantly lower than those of all other techniques, while CT detected more lesions compared with WB-MRI at diagnosis (P = 0.025). With regard to the infiltration patters, relapsed patients presented more diffuse patterns, and more focal lesions located in the limbs compared with newly diagnosed patients. In conclusion, the detection rate of [¹⁸ F]NaF/[¹⁸ F]FDG PET/CT was significantly higher than those of CT, MRI, and X-ray, while the detection rate of X-rays was significantly lower than those of all other imaging techniques except for focal lesions located in the skull.

Advanced Imaging of Multiple Myeloma Bone Disease

Multiple myeloma (MM), a malignancy of mature plasma cells, is the second most common hematologic malignancy and the most frequent cancer to involve the skeleton (1, 2). Bone disease in MM patients is characterized by lytic bone lesions that can result in pathologic fractures and severe pain. While recent advances in MM therapy have significantly increased the median survival of newly diagnosed patients (3), skeletal lesions and their sequelae continue to be a major source of patient morbidity and mortality and bone pain is the most frequent presenting symptom of MM patients (4). Rapid improvements in imaging technology now allow physicians to identify ever smaller skeletal and bone marrow abnormalities, however the clinical value of subtle radiographic findings is not always clear. This review summarizes currently available technologies for assessing MM bone disease and provides guidance for how to choose between imaging modalities.

A prospective study comparing whole-body skeletal X-ray survey with 18F-FDG-PET/CT, 18F-NaF-PET/CT and whole-body MRI in the detection of bone lesions in multiple myeloma patients

Background

For decades, the most widely used imaging technique for myeloma bone lesions has been a whole-body skeletal X-ray survey (WBXR), but newer promising imaging techniques are evolving.

Purpose

To compare WBXR with the advanced imaging techniques 18F-fluorodeoxyglucose (FDG) positron emission tomography (PET)/computed tomography (CT), 18F-sodium fluoride (NaF) PET/CT and whole-body magnetic resonance imaging (WB-MRI) in the detection of myeloma bone lesions.

Material and Methods

Fourteen patients with newly diagnosed multiple myeloma were prospectively enrolled. In addition to WBXR, all patients underwent FDG-PET/CT, NaF-PET/CT, and WB-MRI. Experienced specialists performed blinded readings based on predefined anatomical regions and diagnostic criteria.

Results

In a region-based analysis, a two-sided ANOVA test showed that the extent of detected skeletal disease depends on the scanning technique (P < 0.0001). Tukey’s multiple comparison test revealed that WB-MRI on average detects significantly more affected regions than WBXR (P < 0.005), FDG-PET/CT (P < 0.0001), and NaF-PET/CT (P < 0.05). In a patient-based analysis, a Cochran’s Q test showed that there are no significant differences in the proportion of patients with bone disease detected by the different scanning techniques (P = 0.23). Determination of intrareader variability resulted in Kappa coefficients corresponding to moderate (FDG-PET/CT) and substantial agreement (WB-MRI, WBXR, NaF-PET/CT).

Conclusion

WB-MRI detects on average significantly more body regions indicative of myeloma bone disease compared to WBXR, FDG-PET/CT, and NaF-PET/CT. The lack of significance in the patient-based analysis is most likely due to the small number of study participants.

[Hemato-oncological imaging : Importance of hybrid procedures]

CLINICAL/METHODICAL ISSUE

Biomedical imaging procedures play a major role in hemato-oncological diseases with respect to pre-therapeutic staging and assessment of treatment response.

STANDARD RADIOLOGICAL METHODS

Originally, the therapeutic management was the domain of computed tomography (CT) and whole-body magnetic resonance imaging (MRI).

METHODICAL INNOVATIONS

Over the last decade these purely morphological techniques have gradually been replaced by hybrid imaging techniques, such as positron emission tomography-CT (PET/CT) and PET/MRI, which also provide metabolic and functional information.

PERFORMANCE

For lymphomas, the PET tracer 18F-fluorodeoxyglucose (18 F-FDG) is meanwhile so well-established that its use is a cornerstone of the Lugano classification; however, for multiple myeloma the search for an optimal PET tracer that can also detect early disease stages is still ongoing. Functional MRI techniques, such as diffusion-weighted imaging (DWI), perfusion-weighted imaging and dynamic contrast-enhanced imaging have shown promising results for both lymphomas and multiple myelomas.

ACHIEVEMENTS

The PET/MRI technique can combine the different types of information due to its truly multiparametric approach.

PRACTICAL RECOMMENDATIONS

In the future PET/MRI could possibly become the hybrid imaging technique of choice for hemato-oncological diseases.

Role of 18F-FDG PET/CT in the diagnosis and management of multiple myeloma and other plasma cell disorders: a consensus statement by the International Myeloma Working Group

The International Myeloma Working Group consensus aimed to provide recommendations for the optimal use of ¹⁸fluorodeoxyglucose (¹⁸F-FDG) PET/CT in patients with multiple myeloma and other plasma cell disorders, including smouldering multiple myeloma and solitary plasmacytoma. ¹⁸F-FDG PET/CT can be considered a valuable tool for the work-up of patients with both newly diagnosed and relapsed or refractory multiple myeloma because it assesses bone damage with relatively high sensitivity and specificity, and detects extramedullary sites of proliferating clonal plasma cells while providing important prognostic information. The use of ¹⁸F-FDG PET/CT is mandatory to confirm a suspected diagnosis of solitary plasmacytoma, provided that whole-body MRI is unable to be performed, and to distinguish between smouldering and active multiple myeloma, if whole-body X-ray (WBXR) is negative and whole-body MRI is unavailable. Based on the ability of ¹⁸F-FDG PET/CT to distinguish between metabolically active and inactive disease, this technique is now the preferred functional imaging modality to evaluate and to monitor the effect of therapy on myeloma-cell metabolism. Changes in FDG avidity can provide an earlier evaluation of response to therapy compared to MRI scans, and can predict outcomes, particularly for patients who are eligible to receive autologous stem-cell transplantation. ¹⁸F-FDG PET/CT can be coupled with sensitive bone marrow-based techniques to detect minimal residual disease (MRD) inside and outside the bone marrow, helping to identify those patients who are defined as having imaging MRD negativity.

PET/MR Imaging of Multiple Myeloma

PET-magnetic resonance (MR) is a hybrid imaging modality that combines PET and MR. Evidence for this new modality is in the process of being developed, but both component modalities are well tested in the diagnosis and management of multiple myeloma. It allows advanced bimodality imaging of the whole body with an adaptable field of view and it can be used for monitoring plasma cell dyscrasias for progression to multiple myeloma, for assessing disease burden in patients with known multiple myeloma, for assessing response to therapy and relapse after remission, and for radiation therapy treatment planning.

Treatment response evaluation with 18F-FDG PET/CT and 18F-NaF PET/CT in multiple myeloma patients undergoing high-dose chemotherapy and autologous stem cell transplantation

AIM

The aim of this study was to assess the combined use of the radiotracers ¹⁸F-FDG and ¹⁸F-NaF in treatment response evaluation of a group of multiple myeloma (MM) patients undergoing high-dose chemotherapy (HDT) followed by autologous stem cell transplantation (ASCT) by means of static (whole-body) and dynamic PET/CT (dPET/CT).

PATIENTS AND METHODS

Thirty-four patients with primary, previously untreated MM scheduled for treatment with HDT followed by ASCT were enrolled in the study. All patients underwent PET/CT scanning with ¹⁸F-FDG and ¹⁸F-NaF before and after therapy. Treatment response by means of PET/CT was assessed according to the European Organization for Research and Treatment of Cancer (EORTC) 1999 criteria. The evaluation of dPET/CT studies was based on qualitative evaluation, semi-quantitative (SUV) calculation, and quantitative analysis based on two-tissue compartment modelling and a non-compartmental approach leading to the extraction of fractal dimension (FD).

RESULTS

An analysis was possible in 29 patients: three with clinical complete response (CR) and 26 with non-CR (13 patients near complete response-nCR, four patients very good partial response-VGPR, nine patients partial response-PR). After treatment, ¹⁸F-FDG PET/CT was negative in 14/29 patients and positive in 15/29 patients, showing a sensitivity of 57.5 % and a specificity of 100 %. According to the EORTC 1999 criteria, ¹⁸F-FDG PET/CT-based treatment response revealed CR in 14 patients (¹⁸F-FDG PET/CT CR), PR in 11 patients (¹⁸F-FDG PET/CT PR) and progressive disease in four patients (¹⁸F-FDG PET/CT PD). In terms of ¹⁸F-NaF PET/CT, 4/29 patients (13.8 %) had a negative baseline scan, thus failed to depict MM. Regarding the patients for which a direct lesion-to-lesion comparison was feasible, ¹⁸F-NaF PET/CT depicted 56 of the 129 ¹⁸F-FDG positive lesions (43 %). Follow-up ¹⁸F-NaF PET/CT showed persistence of 81.5 % of the baseline ¹⁸F-NaF positive MM lesions after treatment, despite the fact that 64.7 % of them had turned to ¹⁸F-FDG negative. Treatment response according to ¹⁸F-NaF PET/CT revealed CR in one patient (¹⁸F-NaF PET/CT CR), PR in five patients (¹⁸F-NaF PET/CT PR), SD in 12 patients (¹⁸F-NaF PET/CT SD), and PD in seven patients (¹⁸F-NaF PET/CT PD). Dynamic ¹⁸F-FDG and ¹⁸F-NaF PET/CT studies showed that SUV_average, SUV_max, as well as the kinetic parameters K₁, influx and FD from reference bone marrow and skeleton responded to therapy with a significant decrease (p < 0.001).

CONCLUSION

F-FDG PET/CT demonstrated a sensitivity of 57.7 % and a specificity of 100 % in treatment response evaluation of MM. Despite its limited sensitivity, the performance of ¹⁸F-FDG PET/CT was satisfactory, given that 6/9 false negative patients in follow-up scans (66.7 %) were clinically characterized as nCR, a disease stage with very low tumor mass. On the other hand, ¹⁸F-NaF PET/CT does not seem to add significantly to ¹⁸F-FDG PET/CT in treatment response evaluation of MM patients undergoing HDT and ASCT, at least shortly after therapy.