Original articleTumor Burden Assessment with Positron Emission Tomography with [18-F] 2-fluoro 2-deoxyglucose (FDG PET) Modeled in Metastatic Renal Cell Cancer
Introduction
It has been estimated there were 30,000 new cases of cancers of the kidney and renal pelvis in 1998 with over 11,600 deaths in the United States. There is a preponderance of incidence and deaths in males 17600 versus12300 and 7100 versus 4500, respectively.1 No widely accepted method for evaluating total tumor burden in renal cell cancer is available, including indirect methods, such as an accepted serological marker. The challenge for departments of medical imaging is to provide biologically useful information that may be obtained in a reproducible manner. Follow-up studies of patients with renal cell cancer are generally performed using conventional imaging with plain chest X-ray, computed tomography (CT), and magnetic resonance imaging (MRI).2 The most common measure of tumor burden in CT is a bidimensional measure of a number of index lesions. In addition, a qualitative assessment of the presence or absence of new lesions is made. These are not true tumor burden assessments, the assumption behind an index lesion approach is that all lesions will behave in a similar fashion, but the clonal diversity model of oncogenesis suggests this is not likely to be true.
Assessment of disease burden in tumor types that do not produce characteristic serum markers currently depends on cross-sectional imaging modalities such as MRI and CT. Carefully measured CT-derived parameters are reproducible both in terms of direct volume assessment and bidimensional measurements.3 However, there are shortfalls in this approach in the posttreatment setting, as nonviable masses may appear indistinguishable from residual viable tumor. In addition, the assessment of small tumors with diameters similar to the slice thickness of the CT image is problematic. The use of 2-[F-18]fluoro-2-deoxy-D-glucose-positron emission tomography (FDG PET) to assess viable tumor burden is therefore attractive, as nonviable cells do not take up FDG.
In this paper, we describe the use of a dedicated PET camera to measure tumor volume by a thresholding technique.4 By multiplying the average FDG uptake by the PET-derived tumor volume, estimates can be made of functional tumor burden.5 In addition, the PET-derived estimates of tumor volume were compared to those provided by a CT-based volumetric method.
The most commonly used semiquantitative approach to assess the malignancy of lesions on FDG PET imaging is the standardized uptake value (SUV). The SUV measure attempts to correct for variations in administered dose and body habitus to allow for interpatient and intrapatient comparisons. There are 2 common methods of reporting the SUV based on either the average measured values within a region of interest (ROI), or the maximal pixel value within the ROI. Initial investigations of the SUV parameter have found that it does provide some important biologic information with reduced survival rates found in patients with lung cancer who have high SUV values.6
Section snippets
Materials and Methods
A series of 6 patients with metastatic clear cell renal cancer who were referred for extent of disease evaluation prior to therapy with 131I-labeled chimeric antibody G250 were assessed. All patients were imaged on the dedicated BGO based GE Advance© PET scanner (General Electric Medical Systems, Milwaukee, WI), the performance characteristics of which have been described elsewhere.7 PET scans were performed after injection of approximately 10 mCi of FDG. All scans were performed with imaging
Results
A total of 57 lesions in 6 patients were seen on both FDG PET and CT. All metastatic lesions were included in the PET study, however due to difficulties in CT volume estimation, 16 lesions in bone were excluded from comparative PET/ CT analysis.8
Discussion
Renal cell cancer is known to be FDG avid,9, 10, 11, 12, 13 our work confirms that renal cell cancer metastases are readily demonstrated with this technique.
The rationale behind assessments of tumor burden is that prognosis is related to tumor burden. Treatment induced reduction of tumor burden has been shown to be correlated to improvements in survival. There are many possible methods used to calculate tumor burden including pathologic assessment of resected specimens, serological markers, and
Conclusions
In renal cell cancer, there are no direct or indirect methods for measuring tumor burden. CT scan provides a potential method for evaluating soft-tissue metastasis, but is not accurate to determine the extent of bone involvement. There is a significant correlation for CT-measured volumes and PET TLG, a quantitative PET parameter, for soft-tissue tumors. Thus, FDG PET provides a good estimate of tumor burden due to soft-tissue metastases. Since FDG PET accuracy of detection of
Acknowledgements
The authors wish to acknowledge the support of the Cyclotron core of MSKCC who provided the FDG, as well as the support of the Laurent and Alberta Gerschel Foundation.
References (22)
- et al.
Patterns of tumor recurrence and guidelines for followup after nephron sparing surgery for sporadic renal cell carcinoma
J. Urol.
(1997) J. Metastatic bone diseaseclinical and therapeutic aspects
Bone
(1992)- et al.
FDG PET characterization of renal massespreliminary experience
Clin. Radiol.
(1997) - et al.
Imaging of renal cancer using positron emission tomography with 2-deoxy-2-(18F)-fluoro-D-glucosepilot animal and human studies
J. Urol.
(1991) - et al.
Preoperative carcinoembryonic antigen predicts outcomes in node-negative colon cancer patientsa multivariate analysis of 572 patients
J Am. Coll. Surg.
(1997) - Landis, S.H.; Murray, T.; Bolden, S.; Wingo, P.A. Cancer statistics, 1998 [published erratum appears in CA. Cancer J....
- et al.
Analysis of interobserver and intraobserver variability in CT tumor measurements
Am. J. Roentgenol.
(1996) - et al.
Segmentation of lung lesion volume by adaptive positron emission tomography image thresholding
Cancer
(1996) - et al.
Tumor treatment response based on visual and quantitative changes in global tumor glycolysis using FDG PET imagingthe visual response score (VRS), and the change in total lesion glycolysis (dTLG)
Clin. Pos. Imag.
(1999) - et al.
The prognostic significance of fluorodeoxyglucose positron emission tomography imaging for patients with nonsmall cell lung carcinoma
Cancer
(1998)