Elsevier

Clinical Positron Imaging

Volume 3, Issue 2, March–April 2000, Pages 57-65
Clinical Positron Imaging

Original article
Tumor Burden Assessment with Positron Emission Tomography with [18-F] 2-fluoro 2-deoxyglucose (FDG PET) Modeled in Metastatic Renal Cell Cancer

https://doi.org/10.1016/S1095-0397(00)00041-8Get rights and content

Abstract

Objective: In patients with advanced cancer, total tumor burden affects the likelihood of tumor response and has important implications for prognosis. The aim of this study was to select the optimum 2-[F-18]fluoro-2-deoxy-D-glucose-positron emission tomography (FDG PET) tumor uptake parameter to accurately measure tumor burden in advanced metastatic renal cell cancer, in comparison with volumes measured with computed tomography (CT), as a reference test.

Materials and Methods: Six patients with metastatic renal cell carcinoma measurable on CT were studied. CT and FDG PET scans were carried out on all patients within 4 weeks prior to their entry into a phase I–II radioimmunotherapy trial. CT-based evaluation of disease extent (tumor volume) and 4 PET-based measurements (standardized uptake value[SUVmax], SUVav, volume, and total lesion glycolysis [TLG]) were performed independently by a radiologist (VN) and a nuclear medicine physician (TA). The degree of correlation between conventional (CT) extent of disease and parameters describing tumor concentration of FDG was then determined.

Results: Fifty-seven CT-measurable metastatic lesions in lung, abdomen, and scalp were evaluated in 6 patients. There was a high correlation between CT and FDG PET volume estimates for lesions greater than 5 cm3 in size. However, a PET-derived parameter that embodies both FDG uptake and lesion size, the TLG, correlated better with CT-derived tumor volume than did FDG PET volume alone.

Conclusion: Using CT volume as a gold standard, the optimal PET-based estimate of total tumor burden in patients with metastatic renal cancer is the sum over all lesions of the total lesion glycolysis.

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 r2 = 0.79 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.

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