Clinical investigation: cervix
Measurement of tumor volume by PET to evaluate prognosis in patients with advanced cervical cancer treated by radiation therapy

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Abstract

Purpose: This study evaluated the usefulness of tumor volume measurement with positron emission tomography (PET) in patients with advanced cervical cancer treated by radiation therapy.

Methods and Materials: Fifty-one patients underwent PET before treatment. Primary tumor volume was determined, and volume, FIGO stage, and presence of lymph nodes on the PET study were compared to progression-free survival (PFS) and overall survival (OS).

Results: Tumor volume, lymph node disease, and stage were predictive of PFS, whereas volume and lymph node involvement predicted OS. Lymph node status did not correlate with volume. Dividing patients according to whether the tumor volume was more or less than 60 cm3 predicted PFS and OS. Separation of patients with tumor volumes ≤60 cm3 and no lymph node disease vs. any other combination was strongly predictive of PFS and OS.

Conclusions: The following conclusions were drawn regarding patients with advanced cervical cancer treated with radiation therapy: (1) Tumor volume can be accurately measured by PET; (2) Tumor volume separates patients with a good prognosis from those with a poorer prognosis; (3) A subset of patients with relatively small tumors and no lymph node involvement does remarkably well; (4) Tumor volume does not correlate with the presence of lymph node disease.

Introduction

Positron emission tomography (PET) employing the radiopharmaceutical 18F fluorodeoxyglucose (FDG) is used in staging and follow-up of a wide variety of cancers, including lymphoma, malignant melanoma, and carcinomas of the esophagus, breast, lung, and colon (e.g., Refs. 1, 2, 3). Work from our institution 4, 5 and elsewhere 6, 7, 8 has shown that PET is also valuable in staging patients with cervical carcinoma. FDG-PET readily identifies the primary tumor and accurately assesses spread to lymph nodes and distant metastases.

It is well established that tumor size is an important prognostic factor in patients with cervical carcinoma 9, 10. Although clinical stage also is an important factor, stage does not necessarily correlate with tumor size. The limited reliability of physical examination for estimation of size has led to interest in tumor measurement based on three-dimensional imaging techniques 11, 12, 13, 14, 15. The work presented here is an attempt to increase the already substantial value of PET in patients with advanced cervical cancer by addition of information about the size of the primary tumor. A quantitative technique is described that accurately measures the tumor volume, with the results showing a strong correlation with treatment outcome, especially when combined with detection of lymph node disease.

Section snippets

Patients and treatment

Fifty-one consecutive patients with newly diagnosed advanced cervical carcinoma whose digital data were available were included in this retrospective study. All patients were to be treated by radiation therapy. The patients underwent PET imaging for clinical indications before treatment between January 1998 and September 1999. They were treated exclusively with irradiation and, in 29 patients, concurrent cisplatin-based chemotherapy (16). The radiation therapy consisted of 6 weeks of external

Results

A typical example of the PET/CT correlation used to validate the PET edge detector is presented in Fig. 1. The slice best demonstrating the maximum dimensions of the primary tumor is shown, along with marks indicating the boundaries of the tumor. To retain maximum spatial resolution, the CT dimensions were measured directly from film and not from the interpolated, digitized images shown in the figure.

The results for a threshold value of 40% are shown in Fig. 2, along with the correlation

Discussion

Failure of initial treatment with radiation therapy is associated with a poor salvage rate and reduced long-term survival in patients with advanced cervical carcinoma. It is critically important that the initial course of therapy be effective, because many studies show that the primary cause of poor long-term survival after definitive radiotherapy is failure to achieve local control (e.g., Refs. 23, 24, 25). Thus, ways are needed to identify patients at high risk who may be candidates for more

Acknowledgements

We are grateful to Katherine Trinkaus, Ph.D., for help with the statistical analysis and to Patsa Hungspreugs and Jason Jacob for their work with data analysis.

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    This project was supported in part by Grant No. R01 CA85797 from the National Institutes of Health. This work is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health.

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