International Journal of Radiation Oncology*Biology*Physics
Clinical investigationPreliminary report of using FDG-PET to detect extrapelvic lesions in cervical cancer patients with enlarged pelvic lymph nodes on MRI/CT☆
Introduction
The clinical and pathologic parameters such as clinical stage, tumor size, and pelvic lymph node (LN) involvement are important prognostic factors for cervical cancer 1, 2. In such patients, pelvic LN metastasis was usually reported to be associated with extrapelvic failure. In our previous study, we demonstrated that enlarged pelvic LNs seen on CT or MRI were independent prognostic factors for cervical cancer patients primarily treated with radiotherapy (RT) (3). We also found that for early-stage cervical cancer patients treated with radical surgery and postoperative pelvic RT, pathologically proven LN involvement was the most important prognostic factor for survival and the only significant risk factor for distant metastasis (4). These analyses suggested that more effective methods should be developed to detect extrapelvic metastasis for patients with pelvic LN metastasis shown on imaging or pathologic examination.
Combined chemoradiotherapy (CCRT) is the treatment of choice for patients with locally advanced cervical cancer 5, 6. For patients who have suspected pelvic LN metastasis on pretreatment MRI/CT studies, an important clinical decision is whether prophylactic para-aortic RT (extended field) should be given as part of the CCRT. Although some studies have declared that concomitant chemotherapy with extended field irradiation 7, 8 is feasible, acute hematologic and GI adverse effects inevitably increase, and the effects on the development of late complications need long-term follow-up. Furthermore, the sensitivity of conventional tools to detect systemic metastasis is limited. As shown in our previous study, for patients who completed the pretreatment survey and were treated primarily with RT, more than one-half of recurrences occurred distantly without local failure (3). 18F-fluorodeoxyglucose positron emission tomography (FDG-PET) might be a good tool to survey the paraaortic LNs (PALNs) and other organs for metastasis simultaneously.
FDG-PET has been accepted as a useful tool for clinical staging of several types of malignant tumors, including non–small-cell lung cancer, head-and-neck cancers, and others 9, 10. In cervical cancer, two pilot studies correlated the pathologic findings with the imaging findings and confirmed the better predictive accuracy of FDG-PET compared with MRI/CT in metastatic LNs 11, 12. By integrating conventional and functional imaging studies, more information could be generated to affect the clinical staging and treatment strategy. However, FDG-PET is still a relatively expensive tool in many countries, including Taiwan, and routine use for all cervical cancer patients might not be financially justified. In consideration of the cost-effectiveness of PET, the selection of patients with a greater risk of extrapelvic metastasis was a reasonable choice.
In this prospective study, patients with suspected pelvic LN metastasis but no PALN enlargement on CT and no evidence of distant metastasis using conventional examinations underwent pretreatment FDG-PET. Because the maximal standardized uptake value (maxSUV) is an important reference for interpreting PET data and may provide an alternative means of assessing tumor biologic potential (13), our first aim was to study the correlation of the maxSUV with the tumor and LN characteristics in cervical cancer. Our second aim was to determine the effectiveness of pretreatment FDG-PET in detecting PALN metastasis and other systemic metastases in this high-risk group of patients. In addition, we tried to find the agreement between PET and CT/MRI in pelvic LNs. Finally, we report our preliminary findings of the failure pattern after a minimum of 12 months of follow-up. If the findings from the FDG-PET change the clinical decision substantially and benefit patient treatment, additional clinical trials will be needed to determine the impact on patient outcome.
Section snippets
Methods and materials
Between April and December 2001, 120 patients with newly diagnosed cervical cancer were referred to our department for curative chemoradiotherapy. The usual radiographs and laboratory analysis were performed before treatment. All patients underwent pelvic and abdominal MRI/CT to evaluate the primary tumor extension and LN status. For the potential candidates, the clinical information and imaging study findings, including MRI/CT, were presented and reviewed at a weekly conference that included
Results
The clinical characteristics of the patients are listed in Table 1. Of the 19 patients, 18 (95%) had Stage IB2–IIIB cervical cancer, in agreement with the greater incidence of pelvic LN metastasis in advanced-stage patients. Thirteen patients had multiple positive pelvic LNs on MRI/CT.
Discussion
Several prospective randomized studies have shown that the combination of pelvic RT with cisplatin-based chemotherapy significantly improves local control and prolongs survival in patients with advanced-stage cervical cancer 15, 16, 17, 18. In those studies, PALN irradiation was not given. The incidence of PALN metastases was 16% and 25% by surgical staging, respectively, in Stage II and III patients (19) and should be taken into consideration in the treatment planning. The protocol for
Conclusion
Conventional MRI/CT scans are useful tools for defining the primary tumor extension and detection of enlarged pelvic LNs or PALNs, and they should remain as the first-line imaging modality in staging cervical cancer patients. For patients with enlarged pelvic LNs but no obviously enlarged PALNs on MRI/CT, pretreatment FDG-PET can supplement these conventional imaging studies in determining the extent of tumor spread and in adjusting the irradiation field. Subsequent study of PET scan is
Acknowledgements
The authors thank Dr. Lai-Chu See for her assistance in statistical analysis and Wei-Ju Chen for her assistance with data management.
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Supported by Grant CTRP024 from the Chang Gung Memorial Hospital and University and Grant NSC 92-2314-B-182A-084.