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Ann Thorac Surg 2007;84:1092-1097
© 2007 The Society of Thoracic Surgeons
a Division of Cardiothoracic Surgery, Department of Surgery, University of Alabama at Birmingham School of Public Health, Birmingham, Alabama
b Department of Epidemiology, University of Alabama at Birmingham School of Public Health, Birmingham, Alabama
Accepted for publication May 14, 2007.
* Address correspondence to Dr Cerfolio, Division of Cardiothoracic Surgery, University of Alabama at Birmingham, 703 19th St S, ZRB 739, Birmingham, AL 35294 (Email: robert.cerfolio{at}ccc.uab.edu).
Presented at the Poster Session of the Forty-third Annual Meeting of The Society of Thoracic Surgeons, San Diego, CA, Jan 29–31, 2007.
| Abstract |
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Methods: This retrospective cohort study used a prospective database of patients who underwent neoadjuvant chemoradiotherapy, an initial and repeat FDG-PET/CT scan, and pathologic staging. The accuracy of the clinical stage suggested by repeat FDG-PET/CT was compared with the actual pathologic stage. Receiver operating characteristic (ROC) curves were used to determine when it was most accurate to repeat the FDG-PET/CT after the completion of the last dose of chest radiation.
Results: The study comprised 109 patients, 93 of whom patients received 60 Gy (or higher) of radiotherapy. The median time to restaging was 24 days (range, 2 to 88 days). ROC analysis showed the optimal time to restage patients was 26 days for overall staging (area under the curve [AUC], 0.88) and 29 days for N2 restaging (AUC, 0.82). The accuracy for overall stage was 3 (38%) of 8 for patients for less than 10 days, 28 (72%) of 39 for patients between 11 and 20 days, 42 (88%) of 49 between 21 and 30 days, and 8 (62%) of 13 for 31 days or more. The accuracy for these time intervals for the restaging of the N2 lymph node was 50% (1/2) 40% (2/5), 88% (7/8), and 100% (3/3), respectively.
Conclusions: The optimal time to perform a repeat FDG-PET/CT scan after the completion of neoadjuvant chemotherapy and high-dose radiotherapy to maximize its accuracy for restaging patients with NSCLC is about 1 month after the last dose of radiation.
| Introduction |
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The role of 2-fluoro-2-deoxy-D-glucose (FDG) positron emission tomography (PET) in clinically staging patients initially with NSCLC is well known [2–6]. The role of PET for restaging is also well described and it helps guide further therapy as well as patient selection for surgery [7]. External beam radiation can cause false-positive results on the restaging PET scan [8, 9]. The best time to repeat the PET to maximize its accuracy for predicting the pathologic stage is unknown. The purpose of this study was to determine the ideal time to repeat a PET scan in patients with NSCLC who underwent induction chemoradiotherapy.
| Patients and Methods |
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Radiologic Imaging
Initial staging was performed as described at length by us previously [5]. Briefly, patients had chest CT with intravenous contrast and integrated FDG-PET/CT scans performed on an integrated PET/CT scanner (GE Discovery LS PET-CT Scanner, Milwaukee, WI). Patients were asked to fast for 4 hours and then received 555 MBq (15 mCi) of FDG intravenously, followed by positron emission tomography (PET) after 1 hour. The scans were performed from the skull base to midthigh level. The CT examination was used for attenuation correction of PET images. The scanning time for emission PET was 5 min per bed position. Iterative reconstruction with CT attenuation correction was performed. The most recent CT scan of the chest was also available for visual correlation. Maximum standardized uptake value (maxSUV) of the primary and of each suspicious lymph node station (greater than 2.5) was determined by drawing regions of interest (ROI) on the attenuation corrected FDG-PET images around it. It was then calculated by the software contained within the PET or PET/CT scanner by the formula [10]
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Staging and Restaging
All patients were thoroughly initially clinically staged and pathologically staged before neoadjuvant therapy, as we have described [5], and their tumor (T), node (N), and metastasis (M) stage was recorded. Patients were then carefully restaged clinically and pathologically after the completion of the neoadjuvant chemoradiotherapy also as we have previously described [11] using the T, N, and M classification system [5, 12]. This is partially outlined in Figure 1.
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In general, we plan for doses of 60 to 66 Gy of radiotherapy. The initially positive node is then rebiopsied using repeat endoscopic ultrasound-guided fine-needle aspiration (EUS-FNA) for lymph node stations 4R and 4L (in some patients) and stations 7, 8, and 9 and using video-assisted thoracoscopy for stations 2R, 5, and 6, or open thoracotomy, or both, as previously described at length [5]. If down-staged or if appropriate, or both, patients then underwent thoracotomy, pulmonary resection, and complete thoracic lymphadenectomy. Complete thoracic lymphadenectomy is defined as complete removal (not biopsy) of all visible nodes in the chest; in the right chest, these are lymph node stations 2R, 4R, 7, 8, 9, and the appropriate N1 nodes, and in the left chest, they are stations 4L, 5, 6, 7, 8, 9, and appropriate N1 nodes. Operations were performed within 40 days of the repeat staging studies. Pathologic review was performed with standard techniques, and immunohistochemical staining was used in selected cases at the pathologists discretion.
Definitions
A patient was defined as having unsuspected N2 disease (false negative) if the integrated FDG-PET/CT scan did not suggested cancer in any of the N2 nodes but the patient had pathologic proof of metastatic NSCLC cancer in at least one N2 node. A patient was similarly defined as having a false-positive result if the integrated FDG-PET/CT scan suggested metastatic NSCLC in a specific N2 nodes but the pathologic examination showed the patient did not have disease in that node.
The accuracy of the T status was similarly determined by the false positives and false negatives; however, for calculation of T status and overall accuracy, T1 and T2 were considered the same and T3 and T4 were considered the same. In addition, if the pathologic T was greater than the PET-predicted T, it was called a false negative; for instance, if the FDG-PET suggested a tumor was T2 but after resection it was T3 or T4, this was considered a false negative. If the pathologic T was less than the predicted T, this was called a false positive.
Operative morbidity and mortality was defined as any morbidity or mortality occurring during the hospital stay or within 30 days after discharge from any cause.
Statistical Methods
Analysis was performed using SAS 9.0 (SAS Inst, Cary, NC). Accuracy, defined as true-negative plus the true-positive results divided by the sum of all true and false results, was determined for FDG-PET/CT using the pathology or biopsy results as the gold standard [14]. Receiver operating characteristic (ROC) curves were generated to identify the optimal cut point at maximal sensitivity and specificity from our data.
| Results |
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| Comment |
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There are several theories concerning the effect of radiation on PET scans. The inflammatory effect of radiation may obscure tumor-specific metabolic changes [19]. Others have hypothesized that radiotherapy may trigger an initial increase in glucose metabolism by the tumor cells. Higashi and colleagues [20] found a 9.7-fold increase in FDG uptake in a human ovary adenocarcinoma cell line during days 0 to 12 after low-dose irradiation (30 Gy). Schneeweiss and colleagues [21] observed an increase in FDG uptake by human glioblastoma cells of 11.3% immediately after radiation. Most studies show that radiation leads to false-positive results and an increase in the maximum standardized uptake values. This concept is often discussed and is well recognized by nuclear radiologists, but data are lacking on this type of ill effect of radiation on PET in patients with NSCLC.
We, and others, have shown that the change in the maxSUV is a predictor not only of the pathologic response of the primary pulmonary tumor but also of the mediastinal lymph nodes [22]. The repeat PET helps guide therapy and which area to biopsy based on the change in the maxSUV of previously biopsy-proven areas. The restaging PET should thus be performed on the same scanner as the initial study to help minimize the confounders that can affect the maxSUV. Among the factors that conspire to affect the maxSUV have been described and include the well that counts the amount of FDG given, the techniques of scanning, the amount of delivered FDG, and the patients glucose level.
The standardizing of techniques for PET scanning and rescanning are needed and are now well underway on national and international levels to allow for better comparison of the maxSUV from one center with results from another. Weber and colleagues [23] in 1999 showed the reproducibility of the maxSUV on the same machine. Thus for now, we still recommend that the repeat PET be done at the same center and in the same manner as the first PET scan.
The change in maxSUV may be altered by radiation. In this article, we have shown that the pathologic response rate after neoadjuvant chemoradiotherapy can be interpreted even after high-dose radiation, especially when the second PET scan is performed on the same scanner as the first. In 2004 [11], we showed that the higher the dose of radiation, the more difficult it is to interpret the change in the maxSUV, but one is still able to reliably interpret the repeat PET scan and the maxSUV values even after high dose (66 Gy) preoperative radiation.
We found in this study that the most accurate time to repeat the integrated PET/CT scan was 26 days. We performed a separate analysis for the accuracy of repeat PET to predict the pathology of the mediastinal (N2) lymph nodes and it was maximized at 29 days. We found an accuracy of 88% for both. This is remarkably high, especially when one views this result in light of the fact that the initial integrated PET/CT may only be accurate in about 50% of patients [5].
In this study, the repeat PET was thus more accurate than the initial PET. This result should not be surprising because the repeat PET has the advantage of all of the biopsy results of all areas suggestive for disease identified after the first PET. Thus, areas that were falsely positive on the first scan can now be eliminated on the repeat scan if the maxSUVs of these sites have fallen. Because it is our practice to investigate or biopsy all suggestive sites after the first PET scan, it is not surprising that the repeat PET is more accurate than the first because it "stands on the shoulders" of the initial scan.
Among the strengths of this study are that all patients underwent integrated PET/CT and not just a dedicated PET, and all were performed at one institution on one PET scanner. All patients underwent definitive biopsy or resection and thus all had pathologic confirmation. Finally, one surgeon entered all the data in a prospective database and also performed the staging and operations on all patients. This reduces the confounding variables of the study.
The primary limitation of this study is that we did not examine a continuous interval of days between the last dose of radiation and the repeat PET scan. To state what day is truly the best time to repeat the PET, patients should have received a repeat PET scan each day after the completion of their radiation and had their pathology checked each day as well. This was not done because it is not clinical practical. Finally, the treating oncologist ordered the repeat scans for some patients and thus some scans were ordered sooner or later than we may have preferred. This fact, however, allowed us to perform this study.
The clinical impact of accurate restaging cannot be understated. For example, if a patient has a right upper lobe NSCLC and a biopsy-proven metastatic N2 4R paratracheal mediastinal lymph node and the maxSUV of that node decreases by greater than 50% after repeat PET, we now go directly to thoracotomy if the result of endobronchial ultrasound-guided biopsy (EBUS) specimen of that node is negative. We no longer start off with a video-assisted approach to biopsy the 4R station before thoracotomy.
Another example is the test we select to biopsy the lymph node. If the reduction in a paraesophageal (station 8) lymph node is less than that in a paratracheal lymph node, then we will choose endoscopic EUS-FNA instead of EBUS.
A final potential important concept of the change in the maxSUV concerns several new multiinstitutional studies that may randomize patients who are "complete responders" to surgery versus observation. One was never able to truly predict who was a complete responder before the change in the maxSUV data was presented. The accuracy of restaging is needed for that study to be correctly done to truly know who is a complete responder.
In conclusion, we have shown that the optimal time to perform a repeat integrated FDG-PET/CT scan after the completion of neoadjuvant chemoradiotherapy using high doses of 60 Gy or more in patients with NSCLC is about 1 month.
| References |
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This article has been cited by other articles:
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R. J. Cerfolio, A. S. Bryant, V. L. Jones, and R. M. Cerfolio Pulmonary resection after concurrent chemotherapy and high dose (60 Gy) radiation for non-small cell lung cancer is safe and may provide increased survival Eur. J. Cardiothorac. Surg., April 1, 2009; 35(4): 718 - 723. [Abstract] [Full Text] [PDF] |
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R. J. Cerfolio, A. S. Bryant, A. A. Talati, R. M. Cerfolio, and T. S. Winokur Change in maximum standardized uptake value on repeat positron emission tomography after chemoradiotherapy in patients with esophageal cancer identifies complete responders. J. Thorac. Cardiovasc. Surg., March 1, 2009; 137(3): 605 - 609. [Abstract] [Full Text] [PDF] |
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W. A. Weber The Use of Positron Emission Tomography versus Computerized Tomography Scans in the Assessment of Response to Therapy ASCO Educational Book, January 1, 2009; 2009(1): 474 - 478. [Abstract] [Full Text] [PDF] |
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