Metabolic (FDG–PET) response after radical radiotherapy/chemoradiotherapy for non-small cell lung cancer correlates with patterns of failure☆
Introduction
It could be invaluable to have an early indication of the success of therapy in patients with non-small cell lung cancer (NSCLC) treated with definitive radical radiotherapy (RT) or chemoRT. If it was possible to anticipate future patterns of disease progression, selected patients could potentially benefit from additional therapy. CT scanning is currently the standard method for response assessment after radical RT but it suffers from well-known limitations. These limitations include dependence on the unreliable parameter of lymph node size to determine involvement by tumor [1] and an inability to distinguish between inactive scarring [2] or necrotic tumor and active tumor after therapy [3]. These limitations are exacerbated by the presence of radiation pneumonitis [4] and atelectasis.
In a previous study of 73 patients with NSCLC, we demonstrated that positron emission tomography (PET) using 18F-fluorodeoxyglucose (FDG) is superior to conventional imaging with CT scanning for response assessment after radical RT/chemoRT [5]. Response assessments made with FDG–PET and CT were identical in only 40% of cases. PET showed a much higher rate of complete response than CT. Additionally, PET response (or metabolic response) was much more powerfully correlated with survival than CT response using WHO criteria [6], stage or Eastern Co-Operative Oncology Group (ECOG) performance status (p < 0.0001).
There have to date been no published data on the long-term survival prospects for patients who attain complete or partial metabolic responses to RT, although it is already clear that those in the progressive disease category typically have very short survival. Patients who attain complete metabolic response on PET have no detectable disease and in our earlier report had superior survival compared to those in other response categories. However, because PET cannot detect microscopic volumes of residual disease, prolonged follow up is required to estimate the proportion of complete responders who ultimately attain durable locoregional disease control. Similarly no data have previously been published on the patterns of failure that occur in the different metabolic (PET) response categories.
In this paper, we describe the patterns of failure seen in a cohort of patients who underwent restaging PET scans after radical RT/chemoRT for NSCLC. This series includes the 73 patients described in our initial report and updates their survival. It also includes an additional 15 NSCLC patients treated with radical RT/chemoRT who had both staging and restaging PET scans.
Section snippets
Patients
FDG–PET scanning was performed as part of a prospective study of the value of functional imaging in NSCLC at the Peter MacCallum Cancer Centre (PMCC). This study was initiated in 1996, was approved by the institutional clinical research and ethics committees and was in accordance with the Helsinki declaration of 1975, revised 1983. Patients described in this report had NSCLC treated with radical radiotherapy or chemoradiotherapy and had undergone both staging and elective post-treatment 18FDG
Patient characteristics and responses
The characteristics of the patients in the various response groups are given in Table 1. Most patients (n = 62, 70%) had stage III disease and few had weight loss > 10% of body mass (n = 4, 5%) or ECOG status worse than 1 (n = 12, 14%). Platinum-based chemotherapy was given concurrently with radiotherapy in 73 patients. Standard chemotherapy during the study period (and given to 54 patients) was single agent carboplatin [9]. Other patients received cisplatin/taxol (n = 7) [10] or
Discussion
The results of this study confirm our early reports that FDG PET response (or as it is becoming more widely known, “metabolic response”) assessment after radical RT or chemoRT provides powerful prognostic information. With longer follow up and a larger cohort of patients, it is clear that the differences in survival between the different response categories are maintained over time. Additionally, this study provides new information on the patterns of failure in the different response
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These data were presented at the 45th Annual Meeting of the American Society for Therapetic Radiology and Oncology, Salt Lake City UT, October 2003.