The impact of 18F-fluoro-2-deoxy-d-glucose positron emission tomography (FDG-PET) lymph node staging on the radiation treatment volumes in patients with non-small cell lung cancer
Introduction
In patients with non-small cell lung cancer (NSCLC), considered for radiation treatment, accurate assessment of hilar and mediastinal lymph node (LN) involvement is of utmost importance. The extent of the tumour will not only influence the treatment intention, i.e. curative or palliative, but also the volumes to be treated and, therefore, the toxicity to be expected. Indeed, several authors have suggested that a dose-volume effect for radiopneumonitis exists [6], [8], [9], [10]. Different parameters, derived from dose-volume histograms (DVH's), have been correlated with the incidence of pneumonitis observed, e.g. Vlung(20) or the percentage of the total lung volume receiving more than 20 Gy [6], ,Veff, the effective uniform whole lung dose that would lead to the same probability of pneumonitis [10] and NTDmean, the mean dose to the lung [8]. At the moment, the ability of these parameters to predict the rate of pneumonitis and to guide dose escalation protocols is being assessed in prospective studies [4], [13]. Every measure to limit the volume of normal tissues irradiated, could improve the therapeutic index and could increase the possibility of dose escalation or combined chemo–radiation treatment.
In recent years, 18F-fluoro-2-deoxy-d-glucose positron emission tomography (FDG-PET) in combination with chest computer tomography (CT) has been shown by several authors to improve the accuracy of mediastinal LN staging compared to CT alone [1], [12], [14], [15], [16], [20]. Prompted by the limited data available at the time, the Respiratory Oncology Unit of the Leuven University Hospital, started a prospective study in 1995, to compare the value of CT vs. PET visually correlated with CT (PET-CT) in the loco-regional LN staging of patients with potentially operable NSCLC. The results of the first 68 patients, with 690 LN levels evaluated, clearly established the superiority of combined PET-CT assessment of the mediastinum [18].
In the present paper, the data from 105 patients, enrolled in two previously reported consecutive prospective studies [18], [19], are the basis for a theoretical study, where the possible impact of additional PET information on radiation treatment parameters is examined.
Section snippets
Patients
The LN imaging and surgical pathology data set from two previously reported prospective studies [18], [19], on the role of PET in the loco-regional LN staging in potentially operable NSCLC, was used for the present analysis. The first study included 68 patients and compared the accuracy of CT to the accuracy of PET visually correlated with CT [18]. The second one investigated the additional value of anatometabolic PET-CT fusion images in 56 patients [19]. Due to a slight overlap in inclusion
Results
Imaging and surgical pathology data of 988 LN stations from 105 patients were available for analysis.
As stated earlier, the present theoretical radiotherapy study is based on the data of two prospective studies, previously published [18], [19], evaluating the effectiveness of CT compared with CT combined with PET in assessing the locoregional LN tumour extent in NSCLC patients. The compiled results of both studies are summarized in Table 1, showing the correlation between nodal size on CT,
Discussion
In recent years, several groups including ourselves, have pointed at the superiority of FDG-PET, compared with CT, to accurately identify the presence or absence of mediastinal LN involvement in patients with NSCLC [1], [12], [14], [15], [16], [18], [19], [20].
These data are generally used to define and modify the indications and modalities of invasive surgical staging or treatment. They could, however, also be used to define target volumes for radiation treatment [7], as is done in the present
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