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

https://doi.org/10.1016/S0167-8140(00)00138-9Get rights and content

Abstract

Purpose: 18F-fluoro-2-deoxy-d-glucose positron emission tomography (FDG-PET) combined with computer tomography (PET-CT) is superior to CT alone in mediastinal lymph node (LN) staging in non-small cell lung cancer (NSCLC). We studied the potential impact of this non-invasive LN staging procedure on the radiation treatment plan of patients with NSCLC.

Patients and methods: The imaging and surgical pathology data from 105 patients included in two previously published prospective LN staging protocols form the basis for the present analysis. For 73 of these patients, with positive LN's on CT and/or on PET, a theoretical study was performed in which for each patient the gross tumour volume (GTV) was defined based on CT and on PET-CT data. For each GTV, the completeness of tumour coverage was assessed, using the available surgical pathology data as gold standard. A more detailed analysis was done for the first ten consecutive patients in whom the PET-CT-GTV was smaller than the CT-GTV. Theoretical radiation treatment plans were constructed based on both CT-GTV and PET-CT-GTV. Dose-volume histograms for the planning target volume (PTV), for the total lung volume and the lung volume receiving more than 20 Gy (Vlung(20)), were calculated.

Results: Data from 988 assessed LN stations were available. In the subgroup of 73 patients with CT or PET positive LN's, tumour coverage improved from 75% when the CT-GTV was used to 89% with the PET-CT-GTV (P=0.005). In 45 patients (62%) the information obtained from PET would have led to a change of the treatment volumes. For the ten patients in the dosimetry study, the use of PET-CT to define the GTV, resulted in an average reduction of the PTV by 29±18% (±1 SD) (P=0.002) and of the Vlung(20) of 27±18% (±1 SD) (P=0.001).

Conclusion: In patients with NSCLC considered for curative radiation treatment, assessment of locoregional LN tumour extension by PET will improve tumour coverage, and in selected patients, will reduce the volume of normal tissues irradiated, and thus toxicity. This subgroup of patients could then become candidates for treatment intensification.

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

References (20)

There are more references available in the full text version of this article.

Cited by (0)

View full text