Utilization of PET-CT in target volume delineation for three-dimensional conformal radiotherapy in patients with non-small cell lung cancer and atelectasis

BACKGROUND: To investigate the utilization of PET-CT in target volume delineation for three-dimensional conformal radiotherapy in patients with non-small cell lung cancer (NSCLC) and atelectasis. METHODS: Thirty NSCLC patients who underwent radical radiotherapy from August 2010 to March 2012 were included in this study. All patients were pathologically confirmed to have atelectasis by imaging examination. PET-CT scanning was performed in these patients. According to the PET-CT scan results, the gross tumor volume (GTV) and organs at risk (OARs, including the lungs, heart, esophagus and spinal cord) were delineated separately both on CT and PET-CT images. The clinical target volume (CTV) was defined as the GTV plus a margin of 6-8 mm, and the planning target volume (PTV) as the GTV plus a margin of 10-15mm. An experienced physician was responsible for designing treatment plans Plan(CT) and Plan(PET-CT) on CT image sets. 95% of the PTV was encompassed by the 90% isodose curve, and the two treatment plans kept the same beam direction, beam number, gantry angle, and position of the multi-leaf collimator as much as possible. The GTV was compared using a target delineation system, and doses distributions to OARs were compared on the basis of dose-volume histogram (DVH) parameters. RESULTS: The GTV(CT) and GTV(PET-CT) had varying degrees of change in all 30 patients, and the changes in the GTV(CT) and GTV(PET-CT) exceeded 25% in 12 (40%) patients. The GTV(PET-CT) decreased in varying degrees compared to the GTV(CT) in 22 patients. Their median GTV(PET-CT) and median GTV(PET-CT) were 111.4 cm(3) (range, 37.8 cm(3)-188.7 cm(3)) and 155.1 cm(3) (range, 76.2 cm(3)-301.0 cm(3)), respectively, and the former was 43.7 cm(3) (28.2%) less than the latter. The GTV(PET-CT) increased in varying degrees compared to the GTV(CT) in 8 patients. Their median GTV(PET-CT) and median GTV(PET-CT) were 144.7 cm(3) (range, 125.4 cm(3)-178.7 cm(3)) and 125.8 cm(3) (range, 105.6 cm(3)-153.5 cm(3)), respectively, and the former was 18.9 cm(3) (15.0%) greater than the latter. Compared to Plan(CT) parameters, Plan(PET-CT) parameters showed varying degrees of changes. The changes in lung V(20), V(30), esophageal V(50) and V(55) were statistically significant (Ps< 0.05 for all), while the differences in mean lung dose, lung V(5), V(10), V(15), heart V(30), mean esophageal dose, esophagus Dmax, and spinal cord Dmax were not significant (Ps> 0.05 for all). CONCLUSIONS: PET-CT allows a better distinction between the collapsed lung tissue and tumor tissue, improving the accuracy of radiotherapy target delineation, and reducing radiation damage to the surrounding OARs in NSCLC patients with atelectasis.