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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.

multidisciplinary respiratory medicine

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