Effect of radiotherapy planning using different methods PET-CT defining the target volumes for lung cancer patients

Abstract

Objective To investigate the effect of target volume and normal tissues dose in lung cancer patients with PET-CT of different delineation methods. Methods Two patients were, chosen. After PET-CT scan, the images were transferred to the radiotherapy planning system (Varian Eclipse) for images fusion and treatment planning design. The three gross tumor volumes (GTVs) were defined using a threshold value of 50% of Kmax of the whole lesion(GTV50 ), a threshold value of 40% of Kmax of the whole lesion (GTV40) and a threshold value of SUV = 2.5 (GTV2.5 ), respectively. The Kmax was the maximum voxel value of PET activity (Bq/ml) . The planning target volumes (PTVs) were obtained by addition of an 1.5 cm around the GTV. The normal tissues were defined, including the total lung and spinal cord. Dose distribution was computed for the other two PTVs. Plans were compared using dose volume histograms for lung and spinal cord. Results The results of three methods were different in two patients. The GTVs were 23.1,34.9,49.2 cm3 and 58.1,80.3,163.4 cm3, respectively. The PTVs were 169.5, 222.1, 261.9 cm3 and 286.8, 349.7, 560.5 cm3,respectively. The percentages of whole lung that received a dose of 20 Gy or more were 14.4%, 17.2%, 19.5% and 15.2% ,16.0%, 20.2% ,respectively. The mean lung dose were 16.2%, 19.4% ,21.4% and 12.7%,4.4%, 19.4%. The doses of ≤1 cm3 spinal cord were 30.6% ,34.3% ,44.9% and 27.3% ,35.2% ,67.1%.Conclusions The effect of target volume and normal tissues dose in lung cancer patients with PET-CT of different delineation methods were significant. The threshold value that can cover tumor more completely should be used to define target volumes for radiotherapy when the normal tissues can accepted tolerance dose. Key words: Lung neoplasms; Radiotherapy; Positron emission tomography; X-my computed tomography; Targct volume delineation