Impact of PET-CT image coregistration accuracy on radiation treatment planning for non-small cell lung cancer

Objective To evaluate the accuracy of image coregistration of FDG PET-CT image and the its impact on radiation treatment planning in non-small cell lung cancer(NSCLC). Methods Thirteen patients with well-circumscribed NSCLC lesions were examined by in-line PET-CT . The registration accuracy of PET-CT image was measured with two methods-volume and center of geometry (COG). The volume of interest of each lesion was defined separately on PET, CT and fused images (V_ PET , V_ CT , V_ PET+CT ). The overlap volume of PET and CT image was calculated from formula: V_ PET-CT =V_ PET +V_ CT -V_ PET+CT . The percentage of V_ PET-CT on V_ PET+CT (P_ PET-CT ) was used to assess the fusion accuracy of PET and CT images. The geometric center of gravity (COG) of V_ PET and V_ CT was assessed. The COG distance between the PET image and the CT image (D_ COG ) was measured. The image data were transferred to the radiation treatment planning system. Three plans were made according to different volumes (V_ PET , V_ CT , V_ PET+CT ) with the same prescribed dose of 60?Gy. The dose in lung, heart and spinal cord were recorded in plans and compared with one another. Results The mean of D_ COG was (4.95± 2.41 )?mm(1.00- 8.68?mm ). P_ PET-CT was 46.7%±19.2%(2.7%-70.4%). Misregistration tended to be more pronounced in the lower lung (D_ COG = [4.73±2.50] ?mm, P_ PET-CT =52.0%±23.6%) than in upper lung (D_ COG = [5.21±2.51] ?mm, P_ PET-CT =40.5%±11.4%) (P0.05). The dose to lung (mean lung dose and V_ 20 ),maximal dose to spinal cord ,mean and maximal dose to the heart were higher in plans with V_ PET+CT than in those with V_ PET and V_ CT (P0.05), but statistical difference was not found among the mean spinal cord doses in the three plans (P= 0.05 ). Conclusions The registration of lung lesion in PET-CT image is usually accurate. Misregistration may exert on the target volume delineation in radiation treatment planning with PET-CT fused image for non-small cell lung cancer and result in higher dose to normal tissue. More precise measurement and control of the misregistration must be taken into account when fused PET-CT image were used in making radiotherapy planning.