Improved accuracy of image guided radiation therapy (IMRT) based on bone suppression technique

Purpose: A recently developed image processing methodology, the bone suppression technique, can suppress the conspicuity of bones on chest radiographs, creating sort of soft-tissue images obtained by the dual-energy subtraction technique. This study was performed to evaluate the usefulness of bone suppression fluoroscopy in real-time tracking radiation therapy. Methods and Materials: Dynamic chest radiographs of 9 patients with lung nodules during respiration were obtained using a flat panel detector (FPD) system (CXDI-50RF; Canon Inc.) (120 kV, 0.1 mAs/pulse, 5 fps, SID = 1.0 m). Commercial bone suppression image-processing software (Clear Read Bone Suppression; Riverain Medical) was applied to the dynamic chest radiographs to create corresponding bone suppression images. Automatic target tracking was conducted with in-house software based on the template matching technique. To evaluate the accuracy of target tracking, the maximum tracking error in the resulting images was compared between bone suppression and conventional fluoroscopic images. Results: The accuracy of target tracking was significantly improved in 8 of 9 cases. The average maximum tracking errors in bone suppression and conventional fluoroscopic images were 1.3± 1.0 mm and 3.3± 13.3 mm, respectively. The bone suppression technique was especially effective in the lower lung area where pulmonary vessels, bronchi, and ribs showed complex movements. Conclusion: The bone suppression technique improves tracking accuracy without special equipment and additional patient dose in real-time tracking radiation therapy. Our results indicated its usefulness especially in the lower lung area with complex movements of lung structures and ribs.