Visualization of dose distribution on the endobronchial surface using virtual bronchoscopy in carbon ion radiotherapy

Purpose: To estimate effects of carbon-ion radiotherapy on endobronchial tumor or epithelium, we developed the visualizing application of planning dose distribution on virtual bronchoscopic images. The comparison of tissue responses by actual bronchoscopic findings and planning dose distribution on virtual bronchoscopy would be important to evaluate the accuracy of irradiation and the dose response. We developed the software to superimpose the color map of planning dose distribution on virtual bronchoscopic images.Methods: Respiratory gated CT images using multi-detector CT scanner are taken for the patient of lung cancer. Treatment planning is performed to a set of gated CT images using a HIPLAN. Then the isocenter information file, dose distribution files at each filed and a set of CT volume file are inputted to application software of virtual bronchoscopy. We developed this application based on commercial software of virtual bronchoscopy (AZE Ltd. Virtual Place Advance Plus). Following the geometrical adjustment and interpolation with CT images and dose distribution, the 3-dimensional voxel data set is reconstructed. Each voxel is defined as x, y, z, CT value, and dose at each field. Using volume rendering technique, virtual bronchoscopic images are reconstructed. In proportion as the dose, pixels at endobronchial surface are visualized by color map. Results: Planning dose distribution at each filed or total filed was visualized on the endobronchial surface of virtual bronchoscopy, and was simultaneously displayed on axial, sagittal and coronal multiplanar reconstruction CT images, too. When the observing point on virtual bronchoscopy is moved in the 3-dimensional bronchoscopic image by interactive exploration, the bronchoscopic image with dose map was obtained in real-time. On each cross-sectional CT image, the location and the direction of the observing point were simultaneously displayed and moved in association with the bronchoscopic image. Thus we can observe the dose distribution at any point with any angle on virtual endobronchial surface. Conclusions: We developed the unique dose distribution display system on virtual bronchoscopy. This system is emerging as a useful approach for evaluation of bronchial dose response in comparison of actual bronchoscopic images.Particle Therapy Co-Operative Group PTCOG 4