Assessing ITV and PTV Coverage for Mobile Tumors with Real-Time Fluoroscopy Imaging
K Mooney*, S Chen, S Feigenberg, W D'Souza, University of Maryland School of Medicine, Baltimore, MDSU-C-141-3 Sunday 1:00PM - 1:55PM Room: 141
Purpose: To evaluate the appropriateness of the internal target volume (ITV) and planning target volume (PTV) generated based on 4DCT simulation using real-time kV fluoroscopic imaging.
Methods: 4DCT scans of a moving (3D) phantom with implanted fiducials were acquired using three-dimensional lung tumor locations derived from Cyberknife Synchrony system log files. Data from 5 patients consisting of tumor trajectories derived from the Synchrony model and from three different treatment fractions were used in this analysis. All patients in this study had a peak-to-peak respiratory amplitude between 7-15mm. The fiducials were contoured on ten phases of the 4DCT scans, and ITVs and PTVs (ITV+5mm) were created for each marker. Fluoroscopic images were acquired for all trajectories at a rate of 15Hz for 20-30 seconds in two imaging planes: anterior-posterior and lateral. The markers were tracked using the Varian Intra-fraction Motion Review (IMR) software, using a reference movie frame in which marker locations were matched against their corresponding positions on the DRR. The tracked marker positions were classified as within the ITV, between the ITV and the PTV, and outside the PTV in each frame.
Results: The fiducial was detected inside of the ITV in 82.4% (71.7%) of frames in the lateral plane (AP plane), between the ITV and PTV in 17.4% (28.0%) of lateral (AP) frames, and detected outside the PTV in 0.2% (0.3%) of lateral (AP) frames. When the marker was between the ITV and the PTV, the distance from marker to ITV was >3mm in 21% (27%) in lateral (AP) plane images.
Conclusion: We have developed a method to quantify the degree to which the planned ITV and PTV encompass the extent of tumor motion. The tumor was detected outside of the ITV more often in the AP-plane of imaging, and detected within the PTV in nearly all cases.
Funding Support, Disclosures, and Conflict of Interest: Varian Medical Systems