SU‐GG‐T‐543: 4D Imaging, Planning and Treatment with Cyberknife System

Abstract

Purpose: Complete 4D imaging, planning and treatment delivery for pancreatic cancer. Method and Materials: The patient was scanned using a GE CT scanner while recording respiratory excursion of the chest by monitoring an infrared reflector. Images and respiratory recordings were binned into 10 phases on a GE Advantage workstation. 4D animation was used to observe organ movement. Phase 5 was the most stable and selected as the primary planning CT for contouring on the Cyberknife system. Phases 0, 2, 4, 5, 6, 8 were sent to Cyberknife as a 4D CT with phase tags. Multiplan loaded the primary CT, RT structures and 5 phase tagged CTs. 2 gold seeds inside the pancreas PTV were identified in the primary CT and automatically propagated and registered in the 5 phases. Automatic deformable registration based on intensity was performed. Inverse simplex planning was performed and optimized to give 30Gy in 5 fractions to PTV (GTV+3 mm margin in all directions except toward the duodenum). Results: In the static plan, the 79% isodose‐line (30Gy, maximum 38Gy) covered 96% of the PTV. With organ movement assigned an equal weight for each phase the 79% isodose‐line (29.3Gy, maximum 37Gy) covered 91% of the PTV in the 4D plan. During treatment delivery, detectors monitored respiratory excursion of infrared reflectors that were placed on the chest of the patient and orthogonal x‐ray images were taken every 3 beams. The fiducial seeds were identified in the x‐ray images and correlated with the movement of the infrared reflectors. A movement prediction model of the seeds in Synchrony tracking guided the robot during radiation delivery. Conclusion: True 4D dose delivered by the Cyberknife tracking and delivery system by taking into account of organ motion can be estimated with 4D images and dose calculation during all phases of the respiratory cycle.