SU-E-J-46: Use of Brainlab-ExacTrac IGRT with Dot-Decimal Electron Compensator(BolusECT) for Accurate Patient Positioning.

PURPOSE To Validate Brainlab-ExacTrac IGRT with Dot-Decimal electron compensator(BolusECT) for accurate patient positioning. METHODS Dot-Decimal electron compensators(BolusECT) are used to achieve conformal dose distributions and greater sparing to normal structures for cases with varying patient contours and treated with single electron beam.Setup for such patients is difficult to verify due to the small clearance between theelectron-cone and bolus. Hence additional verification is needed for fast setup to avoid discomfort for the patient. In this study we have explored theuse of Brainlab-ExacTrac IGRT system for such setups.A Preplan isrequired to construct the BolusECT and a post-plan is used for verifying the treatment plan. Before the patient is scanned again with BolusECT for post-plan, tungsten BBs were drilled in the Bolus at different depths and the holeswere filled with wax. Tungsten-BBs have high density and avoid high cost ofgold seeds.A wax phantom and BolusECT were scanned with BBs and a plan was generated. The plan was send to ExacTrac for DRR-generation.The Wax phantom with BolusECT was then set slightly off centered on thetreatment couch and the ExactTrac system was used to align the Phantom. The ExacTrac system was also tried on two patients for accurate setup. RESULTS The ExactTrac system correctly identified the tungsten-BBs and aligned the phantom within +1mm. The SSD was then verified and checked with the planned SSD.The SSD was found to be within +0.5mm. In both patient setups the ExacTrac system gave Lateral, Longitudinal and Vertical Shifts within +1mm and the SSD was found to be within +0.3mm of the planned SSD. CONCLUSIONS The BrainLab- ExacTrac IGRT system isan excellent,fast way of aligning the BolusECT. This avoids discomfort for patients by preventing longer setup times. Use of tungsten-BBs lowers the cost compared to gold seeds. Phantom verification should be performed before implementing this system for actual patient use. The SSDs must be verified after setup.