Room: Exhibit Hall
Purpose: The present paper is to investigate the geometric accuracy and stability of Calypso 4D electromagnetic localization system and attenuation of the electromagnetic array.
Methods: Implantable transponders and surface transponders were placed in QA phantom respectively, analyzed the localization precision by comparing Calypso measured and actual displacement of the phantom isocenter. The actual displacement of the phantom was generated by moving the accelerator couch in three dimensions. The phantom was rotated from -3Â°to 3Â°in Pitch, Roll and Yaw direction respectively by operating accelerator couch. Calypso system reports rotational differences with respect to couch angle. The attenuation of the electromagnetic array was evaluated by measuring the dose of solid water with and without electromagnetic array. The phantom isocenter at the same position was measured repetitively to assess stability of the system.
Results: The average localization shift and standard deviation was found to be 0.02Â±0.01cm for implantable transponders and 0.01Â±0.01cm for surface transponders. The system can report rotations accurately to within 1Â°. The attenuation through the electromagnetic array was measured to be within 2% for both 6MV and 10MV energies at gantry angles between 325Â°and 35Â°clockwise, the attenuation was measured to be within 3.4% at 305Â°and 55Â°gantry angles. The maximum localization excursions were within 0.03cm, the standard deviation of localization excursion was within 0.01cm in repeated measurements. The system was stable without any obvious glitches in localization.
Conclusion: The localization accuracy of the Calypso system is at submillimeter level stablely. The results indicate that the dose difference due to the placement of electromagnetic array is clinically insignificant. Calypso 4D electromagnetic localization system which is accurate and reliable can greatly improve the accuracy of radiotherapy. Routine quality assurance of this peripheral electromagnetic localization system should be performed to ensure accurate operation.
Funding Support, Disclosures, and Conflict of Interest: National Natural Science Foundation of China(61671230)