Validating Delivered Dose In a 3D Printed Phantom Using Surface Guided Gating
Abstract
Purpose
The purpose of this project was to create and use a moving 3D printed phantom to validate delivered dose to a moving target when using surface guidance based beam gating. Surface guidance systems are widely used to automatically do beam hold gating, and this phantom allows direct measurement of treatment planning system calculated doses.
Methods
The phantom was designed to mimic a patient chest surface, with hidden lung lesions. The entire assembly fits over a standard Varian RPM motor, allowing the chest and target lesion to move up and down. The phantom was 3D printed in PLA plastic with 3D printed tabs connecting the different plates where needed. The phantom was designed to be able to hold both a farmer chamber and a diamond detector in different sized lung lesion inserts. The phantom was simulated without motion to imitate the breath hold state, and treatment plans were created for both target sizes. Using surface guidance to gate the beam, each plan was then delivered to the moving phantom, and delivered doses were compared with TPS planned doses.
Results
The phantom motion and tracking with surface guidance worked as intended. The delivered dose to the larger chamber planned with standard fractionation measured 202.8 cGy compared to the TPS calculated dose of 199.4 cGy, a 1.7% error. The smaller SBRT style target and plan with a diamond detector measured a delivered dose of 1012.9 cGy vs a TPS calculated dose of 1005.1 cGy, a 0.77% error.
Conclusion
The phantom was successful and proved to be a useful device for validating surface guidance based beam control gating. Future work could include using this phantom to more accurately determine proper gating windows or including more erratic breathing rhythms.