Four-Dimensional Dosimeter and Quality Assurance Phantom for Adaptive Radiation Therapy
T Meyers1*, N Alsbou2, S Ahmad 1, I Ali1, (1) University of Oklahoma Health Sciences, Oklahoma City, OK,(2) Department of Engineering and Physics, University of Central Oklahoma, Edmond, OK.
Presentations
PO-GePV-M-72 (Sunday, 7/25/2021) [Eastern Time (GMT-4)]
Purpose: To develop a 4D-dosimeter and quality assurance phantom to quantify the effects of respiratory motion on 3D-optimized dose distributions and provide dose verification of futuristic 4D-optimized treatment plans and dose calculation algorithms.
Methods: Dose distributions were measured with a MapCheck2 phantom that was placed on a mobile platform that can move with different motion patterns with adjustable motion amplitude and frequency. This motion phantom was used to measure the dose distributions optimized and calculated in 3D including conformal, IMRT and VMAT plans. The dose distributions were measured with this phantom system static and moving with different motion amplitudes (5-35mm) to quantify motion artifacts on the dose distributions.
Results: Respiratory motion can lead to large dose discrepancies that depends on the patient motion pattern. The increase in motion amplitudes results more blurring in the dose distribution with an increased dose deficit in the tumor and increased dose deposition in the surrounding normal tissue. For a conformal open field plan, the dose profiles changed around the 50% isodose line, with increasing dose spelling outside the field for increasing motion amplitudes 5-35mm. The central axis dose and the surrounding flat region remained unchanged. However, for an intensity modulated plan, the motion artifacts affected the dose distribution overall with underdosing in the treatment planning volume and overdosing outside the treatment field.
Conclusion: This mobile dosimeter and phantom system provided a powerful tool for quantifying the dose deviations induced by cyclic motion on 3D optimized dose distributions. 4D-optimized dose distribution provides and alternative technique for the management of respiratory motion to conventional techniques such as breath holding and beam gating. This 4D phantom will be a necessary dosimetric tool that can be used for the verification of dose distribution calculated by 4D-optimization and dose calculation algorithms to achieve the goals of adaptive radiation therapy.
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