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Using Dual Step Wedge and 2D Scintillator to Achieve Highly Precise and Robust Proton Range Quality Assurance

W Deng*, W Liu , D Robertson , M Bues , T Sio , S Keole , J Shen , Mayo Clinic Arizona, Phoenix, AZ


(Tuesday, 7/31/2018) 4:30 PM - 6:00 PM

Room: Karl Dean Ballroom C

Purpose: To develop a fast method for proton range quality assurance (QA) using a dual step wedge and 2D scintillator and to evaluate the robustness, sensitivity, and long term reproducibility of this method.

Methods: An in-house customized dual step wedge and a 2D scintillator were developed to measure proton ranges. Proton beams with homogenous fluence were delivered through wedge and the images captured by the scintillator were used to calculate the proton ranges by a simple trigonometric method. The range measurements of 97 energies, comprising all clinically available synchrotron energies at our facility (ranges varying from 4 to 32.6 cm), were repeated 10 times in all four gantry rooms for range baseline values. They were then used for evaluating room-to-room range consistencies. The robustness to setup uncertainty was evaluated by measuring ranges with ±2mm setup deviations in the x, y, and z directions. The long term reproducibility was evaluated by one month of daily range measurements by this method.

Results: Ranges of all 97 energies were measured in less than 10 minutes including setup time. The reproducibility in a single day and daily over one month is within 0.1mm and 0.15mm, respectively. The method was very robust to setup uncertainty, with measured range consistencies within 0.15mm for ±2mm couch shifts. The method was also sensitive enough for validating range consistency among gantry rooms and for detecting small range variations.

Conclusion: The new method of using a dual step wedge and scintillator for proton range QA was efficient, highly reproducible, and robust. This method of proton range QA was highly feasible, and appealing from a workflow point of view.

Funding Support, Disclosures, and Conflict of Interest: This research was supported by the Kemper Marley Foundation and Arizona Biomedical Research Commission Investigator Award.


Protons, Quality Assurance, Scintillators


TH- External Beam- Particle therapy: Proton therapy - quality assurance

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