Program Information
Spatial Resolution Requirements for Fragment Identification in a Carbon Ion Spread Out Bragg Peak
R McBeth*, T Borak , Colorado State University, Fort Collins, CO
Presentations
SU-E-T-709 (Sunday, July 12, 2015) 3:00 PM - 6:00 PM Room: Exhibit Hall
Purpose: To determine spatial resolution for detectors used to identify charged fragments in a carbon ion therapy spread out Bragg peak.
Methods: The Geant4 Monte Carlo toolkit was used to simulate a 2 x 2 cm² broad beam of carbon ions incident on a 30 x 30 x 12 cm³ water phantom. The carbon ion energies ranged from 165 MeV/n to 220 MeV/n and intensities were selected in order to simulate a SOBP extending from 6 to 10 cm in depth. Scoring of secondary fragments was performed for different pixel sizes at 3 depths in water. The analysis was designed to identify situations where two or more fragments intercept a pixel coincidently.
Results: Initial results show that increased depths in the phantom require smaller pixel sizes due to increases in fragment population. At a pixel size of 1 x 1 cm², a detector pixel was intercepted by two or more particles 16%, 14% and 30% percent of the time at depths of 6, 8 and 10 cm respectively. The probability of coincident hits decreases with smaller pixel size. At a pixel size of 0.05 x 0.05 cm² a detector pixel was intercepted by two or more particles 0.7%, 0.9%, and 2% of the time at depths of 6, 8 and 10 cm respectively.
Conclusion: Accurate characterization of carbon ion beams requires the consideration of secondary charged particles that have different radiobiological effectiveness. A method for accurate identification in a clinical setting could lead to improved models for treatment planning. This work investigated the spatial resolution requirements for a detector that could be used to perform secondary fragment identification in a spread out Bragg peak. These preliminary results show that detectors with pixel size on the order of 0.5 x 0.5 mm² may be sufficient.
Funding Support, Disclosures, and Conflict of Interest: This work was supported through research grant NNX13AD19G for Early Stage Innovations (ESI) administered through the NASA Space Technology Research Grants Program. No conflict of interest.
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