(Monday, 7/30/2018) 3:45 PM - 4:15 PM
Room: Exhibit Hall | Forum 4
Purpose: To report a new method to predict stopping power ratio (SPR) of proton beam and investigate its accuracy based on hydrogen density in proton therapy.
Methods: The SPR’s of 22 materials were acquired from the National Institute of Standards and Technology (NIST) database and expressed as the linear relation of the hydrogen density (SPR-H). Proton ranges of nine tissue surrogate materials of CIRS (CIRS Tissue Simulation and Phantom Technology, VA, USA) tissue characteristic phantoms are determined using the SPR-H. The water equivalent distance (WED) of the materials are calculated from the Eclipse (Varian Medical Systems, Palo Alto, USA) treatment planning system (TPS). The results are compared to the measured values using a multilayer ionization chamber (MLIC). To further validate the SPR-H model and dose calculation reliability, a phantom setup was designed and irradiated for 9 plugs and for each plug, measured dose from ion chamber was compared to the TPS dose calculations based on SPR-H model.
Results: The agreement between calculated SPR and WED values from SPR-H model and measurements were within 3% for all surrogate tissues except lungs (~9%). For all tissue surrogate materials used for dose calculations, our SPR-H model predicted the ion chamber dose measurements to within 1.5% except for lung (~2.6%).
Conclusion: This study showed SPR prediction based on SPR-H model could facilitate the dose calculation as accurately as the measurements, which could potentially reduce range uncertainty in proton therapy.
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