Room: Exhibit Hall | Forum 2
Purpose: To investigate the use of stopping power ratio (SPR) CT images, created from electron density (Ï?e) and effective atomic number (Zeff) images (from dual-energy CT (DECT)) for proton dose calculation in two commercial proton treatment planning systems (TPS).
Methods: SPR-CT images of 10 tissue surrogate plugs inserted individually into a tissue equivalent phantom were constructed and imported into both the Eclipse (v13.7, Varian Medical Systems, Palo Alto CA) and RayStation (v6, RaySearch Laboratories, Stockholm Sweden) treatment planning systems. A single field treatment plan was created using both the SPR-CT and SECT images for each tissue surrogate plug. To assess accuracy of the dose calculation on SPR-CT images (and the SECT images), the treatment plans were delivered to each phantom/plug, and ion chamber and 2D planar dose measurements were compared to a dose reference point and 2D planar doses in the treatment plans.
Results: For all tissue surrogate materials, calculated dose from both TPSs on the SPR-CT and SECT images were within 1.0% and 1.5% of ion chamber measurements, respectively, except for lung-exhale (1.5% SPR, 4.5% SECT). 2D-gamma pass rates (Â±3% and 3-mm criteria) were greater than 90% for both SPR and SECT plans for all tissue surrogates expect bone (~55%).
Conclusion: For both commercial TPSs, the use of SPR-CT, constructed from DECT images, for proton dose calculation with both clinical TPSs was shown to be accurate within clinical criteria (Â±3%/3 mm) for most tissue surrogates studied. TPS plans in single plug phantoms showed clinically relevant improvements when using SPR-CT compared to standard SECT images.