Purpose: To quantify the dosimetric impact of using the (Siemens Healthineers) DirectDensity algorithm for patients with non-natural body materials such as metallic implants.
Methods: Custom metallic inserts were milled to fit the Gammex 467 RMI electron density phantom. These include aluminum, cobalt, chrome, titanium, and stainless steel as these materials closely mimic the materials used in orthopedic implants. These materials, as well as the standard set of Gammex tissue inserts, were used to create a calibration curve in RayStation Treatment Planning System (TPS). The DirectDensity calibration curve data was provided by Siemens. Seven cases were reanalyzed using the new calibration curves. Plans were calculated with the 120 kV standard scan and the DirectDensity CT scan. The dosimetric differences were evaluated for each case with a focus on healthy tissue around the metallic implants.
Results: For the cases analyzed, there were small differences in tumor coverage with the DirectDensity plan having improved coverage than the standard plan, on the order of 2 percent or less. This is expected as the DirectDensity calibration curve will overestimate the dose for metallic inserts. Similarly, the tissue surrounding the implants showed an overestimation of dose in the DirectDensity plan with deviations noted up to 1 cm away from the insert and up to 6 percent of the prescription dose.
Conclusion: This project has the potential to improve image quality and reduce clinical errors by allowing the clinic to customize scanning protocols for age and body habitus and utilize one calibration curve in the TPS for multiple kV energies. By quantifying the impact of metallic implants using patient data, our study removes any impediment for clinics to implement the DirectDensity algorithm. For clinics that currently employ multiple calibration curves in the TPS this can lead to error reduction and quality improvement for those sites.
Funding Support, Disclosures, and Conflict of Interest: Funding provided by Siemens Healthineers
Not Applicable / None Entered.