Master of Science (MS)
Physics and Astronomy
Volumetric modulated arc therapy (VMAT) is a rotational IMRT technique that uses a radiotherapy linear accelerator gantry with a dynamic MLC, variable dose rate, and variable gantry speed. These new degrees of freedom of VMAT delivery introduced complexities for treatment planning, and Pinnacle3 SmartArc treatment module was recently developed as a solution. However, it was unclear how varying each SmartArc parameter affected the resulting plan quality. The purpose of this study was to systematically examine all planning parameters and quantify the effect of varying each on the quality of a reference plan. Parameters were separated into two categories: commissioning parameters and planning parameters. Commissioning parameters were those available to the user during the machine commissioning process in Pinnacle, i.e. dose rate, gantry speed, MLC size, and MLC speed. Planning parameters were those available to the user during routine treatment planning, i.e. beam energy, collimator angle, arc length, and final gantry spacing. A "baseline" set of commissioning and planning parameters was created that provided clinically acceptable plans for a cylindrical phantom case, simple prostate case, and complex (multi-target) prostate case. Each parameter was independently varied while keeping all other parameters set to the baseline values. The resulting change in each plan was evaluated using dose volume histograms, dose homogeneity indices (DHI), conformity indices (CI) and normal tissue dose metrics. The DHI and CI for the phantom and simple prostate cases varied by less than 0.02 from the baseline values for most parameters. The DHI and CI for the complex prostate case varied by more than 0.02 from the baseline values for most parameters. The dose to normal tissues changed by less than 3% as parameters were varied for the simple prostate case and more than 3% as parameters were varied for the complex prostate case. Most SmartArc parameters had little effect on DHI, CI, and normal tissue sparing for the phantom and simple prostate treatment geometries, but showed significant variations for the complex prostate case. We conclude that SmartArc optimization is largely user-independent and hardware-independent for non-complex prostate treatment geometries. However, certain parameters (especially planning parameters) create a significant change in resulting plan quality for complex prostate treatment geometries.
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Talbert, Catharine Elizabeth, "Comprehensive study of parameters for volumetric modulated arc therapy (VMAT) treatment planning" (2010). LSU Master's Theses. 976.