Room: Exhibit Hall
Purpose: In proton Pencil Beam Scanning (PBS), treatment plans can be optimized using Single-Field Uniform Dose / Optimization (SFUD/SFO) or via Multi-Field Optimization (MFO). In clinical practice, these techniques can be combined to create a hybrid plan. In this study, we develop a method to evaluate plans using metrics applied to field-specific differential dose volume histograms (DVHs).
Methods: Using the Python programming language, an application was developed to read differential DVHs for the primary target volume for each field in a proton PBS treatment plan. The application normalizes each histogram using relative volume and dose relative to the field-specific contribution of the total dose. It then determines the total number of distributions for all histograms in the plan, which serves as an initial classification metric. The program also calculates additional metrics, including distance to maximum dose and the slope of each distribution. Twenty-five patients (9 SFUD, 12 hybrid MFO and 4 MFO) were analyzed using the application and were compared to the expected optimization technique chosen in the treatment plan.
Results: The total number of distributions found had a median value of 2, 4.5 and 6 for SFUD, hybrid MFO and MFO plans respectively. The median value of the distance to maximum dose was 1.46%, 10.9% and 7.3% for SFUD, hybrid MFO and MFO plans respectively. The average slope had a median value of -1.14, -0.16, and -0.07 for SFUD, hybrid MFO and MFO plans respectively.
Conclusion: A classification method for proton PBS plans was developed using the field-specific differential DVHs which can aid in robustness evaluation, image guidance tolerance, plan documentation as well as data analysis.