Room: ePoster Forums
Purpose: In Proton Pencil Beam Scanning, treatment plans can be optimized using Single-Field Uniform Dose / Optimization (SFUD/SFO), Multi-Field Optimization (MFO), or a hybrid. This study determined the optimization method of a plan using metrics derived from field-specific differential dose volume histograms (DVHs).
Methods: An application was developed to read differential DVHs of the primary target volume for each field in a proton PBS treatment plan. After normalizing the DVH to the target volume and maximum field dose, the application calculates the following: the number of distributions per field, the slope and width of each distribution, the dose difference between the maximum dose and mode of each distribution, and the difference between the DVHs of each field. Using these metrics, we formulated a scoring system for 235 treatment plans on a scale from 0-100% where 0-20% were categorized as MFO, 20-40% as hybrid plans with a larger MFO component, 40-70% as hybrid plans with a larger SFUD component, and 70-100% as SFUD.
Results: Our ranking system divided the 235 treatment plans as follows: 33 MFO, 26 Hybrid MFO, 31 Hybrid SFUD, and 145 SFUD. Optimization settings selected prior to planning sorted the plans as 30 MFO, 107 hybrid, and 98 SFUD. Categorizing by treatment site, 88% of brain treatment plans and 76% of prostate treatment plans were SFUD. Head and neck and thorax treatment plans were more evenly distributed with 41% and 37% categorized as SFUD respectively. Craniospinal plans were 38% MFO, and pelvic plans were 38% hybrid SFUD.
Conclusion: Our classification method for proton PBS plans can determine a planâ€™s optimization method and differentiate hybrid treatment plans that contain larger volumes of either MFO or SFUD techniques. This is particularly useful for treatment sites that use hybrid techniques to influence image guidance tolerances and robustness evaluations.
Not Applicable / None Entered.