(Sunday, 7/14/2019) 4:00 PM - 5:00 PM
Room: 302
Purpose: To develop an automated planning script in RayStation for VMAT breast cases including nodal involvement. The technique must also support treatment of the internal mammary chain (IMC) if desired, as well as automatic skin flash.
Methods: 67 patients, previously treated using IMRT, were used as a baseline to develop the script. An iterative algorithm was designed which first determined the lowest mean heart dose possible without sacrificing target coverage. Subsequent steps evaluated plan dose and adjusted objective weights in the treatment planning system, with the goal of lowering doses to other organs while maintaining coverage. Automatic skin-flashing was accomplished by creating an external volume based on PTV expansions and including it in the optimization objectives of the plan. The planning algorithm was refined using scripted batch planning, which permitted evaluation on all 67 patients after each revision. Automated plans were compared to clinical plans at each step and the algorithm was adjusted to improve plan quality for the largest number of patients possible.
Results: Of the 67 patients tested, the algorithm was able to create plans that were dosimetrically equivalent or superior in 61 cases. The automated planning script takes from 30-90 minutes to run and requires no intervention from the dosimetrist once started. Automatic skin-flash was validated by using density overrides to simulate 1 cm swelling of the breast for 12 patients and recalculating the dose; the resulting plans were judged acceptable.
Conclusion: The automated planning algorithm allows a dosimetrist of any experience level to generate a clinically-acceptable VMAT plan for breast treatment with nodal involvement including IMC in less than 2 hours. 90% of the automatic VMAT plans were equal in quality or surpassed the clinical IMRT plans for the same patients. The script has since been deployed clinically at our institution.
Keywords
Breast, Dosimetry, Optimization
Taxonomy
TH- External beam- photons: IMRT dose optimization algorithms
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