Program Information
Mixed-Modality Radiation Therapy Optimisation Using the Column Generation Method
M Renaud*, M Serban , J Seuntjens , McGill University, Montreal, QC
Presentations
TH-CD-708-7 (Thursday, August 3, 2017) 10:00 AM - 12:00 PM Room: 708
Purpose: Linac-delivered treatment plans are typically optimised using a single modality such as photons or individual electron energies. Mixed electron-photon plans could provide dosimetric advantages for sites with a superficial component. The column generation (CG) method, which is an iterative method that constructs apertures with the largest potential to improve the cost function at every iteration, is well suited for mixed-modality optimisation, as the aperture generation and modality selection problem can be solved quickly. We assess the performance of the CG method applied to electron-photon planning and investigate the performance of different aperture addition schemes.
Methods: 6 MV photon beamlets were created for a partial coplanar distribution of beam angles every 20ยบ around a chest wall patient. In addition, five 80-cm-SAD electron beam angles were included and MC-calculated beamlets were generated for energies of 6, 9, 12, 16, and 20 MeV. A photon MLC acted as the sole collimating device for electrons.A dose-normalization-independent formulation of the CG pricing problem was used as a heuristic to rank the quality of generated apertures at every iteration. Treatment plans were created for four aperture addition schemes which incorporated a subset of the apertures generated from the pricing problem.
Results: The mixed plans produced the best target coverage and homogeneity while preserving the normal tissue-sparing advantages of modulated electrons. The heuristic ranking schemes yielded better plans (32% lower cost function) compared to the scheme which added all generated apertures every iteration. All heuristic ranking schemes approximately converged to the same cost function after 125 apertures with one scheme having a 3x faster runtime than the most accurate (slowest) scheme.
Conclusion: Electron-photon planning using the column generation method produced high quality chest wall plans combining the advantages of photon and electron radiotherapy. This work paves the way towards automatic delivery of mixed beam treatments.
Contact Email: