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Towards Auto Selection of Beam Angles and Photon Energies in Mixed Energy Photon IMRT

S Momin1* 2, J Grafe2, R Khan1, (1) Washington University School of Medicine, St Louis, MO, USA (2) Ryerson University, Toronto, ON, CA


(Sunday, 7/12/2020)   [Eastern Time (GMT-4)]

Room: AAPM ePoster Library

Purpose: propose a unique dosimetric score based optimization method for auto-selection of photon energy and corresponding beam angles in mixed energy IMRT.

Methods: The approach first uses a linear objective function to solve mixed photon fluence optimization problem with 5-degree angular resolution, which results in 90 candidate beams for 6 MV and 18 MV. The candidate beams are ranked based on a metric called “target-to-organs at risks dose ratio”, defined as mean dose to PTV divided by summation of mean dose to all OARs. Owing to a global solution to this linear objective function, the direction and energy of given beam is reflected by its metric value. We tested our approach on a left-chestwall (LCW) and a right-chestwall (RCW) IMRT cases. For each case, two sets of plans were created with the same dosimetric objectives and total number of beams: a plan with a combination of manual selection of beam angles and photon energy by an experienced planner, and a second plan with selection of beam angles and energies based on proposed method.

Results: In both cases, the doses to planning target volume (PTV) and unspecified normal tissue were comparable between manual vs ratio method. The auto-selection reduced mean dose to heart (RCW:2.8 Gy vs. 15.3 Gy; LCW: 5.7 Gy vs. 6.8 Gy), esophagus (RCW: 3.1 Gy vs. 10.4 Gy; LCW: 3.7 Gy vs. 8.3 Gy), contralateral lung (RCW: 0.7 Gy vs. 7.5 Gy; LCW: 2.0 Gy vs. 4.6 Gy), and spinal cord (RCW: 1.1 Gy vs. 3.2Gy; LCW: 1.0Gy vs. 4.3Gy), however at slightly higher doses to ipsilateral lung (RCW:12.6Gy vs. 10.2 Gy; LCW:12.2 Gy vs. 12.1Gy).

Conclusion: The results obtained from the preliminary study suggest that the proposed approach is promising in improving the plan quality without compromising the target coverage while reducing dose to organs at risks.


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