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Plan-Delivery-Time-Constrained PBS Proton Treatment Planning Via Minimum MU Per Energy Layer (MMPEL)

H Gao1*, B Clasie2, M McDonald1, K Langen1, T Liu1, Y Lin1, (1) Winship Cancer Institute of Emory University, Atlanta, GA, (2) Massachusetts General Hospital, Boston, MA

Presentations

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

Room: AAPM ePoster Library

Purpose: In proton pencil beam scanning (PBS), the proton dose rate is approximately linearly proportional to the minimum monitor unit (MU) of PBS spots. Treatment plan delivery time can therefore potentially be reduced by increasing the minimum MU value. Currently, commercially available treatment planning systems allow for a single value to be entered as the minimum MU constraint for all PBS spots, and consequently the room to increase this minimum MU for reducing the beam-on time is very limited since higher minimum MU can significantly degrade treatment plan quality.

Methods: The innovation of this work is to develop a new treatment planning method to allow variable minimum MU values for optimizing the plan delivery time as well as the plan quality, i.e., minimum-MU-per-energy-layer (MMPEL) inverse optimization method. MMPEL is formulated as a constrained optimization problem with objectives of dose-volume-histogram based planning constraints and plan delivery time, and minimum-MU constraints per energy layer for deliverable PBS spots. MMPEL is solved by iterative convex relaxations via alternating direction method of multipliers.

Results: Representative prostate, lung, and brain cases were used to validate MMPEL. MMPEL reduced the delivery time to 53.3%, 67.4%, and 66.7% respectively for prostate, lung and brain cases while maintaining the similar plan quality. Accepting a slightly degraded plan quality that still met all physician planning constraints, the treatment time could be further reduced to 25.7%, 34.9%, and 41.3% respectively, or in another word MMPEL accelerated the PBS plan delivery by 2-4 fold.

Conclusions: A new proton PBS treatment planning method with variable minimum-MU constraints per energy layer, namely MMPEL, is developed to optimize the beam-on time of treatment plan delivery at the same time with the plan quality. The preliminary results suggest that MMPEL could significantly reduce the irradiation time.

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