Treatment Planning Considerations for an MR-Linac

This chapter presents a practical guide of treatment planning utilizing MR-Linac delivery platforms and planning systems. Hardware and software requirements for treatment planning systems, as well as the commissioning and quality assurance practices, are described. We provide a general overview of contouring recommendations related to MR-Linac treatment planning, including current contouring initiatives and guidelines, margins, gating, and adaptive considerations. Contouring recommendations are followed by a practical guide to methods for estimating electron density and applications utilizing CT-based planning and MR-based planning. The chapter includes an overview of treatment plan optimization and a review of dose calculation algorithm requirements in MR-Linac treatment planning, as well as their impact on online adaptive treatment planning. We further discuss adaptive planning considerations including offline, online, and real-time adaptive planning techniques that account for anatomical and functional changes in the patient model. Finally, we conclude with an overview of plan evaluation techniques including the impact of dose calculation accuracy, evaluation metrics, and plan summation techniques related to adaptive planning.