Development and Implementation of Trajectory Optimization Technologies for Cranial Stereotactic Radiation Therapy

Abstract

Radiotherapy treatment planning optimization employs metrics for the quantification of plan quality indicators based on a set of input desired criteria by the planner. Patient-specificity in current practice is limited to the customization and refinement of input optimization criteria to contextualize relative urgency. The arc geometry and machine trajectory in radiotherapy planning can create additional opportunities for optimization on a patient-specific basis. This work proposes novel technologies capable of leveraging new degrees of freedom in the domain of radiotherapy to improve radiotherapy plan quality. A series of four manuscripts form the basis for this thesis. The first manuscript, “Overlap Guided Fixed Patient Support Positioning Optimization for Cranial SRT”, is an investigation into the optimization of couch rotation angle in the standard cranial stereotactic VMAT template to reduce the presence of overlap of sensitive structures with the targeted tissues in the aperture of the radiation beam. The second manuscript, “Dynamic Collimator Trajectory Algorithm for Multiple Metastases Dynamic Conformal Arc Treatment Planning”, demonstrates a novel method of reducing the presence of uncollimated non-target anatomy from the aperture of the radiation beam and increases the efficacy of collimation by optimizing the rotation angles of the multi-leaf collimator. Additionally, it proposes the use of dynamically updated collimator angle throughout delivery to maximize the capacity of this optimization. The third manuscript, “Intra-Arc Binary Collimation Algorithm for the Optimization of Stereotactic Radiotherapy Treatment of Multiple Metastases with Multiple Prescriptions”, demonstrates a novel method of aperture design in multiple metastases cranial radiosurgery which maximizes the presence of conformal aperture to increase the efficiency of monitor units, while regularly shielding targets completely to modulate dose to meet target prescription and healthy tissues sparing. Finally, the fourth manuscript, “CODA: Combined Optimization of Dynamic Axes”, is the first investigation into the synergistic optimization of the rotation angle of the collimator, the rotation angle of the treatment couch, and the rotation angle of the gantry to accomplish the objectives of normal tissue sparing and treatment efficiency using a novel organization of cost function and trajectory design. These manuscripts form the basis for automated optimization of linear accelerator trajectories in cranial radiosurgery. Their implementation can result in significant increases in plan quality when compared to state of the art conventional treatment planning. The introduction of these additional forms of optimization can be used to mitigate the effects of inter-planner variation in plan quality by automating the steps performed in expert-planning.