Non-Coplanar Arc Optimization for Stereotactic Ablative Radiotherapy Treatment Planning

Abstract

Stereotactic ablative radiotherapy (SABR) is a technique that delivers a high dose of radiation in a single or small number of fractions and requires rapid fall off outside the target. In current clinical practice it is imperative when treating with ablative doses that radiation to organs-at-risk (OARs) is minimized as much as possible to avoid treatment related toxicity in healthy tissue. Often SABR is delivered with volumetric modulated arc therapy (VMAT), an efficient delivery technique that relies on complex modulation throughout an arc to optimize dose objectives. Non-coplanar optimization methods have been proposed to automatically select geometries that minimize overlap between targets and organs-at-risk (OARs) in the radiation beams-eye-view (BEV). When applied in intensity modulation radiotherapy IMRT or VMAT, these have been shown to significantly reduce dose to OARs as compared to conventional coplanar trajectories. These methods still face barriers to widespread clinical implementation, such as efficiency issues. The purpose of this thesis is to demonstrate that automatically optimized non-coplanar arc geometries for SABR with VMAT leads to dose reductions to OARs. Additionally, this thesis considers the differences between cranial and extracranial SABR and evaluates arc geometry optimization for sites with varying biological complexity. The thesis is comprised of three manuscripts that evaluate the arc geometry optimization for sites treated with SABR. The first manuscript for cranial SABR, “Comparison of anatomically informed template trajectories with patient specific trajectories for stereotactic radiosurgery and radiotherapy,” compares a commercial general arc template with an optimized arc template and patient specific arc geometry, concluding that patient specific geometries were dosimetrically superior. The second manuscript for extracranial SABR, “Static couch non-coplanar arc selection optimization for lung SBRT treatment planning,” demonstrates a patient-specific method to choose arcs that combine dose reduction to OARs with clinically acceptable target conformity. The third manuscript for extracranial SABR, “Biologically optimized non-coplanar arc selection for small and large target volumes in liver SBRT,” shows that choosing optimized arcs has the potential for dose reduction to target-encompassing OARs, such as the liver. These manuscripts address differences and similarities of performing SABR in various sites throughout the body. They offer solutions that are ready to use and require minimal additions to current clinical workflows. Finally, they also demonstrate the dosimetric advantages of non-coplanar arc delivery for multiple disease sites.