Pre-treatment and real-time image guidance for a fixed-beam radiotherapy system

Abstract

Purpose: A radiotherapy system with a fixed treatment beam and a rotating patient positioning system could be smaller, more robust and more cost effective compared to conventional rotating gantry systems. However, patient rotation could cause anatomical deformation and compromise treatment delivery. In this work, we demonstrate an image-guided treatment workflow with a fixed beam prototype system that accounts for deformation during rotation to maintain dosimetric accuracy.Methods: The prototype system consists of an Elekta Synergy linac with the therapy beam orientated directly downward and a custom-built patient rotation system (PRS). A phantom that deforms with rotation was constructed and rotated within the PRS to quantify the performance of two image guidance techniques: motion compensated cone-beam CT for pre-treatment volumetric imaging and Kilovoltage Infraction Monitoring (KIM) for real-time image guidance. The phantom was also irradiated with a 3D conformal beam to evaluate the dosimetric accuracy of the workflow. Results:The motion compensated cone-beam CT was used to verify pre-treatment position and the average calculated position within -0.3 ± 1.1 mm of the phantom's ground truth position at 0°. KIM tracked the position of the target in real-time as the phantom was rotated and the average calculated position was within -0.2 ± 0.8 mm of the phantom's ground truth position. A 3D conformal treatment delivered on the prototype system with image guidance had a 3%/2 mm gamma pass rate of 96.3% compared to 98.6% delivered using a conventional rotating gantry linac. Conclusions:In this work, we have shown that image guidance can be used with fixed-beam treatment systems to measure and account for changes in target position to maintain dosimetric coverage during horizontal rotation. This treatment modality could provide a viable treatment option when there is not enough space for a conventional linear accelerator or where the cost is prohibitive.

Nano X Image Guidance in radiation therapy: feasibility study protocol for cone beam computed tomography imaging with gravity-induced motion

“…This study primarily aims to address the first of these assumptions. Beam adaptation techniques shown described by Liu et al [ 14 ] and a single institutional study (NCT02995603) that is currently underway to assess patient tolerance and acceptance have aimed to address the second and third assumptions, respectively.…”

“…The aim of these reconstruction methods is to reduce the effect that motion has on the CBCT reconstruction, allowing for clear and geometrically accurate images that can assist with image guidance therapy. Studies conducted by Feain et al [ 5 ], Shieh et al [ 13 ], Liu et al [ 14 ] and Gardner et al [ 12 ] have demonstrated several image reconstruction methods that can correct for such gravity-induced motion. The Nano X CBCT projection data set will be used to evaluate the efficacy of similar image reconstruction methods in reducing motion blur artefacts and producing clinically useable volumetric images for treatment guidance.…”