Varian’s HyperSight imaging solution, which brought faster, higher-quality cone-beam CT imaging into the radiotherapy treatment room, was the focus of at least 11 presentations and posters at the 66th Annual AAPM Meeting (American Association of Physicists in Medicine) earlier this year.
“We were gratified to see that early testing by clinical research teams from the U.S. and Canada is confirming that our optional HyperSight solution can do what we designed it to do, which is provide high-quality imaging with enhanced contrast, quickly, over a larger field of view, compared to conventional Varian linear-accelerator-based imaging systems,” said Sasa Mutic, PhD, Head of Radiation Oncology Solutions at Varian. “A HyperSight-equipped radiotherapy clinic can use these images for precise daily localization of the tumor at the time of treatment, and also, for adapting to any changes in patient anatomy over a course of treatment.”
“We were gratified to see that early testing by clinical research teams from the U.S. and Canada is confirming that our optional HyperSight solution can do what we designed it to do, which is provide high-quality imaging with enhanced contrast, quickly, over a larger field of view, compared to conventional Varian linear-accelerator-based imaging systems.”
-- Sasa Mutic, PhD, Head of Radiation Oncology Solutions at Varian. ]
HyperSight with Ethos Adaptive Radiotherapy
Two of the posters and presentations covered aspects of using the HyperSight solution as part of an Ethos adaptive radiotherapy system. One investigated the accuracy of dose calculations done using clinical HyperSight images compared to dose calculated on conventional cone-beam CT (CBCT) images, suggesting that the former “may represent a substantial step forward in the ability of adaptive treatment planning to be performed directly on CBCT” images generated at the time of treatment.1 The other concluded that, using HyperSight imaging, CT-guided online adaptive radiotherapy “is feasible with direct dose calculation on CBCT [images].” This approach “shows potential improvement” over calculating dose on synthetic CT images—which is how adaptive planning is accomplished on an Ethos system without HyperSight imaging.2
“These are the kinds of investigations that the clinical community needs to see if they’re going to trust these images for replanning,” said Sean Davidson, Senior Clinical Research Manager at Varian. “They demonstrate that HyperSight images are good enough to use for direct dose calculation during Ethos adaptive therapy.”
HyperSight on a Halcyon System
One research team evaluated the feasibility of using HyperSight imaging on a Halcyon system in place of treatment planning CT scans for an offline adaptive workflow. They reported that the HyperSight images were “of sufficient image quality relative to planning CT for treatment planning.” They went on to say: “Auto-contouring accurately delineated organs at risk with performance comparable to simulated CT planning images,” and further stated that the dosimetric quality of plans using HyperSight images “resulted in comparable target coverage and sparing of organs at risk.”3
“These results lay a foundation of evidence that clinicians with access to HyperSight imaging may not have to send a patient back for re-simulation, when they see anatomical changes that indicate the need for a new treatment plan,” said Davidson. “Our clinical collaborators have shown that it is possible to do offline adaptive planning using the HyperSight images.”
“These results lay a foundation of evidence that clinicians with access to HyperSight imaging may not have to send a patient back for re-simulation, when they see anatomical changes that indicate the need for a new treatment plan.”
- Sean Davidson, Senior Clinical Research Manager at Varian]
HyperSight on a TrueBeam System
Eight of the posters and presentations covered various aspects of how HyperSight imaging performs on a TrueBeam system.
One research team confirmed that HyperSight images can be acquired in much less time, and that the advanced reconstruction algorithms “all contribute to improved image quality and reduced radiation dose.”4 Similarly, another group of researchers demonstrated that the HyperSight imaging solution acquires images faster than was previously possible on a TrueBeam system, stating that “the faster gantry speed enables reduced image acquisition time without compromising image quality.”5
Another research group investigated the question of whether the faster speed of gantry rotation during HyperSight image acquisition would negatively impact precision through displacement of the imaging isocenter. They found that the speed did not diminish precision, reporting that the 3-D displacement of isocenter “was within 1mm, indicating sufficiency for SBRT treatments.”6
And one research group evaluated the Hounsfield Unit (HU) accuracy of HyperSight on a TrueBeam system. They state that the “recent advances in imaging detector hardware and reconstruction algorithms” that HyperSight represents “have led to the potential for CBCT-based dose calculation.” They conclude that the data “show promise for increased HU precision and accuracy.”7 This, in turn, opens the door to a new, faster workflow for offline adaptation when treating on a TrueBeam system and using HyperSight images to replan.
Evaluation of HyperSight Reconstruction Algorithms
Four of the posters and presentations described evaluations of the HyperSight reconstruction algorithms.
For example, one research group that evaluated the HyperSight metal artifact reduction algorithm reported that it “reduces shadowing and streak artifacts compared to other reconstructions. These results can improve image uniformity and visibility of implant adjacent anatomy, which are important for image guided radiation therapy and future adaptive treatment planning research.”8
And a team that evaluated the extended radial field of view (eFOV) algorithm, which is available with HyperSight on the TrueBeam platform, found that the eFOV algorithm “could be clinically useful for visualization of larger anatomy or treatment plans with an offset isocenter.”9
“With HyperSight, we intended to provide radiation oncology departments with a next generation of in-room imaging that improved spatial and contrast resolution, generated images they could plan on, and reduced the time for image acquisition down to a single breath hold,” said Dr. Mutic. “We were excited to see these early reports that begin to confirm that we are delivering on this intention.”
The statements by Varian’s customers described here are based on results achieved in the customer’s unique clinical setting. Because there is no “typical” clinical setting and many variables exist, there is no guarantee that other customers will achieve the same results.
- 3D Gamma Analysis of Dose Calculation Accuracy Using the Hypersight Imaging Solution. Presenting author: Peter R. Martin, QE2 Cancer Centre, Nova Scotia, Canada.
- Dosimetric Evaluation of CT-Guided Online Adaptive Radiotherapy Plans on a Novel CBCT Imaging System. Presenting author: Haleem Azmy, Washington University in St. Louis School of Medicine.
- Offline Adaptive CBCT Planning Workflow for Varian Halcyon with Hypersight. Presenting author: Barbara Garcia, University of Pennsylvania.
- Characterization of a Novel Kilovoltage X-Ray Image Guidance System Designed for a C-Arm Linear Accelerator. Presenting author: Theodore Higgins Arsenault, University Hospi8tals Seidman Cancer Center.
- Image Quality Analysis of Hypersight Imaging on Varian Truebeam Linear Accelerator. Presenting author: Meghana Ramani, The Ohio State University.
- Winston-Lutz Evaluation of Gated Acquisitions with Increased Gantry Speed on a C-Arm Linac Cone-Beam Computed Tomography Solution. Presenting author: Kenneth W. Gregg, University Hospitals Seidman Cancer Center.
- Evaluation of Hounsfield Unit Accuracy in-Phantom on a Novel C-Arm Linac CBCT Imaging Solution. Presenting author: Kenneth W. Gregg, University Hospitals Seidman Cancer Center.
- Hypersight Imaging for the Truebeam System Metal Artifact Reduction Algorithm Evaluation. Presenting author: Dominic J. DiCostanzo, The Ohio State University.
- Hypersight Imaging for Truebeam Radiotherapy System Extended Radial Field of View Algorithm Evaluation. Presenting author: Ashley Cetnar, The Ohio State University.