Technical Note: The design and function of a horizontal patient rotation system for the purposes of fixed-beam cancer radiotherapy

Feain, Ilana; Coleman, Lloyd; Wallis, Hue; Sokolov, Richard; O’Brien, Ricky; Keall, Paul J.

doi:10.1002/mp.12219

Cited by 12 publications

(17 citation statements)

References 16 publications

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“…Once immobilized, the PRS can move with two degrees of freedom (translation along and rotation about the SI axis) to position and rotate the patient. The design and safety aspects of the PRS has been detailed in Feain et al …”

Section: Materials and Materialsmentioning

confidence: 99%

“…The prototype consists of an Elekta Synergy linear accelerator and a bespoke patient rotation system (PRS). The PRS was designed to safely and conformably immobilize patients in the horizontal position and rotate them along the longitudinal axis with real‐time control . In this paper, we describe the development and the commissioning of this prototype fixed‐beam system.…”

Section: Introductionmentioning

confidence: 99%

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Development and commissioning of a full‐size prototype fixed‐beam radiotherapy system with horizontal patient rotation

et al. 2019

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Purpose Compared to conventional linacs with rotating gantries, a fixed‐beam radiotherapy system could be smaller, more robust and more cost‐effective. In this work, we developed and commissioned a prototype x‐ray radiotherapy system utilizing a fixed vertical radiation beam and horizontal patient rotation. Methods The prototype system consists of an Elekta Synergy linac with gantry fixed at 0° and a custom‐built patient rotation system (PRS). The PRS was designed to immobilize patients and safely rotate them about the horizontal axis. The interlocks and emergency stops of the linac and PRS were connected. Custom software was developed to monitor the system status, control the motion of the PRS and modify treatment plans for the fixed‐beam configuration. Following installation, the prototype system was commissioned for three‐dimensional (3D) conformal therapy based on guidelines specified in AAPM TG‐45 and TG‐142, with modifications for the fixed‐beam geometry made where necessary. Results The system and control software was tested in a variety of machine states and executed motion, stop and beam gating commands as expected. Interlocks and emergency stops of the linac and PRS were found to correctly stop PRS motion and both kV and MV radiation beams when triggered. For 3D conformal treatments, the prototype system met all AAPM TG‐45 and TG‐142 specifications for geometric and dosimetric accuracy. Motion of the PRS was within 0.6 ± 0.3 mm and 0.10° ± 0.07° of input values for translation and rotation respectively. The axis of rotation of the PRS was coincident with the radiation beam axis to less than 1 mm. End‐to‐end treatment verification for 6 MV conformal treatments showed less than 2% difference between planned and delivered dose for all fields. Conclusion In this work, we have developed and commissioned a radiotherapy system that utilizes a fixed vertical radiation beam and horizontal patient rotation. This system is a proof‐of‐concept prototype for a fixed‐beam treatment system without a rotating gantry. Fixed‐beam systems that are smaller and more cost‐effective could help in improving global access to radiotherapy.

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Section: Materials and Materialsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Development and commissioning of a full‐size prototype fixed‐beam radiotherapy system with horizontal patient rotation

et al. 2019

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“…This is especially important for future studies in larger animals. A suitable patient rotation system has been designed for the fixed gantry Nano-X Tatum prototype, featuring pressure-controlled airbags and straps in addition to standard radiotherapy fixation devices (Feain et al 2017a). An MRI-compatible patient rotation system has also been designed and investigated (Whelan et al 2017).…”

Section: Comparison Of Gravity-induced Motion To Respiratory Motionmentioning

confidence: 99%

A CBCT study of the gravity-induced movement in rotating rabbits

Barber¹,

Shieh²,

Counter³

et al. 2018

Phys. Med. Biol.

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Fixed-beam radiotherapy systems with subjects rotating about a longitudinal (horizontal) axis are subject to gravity-induced motion. Limited reports on the degree of this motion, and any deformation, has been reported previously. The purpose of this study is to quantify the degree of anatomical motion caused by rotating a subject around a longitudinal axis, using cone-beam CT (CBCT). In the current study, a purpose-made longitudinal rotating was aligned to a Varian TrueBeam kV imaging system. CBCT images of three live rabbits were acquired at fixed rotational offsets of the cradle. Rigid and deformable image registrations back to the original position were used to quantify the motion experienced by the subjects under rotation. In the rotation offset CBCTs, the mean magnitude of rigid translations was 5.7 ± 2.7 mm across all rabbits and all rotations. The translation motion was reproducible between multiple rotations within 2.1 mm, 1.1 mm, and 2.8 mm difference for rabbit 1, 2, and 3, respectively. The magnitude of the mean and absolute maximum deformation vectors were 0.2 ± 0.1 mm and 5.4 ± 2.0 mm respectively, indicating small residual deformations after rigid registration. In the non-rotated rabbit 4DCBCT, respiratory diaphragm motion up to 5 mm was observed, and the variation in respiratory motion as measured from a series of 4DCBCT scans acquired at each rotation position was small. The principle motion of the rotated subjects was rigid translational motion. The deformation of the anatomy under rotation was found to be similar in scale to normal respiratory motion. This indicates imaging and treatment of rotated subjects with fixed-beam systems can use rigid registration as the primary mode of motion estimation. While the scaling of deformation from rabbits to humans is uncertain, these proof-of-principle results indicate promise for fixed-beam treatment systems.

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“…Researchers have investigated the potential advantages and feasibility of this fixed‐beam cancer radiotherapy. This treatment approach can be used to develop a low‐cost linear accelerator system that benefits low‐ and middle‐income countries …”

Section: Discussionmentioning

confidence: 99%

Technical Note: Density correction to improve CT number mapping in thoracic deformable image registration

Yang

Zhang

et al. 2019

Medical Physics

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Purpose To improve the accuracy of computed tomography (CT) number mapping inside the lung in deformable image registration with large differences in lung volume for applications in vertical CT imaging and adaptive radiotherapy. Methods The deep inspiration breath hold (DIBH) CT image and the end of exhalation (EE) phase image in four‐dimensional CT of 14 thoracic cancer patients were used in this study. Lung volumes were manually delineated. A Demons‐based deformable registration was first applied to register the EE CT to the DIBH CT for each patient, and the resulting deformation vector field deformed the EE CT image to the DIBH CT space. Given that the mass of the lung remains the same during respiration, we created a mass‐preserving model to correlate lung density variations with volumetric changes, which were characterized by the Jacobian derived from the deformation field. The Jacobian determinant was used to correct the lung CT numbers transferred from the EE CT image. The absolute intensity differences created by subtracting the deformed EE CT from the DIBH CT with and without density correction were compared. Results The ratio of DIBH CT to EE CT lung volumes was 1.6 on average. The deformable registration registered the lung shape well, but the appearance of voxel intensities inside the lung was different, demonstrating the need for density correction. Without density correction, the mean and standard deviation of the absolute intensity difference between the deformed EE CT and the DIBH CT inside the lung were 54.5 ± 45.5 for all cases. After density correction, these numbers decreased to 18.1 ± 34.9, demonstrating greater accuracy. The cumulative histogram of the intensity difference also showed that density correction improved CT number mapping greatly. Conclusion Density correction improves CT number mapping inside the lung in deformable image registration for difficult cases with large lung volume differences.

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Technical Note: The design and function of a horizontal patient rotation system for the purposes of fixed-beam cancer radiotherapy

Cited by 12 publications

References 16 publications

Development and commissioning of a full‐size prototype fixed‐beam radiotherapy system with horizontal patient rotation

Development and commissioning of a full‐size prototype fixed‐beam radiotherapy system with horizontal patient rotation

A CBCT study of the gravity-induced movement in rotating rabbits

Technical Note: Density correction to improve CT number mapping in thoracic deformable image registration

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