Cone-beam CT reconstruction with gravity-induced motion

Shieh, Chun‐Chien; Barber, Jeffrey; Counter, William B.; Sykes, J.; Bennett, Peter; Heng, Soo Min; White, Paul A.; Corde, Stéphanie; Jackson, Michael; Ahern, Verity; Feain, Ilana; O’Brien, Ricky; Keall, Paul J.

doi:10.1088/1361-6560/aae1bb

Cited by 6 publications

(21 citation statements)

References 20 publications

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“…One technique to achieve this is to sort image projections into bins based on their angle and reconstruct each bin independently. Similar techniques are used to reconstruct respiratory‐correlated CBCT images with each projection sorted into respiratory phase bins . We have previously shown using anesthetized and immobilized rabbits rotated horizontally that this reconstruction technique can account for gravity‐induced motion, resulting in images with less than 1 mm of motion blur …”

Section: Discussionmentioning

confidence: 99%

“…Similar techniques are used to reconstruct respiratory‐correlated CBCT images with each projection sorted into respiratory phase bins . We have previously shown using anesthetized and immobilized rabbits rotated horizontally that this reconstruction technique can account for gravity‐induced motion, resulting in images with less than 1 mm of motion blur During treatment delivery, a static shift of the radiation beam (or a patient shift) could be used to compensate for motion of the target volume resulting from patient rotation.…”

Section: Discussionmentioning

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: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

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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“…Similar anatomic deformation has also been shown in single organ and animal studies, where the anatomical deformation caused by horizontal rotation led to artefacts in the fixed-gantry CBCT reconstruction (Feain et al, 2016;Barber et al, 2018). Shieh et al developed an algorithm for compensating for gravity induced motion for fixed-beam CBCT scans which was tested on anaesthetised rabbits (Shieh et al, 2018). However, this algorithm A c c e p t e d M a n u s c r i p t compensated for only the rigid motion, and not for any complex deformable motion.…”

Section: Introductionmentioning

confidence: 65%

“…However, this algorithm A c c e p t e d M a n u s c r i p t compensated for only the rigid motion, and not for any complex deformable motion. It has been shown previously that for both humans (Whelan et al, 2017) and rabbits (Barber et al, 2018;Shieh et al, 2018), the non-rigid deformation makes up a significant component of the gravity-induced motion caused by horizontal rotation. Additionally, the authors reported that for one of the rabbits, the reconstruction of the volume using their motion compensation algorithm had significant motion blur, caused by the large motion that occurred during rotation.…”

Section: Introductionmentioning

confidence: 99%

The adaptation and investigation of cone-beam CT reconstruction algorithms for horizontal rotation fixed-gantry scans of rabbits

Gardner¹,

Dillon²,

Shieh³

et al. 2021

Phys. Med. Biol.

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Fixed-gantry radiation therapy has been proposed as a low-cost alternative to the conventional rotating-gantry radiation therapy, that may help meet the rising global treatment demand. Fixed-gantry systems require gravitational motion compensated reconstruction algorithms to produce cone-beam CT (CBCT) images of sufficient quality for image guidance. The aim of this work was to adapt and investigate five CBCT reconstruction algorithms for fixed-gantry CBCT images. The five algorithms investigated were Feldkamp–Davis–Kress (FDK), prior image constrained compressed sensing (PICCS), gravitational motion compensated FDK (GMCFDK), motion compensated PICCS (MCPICCS) (a novel CBCT reconstruction algorithm) and simultaneous motion estimation and iterative reconstruction (SMEIR). Fixed-gantry and rotating-gantry CBCT scans were acquired of 3 rabbits, with the rotating-gantry scans used as a reference. Projections were sorted into rotation bins, based on the angle of rotation of the rabbit during image acquisition. The algorithms were compared using the structural similarity index measure root mean square error, and reconstruction time. Evaluation of the reconstructed volumes showed that, when compared with the reference rotating-gantry volume, the conventional FDK algorithm did not accurately reconstruct fixed-gantry CBCT scans. Whilst the PICCS reconstruction algorithm reduced some motion artefacts, the motion estimation reconstruction methods (GMCFDK, MCPICCS and SMEIR) were able to greatly reduce the effect of motion artefacts on the reconstructed volumes. This finding was verified quantitatively, with GMCFDK, MCPICCS and SMEIR reconstructions having RMSE 17%–19% lower and SSIM 1% higher than a conventional FDK. However, all motion compensated fixed-gantry CBCT reconstructions had a 56%–61% higher RMSE and 1.5% lower SSIM than FDK reconstructions of conventional rotating-gantry CBCT scans. The results show that motion compensation is required to reduce motion artefacts for fixed-gantry CBCT reconstructions. This paper further demonstrates the feasibility of fixed-gantry CBCT scans, and the ability of CBCT reconstruction algorithms to compensate for motion due to horizontal rotation.

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“…We have integrated two image guidance algorithms that allows the magnitude of target motion due to gravitational deformation to be measured during rotation. These algorithms are motion compensated cone-beam CT (CBCT) reconstruction 12 (labelled 1 in Figure 1) and real-time Kilovoltage Intrafraction Monitoring (KIM) 13 (labelled 2 in Figure 1). Analogous to conventional radiotherapy, the motion compensated cone-beam CT algorithm was used to verify patient position prior to treatment delivery, while KIM measured the target position in real-time as the patient is rotated to each beam angle.…”

Section: Introductionmentioning

confidence: 99%

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

Liu¹,

Gardner²,

Heng³

et al. 2021

Phys. Med. Biol.

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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.

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Cone-beam CT reconstruction with gravity-induced motion

Cited by 6 publications

References 20 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

The adaptation and investigation of cone-beam CT reconstruction algorithms for horizontal rotation fixed-gantry scans of rabbits

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

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