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Purpose: Although collimator rotation is an optimization variable that can be exploited for dosimetric advantages, existing Volumetric Modulated Arc Therapy (VMAT) optimization uses a fixed collimator angle in each arc and only rotates the collimator between arcs. In this study, we develop a novel integrated optimization method for VMAT, accounting for dynamic collimator angles during the arc motion.
Methods: Direct Aperture Optimization (DAO) for Dynamic Collimator in VMAT (DC-VMAT) was achieved by adding to the existing dose fidelity objective an anisotropic total variation term for regulating the fluence smoothness, a binary variable for forming simple apertures, and a group sparsity term for controlling collimator rotation. The optimal collimator angle for each beam angle was selected using the Dijkstra's algorithm, where the node costs depend on the estimated fluence map at the current iteration and the edge costs account for the mechanical constraints of multi-leaf collimator (MLC). An alternating optimization strategy was implemented to solve the DAO and collimator angle selection (CAS). Feasibility of DC-VMAT using one full-arc with dynamic collimator rotation was tested on a phantom with two small spherical targets, a brain, a lung and a prostate cancer patient. The plan was compared against a static collimator VMAT (SC-VMAT) plan using three full arcs with 60 degrees of collimator angle separation in patient studies.
Results: With the same target coverage, DC-VMAT achieved 20.3% reduction of R50 in the phantom study, and reduced the average max and mean OAR dose by 4.49% and 2.53% of the prescription dose in patient studies, as compared with SC-VMAT. The collimator rotation co-ordinated with the gantry rotation in DC-VMAT plans for deliverability. There were 13 beam angles in the single-arc DC-VMAT plan in patient studies that requires slower gantry rotation to accommodate multiple collimator angles.
Conclusions: The novel DC-VMAT approach utilizes the dynamic collimator rotation during arc delivery. In doing so, DC-VMAT affords more sophisticated intensity modulation, alleviating the limitation previously imposed by the square beamlet from the MLC leaf thickness and achieves higher effective modulation resolution. Consequently, DC-VMAT with a single arc manages to achieve superior dosimetry than SC-VMAT with three full arcs.
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http://dx.doi.org/10.1002/mp.12915 | DOI Listing |
Malawi Med J
February 2025
Department of Medical Imaging, The First Affiliated Hospital of Xi'an Jiaotong University, Xi'an, PR China.
Objective: This study aimed to investigate the impact of Clear View dual-domain iterative reconstruction (IR) technology on the quality of low-dose abdominal CT images and to determine the optimal weight ratio to optimize image quality.
Methods: We studied 40 patients (28 males, 12 females, aged 19-69) undergoing low-dose abdominal CT scans (CTDI = 5.32 ± 0.
Cureus
January 2025
Department of Radiology, Aichi Medical University, Nagakute, JPN.
Purpose In linac-based stereotactic radiosurgery (SRS) using a multileaf collimator (MLC) for multiple brain metastases (BMs), the appropriate MLC angle rotation is useful to minimize the intervening brain dose by avoiding island blocking between the lesions localized along the direction of leaf movement. However, in some linac systems, the MLC angle cannot be rotated, or the cephalad rotation range of non-coplanar arcs (NCAs) is severely limited. In addition, the significance of MLC angle rotation has yet to be clarified in SRS for single BMs.
View Article and Find Full Text PDFPhys Med
March 2025
Centre Léon Bérard, 28 rue Laennec, 69373 LYON Cedex 08, France; CREATIS, CNRS UMR5220, Inserm U1044, INSA-Lyon, Université Lyon 1, Villeurbanne, France.
Background/introduction: To present an optimal workflow using a rotatable tabletop and a surface guided radiation therapy (SGRT) system for volumetric modulated arc therapy (VMAT) based total-body irradiation (TBI).
Methods: Twenty patients having received either 2 Gy, 8 Gy, or 12 Gy in 2 Gy per fraction were included. They were immobilized using a vacuum cushion and a three-points mask and positioned on a rotatable tabletop.
We propose an iterative optimization approach for wavefront reconstruction in a rotational shearing interferometer based on Zernike polynomials. Two incorrect shearing amounts are optimized simultaneously, enabling the absolute reconstruction of wavefronts with high uniformity in the root mean square (). Simulations under noisy conditions show that the reconstruction error, in terms of peak-to-valley () and , remains within the range.
View Article and Find Full Text PDFThis work investigates how misalignments of collimation lenses affect two performance criteria: minimum throughput within an angular window and maximum beam height. Based on these criteria, we establish an alignment concept for the first section of a LiDAR emitter. The performance criteria are derived from the overall LiDAR system requirements and applied to an optical system consisting of a laser diode array source, a microlens array for slow-axis collimation, and an acylinder for fast-axis collimation.
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