A 3D star shot to determine the gantry, collimator, and couch axes positions

Corns, Robert; Yang, Kaida; Ross, Mason; Bhandari, Shiva; Aryal, Makunda; Ciaccio, Peter

doi:10.1002/acm2.13623

Cited by 3 publications

(1 citation statement)

References 17 publications

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“…1 Each individual beam CAX is determined across the profile's full width at half max (FWHM), and the isocenter is determined by the confluence of each ray with regards to its CAX. The starshot has traditionally been performed using film, [1][2][3] electronic portal imaging device (EPID) 4,5 or other detectors. 6,7 Specifically, groups have applied starshot techniques to verify MR-RT isocenter using in-house cameras and/or phantoms to detect Cherenkov radiation or optical emission.…”

Section: Introductionmentioning

confidence: 99%

Characterization of mechanical and radiation isocenter on an MR‐guided radiotherapy (MRgRT) Linac

Bassiri

Bayouth

Mittauer

2023

J Applied Clin Med Phys

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Background and PurposeIn the emerging paradigm of stereotactic radiosurgery being proposed for MR‐guided radiotherapy (MRgRT), assessment of mechanical geometric accuracy is critical for the implementation of stereotactic delivery. We benchmarked the mechanical accuracy of an MR Linac system that lacks an onboard detector/array. Our mechanical tests utilize a half beam block (HBB) geometry that takes advantage of the sensitivity of a partially occluded detector.Materials and MethodsMechanical tests benchmarked the couch, MLC, and gantry geometric accuracy for an MR‐Linac system. An HBB technique was used to irradiate an ionization chamber profiler (ICP) array with partial occlusion of individual detectors for characterization of MLC skew, beam divergence displacement, and RT isocenter localization. The sensitivity of the partially occluded detector's ICP‐X (detector width) and ICP‐Y (detector length) was characterized by displacing the detector relative to radiation isocenter by 0.2 mm increments, introduced through couch motion. The accuracy of the HBB ICP technique was verified with a starshot using radiochromic film, and the reproducibility was verified on a conventional C‐arm Linac and compared to Winston‐Lutz.ResultsThe sensitivity of the HBB technique as quantified through the dose difference normalized to open field as a function of displacement from RT isocenter was 6.4%/mm and 13.0%/mm for the ICP‐X and ICP‐Y orientation, respectively, due to the oblong detector orientation. Couch positional accuracy and sag was within ±0.1 mm. Maximum MLC positional displacement was 0.7 mm with mean MLC skew at 0.07°. The maximum beam divergence displacement was 0.03 mm. The gantry angle was within 0.1°. Independent verification of the RT isocenter localization procedure produced repeatable results.ConclusionThis work serves for characterizing the mechanical and geometric radiation accuracy for the foundation of an MR‐guided stereotactic radiosurgery program, as demonstrated with high sensitivity and independent validation.

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Section: Introductionmentioning

confidence: 99%

Characterization of mechanical and radiation isocenter on an MR‐guided radiotherapy (MRgRT) Linac

Bassiri

Bayouth

Mittauer

2023

J Applied Clin Med Phys

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A 3D star shot to determine the gantry, collimator, and couch axes positions

Corns

Yang

Ross

et al. 2022

J Applied Clin Med Phys

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A linear accelerator has three independent axes that are nominally intersecting at the isocenter. Modern treatment techniques require the coincidence of these axes to lie within a 1‐mm diameter sphere. A solution to verify this requirement is to wrap a film on a cylindrical surface, align the cylinder to the linac's isocenter and gantry axis, and take multiple exposures of slits, rotating either the gantry, collimator, or couch between exposures. The resulting exposure pattern is the 3D equivalent of the 2D star shot and encodes sufficient information to determine each axis’ position in 3D. Moreover, this method uses a single sheet 8“x10” film, a standard film scanner, and a phantom that can be readily built in‐house, making a practical solution to this 3D‐measurement problem.

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Quality assurance for cancer patient safety: Clinical assessment for precise angles in linac during radiation therapy

Salahuddin,

Buzdar,

Iqbal

et al. 2024

Tumori

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Purpose: Quality assurance for stereotactic body radiation treatment requires that isocentric verification be ensured during gantry rotation at various angles. This study examined statistical parameters on Winston-Lutz tests to distinguish the deviation of angles from isocenter during gantry rotation using machine learning. Method: The Varian TrueBeam linac was aligned with the marked lines on the Ruby phantom. Eight images were captured while the gantry was rotating at a 45° shift. The statistical features were derived from IsoCheck EPID software. The decision tree model was applied to these Winston-Lutz tests to cluster data into two groups: precise and error angles. Results: At 90° and 270° angles, the gantry exhibits isocentric stability compared to other angles. In these angles, the most statistical features were inside the range. Most variations were observed at 0° and 180° angles. In most tests, the angles 45°, 135°, 225°, and 315° showed reasonable performance and with less variation. Conclusion: The comprehensive statistical analyses for gantry rotation of angles assists expert radiotherapists in determining the contribution of each feature that highly affects gantry movement at specific angles. Misalignment between radiation isocenter and imaging isocenter, tuning of the beam at each angle, or a slight change in the position of the Ruby phantom can further improve the inaccuracy that causes the most variations. Better precision can effectively increase patient safety and quality during cancer treatment.

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A 3D star shot to determine the gantry, collimator, and couch axes positions

Cited by 3 publications

References 17 publications

Characterization of mechanical and radiation isocenter on an MR‐guided radiotherapy (MRgRT) Linac

Characterization of mechanical and radiation isocenter on an MR‐guided radiotherapy (MRgRT) Linac

A 3D star shot to determine the gantry, collimator, and couch axes positions

Quality assurance for cancer patient safety: Clinical assessment for precise angles in linac during radiation therapy

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