Long‐term evaluation and cross‐checking of two geometric calibrations of kV and MV imaging systems for Linacs

Chiu, Tsuicheng; Yan, Yulong; Foster, Ryan; Mao, Weihua

doi:10.1120/jacmp.v16i4.5140

Cited by 7 publications

(6 citation statements)

References 8 publications

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“…For accurate IGRT the imaging system and radiation isocenters must coincide . This is achieved on Varian linacs using the IsoCal calibration procedure, which has been validated by Gao et al, 2014 and by Chiu et al, 2015 . The kV and MV systems share a common axis of gantry rotation.…”

Section: Methodsmentioning

confidence: 99%

Evaluation of the truebeam machine performance check (MPC) geometric checks for daily IGRT geometric accuracy quality assurance

Barnes

Greer

2017

J Applied Clin Med Phys

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Machine Performance Check (MPC) is an automated and integrated image‐based tool for verification of beam and geometric performance of the TrueBeam linac. The aims of the study were to evaluate the performance of the MPC geometric tests relevant to OBI/CBCT IGRT geometric accuracy. This included evaluation of the MPC isocenter and couch tests. Evaluation was performed by comparing MPC to QA tests performed routinely in the department over a 4‐month period. The MPC isocenter tests were compared against an in‐house developed Winston–Lutz test and the couch compared against routine mechanical QA type procedures. In all cases the results from the routine QA procedure was presented in a form directly comparable to MPC to allow a like‐to‐like comparison. The sensitivity of MPC was also tested by deliberately miscalibrating the appropriate linac parameter. The MPC isocenter size and MPC kV imager offset were found to agree with Winston–Lutz to within 0.2 mm and 0.22 mm, respectively. The MPC couch tests agreed with routine QA to within 0.12 mm and 0.15°. The MPC isocenter size and kV imager offset parameters were found to be affected by a change in beam focal spot position with the kV imager offset more sensitive. The MPC couch tests were all unaffected by an offset in the couch calibration but the three axes that utilized two point calibrations were sensitive to a miscalibration of the size in the span of the calibration. All MPC tests were unaffected by a deliberate misalignment of the MPC phantom and roll of the order of one degree.

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Section: Methodsmentioning

confidence: 99%

Evaluation of the truebeam machine performance check (MPC) geometric checks for daily IGRT geometric accuracy quality assurance

Barnes

Greer

2017

J Applied Clin Med Phys

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“…Both ETX and CBCT were previously calibrated to the machine radiation isocenter. An IsoCal calibration [11] was performed to calibrate the CBCT. The Winston-Lutz [7] test was thereafter performed with a pointer to calibrate ETX to the radiation isocenter.…”

Section: Setup and Irradiationmentioning

confidence: 99%

Positioning accuracy of a single-isocenter multiple targets SRS treatment: A comparison between Varian TrueBeam CBCT and Brainlab ExacTrac

et al. 2020

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“…Another 8 DOF approach to geometric quality assurance is the work by Mao et al that introduced the gQA phantom that characterize source position and imager deformations for both MV and kV imaging. The long‐term stability and accuracy of this system has already been evaluated . However, some DOF in the system are neglected.…”

Section: Introductionmentioning

confidence: 99%

“…The longterm stability and accuracy of this system has already been evaluated. 5 However, some DOF in the system are neglected. Indeed, gantry rotations around every axis should be measured.…”

Section: Introductionmentioning

confidence: 99%

An EPID‐based method to determine mechanical deformations in a linear accelerator

Gourdeau

Gingras²,

Beaulieu³

et al. 2018

Medical Physics

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Purpose Medical linear accelerators (linac) are delivering increasingly complex treatments using modern techniques in radiation therapy. Complete and precise mechanical QA of the linac is therefore necessary to ensure that there is no unexpected deviation from the gantry's planned course. However, state‐of‐the‐art EPID‐based mechanical QA procedures often neglect some degrees of freedom (DOF) like the in‐plane rotations of the gantry and imager or the source movements inside the gantry head. Therefore, the purpose of this work is to characterize a 14 DOF method for the mechanical QA of linacs. This method seeks to measure every mechanical deformation in a linac, including source movements, in addition to relevant clinical parameters like mechanical and radiation isocenters. Methods A widely available commercial phantom and a custom‐made accessory inserted in the linac's interface mount are imaged using the electronic portal imaging device (EPID) at multiple gantry angles. Then, simulated images are generated using the nominal geometry of the linac and digitized models of the phantoms. The nominal geometry used to generate these images can be modified using 14 DOF (3 rigid rotations and 3 translations for the imager and the gantry, and 2 in‐plane translations of the source) and any change will modify the simulated image. The set of mechanical deformations that minimizes the differences between the simulated and measured image is found using a genetic algorithm coupled with a gradient‐descent optimizer. Phantom mispositioning and gantry angular offset were subsequently calculated and extracted from the results. Simulations of the performances of the method for different levels of noise in the phantom models were performed to calculate the absolute uncertainty of the measured mechanical deformations. The measured source positions and the center of collimation were used to define the beam central axis and calculate the radiation isocenter position and radius. Results After the simultaneous optimization of the 14 DOF, the average distance between the center of the measured and simulated ball bearings on the imager was 0.086 mm. Over the course of a full counter‐clockwise gantry rotation, all mechanical deformations were measured, showing sub‐millimeter translations and rotations smaller than 1° along every axis. The average absolute uncertainty of the 14 DOF (1 SD) was 0.15 mm or degree. Phantom positioning errors were determined with more than 0.1 mm precision. Errors introduced in the experimental setup like phantom positioning errors, source movements or gantry angular offsets were all successfully detected by our QA method. The mechanical deformations measured are shown to be reproducible over the course of a few weeks and are not sensitive to the experimental setup. Conclusion This work presents of new method for an accurate mechanical QA of the linacs. It features a 14 DOF model of the mechanical deformations that is both more complete and precise than other available methods. It has demonstrated sub‐millimeter ...

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Long‐term evaluation and cross‐checking of two geometric calibrations of kV and MV imaging systems for Linacs

Cited by 7 publications

References 8 publications

Evaluation of the truebeam machine performance check (MPC) geometric checks for daily IGRT geometric accuracy quality assurance

Evaluation of the truebeam machine performance check (MPC) geometric checks for daily IGRT geometric accuracy quality assurance

Positioning accuracy of a single-isocenter multiple targets SRS treatment: A comparison between Varian TrueBeam CBCT and Brainlab ExacTrac

An EPID‐based method to determine mechanical deformations in a linear accelerator

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