Off-Isocenter Winston-Lutz Test for Stereotactic Radiosurgery/Stereotactic Body Radiotherapy

Gao, Junfang; Liu, Xiaoqian

doi:10.4236/ijmpcero.2016.52017

Cited by 36 publications

(47 citation statements)

References 7 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…Figure 6 clearly shows that the farther the location from the linac isocenter, the larger is the deviation between the field mechanical center and radiation center. We discussed the cause in detail in our previous article [4]. This phenomenon is mainly attributed to mechanical and radiation uncertainty.…”

Section: Discussionmentioning

confidence: 92%

“…This study tried to meet one of the needs of the above-mentioned QA procedures. We will illustrate one practical QA test, which is called the Winston-Lutz-Gao test [4], on the True Beam STx linac for single iso-multiplemets treatment. This test is testing the congruence accuracy between the field mechanical center and radiation center when the asymmetric beam is implemented to treat off-iso multiple mets.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Winston-Lutz-Gao Test on the True Beam STx Linear Accelerator

Gao¹,

Liu²

2019

IJMPCERO

Self Cite

View full text Add to dashboard Cite

In the linear accelerator-based stereotactic radio surgery (SRS) and stereotactic body radiotherapy (SBRT) programs, single isocenter-multiple metastases' treatment has become more and more popular due to their high efficiency in treatment time. However, the absence of a comprehensive quality assurance program is still the challenge for medical physicists. The Winston-Lutz-Gao test, which we developed two years ago, was performed for the first time on a True Beam STx (Varian Medical System) linear accelerator in this study. Beams were designed by Eclipse with gantry, collimator, and couch full rotations, and a 200-pound weight was placed on the couch to mimic real treatment. The "frameless SRS QA target pointer" from the Brainlab company, with a 3.5-mm metallic ball embedded in the center, was used as a phantom. Images were acquired by the portal imager built-in linear accelerator and analyzed directly by the Image browser in ARIA. We found that the farther the metastases were from the linac isocenter, the worse the congruence was between the beam mechanical and the radiation center. The farthest metastases should be within 6 cm from the linac isocenter per the AAPM TG-142 and American Society for Radiation Oncology (ASTRO) white paper criteria. To the best of our knowledge, this is the first off-isocenter Winston-Lutz test performed on a True Beam STx linear accelerator.

show abstract

Section: Discussionmentioning

confidence: 92%

Section: Introductionmentioning

confidence: 99%

Winston-Lutz-Gao Test on the True Beam STx Linear Accelerator

Gao¹,

Liu²

2019

IJMPCERO

Self Cite

View full text Add to dashboard Cite

show abstract

“…9,[11][12][13][14] Spatial accuracy is determined via a number of quality assurance (QA) tests such as "star shots" to verify isocentricity of the gantry, couch, jaws, and MLCs 15 ; the Winston-Lutz test 16 to measure radiation "wobble" over the range of motion of the linear accelerator gantry and couch; as well as vendor provided tests such as the Varian "machine performance check" (MPC). 17 The coincidence of the radiotherapy isocenter and the kV-CBCT imaging coordinate system is typically determined through separate QA tests, 18 although these can sometimes be integrated into a single process such as is the case with the Varian MPC or by adding pre-or post-kV imaging to the Winston-Lutz test.…”

Section: Introductionmentioning

confidence: 99%

Comprehensive radiation and imaging isocenter verification using NIPAM kV‐CBCT dosimetry

et al. 2020

View full text Add to dashboard Cite

Purpose To develop and demonstrate a comprehensive method to directly measure radiation isocenter uncertainty and coincidence with the cone‐beam computed tomography (kV‐CBCT) imaging coordinate system that can be carried out within a typical quality assurance (QA) time slot. Methods An N‐isopropylacrylamide (NIPAM) three‐dimensional (3D) dosimeter for which dose is observed as increased electron density in kV‐CBCT is irradiated at eight couch/gantry combinations which enter the dosimeter at unique orientations. One to three CBCTs are immediately acquired, radiation profile is detected per beam, and displacement from imaging isocenter is quantified. We performed this test using a 5 mm diameter MLC field, and 7.5 and 4 mm diameter cones, delivering approximately 16 Gy per beam. CBCT settings were 1035–4050 mAs, 80–125 kVs, smooth filter, 1 mm slice thickness. The two‐dimensional (2D) displacement of each beam from the imaging isocenter was measured within the planning system, and Matlab code developed in house was used to quantify relevant parameters based on the actual beam geometry. Detectability of the dose profile in the CBCT was quantified as the contrast‐to‐noise ratio (CNR) of the irradiated high‐dose regions relative to the surrounding background signal. Our results were compared to results determined by the traditional Winston‐Lutz test, film‐based “star shots,” and the vendor provided machine performance check (MPC). The ability to detect alignment errors was demonstrated by repeating the test after applying a 0.5 mm shift to the MLCs in the direction of leaf travel. In addition to radiation isocenter and coincidence with CBCT origin, the analysis also calculated the actual gantry and couch angles per beam. Results Setup, MV irradiation, and CBCT readout were carried out within 38 min. After subtracting the background signal from the pre‐CBCT, the CNR of the dosimeter signal from the irradiation with the MLCs (125 kVp, 1035 mAs, n = 3), 7.5 mm cone (125 kVp, 1035 mAs, n = 3), and 4 mm cone (80 kVp, 4050 mAs, n = 1) was 5.4, 5.9, and 2.9, respectively. The minimum radius that encompassed all beams calculated using the automated analysis was 0.38, 0.48, and 0.44 mm for the MLCs, 7.5 mm cone, and 4 mm cone, respectively. When determined manually, these values were slightly decreased at 0.28, 0.41, and 0.40 mm. For comparison, traditional Winston‐Lutz test with MLCs and MPC measured the 3D isocenter radius to be 0.24 mm. Lastly, when a 0.5 mm shift to the MLCs was applied, the smallest radius that intersected all beams increased from 0.38 to 0.90 mm. The mean difference from expected value for gantry angle was 0.19 ± 0.29°, 0.17 ± 0.23°, and 0.12 ± 0.14° for the MLCs, 7.5 mm cone, and 4 mm cone, respectively. The mean difference from expected for couch angle was −0.07 ± 0.28°, −0.08 ± 0.66°, and 0.04 ± 0.25°. Conclusions This work demonstrated the feasibility of a comprehensive isocenter verification using a NIPAM dosimeter with sub‐mm accuracy which incorporates evaluation of coincidence with imaging coordin...

show abstract

“…The results were similar to those reported here, with maximum off‐center errors of less than 1 mm. As described by Gao et al., the increasing deviation between the center of the mechanical and radiation fields with increasing off‐axis distance may be due to the increasing effect of small rotational errors with increasing off‐axis distance. Furthermore, at off‐axis positions, the penumbra of the radiation field becomes asymmetric and the center of the radiation field becomes less well defined, an effect that is magnified with increasing off‐axis distance.…”

Section: Discussionmentioning

confidence: 82%

“…Analysis of the deviation between CBCT/MV isocenters (or Winston‐Lutz) tests was also in agreement with other studies from the literature. Gao et al . reported deviations between WLT errors of less than 1 mm up to 3 cm off‐axis, and errors of up to 1.72 mm at an off‐axis distance of 5 cm.…”

Section: Discussionmentioning

confidence: 99%

Development of a dedicated phantom for multi‐target single‐isocentre stereotactic radiosurgery end to end testing

Poder

Brown

Porter

et al. 2018

J Applied Clin Med Phys

View full text Add to dashboard Cite

PurposeThe aim of this project was to design and manufacture a cost‐effective end‐to‐end (E2E) phantom for quantifying the geometric and dosimetric accuracy of a linear accelerator based, multi‐target single‐isocenter (MTSI) frameless stereotactic radiosurgery (SRS) technique.MethodA perspex Multi‐Plug device from a Sun Nuclear ArcCheck phantom (Sun Nuclear, Melbourne, FL) was enhanced to make it more applicable for MTSI SRS E2E testing. The following steps in the SRS chain were then analysed using the phantom: magnetic resonance imaging (MRI) distortion, planning computed tomography (CT) scan and MRI image registration accuracy, phantom setup accuracy using CBCT, dosimetric accuracy using ion chamber, planar film dose measurements and coincidence of linear accelerator mega‐voltage (MV), and kilo‐voltage (kV) isocenters using Winston‐Lutz testing (WLT).ResultsThe dedicated E2E phantom was able to successfully quantify the geometric and dosimetric accuracy of the MTSI SRS technique. MRI distortions were less than 0.5 mm, or half a voxel size. The average MRI‐CT registration accuracy was 0.15 mm (±0.31 mm), 0.20 mm (±0.16 mm), and 0.39 mm (±0.11 mm) in the superior/inferior, left/right and, anterior/posterior directions, respectively. The phantom setup accuracy using CBCT was better than 0.2 mm and 0.1°. Point dose measurements were within 5% of the treatment planning system predicted dose. The comparison of planar film doses to the planning system dose distributions, performed using gamma analysis, resulted in pass rates greater than 97% for 3%/1 mm gamma criteria. Finally, off‐axis WLT showed MV/kV coincidence to be within 1 mm for off‐axis distances up to 60 mm.ConclusionA novel, versatile and cost‐effective phantom for comprehensive E2E testing of MTSI SRS treatments was developed, incorporating multiple detector types and fiducial markers. The phantom is capable of quantifying the accuracy of each step in the MTSI SRS planning and treatment process.

show abstract

Off-Isocenter Winston-Lutz Test for Stereotactic Radiosurgery/Stereotactic Body Radiotherapy

Cited by 36 publications

References 7 publications

Winston-Lutz-Gao Test on the True Beam STx Linear Accelerator

Winston-Lutz-Gao Test on the True Beam STx Linear Accelerator

Comprehensive radiation and imaging isocenter verification using NIPAM kV‐CBCT dosimetry

Development of a dedicated phantom for multi‐target single‐isocentre stereotactic radiosurgery end to end testing

Contact Info

Product

Resources

About