Image movement of the Elekta EPID during gantry rotation: Effects on the verification of dose distributions

Köhn, Janett; Licher, Jörg; Mielke, Maja; Loutfi-Krauss, Britta; Blümer, N.; Heine, B.; Rödel, Claus; Scherf, Christian; Ramm, U.

doi:10.1016/j.ejmp.2017.01.017

Cited by 7 publications

(4 citation statements)

References 42 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…In clinical quality assurance procedure, static open‐field EPID images of a ball‐bearing phantom at several gantry angles were evaluated to detect the isocenter shift 12 . However, the real VMAT delivery is more complicated because the gantry rotation speed changes dynamically 5,13,14 . We measured the open‐field EPID images in both clockwise and counterclockwise directions at several rotation speeds by changing the dose rates (100, 400, and 700 MU/min), and generated a set of flex maps.…”

Section: Methodsmentioning

confidence: 99%

“…12 However, the real VMAT delivery is more complicated because the gantry rotation speed changes dynamically. 5,13,14 We measured the open-field EPID images in both clockwise and counterclockwise directions at several rotation speeds by changing the dose rates (100, 400, and 700 MU/min), and generated a set of flex maps. Based on the rotation directions and speed, the flex map for a specific VMAT arc delivery could be interpolated from the set of flex maps we generated,and the acquired EPID image were corrected using the specific flex map.…”

Section: Mlc Motion Modelingmentioning

confidence: 99%

See 1 more Smart Citation

Technical note: Preprocessing of portal images to improve image quality of VMAT‐CT

Chien,

Zhao,

Guo

et al. 2023

Medical Physics

View full text Add to dashboard Cite

BackgroundThe concept of volumetric modulated arc therapy‐computed tomography (VMAT‐CT) was proposed more than a decade ago. However, its application has been very limited mainly due to the poor image quality. More specifically, the blurred areas in electronic portal imaging device (EPID) images collected during VMAT heavily degrade the image quality of VMAT‐CT.PurposeThe goal of this study was to propose systematic methods to preprocess EPID images and improve the image quality of VMAT‐CT.MethodsOnline region‐based active contour method was introduced to binarize portal images. Multi‐leaf collimator (MLC) motion modeling was developed to remove the MLC motion blur. Outlier filtering was then applied to replace the remaining artifacts with plausible data. To assess the impact of these preprocessing methods on the image quality of VMAT‐CT, 44 clinical VMAT plans for several treatment sites (lung, esophagus, and head & neck) were delivered to a Rando phantom, and several real‐patient cases were also acquired. VMAT‐CT reconstruction was attempted for all the cases, and image quality was evaluated.ResultsAll three preprocessing methods could effectively remove the blurred edges of EPID images. The combined preprocessing methods not only saved VMAT‐CT from distortions and artifacts, but also increased the percentage of VMAT plans that can be reconstructed.ConclusionsThe systematic preprocessing of portal images improves the image quality of VMAT‐CT significantly, and facilitates the application of VMAT‐CT as an effective image guidance tool.

show abstract

Section: Methodsmentioning

confidence: 99%

Section: Mlc Motion Modelingmentioning

confidence: 99%

Technical note: Preprocessing of portal images to improve image quality of VMAT‐CT

Chien,

Zhao,

Guo

et al. 2023

Medical Physics

View full text Add to dashboard Cite

show abstract

“…Several studies have examined the effect of gantry and electronic portal imaging device (EPID) sag on both the geometric and dosimetric accuracy of conventional radiotherapy (AAPM 2009, Du et al 2012, Rowshanfarzad et al 2012, Riis et al 2013, Rowshanfarzad et al 2014, Denton et al 2015, Köhn et al 2017, Riis et al 2019, Chen et al 2020, Riis et al 2020. Gantry sag is known to be a major mechanical source of spatial inaccuracy.…”

Section: Introductionmentioning

confidence: 99%

Variation in isocentre location of an Elekta Unity MR-linac through full gantry rotation

et al. 2022

View full text Add to dashboard Cite

Objective: The objective of this study was to separately quantify the stability of the megavoltage imager (MVI) and radiation head of an Elekta Unity MRL, throughout full gantry rotation. Approach: A ball-bearing (BB) phantom was attached to the radiation head of the Unity, while a single BB was placed at isocentre. Images were acquired during rotation, using the MVI. These images were processed using an in-house developed MATLAB program to reduce the errors resulted by noise, and the positions of the BBs in the images were analysed to extract MVI and radiation head sag data. Main results: The results returned by this method showed reproducibility, with a mean standard deviation of 7 µm for the position of BBs across all gantry angles. The radiation head was found to sag throughout rotation, with a maximum course of movement of 0.59 mm. The sag pattern was stable over a period greater than a year but showed some dependence on gantry rotation direction. Significance: As MRL is a relatively new system, it is promising to have data supporting the high level of precision on one Elekta Unity machine. Isolating and quantifying the sources of uncertainty in radiation delivery may allow more sophisticated analysis of how the system performance may be improved.

show abstract

“…EPID has been introduced to LINAC systems since the early 1980s 4 . It was initially developed for verifying the patient position and was later applied to LINAC QA 5‐12 . Compared with films and other QA devices, EPID has two major advantages 13‐15 : first, since EPID is integrated with the LINAC gantry, the QA procedure can be setup more quickly; second, the EPID data are in a digital form, which greatly facilitates the postprocessing, transfer, analysis, and storage of the data.…”

Section: Introductionmentioning

confidence: 99%

An electronic portal image device (EPID)‐based multiplatform rapid daily LINAC QA tool

Wang²,

Mai

et al. 2021

J Applied Clin Med Phys

View full text Add to dashboard Cite

PurposeTo develop an efficient and economic daily quality research tool (DQRT) for daily check of multiplatform linear accelerators (LINACs) with flattening filter (FF) and flattening filter‐free (FFF) photon beams by using an Electronic Portal Image Device (EPID).Materials and MethodsAfter EPID calibration, the monitored parameters were analyzed from a 10 cm × 10 cm open and 60° wedge portal images measured by the EPID with 100 MU exposure. Next, the repeatability of the EPID position accuracy, long‐term stability, and linearity between image gray value and exposure were verified. Output and beam quality stability of the 6‐MV FF and FFF beams measured by DQRT with the introduced setup errors of EPID were also surveyed. Besides, some test results obtained by DQRT were compared with those measured by FC65‐G and Matrixx. At last, the tool was evaluated on three LINACs (Synergy, VersaHD, TrueBeam) for 2 months with two popular commercial QA tools as references.ResultsThere are no differences between repeatability tests for all monitored parameters. Image grayscale values obtained by EPID and exposure show good linearity. Either 6 MV FF or FFF photon beam shows minimal impact to the results. The differences between FC65‐G, Matrixx and DQRT results are negligible. Monitor results of the two commercial tools are consistent with the DQRT results collected during the 2‐month period.ConclusionWith a shorter time and procedure, the DQRT is useful to daily QA works of LINACs, producing a QA result quality similarly to or more better than the traditional tools and giving richer contents to the QA results. For hospitals with limited QA time window available or lack of funding to purchase commercial QA tools, the proposed DQRT can provide an alternative and economic approach to accomplish the task of daily QA for LINACs.

show abstract

Image movement of the Elekta EPID during gantry rotation: Effects on the verification of dose distributions

Cited by 7 publications

References 42 publications

Technical note: Preprocessing of portal images to improve image quality of VMAT‐CT

Technical note: Preprocessing of portal images to improve image quality of VMAT‐CT

Variation in isocentre location of an Elekta Unity MR-linac through full gantry rotation

An electronic portal image device (EPID)‐based multiplatform rapid daily LINAC QA tool

Contact Info

Product

Resources

About