Utilizing an electronic portal imaging device to monitor light and radiation field congruence

Prisciandaro, Joann I.; Herman, Michael; Kruse, Jon J.

doi:10.1120/jacmp.v4i4.2502

Cited by 14 publications

(12 citation statements)

References 7 publications

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“…EPID has been shown as a useful QA tool to perform this test. 11,12 In the EPID-based approach, images of different MLC square field sizes through the custom designed phantom are acquired and automatically analyzed to quantify the field size. This test relies on the visual verification of light field position against the embedded steel-spheres on the phantom.…”

Section: E2 Collimating System Checksmentioning

confidence: 99%

“…Earlier studies have shown the utility of EPIDs for routine linac QA and dose measurements. 5,6 EPIDs have been used for verification of beam flatness and symmetry, 7 MLC leaf position, 8,9 linac isocenter position, 10 coincidence of the light field and radiation field, 11,12 collimator and couch axis of rotation, 13 leaf gap measurements, 14 beam output, and assessment of jaw alignment. 15 With sub-millimeter spatial resolution, EPIDs are well suited for IMRT plan verification and portal dosimetry.…”

Section: Introductionmentioning

confidence: 99%

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Rapid acceptance testing of modern linac using on-board MV and kV imaging systems

et al. 2017

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Section: E2 Collimating System Checksmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Rapid acceptance testing of modern linac using on-board MV and kV imaging systems

et al. 2017

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“…This test can also be performed using EPID with an object opaque for both light and radiation fields. (65)(66)(67) The Picket Fence test can be also accomplished using a film or an EPID. (68) While the radiation is on, a dynamic MLC plan is executed, which continuously moves the abutted leaf ends from one side to the other while halting at designated locations for several seconds.…”

Section: A2 Mlc Commissioningmentioning

confidence: 99%

Clinical commissioning and use of the Novalis Tx linear accelerator for SRS and SBRT

Kim

Jin

Walls

et al. 2012

J Applied Clin Med Phys

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The purpose of this study was to perform comprehensive measurements and testing of a Novalis Tx linear accelerator, and to develop technical guidelines for commissioning from the time of acceptance testing to the first clinical treatment. The Novalis Tx (NTX) linear accelerator is equipped with, among other features, a high‐definition MLC (HD120 MLC) with 2.5 mm central leaves, a 6D robotic couch, an optical guidance positioning system, as well as X‐ray‐based image guidance tools to provide high accuracy radiation delivery for stereotactic radiosurgery and stereotactic body radiation therapy procedures. We have performed extensive tests for each of the components, and analyzed the clinical data collected in our clinic. We present technical guidelines in this report focusing on methods for: (1) efficient and accurate beam data collection for commissioning treatment planning systems, including small field output measurements conducted using a wide range of detectors; (2) commissioning tests for the HD120 MLC; (3) data collection for the baseline characteristics of the on‐board imager (OBI) and ExacTrac X‐ray (ETX) image guidance systems in conjunction with the 6D robotic couch; and (4) end‐to‐end testing of the entire clinical process. Established from our clinical experience thus far, recommendations are provided for accurate and efficient use of the OBI and ETX localization systems for intra‐ and extracranial treatment sites. Four results are presented. (1) Basic beam data measurements: Our measurements confirmed the necessity of using small detectors for small fields. Total scatter factors varied significantly (30% to approximately 62%) for small field measurements among detectors. Unshielded stereotactic field diode (SFD) overestimated dose by ~ 2% for large field sizes. Ion chambers with active diameters of 6 mm suffered from significant volume averaging. The sharpest profile penumbra was observed for the SFD because of its small active diameter (0.6 mm). (2) MLC commissioning: Winston Lutz test, light/radiation field congruence, and Picket Fence tests were performed and were within criteria established by the relevant task group reports. The measured mean MLC transmission and dynamic leaf gap of 6 MV SRS beam were 1.17% and 0.36 mm, respectively. (3) Baseline characteristics of OBI and ETX: The isocenter localization errors in the left/right, posterior/anterior, and superior/inferior directions were, respectively, −0.2±0.2 mm, −0.8±0.2 mm, and −0.8±0.4 mm for ETX, and 0.5±0.7 mm, 0.6±0.5 mm, and 0.0±0.5 mm for OBI cone‐beam computed tomography. The registration angular discrepancy was 0.1±0.2°, and the maximum robotic couch error was 0.2°. (4) End‐to‐end tests: The measured isocenter dose differences from the planned values were 0.8% and 0.4%, measured respectively by an ion chamber and film. The gamma pass rate, measured by EBT2 film, was 95% (3% DD and 1 mm DTA). Through a systematic series of quantitative commissioning experiments and end‐to‐end tests and our initial clinical experience, described in this ...

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“…Megavoltage (MV) electronic portal imaging device (EPID) has been widely used as an on‐line verification tool for treatment field in radiation therapy 1, 2, 3, 4. While the weight of the verification tool appears to be decreased after the emergence of kilovoltage (kV) imager mounted on a linear accelerator, EPID images still have their own advantages.…”

Section: Introductionmentioning

confidence: 99%

Enhancement of megavoltage electronic portal images for markerless tumor tracking

Cheong

Yoon

Park

et al. 2018

J Applied Clin Med Phys

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PurposeThe poor quality of megavoltage (MV) images from electronic portal imaging device (EPID) hinders visual verification of tumor targeting accuracy particularly during markerless tumor tracking. The aim of this study was to investigate the effect of a few representative image processing treatments on visual verification and detection capability of tumors under auto tracking.MethodsImages of QC‐3 quality phantom, a single patient's setup image, and cine images of two‐lung cancer patients were acquired. Three image processing methods were individually employed to the same original images. For each deblurring, contrast enhancement, and denoising, a total variation deconvolution, contrast‐limited adaptive histogram equalization (CLAHE), and median filter were adopted, respectively. To study the effect of image enhancement on tumor auto‐detection, a tumor tracking algorithm was adopted in which the tumor position was determined as the minimum point of the mean of the sum of squared pixel differences (MSSD) between two images. The detectability and accuracy were compared.ResultsDeblurring of a quality phantom image yielded sharper edges, while the contrast‐enhanced image was more readable with improved structural differentiation. Meanwhile, the denoising operation resulted in noise reduction, however, at the cost of sharpness. Based on comparison of pixel value profiles, contrast enhancement outperformed others in image perception. During the tracking experiment, only contrast enhancement resulted in tumor detection in all images using our tracking algorithm. Deblurring failed to determine the target position in two frames out of a total of 75 images. For original and denoised set, target location was not determined for the same five images. Meanwhile, deblurred image showed increased detection accuracy compared with the original set. The denoised image resulted in decreased accuracy. In the case of contrast‐improved set, the tracking accuracy was nearly maintained as that of the original image.ConclusionsConsidering the effect of each processing on tumor tracking and the visual perception in a limited time, contrast enhancement would be the first consideration to visually verify the tracking accuracy of tumors on MV EPID without sacrificing tumor detectability and detection accuracy.

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Utilizing an electronic portal imaging device to monitor light and radiation field congruence

Cited by 14 publications

References 7 publications

Rapid acceptance testing of modern linac using on-board MV and kV imaging systems

Rapid acceptance testing of modern linac using on-board MV and kV imaging systems

Clinical commissioning and use of the Novalis Tx linear accelerator for SRS and SBRT

Enhancement of megavoltage electronic portal images for markerless tumor tracking

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