First Experience With Real-Time EPID-Based Delivery Verification During IMRT and VMAT Sessions

Woodruff, Henry C.; Fuangrod, Todsaporn; Uytven, Eric Van; McCurdy, Boyd; Beek, Timothy Van; Bhatia, Shashank; Greer, Peter B.

doi:10.1016/j.ijrobp.2015.07.2271

Cited by 59 publications

(82 citation statements)

References 26 publications

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“…With submillimeter spatial resolution, and excellent dose measurement accuracy, linearity to dose and dose rate, and capability of collecting the integrated signal or dynamic signal, the EPID has been widely used for machine QA and pretreatment verification such as patient‐specific IMRT verification 7, 8, 9, 10, 11. Recently many authors have investigated using EPID for in vivo dosimetry 6, 12, 13, 14. Some authors compared reconstructed EPID‐based 3D dose distribution inside the patient to the original treatment plan,6, 13, 14 and some authors compared the EPID‐measured doses to the predicted doses at the EPID level 12.…”

Section: Introductionmentioning

confidence: 99%

“…Recently many authors have investigated using EPID for in vivo dosimetry 6, 12, 13, 14. Some authors compared reconstructed EPID‐based 3D dose distribution inside the patient to the original treatment plan,6, 13, 14 and some authors compared the EPID‐measured doses to the predicted doses at the EPID level 12. In addition, some authors implemented real time dose delivery verification by comparing EPID‐measured images to calculated model‐generated transit EPID images 12.…”

Section: Introductionmentioning

confidence: 99%

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Sensitivity study of an automated system for daily patient QA using EPID exit dose images

Zhuang

Olch

2018

J Applied Clin Med Phys

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The dosimetric consequences of errors in patient setup or beam delivery and anatomical changes are not readily known. A new product, PerFRACTION (Sun Nuclear Corporation), is designed to identify these errors by comparing the exit dose image measured on an electronic portal imaging device (EPID) from each field of each fraction to those from baseline fraction images. This work investigates the sensitivity of PerFRACTION to detect the deviation caused by these errors in a variety of realistic scenarios. Integrated EPID images were acquired in clinical mode and saved in ARIA. PerFRACTION automatically pulled the images into its database and performed the user‐defined comparison. We induced errors of 1 mm and greater in jaw, multileaf collimator (MLC), and couch position, 1° and greater in collimation rotation (patient yaw), 0.5–1.5% in machine output, rail position, and setup errors of 1–2 mm shifts and 0.5–1° roll rotation. The planning techniques included static, intensity modulated radiation therapy (IMRT) and VMAT fields. Rectangular solid water phantom or anthropomorphic head phantom were used in the beam path in the delivery of some fields. PerFRACTION detected position errors of the jaws, MLC, and couch with an accuracy of better than 0.4 mm, and 0.5° for collimator rotation error and detected the machine output error within 0.2%. The rail position error resulted in PerFRACTION detected dose deviations up to 8% and 3% in open field and VMAT field delivery, respectively. PerFRACTION detected induced errors in IMRT fields within 2.2% of the gamma passing rate using an independent conventional analysis. Using an anthropomorphic phantom, setup errors as small as 1 mm and 0.5° were detected. Our work demonstrates that PerFRACTION, using integrated EPID image, is sensitive enough to identify positional, angular, and dosimetric errors.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Sensitivity study of an automated system for daily patient QA using EPID exit dose images

Zhuang

Olch

2018

J Applied Clin Med Phys

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“…The OBI gantry angle encoder signal is very precise (±0.05°)19 and is primarily used for cone‐beam CT image reconstructions. This raw signal was extracted from the header of “dark field” image frames from the KV imager using an existing external frame grabber computer 17, 21, 22. This signal was converted to gantry angle versus time using the known KV image frame rate.…”

Section: Methodsmentioning

confidence: 99%

“…Many of these QA procedures, for example, those which rely on machine log files or information within the EPID image header, rely heavily on the gantry angle readout from the linear accelerator itself to synchronize measurements to the treatment plan. This is also the case for a number of EPID‐based patient‐specific QA techniques19, 20 and delivery verification systems 21, 22. Although, as the hardware is developing, the EPID image header of TrueBeam linac has been shown to be more accurate,23, 24 this alone cannot be used for gantry angle QA as it is not independent of the linac control system.…”

Section: Introductionmentioning

confidence: 99%

A novel and independent method for time‐resolved gantry angle quality assurance for VMAT

Fuangrod

Greer

Zwan

et al. 2017

J Applied Clin Med Phys

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Volumetric‐modulated arc therapy (VMAT) treatment delivery requires three key dynamic components; gantry rotation, dose rate modulation, and multi‐leaf collimator motion, which are all simultaneously varied during the delivery. Misalignment of the gantry angle can potentially affect clinical outcome due to the steep dose gradients and complex MLC shapes involved. It is essential to develop independent gantry angle quality assurance (QA) appropriate to VMAT that can be performed simultaneously with other key VMAT QA testing. In this work, a simple and inexpensive fully independent gantry angle measurement methodology was developed that allows quantitation of the gantry angle accuracy as a function of time. This method is based on the analysis of video footage of a “Double dot” pattern attached to the front cover of the linear accelerator that consists of red and green circles printed on A4 paper sheet. A standard mobile phone is placed on the couch to record the video footage during gantry rotation. The video file is subsequently analyzed and used to determine the gantry angle from each video frame using the relative position of the two dots. There were two types of validation tests performed including the static mode with manual gantry angle rotation and dynamic mode with three complex test plans. The accuracy was 0.26° ± 0.04° and 0.46° ± 0.31° (mean ± 1 SD) for the static and dynamic modes, respectively. This method is user friendly, cost effective, easy to setup, has high temporal resolution, and can be combined with existing time‐resolved method for QA of MLC and dose rate to form a comprehensive set of procedures for time‐resolved QA of VMAT delivery system.

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“…The use of transit EPID dosimetry provides a complementary solution to these methods, able to perform an independent end‐to‐end check of the entire chain, verifying data transfer, dose delivery, patient setup, MLC calibration, and dose calculation, and also synthetic CT determination. Moreover, the EPID is already attached to the machine, and allows for automation and even in real‐time treatment verification . However, it also comes with limitations given the position of the panel with respect to the beam, and when used without taking the magnetic field into account in the back‐projection dose engine.…”

Section: Introductionmentioning

confidence: 99%

Two‐dimensional EPID dosimetry for an MR‐linac: Proof of concept

et al. 2019

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Purpose At our institute, in vivo patient dose distributions are reconstructed for all treatments delivered using conventional linacs from electronic portal imaging device (EPID) transit images acquired during treatment using a simple back‐projection model. Currently, the clinical implementation of MRI‐guided radiotherapy systems, which aims for online and real‐time adaptation of the treatment plan, is progressing. In our department, the MR‐linac (Unity, Elekta AB, Stockholm, Sweden) is now in clinical use. The aim of this work is to demonstrate the feasibility of two‐dimensional (2D) EPID dosimetric verification for the magnetic resonance (MR)‐linac by comparing back‐projected EPID doses to ionization chamber (IC) array dose distributions. Materials and methods Our conventional back‐projection algorithm was adapted for the MR‐linac. The most important changes involve modeling of the attenuation by and scatter from the cryostat. The commissioning process involved the acquisition of square field EPID measurements using various phantom setups (varying SSD, phantom thickness, and field size). Commissioning models were created for gantry 0°, 90°, and 180° and verified by comparing EPID‐reconstructed 2D dose distributions to measurements made with the OCTAVIUS 1500 IC array (PTW, Freiburg, Germany) for two prostate and one rectum IMRT plans (25 beams total). The average of the γ parameters (y‐mean and y‐pass rate) and the dose difference at a reference point were reported. Due to their construction, the attenuation of couch, bridge, and cryostat shows a much stronger dependence on gantry angle in the MR‐linac compared to conventional linacs. We present a method to correct for these effects. This method is validated by dose reconstruction of the 25 intensity‐modulated radiation therapy beams recorded at a certain gantry angle using the model of another gantry angle, combined with the correction method. Results For dose verification performed at a gantry angle identical to the commissioned model, the average y‐mean and y‐pass rate values (3% global dose, 2 mm, 10% isodose) were 0.37 ± 0.07 and 98.1, 95% CI [98.1 ± 2.4], respectively. The average dose difference at the reference point was −0.5% ± 1.8%. Verification at gantry angles different from the commissioned model (i.e., using the gantry angle dependent correction) reported 0.39 ± 0.08 and 97.6, 95% CI [96.9, 98.3] average y‐mean and y‐pass rate values. The average dose difference at the reference point was −0.1% ± 1.8%. Conclusion The EPID dosimetry back‐projection model was successfully adapted for the MR‐linac at gantry 0°, 90°, and 180°, accounting for the presence of the MRI housing between phantom (or patient) and the EPID. A method to account for the gantry angle dependence was also tested reporting similar results.

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First Experience With Real-Time EPID-Based Delivery Verification During IMRT and VMAT Sessions

Cited by 59 publications

References 26 publications

Sensitivity study of an automated system for daily patient QA using EPID exit dose images

Sensitivity study of an automated system for daily patient QA using EPID exit dose images

A novel and independent method for time‐resolved gantry angle quality assurance for VMAT

Two‐dimensional EPID dosimetry for an MR‐linac: Proof of concept

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