Comparison of two different EPID-based solutions performing pretreatment quality assurance: 2D portal dosimetry versus 3D forward projection method

Bresciani, S.; Poli, Matteo Umberto; Miranti, A.; Maggio, A.; Dia, A. Di; Bracco, Christian; Gabriele, P.; Stasi, M.

doi:10.1016/j.ejmp.2018.06.005

Cited by 26 publications

(32 citation statements)

References 21 publications

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“…One of the approaches to accomplish this is the use of in vivo dose verification using megavoltage (MV) transmission images gathered during treatment by an Electronic Portal Imaging Device (EPID), which has been demonstrated to be a powerful tool for error detection in radiotherapy. [15][16][17][18][19] Previously, Cancer-Care Manitoba has implemented a 3D in vivo patient dose verification system that relies on transmission EPID images. [20][21][22][23][24][25] It supports modern radiotherapy techniques that use conventional co-planar beam arrangements, such as IMRT and VMAT, 23 and has been validated for those treatment delivery methods using coplanar geometry and static couch at 0°.…”

Section: Introductionmentioning

confidence: 99%

“…Advanced quality assurance (QA) and dose verification procedures help reduce these risks. One of the approaches to accomplish this is the use of in vivo dose verification using megavoltage (MV) transmission images gathered during treatment by an Electronic Portal Imaging Device (EPID), which has been demonstrated to be a powerful tool for error detection in radiotherapy 15‐19 . Previously, CancerCare Manitoba has implemented a 3D in vivo patient dose verification system that relies on transmission EPID images 20‐25 .…”

Section: Introductionmentioning

confidence: 99%

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Verification of the delivered patient radiation dose for non‐coplanar beam therapy

Kutuzov

Beek

McCurdy

2021

J Applied Clin Med Phys

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Purpose: There is an increased interest in using non-coplanar beams for radiotherapy, including SBRT and SRS. This approach can significantly reduce doses to organs-at-risk, however, it requires stringent quality assurance, especially when a dynamic treatment couch is used. In this work, new functionality that allows using non-coplanar beam arrangements in addition to conventional coplanar beams was added and validated to the previously developed in vivo dose verification system.Methods: The existing program code was modified to manage the additional treatment couch parameters: angle and positions. Ten non-coplanar test plans that use a static couch were created in the treatment planning system. Also, two plans that use a dynamic treatment couch were created and delivered using Varian Developer mode, since the treatment planning system does not support a dynamic couch. All non-coplanar test trajectories were delivered on a simple geometric phantom, using an Edge linear accelerator (Varian Medical Systems) with the megavoltage imager deployed and acquiring megavoltage transmission images that were used to calculate the delivered 3D dose distributions in the phantom with the updated dose calculation algorithm. The reconstructed dose distributions were compared using the 3D chi-comparison test with 2%/2mm tolerances to the corresponding reference dose distributions obtained from the treatment planning system. Results:The chi-comparison test resulted in at least a 97.0% pass rate over the entire 3D volume for all tested trajectories. For static gantry, static couch noncoplanar fields, and non-coplanar arcs using dynamic couch the pass rates observed were at least 98%, while for the static couch, non-transverse coplanar arc fields, pass rates were at least 97%.Conclusions: A model-based 3D dose calculation algorithm has been extended and validated for a variety of non-coplanar beam trajectories of different complexities.This system can potentially be applied for quality assurance of treatment delivery systems that use complex, non-coplanar beam arrangements.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Verification of the delivered patient radiation dose for non‐coplanar beam therapy

Kutuzov

Beek

McCurdy

2021

J Applied Clin Med Phys

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“…Additional conventional QA methods include fluence measurements, with associated dose recalculation and comparison with the planned patient dose, [7][8][9] and linac-log file analysis with dose recalculation. 10,11 On the positive side, the decision metrics for those dose recalculation methods are often based on the clinically relevant quantity, estimated patient dose, allowing straight forward assessment of potential clinical relevance of observed variances.…”

Section: Introductionmentioning

confidence: 99%

An error detection method for real‐time EPID‐based treatment delivery quality assurance

et al. 2020

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To quantify the error detection power of a new treatment delivery error detection method. The method validates monitor unit (MU) resolved beam apertures using real-time EPID images. Methods: The on-board EPID imager was used to measure cine-EPID (~10 Hz) images for 27 beams from 15 VMAT/SBRT clinical treatment plans and five nonclinical plans. For each frame acquisition, planned apertures were interpolated from the treatment plan multileaf collimator (MLC) positions expected during the frame acquisition interval. Inaccurate deliveries were identified by monitoring in-aperture missed fluence and out-of-aperture excess fluence beyond a specified buffer. Delivery errors were simulated by perturbing the planned MLC positions before comparison with nonperturbed measured apertures. Systematic 1-5 mm MLC leaf shifts were used to train a logistic regression model to determine the error detection threshold. Model accuracy was monitored using tenfold cross-validation. The model's error detection ability was tested with other error modes: plan control point (CP) weight perturbations, collimator rotations, random MLC leaf position errors, EPID imager shift, and stuck MLC leaf. The error detection accuracy was evaluated using the Matthews correlation coefficient (MCC) and the false positive rate (FPR). Per-beam error thresholds of >1, >5, and >10% errant frames were tested to label per-beam errors. The model also was tested for its ability to distinguish five cases with highly similar plans and compared with gamma analysis. Results: Delivery errors were detected by monitoring intended per-frame images with a 2 mm MLC buffer. Frame-by-frame aperture errors were identified with an optimal threshold of 0.3% of the expected aperture area. The per-frame FPR was 0.02%. The MCC was 1.00 (perfect classification) for detection based on 1% of frames for random CP weight shift, 3 mm random MLC shifts, 90°and 180°collimator rotations, and an MLC leaf stuck after 10% of the beam delivery. The MCC for 2°, 4°, and 8°collimator rotation were 0.53, 0.76, and 0.96, respectively, for the 1% of beam delivery threshold. The 3 mm EPID shift had poor detection, with a minimum MCC of 0.14. The highly similar plans were reliably detected by the aperture check but were not detectable with gamma analysis. Conclusion: The high error detection sensitivity and low FPR makes the aperture check error detection method well suited to pretreatment and during-treatment beam delivery quality assurance (QA). The aperture check detects subtle beam delivery errors, including those resulting from MLC leaf positioning deviations, CP MU shifts, and stuck MLC leaves. Furthermore, the method can distinguish between highly similar treatment plans. Since the aperture check method monitors for the aperture shapes over a given MU interval, it is also sensitive to errors in MU per CP, without requiring dosimetric calibration of the EPID. The aperture check is one part of a Swiss cheese error detection scheme, which provides redundant error testing of multiple error modes, in...

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“…The technology to verify dose delivery by direct dose measurement for every beam, every fraction, and every patient is not always practical. Hence, there are numerous solutions to verify the pre-treatment delivery to a phantom [1,2]. However, pretreatment QA is the least sensitive tool to detect errors out of all control checks in radiation oncology [3], highlighting the need for real-time patient specific QA.…”

Section: Introductionmentioning

confidence: 99%

Two-dimensional real-time quality assurance dosimetry system using μ-Al2O3:C,Mg radioluminescence films

Nascimento

Verellen

Goossens

et al. 2020

Physics and Imaging in Radiation Oncology

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Background and purpose: There is a continual need for more accurate and effective dosimetric systems for quality assurance (QA) as radiotherapy evolves in complexity. The purpose of this project was to introduce a new system that minimally perturbs the main beam, while assessing its real time 2D dose-rate and field shapes. The system combined reusability, linear dose-rate response, and high spatial and time resolution in a single radiation detection technology that can be applied to surface dose estimation and QA. Materials and methods: We developed a 2D prototype system consisting of a camera, focusing lenses and short pass filter, placed on the head of a linear accelerator, facing an Al 2 O 3 :C,Mg radioluminescent film. To check the appropriateness of multi-leaf collimator, stability/reproducibility QA tests were prepared using the treatment planning system: including the routinely used alternating leaves, chair and pyramid checks. Results: The Al 2 O 3 :C,Mg film did not perturb the dose vs. depth dose curves determined with a point detector (-0.5% difference). Our results showed a dose-rate linear film response (R 2 = 0.999), from 5 to 600 MU/min. Measured output factors agreed with reference data within ~1%, indicating a potential for small field dosimetry. Both chair and pyramid measured profiles were comparable with those obtained with the treatment planning system within 1%. The alternating leaves test showed an average discrepancy in the valleys of 14%. Conclusions: The prototype demonstrated promising results. It obviated the need for corrections regarding the relative position of the camera, confirming accurate dose-rate delivery and detection of radiation fields.

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Comparison of two different EPID-based solutions performing pretreatment quality assurance: 2D portal dosimetry versus 3D forward projection method

Cited by 26 publications

References 21 publications

Verification of the delivered patient radiation dose for non‐coplanar beam therapy

Verification of the delivered patient radiation dose for non‐coplanar beam therapy

An error detection method for real‐time EPID‐based treatment delivery quality assurance

Two-dimensional real-time quality assurance dosimetry system using μ-Al2O3:C,Mg radioluminescence films

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