Time-Resolved Versus Integrated Transit Planar Dosimetry for Volumetric Modulated Arc Therapy

Persoon, L.; Podesta, Mark; Nijsten, S.; Troost, E.G.C.; Verhaegen, Frank

doi:10.1177/1533034615617668

Cited by 22 publications

(22 citation statements)

References 31 publications

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“…Although initially developed for patient setup verification, EPIDs show also useful dosimetric characteristics [36][37][38][39] that have made them suitable for the implementation of IVD verification solutions [8,[40][41][42][43][44][45][46][47][48][49][50]. Beginning in the early 2000 s, the current generation of amorphous-silicon flat-panel EPID technology became commercially available from major linac manufacturers and today is a ubiquitous choice on newly purchased linacs.…”

Section: Epid Dosimetry For Ivdmentioning

confidence: 99%

“…These frames can be grouped according to time, control point, or gantry angle. Offline assessment is performed after delivery and can be performed using both time-resolved and non-time-resolved methods [7,44]. Online assessment is performed in real time using time-resolved analysis so that assessment is made before the total dose has been delivered to the patient, with the aim to interrupt treatment [51,52].…”

Section: Epid Dosimetry For Ivdmentioning

confidence: 99%

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In vivo dosimetry in external beam photon radiotherapy: Requirements and future directions for research, development, and clinical practice

Olaciregui-Ruiz

Beddar

Greer

et al. 2020

Physics and Imaging in Radiation Oncology

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External beam radiotherapy with photon beams is a highly accurate treatment modality, but requires extensive quality assurance programs to confirm that radiation therapy will be or was administered appropriately. In vivo dosimetry (IVD) is an essential element of modern radiation therapy because it provides the ability to catch treatment delivery errors, assist in treatment adaptation, and record the actual dose delivered to the patient. However, for various reasons, its clinical implementation has been slow and limited. The purpose of this report is to stimulate the wider use of IVD for external beam radiotherapy, and in particular of systems using electronic portal imaging devices (EPIDs). After documenting the current IVD methods, this report provides detailed software, hardware and system requirements for in vivo EPID dosimetry systems in order to help in bridging the current vendor-user gap. The report also outlines directions for further development and research. In vivo EPID dosimetry vendors, in collaboration with users across multiple institutions, are requested to improve the understanding and reduce the uncertainties of the system and to help in the determination of optimal action limits for error detection. Finally, the report recommends that automation of all aspects of IVD is needed to help facilitate clinical adoption, including automation of image acquisition, analysis, result interpretation, and reporting/documentation. With the guidance of this report, it is hoped that widespread clinical use of IVD will be significantly accelerated.

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Section: Epid Dosimetry For Ivdmentioning

confidence: 99%

Section: Epid Dosimetry For Ivdmentioning

confidence: 99%

In vivo dosimetry in external beam photon radiotherapy: Requirements and future directions for research, development, and clinical practice

Olaciregui-Ruiz

Beddar

Greer

et al. 2020

Physics and Imaging in Radiation Oncology

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“…Extension to volumetric-modulated arc therapy (VMAT), on the other hand, requires considerable work. To produce true in-patient dose data, 2-D dose maps are needed at every gantry angle (an integrated image over all the arc is less sensitive to dosimetric variations 42 ). This would require CT-based calculation of water equivalent thicknesses, from the source to each pixel, at every gantry angle.…”

Section: Discussionmentioning

confidence: 99%

A Simple Method for 2-D In Vivo Dosimetry by Portal Imaging

Peca

Brown

Smith

2017

Technol Cancer Res Treat

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Purpose:To improve patient safety and treatment quality, verification of dose delivery in radiotherapy is desirable. We present a simple, easy-to-implement, open-source method for in vivo planar dosimetry of conformal radiotherapy by electronic portal imaging device (EPID).Methods:Correlation ratios, which relate dose in the mid-depth of slab phantoms to transit EPID signal, were determined for multiple phantom thicknesses and field sizes. Off-axis dose is corrected for by means of model-based convolution. We tested efficacy of dose reconstruction through measurements with off-reference values of attenuator thickness, field size, and monitor units. We quantified the dose calculation error in the presence of thickness changes to simulate anatomical or setup variations. An example of dose calculation on patient data is provided.Results:With varying phantom thickness, field size, and monitor units, dose reconstruction was almost always within 3% of planned dose. In the presence of thickness changes from planning CT, the dose discrepancy is exaggerated by up to approximately 1.5% for 1 cm changes upstream of the isocenter plane and 4% for 1 cm changes downstream.Conclusion:Our novel electronic portal imaging device in vivo dosimetry allows clinically accurate 2-dimensional reconstruction of dose inside a phantom/patient at isocenter depth. Due to its simplicity, commissioning can be performed in a few hours per energy and may be modified to the user’s needs. It may provide useful dose delivery information to detect harmful errors, guide adaptive radiotherapy, and assure quality of treatment.

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“…Although electronic portal imaging devices (EPIDs) were originally designed for patient position verification, their use for dosimetric applications has been acknowledged both for pretreatment and in vivo dose verification. The dose response characteristics of amorphous silicon (a-Si) EPIDs have been broadly studied, [1][2][3][4][5][6][7][8] and several EPID-based solutions are being used both for intensity-modulated radiation therapy (IMRT) [9][10][11][12][13][14][15] and VMAT [16][17][18][19][20] treatments.…”

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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Time-Resolved Versus Integrated Transit Planar Dosimetry for Volumetric Modulated Arc Therapy

Cited by 22 publications

References 31 publications

In vivo dosimetry in external beam photon radiotherapy: Requirements and future directions for research, development, and clinical practice

In vivo dosimetry in external beam photon radiotherapy: Requirements and future directions for research, development, and clinical practice

A Simple Method for 2-D In Vivo Dosimetry by Portal Imaging

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

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