Validation of a method for <i>in vivo</i> 3D dose reconstruction for IMRT and VMAT treatments using on‐treatment EPID images and a model‐based forward‐calculation algorithm

Uytven, Eric Van; Beek, Timothy Van; McCowan, Peter M.; Chytyk-Praznik, Krista; Greer, Peter B.; McCurdy, Boyd

doi:10.1118/1.4935199

Cited by 60 publications

(52 citation statements)

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“…Several studies have already investigated the dosimetric characteristics and performance of these devices. [21][22][23][24][25] A clear advantage of EPIDs is their availability which makes them suitable for large scale implementations. 16,17 Some EPID-based approaches already allow for patient specific QA by reconstructing 3D dose distributions within the patient or phantom anatomy.…”

Section: Introductionmentioning

confidence: 99%

Transit and non‐transit 3D EPID dosimetry versus detector arrays for patient specific QA

Olaciregui-Ruiz

Vivas-Maiques

Kaas

et al. 2019

J Applied Clin Med Phys

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Purpose Despite their availability and simplicity of use, Electronic Portal Imaging Devices (EPIDs) have not yet replaced detector arrays for patient specific QA in 3D. The purpose of this study is to perform a large scale dosimetric evaluation of transit and non‐transit EPID dosimetry against absolute dose measurements in 3D. Methods After evaluating basic dosimetric characteristics of the EPID and two detector arrays (Octavius 1500 and Octavius 1000SRS), 3D dose distributions for 68 VMAT arcs, and 10 IMRT plans were reconstructed within the same phantom geometry using transit EPID dosimetry, non‐transit EPID dosimetry, and the Octavius 4D system. The reconstructed 3D dose distributions were directly compared by γ‐analysis (2L2 = 2% local/2 mm and 3G2 = 3% global/2 mm, 50% isodose) and by the percentage difference in median dose to the high dose volume (%∆HDVD50). Results Regarding dose rate dependency, dose linearity, and field size dependence, the agreement between EPID dosimetry and the two detector arrays was found to be within 1.0%. In the 2L2 γ‐comparison with Octavius 4D dose distributions, the average γ‐pass rate value was 92.2 ± 5.2%(1SD) and 94.1 ± 4.3%(1SD) for transit and non‐transit EPID dosimetry, respectively. 3G2 γ‐pass rate values were higher than 95% in 150/156 cases. %∆HDVD50 values were within 2% in 134/156 cases and within 3% in 155/156 cases. With regard to the clinical classification of alerts, 97.5% of the treatments were equally classified by EPID dosimetry and Octavius 4D. Conclusion Transit and non‐transit EPID dosimetry are equivalent in dosimetric terms to conventional detector arrays for patient specific QA. Non‐transit 3D EPID dosimetry can be readily used for pre‐treatment patient specific QA of IMRT and VMAT, eliminating the need of phantom positioning.

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Section: Introductionmentioning

confidence: 99%

Transit and non‐transit 3D EPID dosimetry versus detector arrays for patient specific QA

Olaciregui-Ruiz

Vivas-Maiques

Kaas

et al. 2019

J Applied Clin Med Phys

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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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“…The use of EPID-based 3D dosimetry in external beam radiotherapy has been addressed in several studies [e.g., [1][2][3]. The first two papers describe the use of the incident fluence, determined from a measured EPID transit image, followed by Monte Carlo techniques to assess the delivered 3D patient dose distribution.…”

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

“…The first two papers describe the use of the incident fluence, determined from a measured EPID transit image, followed by Monte Carlo techniques to assess the delivered 3D patient dose distribution. Van Uytven et al [3] have developed an algorithm that converts also a measured EPID transit image to incident fluence, and employs thereafter a collapsed-cone convolution calculation to determine the delivered 3D patient dose distribution.In the Netherlands Cancer Institute (NKI) a back-projection algorithm has been implemented for the 3D dose verification of almost all IMRT/VMAT and 3DCRT treatments using in vivo EPID dosimetry [4]. Details of our method and its clinical implementation have been described elsewhere [5].…”

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confidence: 99%

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New developments in EPID-based 3D dosimetry in The Netherlands Cancer Institute

Mijnheer

Rozendaal

Olaciregui-Ruiz

et al. 2017

J. Phys.: Conf. Ser.

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Abstract. EPID-based offline 3D in vivo dosimetry is performed routinely in The NetherlandsCancer Institute for almost all RT treatments. The 3D dose distribution is reconstructed using the EPID primary dose in combination with a back-projection algorithm and compared with the planned dose distribution. Recently the method was adapted for real-time dose verification, performing 3D dose verification in less than 300 ms, which is faster than the current portal frame acquisition rate. In this way a possibility is created for halting the linac in case of large delivery errors. Furthermore, a new method for pre-treatment QA was developed in which the EPID primary dose behind a phantom or patient is predicted using the CT data of that phantom or patient in combination with in-air EPID measurements. This virtual EPID primary transit dose is then used to reconstruct the 3D dose distribution within the phantom or patient geometry using the same dose engine as applied offline. In order to assess the relevance of our clinically applied alert criteria, we investigated the sensitivity of our EPID-based 3D dose verification system to detect delivery errors in VMAT treatments. This was done through simulation by modifying patient treatment plans, as well as experimentally by performing EPID measurements during the irradiation of an Alderson phantom, both after deliberately introducing errors during VMAT delivery. In this presentation these new developments will be elucidated. IntroductionThe use of EPID-based 3D dosimetry in external beam radiotherapy has been addressed in several studies [e.g., 1-3]. The first two papers describe the use of the incident fluence, determined from a measured EPID transit image, followed by Monte Carlo techniques to assess the delivered 3D patient dose distribution. Van Uytven et al [3] have developed an algorithm that converts also a measured EPID transit image to incident fluence, and employs thereafter a collapsed-cone convolution calculation to determine the delivered 3D patient dose distribution.In the Netherlands Cancer Institute (NKI) a back-projection algorithm has been implemented for the 3D dose verification of almost all IMRT/VMAT and 3DCRT treatments using in vivo EPID dosimetry [4]. Details of our method and its clinical implementation have been described elsewhere [5]. Briefly, our back-projection algorithm uses EPID measurements behind a patient or a phantom to determine the EPID primary dose, i.e. the dose component at the level of the EPID resulting from the primary radiation coming from the accelerator head. Using this EPID primary dose, a fast pencil beamtype of dose calculation algorithm reconstructs the 3D dose distribution in a patient or phantom in combination with the CT data of that patient or phantom. Reconstructed 3D dose distributions are then compared with planned dose distributions using 3D γ-evaluation within the 50% isodose surface using global 3%/3mm indicators. This rather high threshold was chosen to avoid artificial improvement of the

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Validation of a method for in vivo 3D dose reconstruction for IMRT and VMAT treatments using on‐treatment EPID images and a model‐based forward‐calculation algorithm

Cited by 60 publications

References 56 publications

Transit and non‐transit 3D EPID dosimetry versus detector arrays for patient specific QA

Transit and non‐transit 3D EPID dosimetry versus detector arrays for patient specific QA

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

New developments in EPID-based 3D dosimetry in The Netherlands Cancer Institute

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