Online 3D EPID‐based dose verification: Proof of concept

Spreeuw, H.; Rozendaal, R.; Olaciregui-Ruiz, Ígor; González, P.; Mans, A.; Mijnheer, Ben J.; Herk, Marcel van

doi:10.1118/1.4952729

Cited by 51 publications

(48 citation statements)

References 21 publications

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“…DoseTracker accurately predicted the instantaneous validity of the ongoing radiation treatment throughout beam delivery with high frequency and high sensitivity and specificity for all clinically relevant γ ‐fail rate action thresholds. Unlike previous studies of a similar nature, the reconstructed doses and dose evaluations were all benchmarked and validated against simultaneous phantom measurements.…”

Section: Discussionmentioning

confidence: 99%

“…Offline in vivo dosimetry based on electronic portal imaging devices (EPIDs) has been used for some time at several institutions . Recently, real‐time dose delivery verification has been demonstrated, either in two dimensions (2D) by comparison of measured and predicted EPID frames or in 3D by actual real‐time dose reconstruction . However, these methods disregard tumor motion.…”

Section: Introductionmentioning

confidence: 99%

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First online real‐time evaluation of motion‐induced 4D dose errors during radiotherapy delivery

et al. 2018

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

First online real‐time evaluation of motion‐induced 4D dose errors during radiotherapy delivery

et al. 2018

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“…Other work proposing a solution for online dose reconstruction for S&S IMRT and VMAT was performed based on electronic portal imaging devices . This approach mainly aims at the detection of severe treatment errors, which may then result in halting the treatment delivery.…”

Section: Discussionmentioning

confidence: 99%

Online dose reconstruction for tracked volumetric arc therapy: Real‐time implementation and offline quality assurance for prostate SBRT

et al. 2017

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Purpose: Firstly, this study provides a real-time implementation of online dose reconstruction for tracked volumetric arc therapy (VMAT). Secondly, this study describes a novel offline quality assurance tool, based on commercial dose calculation algorithms. Methods: Online dose reconstruction for VMAT is a computationally challenging task in terms of computer memory usage and calculation speed. To potentially reduce the amount of memory used, we analyzed the impact of beam angle sampling for dose calculation on the accuracy of the dose distribution. To establish the performance of the method, we planned two single-arc VMAT prostate stereotactic body radiation therapy cases for delivery with dynamic MLC tracking. For quality assurance of our online dose reconstruction method we have also developed a stand-alone offline dose reconstruction tool, which utilizes the RayStation treatment planning system to calculate dose. Results: For the online reconstructed dose distributions of the tracked deliveries, we could establish strong resemblance for 72 and 36 beam co-planar equidistant beam samples with less than 1.2% deviation for the assessed dose-volume indicators (clinical target volume D98 and D2, and rectum D2). We could achieve average runtimes of 28-31 ms per reported MLC aperture for both dose computation and accumulation, meeting our real-time requirement. To cross-validate the offline tool, we have compared the planned dose to the offline reconstructed dose for static deliveries and found excellent agreement (3%/3 mm global gamma passing rates of 99.8%-100%). Conclusion: Being able to reconstruct dose during delivery enables online quality assurance and online replanning strategies for VMAT. The offline quality assurance tool provides the means to validate novel online dose reconstruction applications using a commercial dose calculation engine.

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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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Online 3D EPID‐based dose verification: Proof of concept

Abstract: A prototype online 3D dose verification tool using portal imaging has been developed and successfully tested for two different kinds of gross delivery errors. Thus, online 3D dose verification has been technologically achieved.

Cited by 51 publications

References 21 publications

First online real‐time evaluation of motion‐induced 4D dose errors during radiotherapy delivery

First online real‐time evaluation of motion‐induced 4D dose errors during radiotherapy delivery

Online dose reconstruction for tracked volumetric arc therapy: Real‐time implementation and offline quality assurance for prostate SBRT

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

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