Specialist dosimetry and QA vendor PTW has teamed up with medical physicists in the Netherlands to integrate 3D EPID dosimetry within its VERIQA patient QA platform
Ease-of-use and workflow efficiency meet true 3D patient dosimetry and independent radiotherapy QA. That’s the advance billing for VERIQA RT EPID 3D, a suite of 3D EPID dosimetry software that combines phantomless pretreatment and in vivo 3D EPID dosimetry into a single, fully automated QA solution.
Developed by the Netherlands Cancer Institute – Antoni van Leeuwenhoek Hospital (NKI-AVL) in Amsterdam and implemented by dosimetry and QA specialist PTW of Freiburg, Germany, the new software module – which is scheduled for full commercial release in the first quarter of next year – represents the latest extension to the vendor’s VERIQA platform for comprehensive patient QA.
Underpinning the product innovation within VERIQA RT EPID 3D is NKI-AVL’s clinically proven back-projection algorithm, which has been deployed for pretreatment QA and in vivo verification on more than 75,000 patients since 2005 (see “Illuminating 3D back-projection”, below). What’s more, VERIQA RT EPID 3D also uses PTW’s patent-pending Monte Carlo-based inhomogeneity correction. The combination of these two powerful algorithms ensures high-accuracy patient dose reconstruction for all treatment sites (including those – like the lung – characterized by significant density inhomogeneities across their extent).
Collaborate, innovate, automate
Operationally, it helps that PTW has a long-standing collaboration with the NKI-AVL radiation oncology department. From that comes first-hand experience of the latter’s deep domain knowledge and clinical know-how in pretreatment and in vivo EPID dosimetry – insights that will prove crucial for maximizing the long-run clinical benefits and outcomes associated with VERIQA RT EPID 3D.
“The medical physics team at NKI-AVL understands EPID dosimetry inside out – both scientifically and clinically – and is willing to share its knowledge and experience,” explains Julia-Maria Osinga-Blättermann, PTW’s product manager for VERIQA RT EPID 3D. “That sort of engagement makes NKI-AVL a natural fit for PTW and the ideal partner to help us provide a more user-focused EPID dosimetry solution and integrate it into the VERIQA platform.”
Prominent among PTW’s must-have requirements for VERIQA RT EPID 3D is a high degree of automation. That means keeping user interventions to a minimum, says Osinga-Blättermann, with the same standardized and automated workflows used to calculate the 3D patient dose for comparison with the “ground truth” dose prescription from the treatment planning system (TPS). “In the clinic,” she adds, “the user just has to transport the TPS data into VERIQA and acquire the EPID images in vivo during patient treatment or ‘through air’ for the pretreatment QA.”
The name of the game here is 3D patient dosimetry. Put simply, VERIQA RT EPID 3D enables a true 3D dose verification from the acquired EPID images by reconstructing the dose in the patient anatomy. This yields the significant clinical advantage of comparing the EPID-reconstructed dose directly to the planned patient dose as well as the calculation of patient dose–volume histograms (DVHs) for both pretreatment and in vivo dosimetry. “Once a treatment plan has been sent to VERIQA,” explains Osinga-Blättermann, “VERIQA RT EPID 3D will automatically import and assign corresponding EPID images and knows exactly what to do from calculation and evaluation through to notification and documentation.”
A win-win partnership
Reciprocity, of course, provides the framework for all successful collaborations. In this way, the exclusive commercial agreement with PTW also makes sense for the NKI-AVL radiation oncology team – not least in terms of associated licensing revenues, reputation, as well as the wider dissemination and clinical uptake of its proprietary back-projection algorithm and EPID dosimetry know-how.
“Translation of software innovation into clinical impact is part of the operational DNA here,” explains Igor Olaciregui-Ruiz, software physics lead in the NKI-AVL EPID dosimetry group (and therefore instrumental in further enhancing the clinic’s back-projection algorithm). “We want to see the software we’ve built adopted at-scale by the radiation oncology community – but we cannot do that ourselves,” he adds. “It’s much easier to do it in partnership with an established commercial player like PTW.”
In the clinic, meanwhile, VERIQA RT EPID 3D is set to yield significant workflow efficiencies in terms of QA preparation and execution. For starters, the software will give medical physicists the opportunity to streamline and fast-track their pretreatment QA – given that generating EPID images “through air” without the need for a phantom means a lot less effort all round. Those upsides extend to safer treatments, not least because VERIQA RT EPID 3D is able to catch clinically relevant errors through in vivo reconstruction of the actual dose delivered to the patient from EPID images acquired during patient irradiation. This makes it possible to not only detect dose errors that may go unnoticed during pretreatment verification (e.g. changes in the patient position or anatomy), but also to quantitatively assess their dosimetric impact.
“The new VERIQA RT EPID 3D module is like a Swiss army knife: it delivers a fast patient QA solution and provides your radiotherapy treatment chain with an extra safety net,” notes Anton Mans, a medical physicist at NKI-AVL who’s responsible for treatment planning and delivery using EPID dosimetry.
Right now, PTW is finalizing the integration of VERIQA RT EPID 3D into the modular structure of its flagship VERIQA patient QA platform. For the medical physics team, that will ultimately mean verification of each fraction over the course of the patient’s treatment plan – and, at a more granular level, the ability to track the trend of the EPID-reconstructed patient dose over time.
The integration is important along another coordinate, with VERIQA RT EPID 3D also able to leverage VERIQA’s existing Monte Carlo 3D dose engine. The latter is used to calculate an inhomogeneity correction for treatment sites where the back-projection algorithm traditionally falters owing to significant variations in tissue density – for example, dosimetric verification in the lung and oesophagus.
“On top of the EPID back-projected dose,” notes Osinga-Blättermann, “we apply this Monte Carlo inhomogeneity correction to guarantee that we always have the correct 3D patient dose regardless of treatment site.”
Illuminating 3D back-projection
Unlike EPID dosimetry solutions using the so-called “forward approach”, VERIQA RT EPID 3D relies on a back-projection algorithm to enable true 3D dose verification from the acquired EPID images by reconstructing the dose in the patient anatomy. This allows direct comparison with the planned patient dose and the use of clinically relevant comparison metrics such as patient DVHs.
In the forward approach (shown above for in vivo EPID dosimetry), the EPID images are acquired during patient treatment; the treatment plan is used to forward-calculate (predict) EPID images; the measured images are compared against predicted images.
With VERIQA RT EPID 3D’s back-projection approach (shown above for in vivo dosimetry), the EPID images are acquired during patient treatment; the EPID measured dose is back-projected into the patient anatomy; and the reconstructed patient dose is compared against planned dose. Note that the same concept also holds true for EPID-based pretreatment dosimetry.
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- Source: https://physicsworld.com/a/reimagining-patient-qa-3d-epid-dosimetry-leverages-monte-carlo-calculations/
