ESTRO 2025 - Abstract Book

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Radiotherapy &Oncology Journal of the European SocieTy for Radiotherapy and Oncology

Volume 206 Supplement 1 (2025)

Radiotherapy & Oncology is available online: For ESTRO members: http://www.thegreenjournal.com For institutional libraries: http://www.sciencedirect.com

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P. Blanchard

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2-6 May 2025 Vienna, Austria

Table of contents

Invited Speaker..................................................................................................................................................................1-163

BRACHYTHERAPY

Breast.............................................................................................................................................................................. 164-172 Gastro-intestinal, paediatric brachytherapy, miscellaneous.....................................................................................173-195 General........................................................................................................................................................................... 196-205 Gynaecology................................................................................................................................................................... 206-287 Head & neck, skin, eye..................................................................................................................................................288-314 Physics............................................................................................................................................................................ 315-367 Urology ..........................................................................................................................................................................368-402

CLINICAL

Biomarkers..................................................................................................................................................................... 403-421 Breast.............................................................................................................................................................................. 422-641 CNS.................................................................................................................................................................................. 642-769 Gynaecology................................................................................................................................................................... 770-889 Haematology.................................................................................................................................................................. 890-924 Head & neck.................................................................................................................................................................925-1145 Lower GI.....................................................................................................................................................................1146-1284 Lung............................................................................................................................................................................1285-1453 Mixed sites, palliation...............................................................................................................................................1454-1611 Paediatric tumours....................................................................................................................................................1612-1657 Sarcoma, skin cancer, malignant melanoma..........................................................................................................1658-1735 Upper GI.....................................................................................................................................................................1736-1871 Urology.......................................................................................................................................................................1872-2147

INTERDISCIPLNARY

Education in radiation oncology..............................................................................................................................2148-2211 Global health..............................................................................................................................................................2212-2256 Health economics & health services research........................................................................................................2257-2339 Other ..........................................................................................................................................................................2340-2418

PHYSICS

Autosegmentation.....................................................................................................................................................2419-2565 Detectors, dose measurement and phantoms......................................................................................................2566-2684 Dose calculation algorithms.....................................................................................................................................2685-2714 Dose prediction, optimisation and applications of photon and electron planning............................................2715-2942 Image acquisition and processing including ML based methods.........................................................................2943-3073 Inter-fraction motion management and offline adaptive radiotherapy .............................................................3074-3194 Intra-fraction motion management and real-time adaptive radiotherapy ..........................................................3195-3357 Machine learning models and clinical applications...............................................................................................3358-3455 Optimisation, algorithms and applications for ion beam treatment planning...................................................3456-3577 Quality assurance and auditing . .............................................................................................................................3578-3708 Radiomics, functional and biological imaging and outcome prediction..............................................................3709-3870

RADIOBIOLOGY

Immuno-radiobiology . ..............................................................................................................................................3871-3890 Microenvironment .....................................................................................................................................................3891-3908 Normal tissue radiobiology ......................................................................................................................................3909-3961 Tumour radiobiology . ...............................................................................................................................................3962-4030

RTT

Patient care, preparation, immobilisation and IGRT verification protocols ........................................................4031-4148 Patient experience and quality of life ......................................................................................................................4149-4214 Education, training, advanced practice and role developments . .........................................................................4215-4279 Service evaluation, quality assurance and risk management ...............................................................................4280-4308 Treatment planning, OAR and target definitions ...................................................................................................4309-4409

Late-breaking .............................................................................................................................................................4410-4434

SPEAKER ABSTRACT Invited Speaker

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Speaker Abstracts TOPGEAR Trevor Leong Radiation Oncology, Peter MacCallum Cancer Centre, Melbourne, Australia. Sir Peter MacCallum Department of Oncology, University of Melbourne, Melbourne, Australia

Abstract:

TOPGEAR is an international randomised phase 3 trial of preoperative chemoradiation for resectable gastric and gastro-oesophageal junction cancer. The final results of TOPGEAR were presented at ESMO 2024 in Barcelona with simultaneous publication in the New England Journal of Medicine. Overall, the TOPGEAR data was not favourable for radiation oncology, and together with results from several other recent phase 3 trials, suggests a diminished role for radiotherapy in gastrointestinal malignancies, particularly gastro-oesophageal cancer. Nevertheless, there are many positive aspects of the TOPGEAR trial, including the comprehensive quality assurance program and global recruitment of participants. This talk will discuss the strengths of the trial, areas for improvement, and strategies for future development of radiotherapy in gastro-oesophageal cancer. The talk will also review media reporting of the TOPGEAR results and its influence on clinician perception of radiotherapy.

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Speaker Abstracts Is in-house development cost effective? Peter Remeijer Department of Radiotherapy, The Netherlands Cancer institute, Amsterdam, Netherlands

Introduction

Historically, in-house software development has been important in specialized fields like radiation oncology, especially where industry solutions were unavailable or insufficient. Institutions such as the Netherlands Cancer Institute (NKI) have developed software to meet both specific clinical and research needs, and were also successful in setting up collaborations with industry. Because of the small scale of many of these developments, and limited regulatory demands, the required investments remained manageable. Recent regulatory changes, however, for example the Medical Device Regulation (MDR) in Europe, have significantly increased the complexity and cost of in-house software development. Compliance demands extensive documentation, validation, prospective risk assessments, and adherence to strict quality management systems. While external audits may not be required for in-house developed applications, the internal regulatory process adds substantial time and effort as well. Furthermore, modern software development practices also contribute to rising costs. Version control, automated testing (unit, system, and integration tests), and maintaining separate environments for development, testing, acceptance, and production require additional infrastructure and effort. While these practices enhance the quality and maintainability of the software, they also extend development timelines and required resources.

The cost of in-house developed software versus commercial software

To illustrate the cost of developing medical in-house software, including MDR compliance, we examine two recent in-house software developments at the NKI: AI autocontouring for brachytherapy 1 , and SmartAdapt 2 . Both applications do not involve any user interaction and generate DICOM outputs (RTstructs, and virtual CT scans and

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virtual RTstructs, respectively) based on predefined input parameters. The applications were developed within a DevOps framework, utilizing Microsoft Azure, with dedicated teams of two to three full-time equivalents (FTEs).

All applications were built around a microservice infrastructure, aimed at scalability, maintainability, and the reusability of software. The total development time was 2 years for AI autocontouring for brachytherapy, and 0.7 years for SmartAdapt. These are the estimated development costs for the two applications, with MDR compliance included in the development estimates: AI autocontouring brachy SmartAdapt

Personnel costs

€200,000 (1 FTE, 2 y)

210,000 (3 FTE, 0.7 y)

Cloud computing and storage

€40,000

€21,000

Total development cost

€240,000

€231,000

Annual maintenance

€25,000

€25,000

A direct comparison of these solutions to commercially available ones is difficult. However, looking at applications in RT with similar complexity, e.g. auto-segmentation, or automatic DICOM routing modules, the cost for a perpetual site license would be on the order of €50,000 - €150,000, and annual service costs are typically on the order of 5 15% of that. Based on these estimates, in-house development is likely no longer the most cost-effective option when considering financial investment alone. Furthermore, the added benefit of using commercial solutions is the guarantee of a support organization backing the application, whereas maintaining full support for in-house developed solutions is challenging. No. Despite financial drawbacks, there are strong arguments in favor of continuing in-house development, especially when it enables pushing beyond the state of the art. Many groundbreaking innovations in radiation therapy (RT) originated from in-house efforts before becoming industry standards. For example, inverse planning, portal imaging, CBCT based image guidance, VMAT, portal dosimetry, and the MR-linac, all started as research initiatives in clinics before becoming mainstream technology. These advancements may never have emerged if institutions had relied solely on commercial vendors, whose interests are mainly market-driven. Furthermore, while the cost comparison with commercial software is important, if in-house development enables a large efficiency step which is not available through commercial means, its development may still be cost effective. For example, our AI autocontouring for brachy development, which is not commercially available yet, reduces the contouring time by 30 minutes per patient. However, to maximize impact and long-term feasibility, in-house development should ideally be pursued in collaboration with manufacturers, ensuring that pioneering technologies can transition into widely available products. Furthermore, such collaborations may help in financing the initial investment of the in-house development. Should we abandon in-house development?

Conclusion

Ultimately, in-house software development is most likely not cost-effective under current regulatory constraints. However, it remains strategically important when it facilitates innovation or efficiency beyond existing commercial solutions.

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Speaker Abstracts Investing for healthcare innovation Florian Schuster Board, Venga Ventures, Cambridge, United Kingdom

Abstract:

Balancing Risk and Return in Radiotherapy Investments

Life sciences and biotech investors face significant challenges due to high failure rates and the need for market acceptable returns. Typically, only about 10% of investee companies achieve meaningful success with another 20 40% breaking even. To compensate for failures, investors must target companies with potential 20x returns on invested capital. This risk-return balance is crucial for the sustainability of biotech funds compared to other asset classes. In the radiotherapy market, radioligand companies offer promising business models with large markets and early cash flows through pharma deals. In contrast, device companies face slow and saturated markets with limited early cash flows, making them less attractive for venture investment. A reevaluation of business models, such as pay-per treatment models, could accelerate innovation in the device space by aligning returns with outcomes, potentially preventing market failures. Clinicians can support innovation by adjusting their risk assessment and purchasing decisions accordingly.

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Speaker Abstracts Why do innovative healthcare products cost so much? Tracy Underwood Research Department, Leo Cancer Care, Crawley, United Kingdom. Department of Medical Physics and Biomedical Engineering, University College London, London, United Kingdom

Abstract:

Innovative healthcare products play a crucial role in improving the lives of patients and their families. While advancements are vital for better outcomes and quality of life, new products often come with high costs, reflecting the complex processes required to turn them into a reality. For radiotherapy in particular, the market is relatively small compared to other sectors such as radiology. Further, radiotherapy delivery systems are more complicated and usually contain 3D imaging systems as QA devices. The financial burden of developing this cutting-edge technology is spread over a smaller customer base, leading to increased prices.

This presentation will explore investment figures and examine costs involved in bringing innovative healthcare products to market. The difficult journey from concept to clinic will be considered.

Key areas of healthcare company spending will be discussed. For instance, research and development is essential not only for the creation of new technologies but also for refining them. Unfortunately, not all attempts are successful, so the cost of failed research and development must also be factored in. The regulatory compliance required to meet standards from organizations such as the FDA or CE is also extremely costly.

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Companies must submit extensive documentation and conduct a vast range of tests to ensure that their products meet rigorous safety standards. The manufacturing, and supply chains required to produce and deliver complex equipment also adds to costs, as these products often require highly specialized components and materials, which can be expensive to source and manufacture. Product servicing requires highly skilled, high-cost engineers. Finally effective marketing and distribution strategies are essential to the commercial success of any healthcare product. Variations in regulations across countries further complicate the process. Some regions have stricter requirements, adding more costs for certification and approval, while others may offer government incentives, such as subsidies or tax breaks for research or medical advancements. Comparing medical devices to pharmaceuticals, we will see that the costs of developing and bringing these products to market have some similarities but also important differences. In summary, this presentation will explore the financial challenges associated with developing innovative healthcare products. While the cost of innovative healthcare products can be high, this investment is essential to achieving better health outcomes, driving medical progress, and providing long-term value to patients and healthcare systems.

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Speaker Abstracts Determining the value of innovation Miet Vandemaele Human structure and repair, Ghent University, Ghent, Belgium. Radiation Oncology, Ghent University Hospital, Ghent, Belgium

Abstract:

Since its introduction in 2010, value-based healthcare has been used as a strategic approach to maximise patient benefits while safeguarding the economic sustainability of healthcare systems. In this strategy, 'value' is defined by measuring outcomes that matter most to patients against the cost of delivering these outcomes over the entire cycle of care. In radiation oncology, appraisal of patient-relevant benefit, and costs of new interventions can be difficult due to the rapid pace of innovation, the need for operator expertise and the learning curve that typically accompanies new technologies. These challenges can delay the clinical implementation of radiotherapy innovations, but equally put patients at risk of exposure to substandard treatments or add strain on limited healthcare budgets. Moreover, the difficulty in generating evidence on meaningful benefit and costs leads to uncertainty for industry, healthcare providers and policymakers. The ESTRO Value-based Radiation Oncology (VBRO) project has set out to develop an appraisal framework, tailored for the diverse range of technologies and interventions in radiotherapy. By identifying innovations most likely to deliver meaningful patient benefits, this framework seeks to enhance access to evidence-based radiotherapy innovations, providing healthcare providers and policymakers with the necessary evidence to support clinical implementation and reimbursement decisions. Ultimately, this value-based framework aims to improve patient outcomes while keeping costs for society acceptable.

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Speaker Abstracts In vivo dosimetry: What can it catch? Evy Bossuyt Physics, Iridium Netwerk, Antwerp, Belgium

Abstract:

In vivo dosimetry (IVD) is recommended in radiotherapy to catch treatment delivery errors and to assist in treatment adaptation. Large scale clinical implementation however is not always easy. Recently, commercially automated systems have made it feasible to perform transit dosimetric quality assurance on a very large scale. We started using such a system for all our machines and all our patients in 2018 using transit EPID images. Over the years, we analyzed results for more than 23000 patients in total, including causes and actions for failed fractions. We were able to catch not only deviations in patient positioning and anatomy changes, but also errors in planning, imaging, treatment delivery, simulation, breath hold and positioning devices. The detectability of a specific type of error however depends very much on the specificity and sensitivity of a particular IVD system for that type of error including also dependency on treatment site, delivery technique, and/or indicator used. This talk will NOT give an extensive overview of all possibilities for IVD systems discussing advantages and limitations. It will refer however to some excellent references and will give some recommendations showing case examples of EPID based IVD to illustrate the wide variety of detectable deviations.

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Speaker Abstracts The ability of PSQA systems to detect errors Joerg Lehmann

Institute of Medical Physics, University of Sydney, Sydney, Australia. Department of Radiation Oncology, Calvary Mater Newcastle, Newcastle, Australia. School of Information and Physical Sciences, University of Newcastle, Newcastle, Australia Abstract: The ability of clinical patient specific quality assurance (PSQA) systems to detect errors has been prominently questioned over 10 years ago: Comparing the outcomes of the irradiations of their intensity modulated radiation therapy (IMRT) head and neck audit phantoms with corresponding results of the institutions in-house PSQA, the IROC Houston team found that the clinical PSQA systems showed poor ability to predict a failing IROC Houston phantom result with an overall sensitivity of 2-18%. [1] One approach to formally assess the sensitivity of clinical PSQA systems involves purposefully introducing errors into test plans and asking centres to perform PSQA for such plans relative to the dose from the original error-free plan [2]. This can be applied to many phantom based PSQA methods and those involving the Electronic Portal Imaging device (EPID). Matching expected errors in the treatment planning and delivery process, the purposefully introduced errors can be grouped in three categories: treatment planning system (TPS) beam model errors, machine related treatment delivery errors and patient related treatment delivery errors. While some of the latter can be included with pre treatment PSQA (e.g. a setup error resulting in a shift of isocentre), others require an extended definition of PSQA, which includes in vivo assessment. For relevance, purposefully introduced errors should be selected based on a process such as a Failure Mode and Effect Analysis (FMEA) [3]. To be realistic the magnitude of introduced errors should be such that they would be relevant to PSQA and not be already caught with other measures such as routine

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machine QA. Assessing the sensitivity and specificity of PSQA is core to the work of ESTRO / AAPM Task Group 360, the report of which will provide details of different approaches to take. It is important to assess the complete clinically employed PSQA process and not just focus on the hardware and/or software used for PSQA. Selecting options and parameters in the PSQA workflow can significantly impact its ability to detect relevant problems in treatment plans and their deliverability. In order to be a viable QA tool, PSQA needs to be independent of the TPS commissioning process and vice versa. Tuning PSQA to local beam models can hide problems with the beam model, including inaccuracies in small-field output factors and MLC model parameters, and hence should be avoided. Like other QA measures, PSQA needs to be assessed in terms of its sensitivity to errors it is designed to catch. References: [1] Kry S.F. et al. Institutional Patient-specific IMRT QA Does Not Predict Unacceptable Plan Delivery IJROBP 90(5) 2014 [2] Lehmann, J. et al. SEAFARER–A new concept for validating radiotherapy patient specific QA for clinical trials and clinical practice. Radiotherapy and Oncology 171 2022 [3] O'Daniel J et al Which failures do patient-specific quality assurance systems need to catch? Med Phys 52 2025

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Speaker Abstracts The impact of poor beam modelling parameters on clinical plans Stephen Kry Radiation Physics, UT MD Anderson Cancer Center, Houston, USA

Abstract:

Modelling of the MLC, source, and scattering parameters is a central element of commissioning the treatment planning system. While modelling these components is critical for dose calculation accuracy, particularly for modulated treatments, the existing guidance on how to determine these values often lacks critical details to provide a uniform result. Moreover, these parameters often lack robust physical meaning, and are therefore often reduced to fudge factors. As a result, there is substantial variability in what these values are. Modelled values in the treatment planning system are more varied than consistently measured values on current linacs. This can introduce uncertainty and errors into the modelled dose distribution from the treatment planning system. The impact of this variability depends on the parameter in question, but recent studies have shown that this impact can be substantial. Moreover, the use of atypical parameter values (i.e., <10 th percentile or >90 th percentile) was correlated with poorer performance on dosimetric audits. In this talk we will review the observed spread in TPS modelling parameters, the dosimetric impact of suboptimal values, and evidence of the prevalence of suboptimal modelling across the community. The confounding impact of plan complexity will be reviewed, along with current efforts to standardize determination of MLC-based parameters.

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Speaker Abstracts Impact of suboptimal process steps in film dosimetry Sabeena Beveridge, Andrew Alves, Sarah Judd, Katherine Collins Australian Clinical Dosimetry Service, Australian Radiation Protection And Nuclear Safety Agency, Melbourne, Australia Abstract: Film dosimetry is an excellent tool for radiotherapy treatment verification and quality assurance due to its high spatial resolution and two-dimensional (2D) dose distributions. There is a reluctance in the clinical environment to adopt film dosimetry programs which can be attributed to lack of resources and the time required for processing. Unless the user has a very good understanding of film dosimetry and the uncertainties associated with each component in the process, there is a high risk of incorrectly applying procedures and corrections which can lead to incorrect results and impact patient quality assessments. The Australian Clinical Dosimetry Service (ACDS) uses film as the primary dosimeter when assessing end-to-end type audits. Uncertainty contributions from the Linac, ion chamber, film, scanner, processing software, and positioning have been minimized to achieve a film dosimetry uncertainty of 2.3%. The largest reductions in uncertainty are from scanner corrections, film calibration corrections, and film-to-plan position accuracy. However, errors are still seen that allude our most experienced users. Quality control (QC) measures have been put in place throughout the ACDS film process to ensure the process remains consistent. A key methodology the ACDS uses to reduce film uncertainty is with the use of reference films. A calibration film set comprising of 12 doses is acquired using the on-site Linac (Electa Versa HD). Three reference films are irradiated at the auditing facility, which range from 10 Gy to 20 Gy (including a 0 Gy film), and are scanned with each audit film. Table 1 lists the estimated uncertainty for the components within this process. Some of these components can be reduced through improving procedures and applying corrections (Type A), however, some sources of error cannot be manipulated and must be accepted (Type B). The total uncertainty for the ACDS reference film procedure is ±0.83%, assuming that film uniformity and data entry are correct. QC within the process verifies that the film has not been rotated or positioned incorrectly on the scanner. With the release of EBT4 film (Ashland ISP Inc., Wayne, NJ, USA), it is expected that film uniformity is improved, however, the ACDS has evaluated reference film factors with both EBT3 and EBT4 film and have found no significant difference between the two types of film (p = 0.57, comparison of the means). Considerations in how film is positioned when comparing it to the planned dose is sometimes overlooked – where auto-positioning film to fit the planar dose is used to obtain best-fit results. Positioning errors due to IGRT misalignments can be ignored when the user relies on the software to process film results. Since SRS requires patient positioning to be within 1 mm, then film positioning should be within this tolerance to be valid. A recent study by Beveridge et al. 1 assessed the baseline film processing results from six Dosimetry Audit Networks (DANs) that had well-established film dosimetry programs. Only two out of the six DANs had consistent results within ±5% of the known dose. Most of the errors were due to software processing where users were not aware of how the software behaved during parts of the process. This has emphasized the importance of not relying on software to produce accurate results, but instead ensuring that appropriate quality measures are considered throughout the process.

1 Beveridge S, Alves A, Hussein M, Clark CH, Jornet N, Viegas CB, Reniers B, Alvarez PE, Azangwe G, Chelminski K, Dimitriadis A, Kazantsev P, Swamidas J. A framework for validating radiotherapy film dosimetry based on an international intercomparison. Medical Physics, Vol. 51(12), pp 9071 9087, 2024.

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Speaker Abstracts Exploring and understanding the needs for accurate measurements using Computer Simulation tools Andrew W Beavis 1,2,3 , Catharine H Clark 2,4,5 , Russell Thomas 2,4 , Nathalia Almeida Costa 4 , Richard Amos 2 , Andrew Nisbet 2 , James W Ward 3 1 Medical Physics, Hull University Teaching Hospitals (NHS) Trust, Cottingham, United Kingdom. 2 Medical Physics & Biomedical Engineering, University College London, London, United Kingdom. 3 Research and Development, Vertual Ltd, Hull, United Kingdom. 4 Metrology for Medical Physics, National Physical Laboratory, Teddington, United Kingdom. 5 Medical Physics, University College London Hospitals (NHS) Trust, London, United Kingdom

Abstract:

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Background

The radiotherapy community faces global challenges to expand and improve the quality of training for its workforce. The lack of availability of clinical equipment for training sessions and of experienced clinical Physicists are limitations experienced both in countries with well-developed training programmes and those seeking to establish professional societies and training schemes to modernise their radiotherapy services. Computer simulation training tools provide practical solutions, offering interactive experiential learning and standardisation to learning. A key benefit is the ability to safely explore errors and their impact. In the radiotherapy physics context, the impact of poor measurement practice or not following protocols appropriately can be explored virtually without risk of actual machine miscalibration. The Virtual Environment for Radiotherapy Training (VERT) system has been established in Radiographer/RTT training centres in approximately 40 countries and has become a standard in their training. The system includes simulation of physics metrology equipment, including scanning water phantoms and solid water blocks, ionisation chambers and small field detectors. These are used to practice and understand measurement processes related to Linac QC. These simulations have been further developed to provide a sophisticated virtual experimental platform wherein random and systematic errors may be included and measurement uncertainties are tracked. To broaden the accessibility of VERT beyond the classroom, a cloud-based Learning Management system (LMS) has been implemented that serves the VERT software to individual users at their chosen place of study, enabling guided, self-paced, asynchronous learning and to undertake exercises to assess knowledge and competency acquisition.

TRS398/ TRS483 simulations

The IAEA TRS398 and TRS483 protocols for the dosimetry of standard MV x-ray clinical treatment beams and very small treatment beams are implemented in VERT. These include sophisticated simulations of the required measurements. Workflow GUIs guide the trainee through the details of the protocols to create the correction factors needed to calibrate appropriate ionisation chambers to measure the dose produced by the 6MV and 15MV beam simulations available on the virtual Linacs. For small fields, FFF measurements are also simulated.

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The virtual dosimetry equipment in VERT can be set up with positioning/ alignment errors. These can be used to gain appreciation of their impact or purposefully introduced (by the teachers) in assessments to test if the trainee can spot and correct them. Similarly, systematic and random beam output or calibration errors can be simulated. Measurements are subject to random fluctuations, with configurable magnitude, requiring repeat measurement to be taken to assess the mean value and associated uncertainty in measurement. Along with the more general features available in VERT, the TRS398 and TRS 483 modules have been used during the ESTRO Practical Dosimetry Audit course (2023) at the UK National Physical Laboratory (NPL), their own Practical Course in Reference Dosimetry (2023/ 2024) and integrated into the Radiotherapy Physics module of the University College London (UCL) Physics and Engineering in Medicine MSc (2025). During the NPL courses VERT was used alongside practical measurement sessions on their Linacs, to virtually explore simulated error scenarios, impact of uncertainties, equipment management and the faculty’s vast experience of commonly experienced problems. The latter included ‘detector choice uncertainty’ for very small field factors, which otherwise could not be accommodated in practical sessions due to time constraints. The impact of the use of wrong field sizes during TPR20/10 measurement, SSD errors, wrong energy selection, lack of monitoring the ambient conditions by changing room temperature and pressure were explored extensively.

Participant feedback was enthusiastic, and faculty reflected that simulation sessions had broadened the teaching, adding value to training beyond that given by the practical training.

VERT was used in the classroom on the UCL MSc course to provide virtual clinical demonstrations; course work was set for the students as follow up to the lectures to assess their understanding, using the remote access VERT LMS.

Conclusion

VERT allows trainees to understand the need for accuracy by providing a platform to explore the impact of poor measurement processes and has proven to add value to existing professional training courses for Radiotherapy Physicist training. The key benefit of simulation training is the ability to safely explore ‘never-events’ and errors. It standardises the training experience and is likely to help expand training schemes where provision of resources, expertise and travel prove challenging.

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Speaker Abstracts Same-day radiotherapy without prior CT simulation Joshua Schiff Department of Radiation Oncology, Keck School of Medicine, University of Southern California, Los Angeles, USA

Abstract:

The standard clinical workflow for radiation oncology treatment consists of a consultation appointment followed by a computed tomography (CT) simulation appointment, treatment planning, and treatment delivery, often occuring over the course of several days to weeks. With workflow and technologic advancement in radiation oncology over the last several years, much work has been done to optimize this workflow to increase the efficiency with which a patient is able to get on beam. One such advancement has been direct to unit, or simulation-free, radiotherapy in which traditional CT simulation is forgone and a patient's diagnostic imaging is used for treatment planning. In these workflows, a diagnostic scan based pre-plan is created and used for treatment planning, often coupled with the use of advanced on-board imaging acquired on the day of direct to unit radiotherapy to optimize patient alignment. Direct to unit radiotherapy is most commonly used for conventional palliative radiotherapy delivery in

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order to expedite treatment for our sickest patients. Substantial data has emerged in the last few years demonstrating that direct to unit paradigms are feasible and may increase the speed with which patients are able to be treated in radiation oncology. Herein we will discuss the basics of palliative direct to unit radiotherapy including a general workflow and case based discussion as well as some of the relevant data supporting this novel treatment paradigm.

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Speaker Abstracts Simulation-free radiation therapy: Clinical consideration Eva Versteijne Radiation Oncology, AmsterdamUMC, Amsterdam, Netherlands

Abstract: As radiation oncology evolves toward more patient-centered and efficient treatment paradigms, adaptive radiotherapy—particularly in a simulation-free context—is emerging as a promising strategy to streamline care and improve outcomes. This presentation will explore the rationale, clinical workflow, and early outcomes associated with simulation-free radiation therapy (SFRT) within adaptive treatment frameworks, highlighting its clinical relevance, implementation, and future directions. Patient cases will be presented to illustrate the impact on treatment timelines, patient experience, and operational logistics. Simulation-free radiotherapy eliminates the need for a dedicated planning CT by using existing diagnostic imaging (such as diagnostic CT or MRI) or on-board imaging modalities like cone-beam CT (CBCT) for both treatment planning and delivery. This approach is particularly valuable when rapid treatment initiation is critical, and has already been applied in select indications—most notably palliative radiotherapy and early feasibility studies in stereotactic and curative settings. By omitting the conventional simulation step, SFRT offers several advantages: faster time-to-treatment, reduced burden on patients (especially the frail or ill), and increased workflow efficiency. When combined with adaptive techniques, SFRT allows daily anatomical changes to be incorporated into the treatment plan, enabling improved target coverage and sparing of healthy tissue. Clinical experience suggests that SFRT, integrated within an adaptive framework, can maintain or even enhance dosimetric accuracy. Looking ahead, SFRT holds significant potential to support rapid and adaptive radiotherapy, particularly when integrated with emerging technologies such as AI-driven organ-at-risk delineation and automated planning systems. Broader adoption will depend on developing standardized protocols and multi-institutional collaboration to validate and harmonize outcomes across centers. This talk will provide clinicians, physicists, and researchers with a practical and forward-looking perspective on simulation-free adaptive radiotherapy—demonstrating not only that it is feasible, but that it may become a cornerstone of next-generation radiation oncology practice.

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Speaker Abstracts Simulation-free radiation therapy: Physics consideration Alex T Price Radiation Oncology, University Hospitals, Cleveland, USA. School of Medicine, Case Western Reserve University, Cleveland, USA

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ESTRO 2025

Abstract: Traditionally, CT simulation (simCT) has been essential for the development of immobilization, target delineation, and electron density mapping. However, modern advancements in onboard imaging (OBI), treatment planning techniques, and adaptive radiotherapy (ART) challenge the longstanding requirement for simulation-based radiation therapy (RT). "Direct-to-Unit" (DTU) workflows—often called “simulation-free” or “simulation-omitted”- require high image quality for structure identification, robust planning geometries, and accurate dose calculation methods for successful DTU approaches. Emerging advanced technologies such as HU-accurate CBCT-guided RT (CBCTgRT), MR guided RT (MRgRT), ART, and hybrid approaches now facilitate this transition to DTU. This presentation reviews the physics evidence demonstrating the image quality and dose calculation accuracy of onboard imaging for DTU while highlighting other clinical considerations for the safe delivery of DTU-RT. When assessing the image quality of modern CBCTgRT systems, it has been demonstrated that there is improved visibility for structure delineations while also minimizing the number of difficult-to-delineate areas within CBCTs. Additionally, contouring studies have shown non-inferiority compared to traditional simulation CTs. When preparing CBCTgRT techniques with the planning dataset established as a diagnostic CT, beam geometries that reduce the uncertainty of the delivered dose are encouraged. For dose calculation on a diagnostic CT, these scans provide HU values that are similar to those of planning CTs for most tissues, with minimal impact on target coverage, even if larger differences are present. Studies demonstrate multiple viable strategies for HU-corrected CBCT-based dose calculation, including deformable registration, direct acquisition, and synthetic CT generation. These approaches yielded clinically acceptable dose distributions, with differences typically less than 1%. MRgRT offers enhanced soft-tissue contrast, which can assist in localization for diseases where CT soft-tissue visualization poses challenges. Low-field MR images have demonstrated superior or equivalent visibility compared to earlier generations of CBCT. Delineation studies indicate no significant volume differences when measured against CT for specific disease sites. MRI-based dose calculations utilizing bulk density overrides, deformable CT, or synthetic CTs show minimal differences in PTV and OAR doses (less than 0.5%). Finally, there are examples of multi-modality use cases, such as hippocampal avoidance (HA). For emergent whole brain RT, upstream contouring with diagnostic MRI images, along with synthetic CTs or HU-calibrated CBCTs, enables HA planning without simCT. This workflow has reduced planning time to less than 15 minutes and on-table adaptation time to less than 40 minutes. Since the timeline and processes for DTU change, quality assurance (QA) will need refinement and updates to address the modern challenges encountered during DTU. This includes real-time QA, plan integrity assessment, and comparisons to population-based metrics for these disease sites to ensure high-quality planning approaches. In conclusion, CBCT and MRI now meet or approach clinical requirements for localization, delineation, and dose calculation—key criteria for enabling DTU workflows. However, standardized image quality metrics and robust HU calibration protocols remain essential for broader clinical adoption. As RT workflows evolve beyond simulation, these findings support a paradigm shift toward greater flexibility, efficiency, and patient-centric care in radiotherapy.

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Speaker Abstracts Celiac plexus radiosurgery Marcin Miszczyk 1,2 , Yaacov R Lawrence 3,4

1 Comprehensive Cancer Center, Medical University of Vienna, Vienna, Austria. 2 Collegium Medicum - Faculty of Medicine, WSB University, Dąbrowa Górnicza, Poland. 3 Department of Radiation Oncology, Sheba Medical Center, Ramat Gan, Israel. 4 School of Medicine, Tel Aviv University, Tel Aviv, Israel

Abstract:

Retroperitoneal pain syndrome, particularly prevalent among patients with advanced pancreatic cancer, represents an unmet need. This debilitating pain, originating from the upper abdominal viscera and transmitted via the celiac

S14

Invited Speaker

ESTRO 2025

plexus—a complex network of nerves near the aorta— is associated with poor quality of life, decreased physical independence, increased rates of depression, and shortened survival. In many patients, the high doses of opiods required to overcome the pain are associated with significant side effects. Celiac Plexus Radiosurgery was developed to be a transformative, non-invasive solution, delivering a high single-dose of radiation precisely targeted at the peri-aortic region where celiac plexus is located (Jacobson et al., 2022, BMJ Open). The innovation of Celiac Plexus Radiosurgery lies in its novel adaptation of radiosurgical technology, traditionally reserved for tumor ablation, to disrupt neural pain transmission pathways. Unlike invasive procedures such as neurolytic celiac plexus blocks, which carry procedural risks and often result in inconsistent outcomes, this method leverages the pinpoint accuracy of modern radiosurgery to comprehensively and safely target the celiac plexus while sparing surrounding tissues. The single-session delivery further enhances its appeal, minimizing the treatment burden on patients and not requiring an interruption to systemic treatment regimens. Finally, a novel approach towards treatment planning, utilizing several planning target regions with prescription dose depending on the distance from organs-at-risk, allows for safe treatment delivery despite a very high, ablative dose being delivered in close proximity to small bowel. In a recently published multicenter international phase II clinical trial which included 125 treated patients (Lawrence et al., Lancet Oncology, 2024), Celiac Plexus Radiosurgery demonstrated clinical efficacy. At three weeks post treatment, over half of the evaluable patients reported pain relief, with some achieving complete resolution of symptoms. This effect led to a significant reduction in analgesics uptake at six weeks. The treatment’s safety profile proved manageable, considering the palliative advanced-disease setting, with 11 serious adverse events of grade 3 or worse recorded in total, two of which were considered to be probably associated with treatment (abdominal pain and nausea). The method’s recognition in international guidelines underscores its potential as a standard of care. We continue research in this direction, including efforts to improve and facilitate clinical implementation (Miszczyk et al., 2024, Contemp Oncol). • Jacobson G, Fluss R, Dany-BenShushan A, et al. Coeliac plexus radiosurgery for pain management in patients with advanced cancer : study protocol for a phase II clinical trial. BMJ Open. 2022;12(3):e050169. doi:10.1136/bmjopen 2021-050169 • Lawrence YR, Miszczyk M, Dawson LA, et al. Celiac plexus radiosurgery for pain management in advanced cancer: a multicentre, single-arm, phase 2 trial. Lancet Oncol. 2024;25(8):1070-1079. doi:10.1016/S1470-2045(24)00223-7 • Miszczyk M, Malec-Milewska M, Suleja A, et al. Celiac plexus radiosurgery - an introduction to the method and a practical manual. Contemp Oncol (Pozn). 2024;28(3):242-244. doi:10.5114/wo.2024.144315

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Speaker Abstracts RTT roles for single fraction SBRT: Game changer? Claudio Votta, Lorenzo Placidi, Luca Boldrini Dipartimento di Diagnostica per Immagini, Radioterapia Oncologica ed Ematologia, Fondazione Policlinico Universitario "A. Gemelli" IRCCS, Rome, Italy

Abstract:

The introduction of single-fraction stereotactic body radiotherapy (SBRT) is redefining the landscape of radiotherapy (RT), bringing it closer to a surgical-like approach. This paradigm shift has significant implications for radiation therapy technologists (RTTs), requiring the development of new skills, adaptation to hybrid systems, and an optimized clinical workflow. Compared to conventional fractionated treatments, single-fraction SBRT demands an unprecedented level of precision, as any deviation from the intended treatment plan can have a direct impact on patient outcomes.