Treatment planning and delivery practice of lung SBRT: Results of the 2022 ESTRO physics survey.

BACKGROUND AND PURPOSE: The use of Stereotactic Body Radiation Therapy (SBRT) in lung cancer is increasing. However, there is no consensus on the most appropriate treatment planning and delivery practice for lung SBRT. To gauge the range of practice, quantify its variability and identify where consensus might be achieved, ESTRO surveyed the medical physics community. MATERIALS AND METHODS: An online survey was distributed to ESTRO's physicist membership in 2022, covering experience, dose and fractionation, target delineation, dose calculation and planning practice, imaging protocols, and quality assurance. RESULTS: Two-hundred and forty-four unique answers were collected after data cleaning. Most respondents were from Europe the majority of which had more than 5 years' experience in SBRT. The large majority of respondents deliver lung SBRT with the VMAT technique on C-arm Linear Accelerators (Linacs) employing daily pre-treatment CBCT imaging. A broad spectrum of fractionation schemes were reported, alongside an equally wide range of dose prescription protocols. A clear preference was noted for prescribing to 95% or greater of the PTV. Several issues emerged regarding the dose calculation algorithm: 22% did not state it while 24% neglected to specify the conditions under which the dose was calculated. Contouring was usually performed on Maximum or Average Intensity Projection images while dose was mainly computed on the latter. No clear indications emerged for plan homogeneity, complexity, and conformity assessment. Approximately 40% of the responders participated in inter-centre credentialing of SBRT in the last five years. Substantial differences emerged between high and low experience centres, with the latter employing less accurate algorithms and older equipment. CONCLUSION: The survey revealed an evident heterogeneity in numerous aspects of the clinical implementation of lung SBRT treatments. International guidelines and codes of practice might promote harmonisation.

Multi-institutional generalizability of a plan complexity machine learning model for predicting pre-treatment quality assurance results in radiotherapy.

Background and purpose: Treatment plans in radiotherapy are subject to measurement-based pre-treatment verifications. In this study, plan complexity metrics (PCMs) were calculated per beam and used as input features to develop a predictive model. The aim of this study was to determine the robustness against differences in machine type and institutional-specific quality assurance (QA). Material and methods: A number of 567 beams were collected, where 477 passed and 90 failed the pre-treatment QA. Treatment plans of different anatomical regions were included. One type of linear accelerator was represented. For all beams, 16 PCMs were calculated. A random forest classifier was trained to distinct between acceptable and non-acceptable beams. The model was validated on other datasets to investigate its robustness. Firstly, plans for another machine type from the same institution were evaluated. Secondly, an inter-institutional validation was conducted on three datasets from different centres with their associated QA. Results: Intra-institutionally, the PCMs beam modulation, mean MLC gap, Q1 gap, and Modulation Complexity Score were the most informative to detect failing beams. Eighty-tree percent of the failed beams (15/18) were detected correctly. The model could not detect over-modulated beams of another machine type. Inter-institutionally, the model performance reached higher accuracy for centres with comparable equipment both for treatment and QA as the local institute. Conclusions: The study demonstrates that the robustness decreases when major differences appear in the QA platform or in planning strategies, but that it is feasible to extrapolate institutional-specific trained models between centres with similar clinical practice. Predictive models should be developed for each machine type.

Recommendation on the technical and dosimetric data to be included in stereotactic body radiation therapy clinical trial publications based on a systematic review.

The results of phase II and III trials on Stereotactic Body Radiation Therapy (SBRT) increased adoption of SBRT worldwide. The ability to replicate clinical trial outcomes in routine practice depends on the capability to reproduce technical and dosimetric procedures used in the clinical trial. In this systematic review, we evaluated if peer-reviewed publications of clinical trials in SBRT reported sufficient technical data to ensure safe and robust implementation in real world clinics. Twenty papers were selected for inclusion, and data was extracted by a working group of medical physicists created following the ESTRO 2021 physics workshop. A large variability in technical and dosimetric data were observed, with frequent lack of required information for reproducing trial procedures. None of the evaluated studies were judged completely reproducible from a technical perspective. A list of recommendations has been provided by the group, based on the analysis and consensus process, to ensure an adequate reproducibility of technical parameters in primary SBRT clinical trials. Future publications should consider these recommendations to assist transferability of the clinical trial in real world practice.

On the beam hardening correction of the Transit-Guided Radiation Therapy attenuation model.

PURPOSE: The Transit-Guided Radiation Therapy (TGRT) technique is a novel technique aimed to quantify the position error of a patient by using the transit portal images (TPI) of the treatment fields. Despite of the promising preliminary results, about 4% of the cases would have led to position overcorrections. In this work, the TGRT formalism is refined to improve its accuracy and, especially, to decrease the risk of overcorrections. METHODS: A second free parameter accounting for beam hardening has been added to the attenuation model of the TGRT formalism. Five treatment plans combining different delivery techniques and tumour sites have been delivered to an anthropomorphic phantom. TPIs have been obtained under a set of random couch shifts for each field. For each TPI, both the original and the refined TGRT formalism have been used to estimate the underlying true shift. RESULTS: With respect the original formalism, the refined formalism: (i) decreased both the number (from 5% to 1%) and the magnitude of the overcorrections; (ii) lowered the detection threshold (from approximately 1 mm to <0.3 mm); (iii) largely improved the accuracy in tumour sites with large mass thickness variations; and (iv) largely improved the accuracy for true shifts below 5 mm. For true shifts above 5 mm, the accuracy was slightly impaired. CONCLUSIONS: The refined TGRT formalism performed globally better than the original TGRT formalism and it largely reduced the risk of overcorrections. Further refinements of the TGRT formalism should focus on true shifts above 5 mm.

The QuADRANT study: Current status and recommendations for improving uptake and implementation of clinical audit of medical radiological procedures in Europe. The radiotherapy perspective.

BACKGROUND: QuADRANT was a research project funded by the European Commission to evaluate clinical audit uptake and implementation across Europe, with an emphasis on clinical audit as mandated within the BSSD (Basic Safety Standards Directive). AIM: Focusing on the QuADRANT objectives - to obtain an overview of European clinical audit activity; identify good practices, resources, barriers and challenges; provide guidance and recommendations going forwards; identify the potential for European Union action on quality and safety focusing on the field of radiotherapy. RESULTS: A pan-European survey, expert interviews and a literature review conducted within the framework of the QuADRANT project indicated that developments in national clinical audit infrastructure are required. While in radiotherapy, there is a strong tradition and high level of experience of dosimetry audits and well-established practice through the IAEA's QUATRO audits, few countries have a well-established comprehensive clinical audit programme or international/national initiatives on tumour specific clinical audits. Even if sparse, the experience from countries with established system of quality audits can be used as role-models for national professional societies to promote clinical audit implementation. However, resource allocation and national prioritisation of clinical audit are needed in many countries. National and international societies should take the initiative to promote and facilitate training and resources (guidelines, experts, courses) for clinical audits. Enablers used to enhance clinical audit participation are not widely employed. Development of hospital accreditation programmes can facilitate clinical audit uptake. An active and formalised role for patients in clinical audit practice and policy development is recommended. Because there is a persisting variation in European awareness of BSSD clinical audit requirements, work is needed to improve dissemination of information on the legislative requirements relating to clinical audit in the BSSD and in relation to inspection processes. The aim is to ensure these include clinical audit and that they encompass all clinics and specialties involved in medical applications using ionising radiation. CONCLUSION: QuADRANT provided an overarching view of clinical audit practice in Europe, with all its related aspects. Unfortunately, it showed that the awareness of the BSSD requirements for clinical audit are highly variable. Therefore, there is an urgent need to dedicate efforts towards ensuring that regulatory inspections also incorporate an assessment of clinical audit program(s), affecting all aspects of clinical work and specialties involved in patient exposure to ionising radiation.

QuADRANT: a study on uptake and implementation of clinical audit of medical radiological procedures in Europe-expert recommendations for improvement, endorsed by the ESR.

BACKGROUND: QuADRANT was a study funded by the European Commission to evaluate clinical audit uptake and implementation across Europe, with an emphasis on clinical audit as mandated within the BSSD (Basic Safety Standards Directive). AIMS: QuADRANT objectives-obtain an overview of European clinical audit activity; identify good practices and resources, barriers and challenges; provide guidance and recommendations going forwards; identify the potential for European Union action on quality and safety in the three core project specialties, radiology, radiotherapy and nuclear medicine. FINDINGS AND RECOMMENDATIONS: QuADRANT identified that developments in national clinical audit infrastructure are required. National professional societies can be pivotal in improving clinical audit implementation, but resource allocation and national prioritisation of clinical audit are needed in many countries. Lack of staff time and expertise are also barriers. Enablers to enhance clinical audit participation are not widely employed. Development of hospital accreditation programmes can facilitate clinical audit uptake. An active and formalised role for patients in clinical audit practice and policy development is recommended. There is persisting variation in European awareness of BSSD clinical audit requirements. Work is needed to improve dissemination of information on the legislative requirements relating to clinical audit in the BSSD and in relation to inspection processes to ensure these include clinical audit and that they encompass all clinics and specialties involved in medical applications using ionising radiation. CONCLUSION: QuADRANT provides an important step towards enhancing clinical audit uptake and implementation across Europe and improving patient safety and outcomes.

Plan quality assessment in clinical practice: Results of the 2020 ESTRO survey on plan complexity and robustness.

PURPOSE: Plan complexity and robustness are two essential aspects of treatment plan quality but there is a great variability in their management in clinical practice. This study reports the results of the 2020 ESTRO survey on plan complexity and robustness to identify needs and guide future discussions and consensus. METHODS: A survey was distributed online to ESTRO members. Plan complexity was defined as the modulation of machine parameters and increased uncertainty in dose calculation and delivery. Robustness was defined as a dose distribution's sensitivity towards errors stemming from treatment uncertainties, patient setup, or anatomical changes. RESULTS: A total of 126 radiotherapy centres from 33 countries participated, 95 of them (75%) from Europe and Central Asia. The majority controlled and evaluated plan complexity using monitor units (56 centres) and aperture shapes (38 centres). To control robustness, 98 (97% of question responses) photon and 5 (50%) proton centres used PTV margins for plan optimization while 75 (94%) and 5 (50%), respectively, used margins for plan evaluation. Seventeen (21%) photon and 8 (80%) proton centres used robust optimisation, while 10 (13%) and 8 (80%), respectively, used robust evaluation. Primary uncertainties considered were patient setup (photons and protons) and range calculation uncertainties (protons). Participants expressed the need for improved commercial tools to control and evaluate plan complexity and robustness. CONCLUSION: Clinical implementation of methods to control and evaluate plan complexity and robustness is very heterogeneous. Better tools are needed to manage complexity and robustness in treatment planning systems. International guidelines may promote harmonization.

The 3rd ESTRO-EFOMP core curriculum for medical physics experts in radiotherapy.

PURPOSE: To update the 2011 ESTRO-EFOMP core curriculum (CC) for education and training of medical physics experts (MPE)s working in radiotherapy (RT), in line with recent EU guidelines, and to provide a framework for European countries to develop their own curriculum. MATERIAL AND METHODS: Since September 2019, 27 European MPEs representing ESTRO, EFOMP and National Societies, with expertise covering all subfields of RT physics, have revised the CC for recent advances in RT. The ESTRO and EFOMP Education Councils, all European National Societies and international stakeholders have been involved in the revision process. RESULTS: A 4-year training period has been proposed, with a total of 240 ECTS (European Credit Transfer and Accumulation System). Training entrance levels have been defined ensuring the necessary physics and mathematics background. The concept of competency-based education has been reinforced by introducing the CanMEDS role framework. The updated CC includes (ablative) stereotactic-, MR-guided- and adaptive RT, particle therapy, advanced automation, complex quantitative data analysis (big data/artificial intelligence), use of biological images, and personalized treatments. Due to the continuously increasing RT complexity, more emphasis has been given to quality management. Clear requirements for a research project ensure a proper preparation of MPE residents for their central role in science and innovation in RT. CONCLUSION: This updated, 3rd edition of the CC provides an MPE training framework for safe and effective practice of modern RT, while acknowledging the significant efforts needed in some countries to reach this level. The CC can contribute to further harmonization of MPE training in Europe.

Professional practice changes in radiotherapy physics during the COVID-19 pandemic.

BACKGROUND AND PURPOSE: The COVID-19 pandemic has imposed changes in radiotherapy (RT) departments worldwide. Medical physicists (MPs) are key healthcare professionals in maintaining safe and effective RT. This study reports on MPs experience during the first pandemic peak and explores the consequences on their work. METHODS: A 39-question survey on changes in departmental and clinical practice and on the impact for the future was sent to the global MP community. A total of 433 responses were analysed by professional role and by country clustered on the daily infection numbers. RESULTS: The impact of COVID-19 was bigger in countries with high daily infection rate. The majority of MPs worked in alternation at home/on-site. Among practice changes, implementation and/or increased use of hypofractionation was the most common (47% of the respondents). Sixteen percent of respondents modified patient-specific quality assurance (QA), 21% reduced machine QA, and 25% moved machine QA to weekends/evenings. The perception of trust in leadership and team unity was reversed between management MPs (towards increased trust and unity) and clinical MPs (towards a decrease). Changes such as home-working and increased use of hypofractionation were welcomed. However, some MPs were concerned about pressure to keep negative changes (e.g. weekend work). CONCLUSION: COVID-19 affected MPs through changes in practice and QA procedures but also in terms of trust in leadership and team unity. Some changes were welcomed but others caused worries for the future. This report forms the basis, from a medical physics perspective, to evaluate long-lasting changes within a multi-disciplinary setting.

Artificial Intelligence in magnetic Resonance guided Radiotherapy: Medical and physical considerations on state of art and future perspectives.

Over the last years, technological innovation in Radiotherapy (RT) led to the introduction of Magnetic Resonance-guided RT (MRgRT) systems. Due to the higher soft tissue contrast compared to on-board CT-based systems, MRgRT is expected to significantly improve the treatment in many situations. MRgRT systems may extend the management of inter- and intra-fraction anatomical changes, offering the possibility of online adaptation of the dose distribution according to daily patient anatomy and to directly monitor tumor motion during treatment delivery by means of a continuous cine MR acquisition. Online adaptive treatments require a multidisciplinary and well-trained team, able to perform a series of operations in a safe, precise and fast manner while the patient is waiting on the treatment couch. Artificial Intelligence (AI) is expected to rapidly contribute to MRgRT, primarily by safely and efficiently automatising the various manual operations characterizing online adaptive treatments. Furthermore, AI is finding relevant applications in MRgRT in the fields of image segmentation, synthetic CT reconstruction, automatic (on-line) planning and the development of predictive models based on daily MRI. This review provides a comprehensive overview of the current AI integration in MRgRT from a medical physicist's perspective. Medical physicists are expected to be major actors in solving new tasks and in taking new responsibilities: their traditional role of guardians of the new technology implementation will change with increasing emphasis on the managing of AI tools, processes and advanced systems for imaging and data analysis, gradually replacing many repetitive manual tasks.

Towards an updated ESTRO-EFOMP core curriculum for education and training of medical physics experts in radiotherapy - A survey of current education and training practice in Europe.

PURPOSE: ESTRO-EFOMP intend to update the core curriculum (CC) for education and training of medical physicists in radiotherapy in line with the European Commission (EC) guidelines on Medical Physics Experts (MPE), the CanMEDS methodology and recent developments in radiotherapy. As input, a survey of the current structure of radiotherapy MPE national training schemes (NTS) in Europe was carried out. METHODS: A 35-question survey was sent to all European medical physics national societies (NS) with a focus on existence of an NTS, its format and duration, required entry-level education, and financial support for trainees. RESULTS: Twenty-six of 36 NS responded. Twenty had an NTS. Minimum required pre-training education varied from BSc in physics or related sciences (5/2) to MSc in medical physics, physics or related sciences (6/5/2) with 50-210 ECTS in fundamental physics and mathematics. The training period varied from 1 to 5 years (median 3 years with 50% dedicated to radiotherapy). The ratio of time spent on university lectures versus hospital training was most commonly 25%/75%. In 14 of 20 countries with an NTS, a research project was mandatory. Residents were paid in 17 of 20 countries. The recognition was mostly obtained by examination. Medical physics is recognised as a healthcare profession in 19 of 26 countries. CONCLUSIONS: The NTS entrance level, duration and curriculum showed significant variations. This survey serves to inform the design of the updated CC to define a realistic minimum training level for safe and effective practice aiming at further harmonization in line with EC guidelines.

Grand challenges for medical physics in radiation oncology.

Medical physics has made considerable contributions to recent advances in radiation oncology. Medical physicists are key players in the clinical and scientific radiation oncology context due to their unique skill sets, flexibility, clinical involvement and intrinsic translational character. The continuing development and widespread adoption of "high-tech" radiotherapy has led to an increased need for medical physics involvement. More recently, our field is rapidly changing towards an era of "precision oncology". These changes have opened new challenges for the definition of the professional and scientific roles and responsibilities of medical physicists. In this paper, we have identified four grand challenges of medical physics in radiation oncology: (1) improving target volume definition, (2) adoption of artificial intelligence and automation, (3) development of predictive models of biological effects for precision medicine, and (4) need for leadership. New visions and suggestions to orientate medical physics to successfully face these new challenges are summarized. We foresee that the scientific and professional challenges of our times are pushing medical physicists to accelerate toward multidisciplinarity. Medical physicists are expected to innovatively drive interactions and collaborations with other specialists outside radiation oncology while the radiation physics core will remain central. Medical physicists will retain strong and pivotal roles in quality, safety and in managing ever more complex technologies. The new challenges will require medical physicists to continuously update skills and innovate education, adapt curricula to include new fields, reinforce multi-disciplinary attitude and spirit of innovation. These challenges require visionary and open leadership, which is able to merge established roles with the exciting new fields where medical physics should increasingly contribute.

What is plan quality in radiotherapy? The importance of evaluating dose metrics, complexity, and robustness of treatment plans.

Plan evaluation is a key step in the radiotherapy treatment workflow. Central to this step is the assessment of treatment plan quality. Hence, it is important to agree on what we mean by plan quality and to be fully aware of which parameters it depends on. We understand plan quality in radiotherapy as the clinical suitability of the delivered dose distribution that can be realistically expected from a treatment plan. Plan quality is commonly assessed by evaluating the dose distribution calculated by the treatment planning system (TPS). Evaluating the 3D dose distribution is not easy, however; it is hard to fully evaluate its spatial characteristics and we still lack the knowledge for personalising the prediction of the clinical outcome based on individual patient characteristics. This advocates for standardisation and systematic collection of clinical data and outcomes after radiotherapy. Additionally, the calculated dose distribution is not exactly the dose delivered to the patient due to uncertainties in the dose calculation and the treatment delivery, including variations in the patient set-up and anatomy. Consequently, plan quality also depends on the robustness and complexity of the treatment plan. We believe that future work and consensus on the best metrics for quality indices are required. Better tools are needed in TPSs for the evaluation of dose distributions, for the robust evaluation and optimisation of treatment plans, and for controlling and reporting plan complexity. Implementation of such tools and a better understanding of these concepts will facilitate the handling of these characteristics in clinical practice and be helpful to increase the overall quality of treatment plans in radiotherapy.

National societies' needs as assessed by the ESTRO National Societies Committee survey: A European perspective.

PURPOSE: To determine how ESTRO can collaborate with Radiation Oncology National Societies (NS) according to its mission and values, and to define the new roadmap to strengthen the NS network role in the forthcoming years. MATERIALS AND METHODS: The ESTRO NS committee launched a survey addressed to all European National Societies, available online from June 5th to October 30th 2018. Questions were divided into three main sections: (1) general information about NS; (2) relevant activities (to understand the landscape of each NS context of action); (3) relevant needs (to understand how ESTRO can support the NS). Eighty-nine European NS were invited to participate. Respondents were asked to rank ESTRO milestones in order of importance, indicating the level of priority to their society. RESULTS: A total of 58 out of 89 NS (65.2%) from 31 European countries completed the questionnaire. The majority of NS ranked "Optimal patient care to cure cancer and to reduce treatment-related toxicity" as the highest level of priority. This aligns well with the ESTRO vision 2030 "Optimal health for all together." NS also indicated a high need for more consensus guidelines and exchange of best practices, access to high quality accredited education, implementation of the ESTRO School Core Curriculum at the national level, and defining quality indicators and standard in Radiation Oncology, improved communication and increased channelling of information. CONCLUSION: The results of this survey will be used to strengthen the relations between ESTRO and European NS to promote and develop initiatives to improve cancer care.

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

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.

IAEA methodology for on-site end-to-end IMRT/VMAT audits: an international pilot study.

Background: The IAEA has developed and tested an on-site, end-to-end IMRT/VMAT dosimetry audit methodology for head and neck cases using an anthropomorphic phantom. The audit methodology is described, and the results of the international pilot testing are presented.Material and methods: The audit utilizes a specially designed, commercially available anthropomorphic phantom capable of accommodating a small volume ion chamber (IC) in four locations (three in planning target volumes (PTVs) and one in an organ at risk (OAR)) and a Gafchromic film in a coronal plane for the absorbed dose to water and two-dimensional dose distribution measurements, respectively. The audit consists of a pre-visit and on-site phases. The pre-visit phase is carried out remotely and includes a treatment planning task and a set of computational exercises. The on-site phase aims at comparing the treatment planning system (TPS) calculations with measurements in the anthropomorphic phantom following an end-to-end approach. Two main aspects were tested in the pilot study: feasibility of the planning constraints and the accuracy of IC and film results in comparison with TPS calculations. Treatment plan quality was scored from 0 to 100.Results: Forty-two treatment plans were submitted by 14 institutions from 10 countries, with 79% of them having a plan quality score over 90. Seventeen sets of IC measurement results were collected, and the average measured to calculated dose ratio was 0.988 ± 0.016 for PTVs and 1.020 ± 0.029 for OAR. For 13 film measurement results, the average gamma passing rate was 94.1% using criteria of 3%/3 mm, 20% threshold and global gamma.Conclusions: The audit methodology was proved to be feasible and ready to be adopted by national dosimetry audit networks for local implementation.

Pseudo skin flash on VMAT in breast radiotherapy: Optimization of virtual bolus thickness and HU values.

PURPOSE: Optimisation strategies for volumetric modulated arc therapy (VMAT) in most treatment planning systems for breast cancer do not account for patient positioning, breathing, or anatomical changes. To overcome this limitation, a pseudo-skin flash strategy using a virtual bolus has been proposed. Using this strategy, we determined optimal thickness and value of Hounsfield units (HU) assigned to the virtual bolus to ensure adequate CTV irradiation. MATERIALS AND METHODS: We modified the original computed tomography data (CT0) by adding combinations of thicknesses and densities of a virtual bolus on PTVs (CT') of seven bilateral breast cancer patients. Using a single optimization objective template, we obtained a VMAT plan on CT' and recalculated this on the CT0. Optimal CT' parameters were defined as those that minimized dose differences between CT' and CT0 plans regarding PTV and OAR dose-volume parameters. We studied bolus parameters regarding robustness by shifting the isocenter 5 and 10 mm in the breathing direction for each CT0 plan. RESULTS: The minimal dosimetric impact was between -400 and -600 HU depending on bolus thickness. OARs doses were not significantly affected. Best robustness was found for -500 HU and 15 mm bolus thickness against shifts of up to 10 mm in the breathing direction. CONCLUSION: Our results support a bolus thickness equal to the CTV-PTV margin plus 5 mm and a virtual bolus HU value around -500 and -400 depending on the bolus thickness chosen. These findings could play a useful role in maximisingrobustness and minimising the need for plan renormalization.