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Artificial Intelligence in Adaptive Radiation Therapy
changes [3]. The highly dynamic nature of real-time ART demands AI models that can keep pace with the fast-moving components of the treatment delivery system. Compared to online ART, real-time ART requires far greater performance on AI tools, where even minor delays in image processing, motion predictions, or treat­ment adaptation could compromise treatment efcacy and patient outcomes. Conquering these real-time performance challenges involves not only speed but also accuracy and robustness. Signicant further advancements in neural network architecture, enhanced computational efciency, and rigorous validation are neces­sary to ensure the seamless and reliable integration of AI into real-time ART workows.

14.5 Operational challenges

Integrating AI into ART is a complex undertaking that introduces several opera­tional challenges. These challenges stem from the intricacies involved in incorporat­ing any AI systems into clinical workows, the requirement for extensive training and education for healthcare professionals, and the necessity to maintain a seamless operation within a high-stakes clinical environment.
14.5.1 Clinical validation
The clinical validation of AI models for ART poses signicant challenges, primarily due to the lack of standardized evaluation metrics and criteria [34]. Unlike tradi­tional medical devices and software, AI models require rigorous validation to ensure their safety, efcacy, and reliability. In ART, where online and real-time decisions can directly impact patient outcomes, the stakes are particularly high. The lack of standardization complicates the process of model evaluation across different disease sites, clinical settings, and patient populations. This variability can lead to incon­sistencies in evaluation results, making it difcult to determine an AI models true clinical utility. Moreover, the dynamic nature of ART, which involves continuous adaptation to patient-specic changes (e.g. patient anatomy and tumor character­istics), necessitates that AI models undergo extensive testing in diverse and evolving scenarios. For example, an auto-segmentation model for online ART treating bladder cancer will need to manage varying levels of bladder llings [2].
To address these challenges, establishing standardized evaluation metrics and criteria is essential. Collaborative efforts involving government agencies (e.g. the US FDA, NIH, NCI), professional societies (e.g. AAPM and ASTRO), clinical users, research investigators, and industrial vendors are essential to establish standardized qualitative and quantitative evaluation metrics and methods [25, 34, 35]. Additionally, creating and sharing large, annotated datasets representative of diverse patient populations can improve the robustness and generalizability of AI models. Implementing rigorous testing protocols that simulate real-world clinical scenarios can further enhance the reliability of AI systems in ART. The streamlined clinical validation process can lead to safer and more effective AI-driven ART.
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14.5.2 Workow integration
Integrating AI into ART is not as simply as adding a new tool into the existing process. Most of the current online ART platforms operate within closed-loop systems using proprietary software, allowing only vendor-approved AI models and their authorized collaborators to integrate into the clinical workow [12, 17]. As a result, inserting any alternative or new AI tools into the closed-loop workow is challenging, if not impossible. Data extraction from the online ART system is difcult, and even if access is granted, the data transfer between the ART platform and third-party software is time-consuming and prone to communication errors (e.g. incomplete transfer of DICOM data). This substantial limitation and the associated liability issues discourage researchers and developers from investing in independent AI tools for online ART. The challenge is even more signicant for real-time ART, where immediate adjustments to treatment delivery systems are required [1].
It is also technically challenging to integrate the closed-loop online ART platform with existing clinical systems, particularly when they are provided by different vendors. Varian Ethos, as the most popular CBCT-based online ART platform, has been widely implemented in all Varian environments using the Eclipse treatment planning system (TPS) and ARIA record and verication (R&V) system [17]. Such an integration, although not yet seamless, has been thoroughly examined by the vendor during the design, manufacturing, and evaluation processes. While it has been demonstrated that the Ethos system can work with other TPSs (e.g. RayStation by RaySearch Laboratories, Stockholm, Sweden) and R&V systems (e.g. MOSAIQ by Elekta, Stockholm, Sweden), such a non-uniform integration requires special attention for data transfer, and increases the manpower and resources needed for maintenance [29].
14.5.3 Staff training
Providing ART team members with adequate training on basic concepts of AI and the specic AI tools involved in the ART workow is an essential requirement for successful clinical implementation [36]. First, much of the current workforce in radiation therapy did not receive formal education or training in AI. The introduction of AI into clinical practice represents a signicant paradigm shift, requiring the ART team members to acquire new competencies and understand complex AI-driven processes. This gap necessitates substantial investment in train­ing programs designed to bridge the knowledge divide [37]. Effective training should encompass both theoretical understanding of AI concepts and practical skills for operating AI systems. Second, AI is a rapidly evolving eld, with new algorithms, techniques, and tools emerging continuously. Practitioners must stay current with the latest advancements to utilize AI effectively and safely in ART. Continuous education is essential to ensure that practitioners are up to date with the latest developments and best practices. This need for ongoing learning requires a commit­ment to professional development and access to updated educational resources. Institutions and professional organizations play a critical role in facilitating
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Artificial Intelligence in Adaptive Radiation Therapy
continuous education, ensuring that ART professionals are equipped with the latest knowledge and best practices [38].
Developing and implementing comprehensive training and continuing education programs can be resource-intensive and time-consuming, presenting a signicant barrier for individual institutions. Therefore, it is important for professional organizations (e.g. AAPM, ASTRO, and ESTRO) to offer formal AI training through regular workshops, courses, and access to current literature, and provide certicate to demonstrate competency on practicing AI in clinical settings [18]. By tackling these challenges, the ART workforce can harness the full potential of AI in ART, ultimately improving patient outcomes.
14.5.4 User experiences
Successful implementation of AI in ART requires collaboration and coordination among various stakeholders, including radiation oncologists, medical physicists, IT professionals, and administrators. Each group brings a unique perspective and set of expertise to the table, and effective communication and teamwork are essential to address the multifaceted challenges posed by AI integration. Establishing clear roles, responsibilities, and lines of communication can help facilitate smoother collabo­ration and ensure that all stakeholders are aligned in their goals and objectives [39].
Distinctive from many other RT technologies, ART is mostly executed in a close­looped software environment provided by the vendor of the treatment machine. In such a highly integrated system, it is impractical, if not impossible, to use any AI model trained or rened by institutional data. Despite the variations in clinical practice between different institutions (e.g. contouring, planning), all users of ART need to use the same AI model provided by the vendor [25]. Therefore, this puts additional burden on medical physicists (who often take charge of the clinical implementation of ART) to gain their fellow radiation oncologiststrust in the results provided by the vendor models. While clinicians often appreciate the efciency gain provided by AI, they may want to maintain clinical consistency between their adaptive and non-adaptive patients. Therefore, when introducing ART, the medical physicists should provide clear guidance on how to facilitate the clinicians to achieve clinical consistency while not losing the efciency gain [40].
14.5.5 Quality management program
Establishing robust quality assurance (QA) and monitoring processes to continu­ously track AI model performance, detect potential errors, and ensure ongoing safety and efcacy is essential [39]. This includes developing contingency plans for situations where AI systems fail or produce unexpected results, ensuring that clinicians can seamlessly revert to conventional treatment approaches or seek alternative decision support mechanisms.
Failure mode and effects analysis (FMEA), a systematic approach to identifying and mitigating potential failures, can play a crucial role in ensuring the safe and effective integration of AI into ART workow. The FMEA framework is docu­mented in the American Association of Physicists in Medicines (AAPM) Task
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Artificial Intelligence in Adaptive Radiation Therapy
Group 100 (TG-100) report [41]. FMEA can identify potential failure modes, analyze their potential impacts on patient safety and treatment outcomes, and prioritizes actions to mitigate those risks. AAPM TG-100 outlined how to develop and implement quality management programs [42]. For an AI-driven ART program, the team should optimize the allocation of resources towards preventing the most substantial risks indicated by the FMEA. Moreover, AAPM TG-100 provided important guidance on how to build effective quality management tools, such as checklists. Once properly implemented, FMEA can safeguard every step in the ART workow in which AI plays important roles, from data collection and model development to clinical deployment and maintenance. Integration of FMEA as an organic part of AI development in ART will also help foster a culture of safety and trust among different role groups (e.g. physicians, physicists, dosimetrists, and therapists) [42].
The most common AI application in online ART is auto-segmentation of online images, typically CBCT or MR images [43]. FMEA could help identify vulner­abilities in the clinical workow and provide insights for quality improvements. AAPM TG-275 suggested that errors in target and organ delineation ranked among the highest failure modes, as inaccurate segmentation could jeopardize tumor control and increase the risk of complications [44]. Contouring errors originating from AI-generated contours could go undetected during the planning and review process, despite the required review by physicians and physicists. This risk would become even more signicant in online ART, when the clinical team is under enormous pressure to minimize the time interval between imaging and treatment. To mitigate this risk, it is crucial to develop a robust QA tool to catch such errors. Relying on human consciousness in manual checks is not enough to minimize such a risk in online ART [45]. A potential solution is implementing a secondary automated system capable of identifying discrepancies between the physician-edited primary contour and an independently generated secondary auto-contour, thereby enhancing safety and accuracy in online ART.
14.5.6 Financial challenges
ART requires more initial nancial investment into hardware, software, personnel training, and other recourses. The highly complex clinical workow also requires more manpower and treatment machine time. Consequently, each adaptive treat­ment session is more costly than a conventional, non-adaptive session [46]. However, as of 2025, ART is not assigned a specic Current Procedural Terminology (CPT) code by the US Center for Medicare and Medicaid Services (CMS), meaning there is no dedicated reimbursement mechanism under Medicare, and billing for this technology is considered a gray areawith most practices likely including the additional work within existing treatment codes. Essentially, providers are not currently receiving separate payment for the adaptive component of radiation therapy treatment.
The nancial implications of AI implementation in ART cannot be overlooked, either. The integration of AI tools into ART workow signicantly reduces the time
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Artificial Intelligence in Adaptive Radiation Therapy
required for each session, resulting in faster treatment adaptation and potentially better clinical outcomes. Despite these operational advantages, investments in AI technologies, including hardware, software, and training, represent a signicant nancial commitment. The lack of clear reimbursement guidelines further compli­cates the nancial viability of AI implementation, adding constraints on its adoption, ongoing use, and maintenance within ART workow. Given the consid­erable capital and operational costs involved, healthcare institutions must carefully evaluate the cost–benet ratio to ensure that the expected improvements in treat­ment precision and workow efciency justify the investment. Successfully imple­menting AI in ART requires strategic planning, securing appropriate funding, and optimizing resource allocation to sustain long-term benets [47].

14.6 Ethical, regulatory, and legal challenges

The ethical, regulatory, and legal considerations of using AI in ART are complex and multifaceted. Addressing these challenges requires a collaborative approach involving healthcare professionals, AI vendors, professional societies, regulatory agencies, and legal experts. By fostering an environment of transparency, account­ability, and innovation, the potential of AI in ART can be harnessed to improve patient outcomes while upholding ethical principles and legal standards.
14.6.1 Ethical issues
A variety of ethical issues must be carefully addressed to ensure responsible and equitable use of the AI technologies in ART. A primary ethical issue is the potential for bias within AI algorithms [48]. AI systems are trained on data that may reect historical biases or inequities, leading to suboptimal outcomes for under-represented patient populations. For example, prostate cancer is one of the disease sites most frequently treated using ART. Black patients exhibit higher PSA levels and Gleason score > 6 compared to white patients [49]. Addressing these biases requires diligent efforts in the collection, curation, and validation of diverse datasets that accurately represent all patient demographics. Ensuring transparency in the development and deployment of AI systems is crucial to build trust and condence among both patients and healthcare professionals.
Furthermore, maintaining human oversight on AI under signicant time pressure is a unique challenge for online ART [36]. When decisions must be made rapidly, ART practitioners may feel compelled to lower their ethical standards for oversight to expedite the treatment process. This urgency can lead to insufcient scrutiny of AI-generated contours and plans, potentially resulting in errors that could have been avoided with more thorough evaluation. Furthermore, there is a risk that clinicians might favor the adaptive re-plan over the original plan due to nancial incentives, even when the re-plan offers no clear clinical advantage. This raises concerns about the integrity of decision-making. Additionally, the reliance on AI systems in time­sensitive scenarios might inadvertently diminish the role of human judgment and expertise, leading to over-reliance on technology. To address these ethical challenges, it is crucial to establish robust guidelines and training programs that emphasize the
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Artificial Intelligence in Adaptive Radiation Therapy
importance of maintaining high ethical standards in oversight, regardless of time constraints [18]. Transparency in the nancial incentives associated with treatment decisions should also be ensured to prevent conicts of interest.
14.6.2 Regulatory and legal issues
Healthcare institutions must navigate a complex landscape of regulatory require­ments related to data privacy, including the Health Insurance Portability and Accountability Act (HIPAA) in the United States, the General Data Protection Regulation (GDPR) in Europe, and other national and international regulations. Compliance with these regulations requires continuous monitoring and adaptation of data protection practices to meet evolving legal standards [25]. In the United States, AI models used in ART workow may require model-specic approval from the US Food and Drug Administration (FDA). While it is the vendors responsi­bility to obtain initial 510(k) clearance and maintain continuing compliance, it is the medical physicists responsibility to verify the approval and compliance, particularly when preparing for initial commissioning and major model or software upgrades. Moreover, the medical physicists need to establish a quality management program to ensure that the local use of the AI models follows the regulatory approval and vendor recommendation. Any customized use of the integrated AI tools should undergo through evaluation in consultation with the vendor. The use of third-party or research AI tools without approval from the primary vendor may not only pose signicant clinical risks, but also jeopardize regulatory compliance. Similarly, research that seeks to alter the standard workow of the AI solutions also needs to be designed and applied with great caution.
The deployment of AI in ART raises several legal concerns that must be addressed to mitigate risks and ensure compliance with applicable laws and regulations [50]. One prominent legal issue is liability in the event of errors or adverse outcomes. Determining liability can be complex when AI systems are involved in clinical decision-making. Legal frameworks must clarify the responsi­bilities and accountability of various stakeholders, including AI developers, health­care providers, and institutions. Establishing clear guidelines for the documentation and reporting of AI-driven decisions is essential to facilitate transparency and accountability in clinical practice. Additionally, legal considerations extend to data protection and privacy laws that govern the collection, storage, and use of patient data in AI systems. Legal frameworks must also address cross-border data transfers and international collaborations, providing guidelines for the secure and compliant exchange of data in a global healthcare landscape.

14.7 Summary

In conclusion, the journey towards the effective implementation of AI in ART is marked by challenges spanning the data, technical, operational, as well as ethical, regulatory, and legal domains. Overcoming these challenges requires a multi­disciplinary approach with strong collaboration among healthcare providers, data scientists, AI vendors, professional societies, and regulatory bodies. As technologies
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Artificial Intelligence in Adaptive Radiation Therapy
continue to evolve, the synergy between AI and ART is poised to revolutionize radiation therapy paradigms, offering more precise, effective, and personalized cancer care.

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Artificial Intelligence in Adaptive Radiation Therapy
Yi Wang and X. Sharon Qi
Chapter 15
Offline computed tomography-based and online
cone beam computed tomography-based
adaptive radiation therapy
Joel A Pogue, Natalie Viscariello, Dennis N Stanley, Joseph Harms,
Richard A Popple and Carlos E Cardenas
Adaptive radiotherapy (ART) encompasses ofine and online approaches to adjust treatment plans based on anatomical and physiological changes during the course of radiotherapy. This chapter reviews the clinical considerations, technical workows, and current limitations of both ofine computed tomography (CT)-based and online cone beam computed tomography (CBCT)-based ART (gure 15.1). Ofine ART workows involve re-simulation and re-planning triggered by observed anatomical changes, with dose recalculation aided by deformable registration or synthetic CT generation. Online CBCT-guided ART systems, such as Varian Ethos, Elekta Evo, and United Imagings uRT-linac, enable real-time plan adaptation with on-board imaging and fast optimization engines. Key challenges include image quality, synthetic CT accuracy, increased workload, and quality assurance (QA) without interrupting clinical throughput. The integration of AI, knowledge-based planning, and adaptive triggers offers new avenues for workow efciency and clinical impact. This chapter provides practical guidance for the implementation, patient selection, and QA strategies essential for the successful clinical deployment of both ART paradigms.

15.1 Clinical considerations for CT-based offline ART

Radiation therapy is generally delivered over the c ourse of weeks. During this time, patient anatomy may change, potentially impacting target coverage and delivery of unnecessary dose to surrounding tissues. Common examples of changes that impact the delivered dose distribution include tumor regression, weight loss, changes in swelling, and variable organ lling. In response to these changes, ofine adaptive radiation therapy (ART) may be employed to ensure that patients are treated as initially intended. Ofine ART consists of taking a repeat CT simulation during the course of an RT course and re-optimizing the treatment plan. The ART
doi:10.1088/978-0-7503-6119-4ch15 15-1 ª IOP Publishing Ltd 2025. All rights,
including for text and data mining (TDM), artificial intelligence (AI) training, and similar technologies, are reserved.