S3024
Invited Speaker
ESTRO 2026
must allow for professional autonomy to make a clinical judgement. For the provision of optimal care, patient-centred goals should remain central to the decisions we make every day. We need to promote a culture of thoughtful practice which is clinically informed, rather than purely protocol-driven. 5391 Uncertainties in radiotherapy: Reduced or simply shifted? Marcel van Herk Radiotherapy related research, University of Manchester, Manchester, United Kingdom Accuracy of radiotherapy delivery has significantly improved in the past decades. Virtually all treatments are now image-guided, while some are delivered with online adaptation. This means that setup error and organ motion and deformation can be considered solved problems. However, this does not mean that all
principles of cancer research and included supervised practical exercises and basic data interpretation. The format aimed to combine education, participation, and dialogue in a real research environment. Results: Direct participation in laboratory activities improved the visibility and accessibility of translational cancer research for patients, children, and families. Patients gained insight into the conduct of laboratory- based cancer research and its potential contribution to the development of more individualized therapeutic strategies. Involving patients in selected experimental steps also increased patient engagement and strengthened their connection to the research process. Among schoolchildren, practical exposure to laboratory work promoted curiosity, active learning, and a better understanding of how cancer research is translated into clinical benefit. Researchers also benefited from the initiative through better communication, fruitful reflection on fundamental principles and closer interaction with the public. Conclusion: Hands-on laboratory engagement is a feasible and impactful tool to connect patients, families, and pupils with translational cancer research. It can foster trust, improve scientific understanding, stimulate early interest in research, and strengthen the relationship between science and society. 5388 From plan to patient: When is a treatment good enough in daily practice Elizabeth Forde Applied Radiation Therapy Trinity, Trinity College Dublin, Dublin, Ireland. Trinity St James Cancer Institute, Trinity College Dublin, Dublin, Ireland Radiotherapy is an imperfect science. It is prescribed and delivered by people, treating people. Clinical decisions are made in complex, human systems and compromises are inevitable. Radiation Therapists are frequently referred to as “perfectionists”, and whilst striving for best practice is always encouraged, the pursuit of perfection may lead to decision paralysis both in treatment planning and at treatment delivery. This can result in delayed treatments, or add complexity without improving clinical outcomes. At times, a plan or treatment is “good enough” when it safely achieves what matters most to the patient, rather than striving for quantitative, and often unattainable, metrics. Whilst we need to know when to accept less than perfection, we equally need to know when to act. “Good enough” is not acceptable when patient safety, adequate staff training, or ethical standards are at risk. We still need to define boundaries and thresholds, but clinical protocols and decision aids
the uncertainties in radiotherapy have been eliminated. The most important remaining
uncertainties are in the definition of the GTV and the CTV. For instance, even in the most accurate treatment of all: SRS of brain metastasis, observer disagree about target volumes with a range of contour locations of about 1.5 mm (Wang et al Neurooncol 2024), and brain shifts between the MRI scan and treatment can cause motion between 0.3 and 2.5 mm even without measurable changes in oedema (Hessen et al. Clin T Radiat Oncol 2017). These errors warrant a margin of 2 mm. The benefits of increasingly aggressive motion management strategies may be very small as long as such uncertainties have not been addressed. There is also a trend for wanting zero margins. But because the uncertainties are not zero, this means that underdose will occur that will be technique and centre-dependent. The effect of underdose of tumour cells (as part of GTV or CTV) is a biological question and is an important topic for future research. However, it is important to understand the physical effect of uncertainty first before we mess with margins! To answer the question in the title, we are now at the stage where uncertainties are shifting and no longer reducing and we should allocate our resources to address the weakest link in the radiotherapy chain rather than on ever-advancing motion management.
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