ESTRO 2024 - Abstract Book

S30 ESTRO 2024 This talk will summarize and discuss recent findings on CEBL occurrence and demonstrate the potential of such spatially resolved functional imaging endpoint to approach the RBE question in a new mechanistic way. Hypothesis driven risk modelling for CEBL occurrence on voxel-level has been developed, being able to predict precisely the point of lesion occurrence in the patient anatomy considering absorbed dose, dose-averaged LET and proximity to the cerebral ventricles as risk factors [3,4]. These findings triggered considerations on European level to acknowledge the periventricular region as organ at risk and induced efforts to collect respective clinical data for further investigations. Meanwhile, a randomized prospective trial has been initiated at the Heidelberg Ion Beam Therapy Centre and OncoRay to test the hypothesis, that a model-based risk-minimizing PT treatment planning turns into less CEBLs observed within two years after PT, which represents an “end-to-end test” for the novel methodological approach. Remaining challenges in understanding the mechanisms of CEBL occurrence and development, the clinical relevance of CEBLs, and further clinical risk factors affecting patient’s individual predisposition will be outlined as well to underline the need for further preclinical and clinical investigations. Invited Speaker

References:

[1] Underwood TS et al., Radiother. Oncol., 10.1016/j.radonc.2022.08.014 [2] Sørensen BS et al., Radiother. Oncol., 10.1016/j.radonc.2021.08.016 [3] Bahn E et al., IJROBP 2020, 10.1016/j.ijrobp.2020.03.013 [4] Eulitz J et al., Radiother. Oncol., 10.1016/j.radonc.2022.11.011

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Description of IGRT current problems and potential solutions

Núria Jornet

Hospital de la Santa Creu i Sant Pau, Radiofísica i Radioprotecció, Barcelona, Spain

Abstract:

Image-Guided Radiotherapy (IGRT) stands as a breakthrough in modern radiotherapy, significantly impacting treatment outcomes by improving patient positioning, refining targeting precision, and minimizing uncertainties associated with anatomical changes. Notably, kilovoltage (kV) imaging, with a particular emphasis on kV cone-beam computed tomography (CBCT), has emerged as the primary in-room imaging technique during radiotherapy treatments. This preference is attributed to the ease of registration with digitally reconstructed radiographs (DRRs) and planning CT scans and the default inclusion of kV-CBCT in all linear accelerators. In contemporary practice, the automation of registration and the seamless transfer of couch motion data to the linear accelerator have further streamlined procedures. Recent surveys demonstrate the routine use of daily CBCT for most patients. However, there’s a growing concern about the radiation doses associated with kV imaging, necessitating a thorough justification and optimization approach following the principles outlined in the Basic Safety Standards Directive (BSSD2013/59). The best optimization approach is to perform only the necessary imaging and refrain from unnecessary procedures. Therefore, it is time to critically review our IGRT protocols, aiming to redefine not only the imaging modality and characteristics but also the frequency of imaging. This reevaluation should extend to providing comprehensive guidance on image registration, encompassing considerations for support structures, defining tolerances, and establishing a clear action plan in the event that tolerances are exceeded. Such a meticulous review and adjustment of protocols will contribute to an optimized and judicious use of IGRT resources, aligning with the imperative of minimizing unnecessary exposures while ensuring the highest standards of patient care. Some of the current IGRT problems are: