S1864
Physics - Dose prediction/calculation, optimisation and applications for photon and electron planning
ESTRO 2026
Digital Poster 2012 Combining arcs and static ports – trim the dose or tune the shape? Eva Onjukka 1,2 , Olubunmi Olumuyiwa 1 , Vanessa Panettieri 3,4 1 Nuclear Medicine and Medical Physics, Karolinska University Hospital, Stockholm, Sweden. 2 Oncology- Pathology, Karolinska Institutet, Stockholm, Sweden. 3 Department of Physical Sciences, Peter MacCallum Cancer Centre, Melbourne, Australia. 4 Sir Peter MacCallum Department of Oncology, The University of Melbourne, Melbourne, Australia Purpose/Objective: The introduction of intensity-modulated radiotherapy (IMRT) and volumetric modulated arc therapy (VMAT) has revolutionised the treatment of head and neck cancers by enabling highly conformal dose distributions and precise sparing of organs of interest (OIs). However, these benefits come at the cost of an increased volume of normal tissue receiving low doses, due to dose redistribution across the body (the so-called low-dose bath). The dose received by all of the normal tissues can play a role in the risk of secondary cancers and lymphopenia. The aim of this work was to evaluate whether RapidArc Dynamic, combining dynamic arcs with integrated static-angle modulated ports (STAMPs), can reduce the integral dose while effectively sparing OIs. Material/Methods: In a planning study including 48 oropharynx patients, we previously demonstrated superior sparing of central OIs when applying the RapidArc Dynamic with a single dynamic arc and one anterior STAMP (arc/static-port), compared to 2-arc VMAT. Knowledge- based autoplanning was used to avoid user- dependence of the plan quality. In the current analysis, we evaluated the distribution of dose outside the elective planning target volume (prescribed 51.68 Gy in 34 fractions), represented by the volume contained by a series of isodoses and the mean dose (Dmean) to the patient volume (covered by the CT scan). In addition, the oesophageal organ equivalent dose (eOED), which determines the risk of secondary oesophageal cancer, was calculated, similarly to [1]. These parameters were compared with the Spearman signed rank test (p<0.05 considered significant), for the arc/static-port and VMAT plans, respectively. Results: For all isodoses between 85% and 5%, the volume encompassed was smaller for the arc/static-port plan compared to the 2-arc VMAT plan (Figure 1, Table 1). The patient volume Dmean was also significantly lower, as well as the oesophageal Dmean. The eOED was lower with the arc/static-port technique, indicating a lower estimated risk of secondary oesophageal
OAR workflow.
Conclusion: Clinically acceptable plans were generated in less than ten minutes by DL dose prediction-driven workflows for same-day single-fraction SABR to solitary metastasis in the lung. References: [1] Palma DA, Olson R, Harrow S, Gaede S, Louie A V, Haasbeek C, et al. Stereotactic ablative radiotherapy versus standard of care palliative treatment in patients with oligometastatic cancers (SABR-COMET): a randomised, phase 2, open-label trial. The Lancet 2019;393:2051–8. https://doi.org/10.1016/S0140- 6736(18)32487-5.[2] Guo C, Huang P, Li Y, Dai J. Accurate method for evaluating the duration of the entire radiotherapy process. J Appl Clin Med Phys 2020;21:252–8. https://doi.org/10.1002/acm2.12959.[3] Roy S, Koehler G, Ulrich C, Baumgartner M, Petersen J, Isensee F, et al. MedNeXt: Transformer-Driven Scaling of ConvNets for Medical Image Segmentation, 2023, p. 405–15. https://doi.org/10.1007/978-3-031-43901- 8_39. Keywords: dose prediction; lung metastasis; same- day RT
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