ESTRO 2023 - Abstract Book

S1604

Digital Posters

ESTRO 2023

Results For the static plans, median V95/D5-D95 to the CTV over all cases were 98% and 10.3% respectively. Median(max) motion amplitudes extracted from all 4DCTs for all patients ranged from a minimum of 0.4mm(75%) up to 11.1mm(49%), resulting in energy changes for 3D tracking requiring a beamline acceptance of up to ±3% dp/p. In this scenario, 3D tracking achieved V95/D5-D95 values close to the static: 92.4% and 17.2%. For the conventional acceptance, which limits range tracking, the same indices decreased marginally to 92.1% and 17.1%. Rescanning was found to have a positive effect on treatment quality for the ideal cases (V95= 96.6%, D5-D95=14.6%), but negatively impacted results for limited acceptance (V95= 87.9%, D5 D95=18%), with rescanning increasing the acceptance requirements up to ±7% dp/p.

Conclusion Respiratory synchronized tracking was simulated under realistic conditions of breathing variability. The ideal acceptance requirements for the treatment of lung cancer are not far from what is available in the clinic today, and current proton therapy units would technically already allow the delivery of treatments with tumor tracking. Nevertheless, alternative options such as visual coaching or robust planning should be considered, as rescanning could be challenging with this approach.

References: Giovannelli AC, et al. . Med Phys., https://doi.org/10.1002/mp.15449 Fattori G, et al. Sci Rep., https://doi.org/10.1038/s41598-020-71821-1

PO-1863 Full course 4D IMPT dose assessments for thoracic targets with large motion

S. Visser 1 , E.W. Korevaar 1 , R. Wijsman 1 , C.T. Muijs 1 , J.A. Langendijk 1 , P. Pisciotta 1 , G. Gutteres Marmitt 1 , C. O.Ribeiro 1 , S. Both 1

1 UMCG, Radiotherapy, Groningen, The Netherlands

Purpose or Objective Despite the dosimetric benefits of intensity-modulated proton therapy (IMPT), plan robustness may be compromised due to its sensitivity to treatment uncertainties. For target volumes located in the thorax, there is an additional uncertainty due to motion and interplay effects. Before clinical implementation, we investigated the robustness of our clinical protocol by simulating the treatment with the 4D robustness evaluation method (4DREM). In clinical context, we use a combination of 3D robustness evaluation (3DREM) and 4D dose reconstruction (4DREAL) throughout the patient’s treatment. In this study, we investigate plan robustness outcomes obtained with these three methods for thoracic targets with large motion treated at our proton centre.

Materials and Methods