ESTRO 2023 - Abstract Book

S1677

Digital Posters

ESTRO 2023

The absolute pitch deviation was greater for the marker-laser method than for the SI method (p<0.01), while the absolute roll deviation was smaller for the marker-laser method than for the SI-based method (p<0.01). Median and inter-quartile range values are presented in the table, and the figure shows the absolute distributions of the rotational deviations. However, since rotational deviations result in increasing misalignment further from the isocenter, pitch deviations have a greater impact on the accuracy of the set-up. For a patient with PALN CTV (CC length of 18.8 cm and AP depth of 10.9 cm) the pitch-related vertical deviation at the cranial end of the target is much greater than the corresponding roll-related longitudinal deviation at the outer A/P location, estimated based on the upper end of the IQR for rotational deviations (see table).

Fewer patients (10/25) needed to be re-imaged when using SI, compared with marker-laser (17/25) as positioning method.

Conclusion By introducing SI as a set-up method for gynecological cancer patients, higher positioning accuracy can be achieved compared to the marker-laser set-up method.

PO-1924 Robust evaluation of proton therapy within a randomized clinical trial for high-risk prostate cancer

S. Tilbaek 1 , S. Petersen 1 , A. Vestergaard 1 , L. Stolarczyk 1 , H.S. Rønde 1 , T. Johansen 1,2 , L. Bentzen 3 , J. Søndergaard 4 , M. Høyer 1 , L. Muren 1 1 Aarhus University Hospital, Danish Center for Particle Therapy, Aarhus, Denmark; 2 Rigshospitalet, Department of Oncology, Copenhagen, Denmark; 3 Vejle Hospital, University of Southern Denmark, Department of Oncology, Vejle, Denmark; 4 Aalborg University Hospital, Department of Oncology, Aalborg, Denmark Purpose or Objective Robust evaluation (RE) of a proton treatment plan in the planning stage (PS-RE) takes into account geometrical uncertainties in the form of isocenter shifts as well as range uncertainties. Pelvic anatomical variations include shape and position