ESTRO 2022 - Abstract Book

S417

Abstract book

ESTRO 2022

Results The extensive evaluation approach showed that robust planning leads to achieving the intended dose with only a minor risk for underdosage in half of the patients. In contrast, respiratory motion reduces the probability of target coverage for the ITV fluence planning approach (p-value<0.001), as illustrated by the larger variance in dose coverage (Figure 2). No significant difference in dose coverage probability at D50% was found between the robust and the two isodose based plans, however robust planning was found to have a higher probability for a more homogeneous tumor dose (p-value<0.001).

Conclusion The results show that tumor motion not covered by the 4DCT gives a risk of underdosage but that this effect is mostly minor for robust optimization and isodose-based planning, but with higher variance for the latter. The robustness of any planning method against irregular tumor motion needs to be thoroughly evaluated before clinical implementation. The novel approach to study the impact of irregular motion will also be applied for proton therapy.

MO-0470 Markerless lung tumor localization in cine MV images of deep-inspiration breath-hold IMRT treatments

S. Rohrer 1,2 , D.S. Møller 3,4 , L. Hoffmann 4,3 , S. Skouboe 1 , M.L. Ehmsen 1 , T. Ravkilde 4 , M. Knap 3 , P.R. Poulsen 1,3

1 Aarhus University Hospital, Danish Center for Particle Therapy, Aarhus, Denmark; 2 University of Zurich, Physik-Institut, Zurich, Switzerland; 3 Aarhus University Hospital, Department of Oncology, Aarhus, Denmark; 4 Aarhus University Hospital, Department of Medical Physics, Aarhus, Denmark Purpose or Objective Radiotherapy of lung cancer often involves considerable irradiation doses to normal tissue because safety margins are needed to account for respiratory motion and other geometrical uncertainties. Treatment in deep inspiration breath-hold (DIBH) may reduce the motion and the needed margins. However, poor correlation between the external signal used to gate the DIBH treatment and the internal target position can limit the targeting accuracy and thus the benefit of the DIBH