ESTRO 2023 - Abstract Book

S1671

Digital Posters

ESTRO 2023

Conclusion Template based planning leads to fast and acceptable plans for daily plan adaptation for the majority of adaptive fractions. Nevertheless, complete replanning may significantly increase plan quality, especially in fractions with large anatomic variations compared to the reference situation and thus ensure dose coverage to the PTV

PO-1919 SBRT for central lung lesions: large biological delivered dose deviations for the bronchi

E. Lindbäck 1,2 , K. Al Jirf 3 , L. Hoffmann 4,5 , D. Sloth Møller 4,5 , K. Karlsson 1,2 , S. Nyberg Thomsen 4,5 , K. Lindberg 2,3 , A. Ahmed Khalil 4,5 , J. Uzan 6 , E. Onjukka 1,2 1 Karolinska University Hospital, Department of Medical Radiation Physics and Nuclear Medicine, Stockholm, Sweden; 2 Karolinska Institute, Department of Oncology and Pathology, Stockholm, Sweden; 3 Karolinska University Hospital, Department of Cancer, Stockholm, Sweden; 4 Aarhus University, Department of Clinical Medicine, Aarhus, Denmark; 5 Aarhus University Hospital, Department of Oncology, Aarhus, Denmark; 6 Raysearch, Service, Stockholm, Sweden Purpose or Objective Stereotactic Body Radiation Therapy (SBRT) for centrally located lung lesions is associated with the risk of fatal bleeding, potentially resulting from damage to the main and intermediate bronchi, hereafter referred to as bronchi. When studying dose response of thoracic organs at risk (OAR), considering uncertainties in dose from the breathing motion and heterogenous hypofractionated dose distributions is important. The current study estimates the relative contribution from breathing motion and set-up deviations, respectively, to the uncertainty in dose to the bronchi, based on 4DCT phase images and CBCT images. Materials and Methods Thirteen patients treated for central lung tumours were retrospectively included and imported into RayStation 12A-R; median [IQR] of the GTV to bronchi distance was 6 [2 – 18] mm. The periphery of the planning target volume (PTV) was prescribed 7 Gy x 8, corresponding to 14 Gy/fraction in EQD2 ( α / β = 3 Gy). Typically, the maximum dose was around 150%. Treatment plans were created on a separate free breathing treatment planning CT (TPCT). Bronchi were delineated on each online tumour-match CBCT and each of the eight (or ten) 4DCT phase images by an oncologist. Original treatment plans were created in Eclipse, but dose distributions were recalculated in RayStation on the TPCT, CBCT and 4DCT phase images, based on online match position and DICOM frame of reference, respectively. The bronchi DVH for each image dose was exported and converted to EQD2 ( α / β = 3 Gy). D0.1cc values were compared to the planned dose in EQD2 for all image doses. The hypothesis of equal magnitude of this deviation in D0.1cc, comparing CBCT and 4DCT, was tested in a Mann-Whitney U test.