ESTRO 2021 Abstract Book

S130

ESTRO 2021

Conclusion RRMM has been widely implemented in European particle therapy center as clinical practice. A significant interest was reported to implement more active RRMM in the future, in particular for lung cancer, requiring more support to address technical limitations. Acknowledgement: We thank all particle therapy centers for answering the questionnaire. OC-0201 Breast specific cone-beam CT calibration for daily dose verification in proton therapy T. Omand Kirkegaard Sørensen 1,2 , L. Muren 1 , U.V. Elstrøm 1 , C. Kronborg 1 , B.V. Offersen 1,3 , S.E. Petersen 1 , L.B. Stick 1 , V.T. Taasti 4 , M.F. Jensen 1 1 Danish Centre for Particle Therapy, Aarhus University Hospital, Aarhus, Denmark; 2 Department of Physics and Astronomy, Aarhus University, Aarhus, Denmark; 3 Department of Experimental Clinical Oncology, Aarhus University Hospital, Aarhus, Denmark; 4 Department of Radiation Oncology, Maastricht University Medical Centre, Maastricht, The Netherlands Purpose or Objective Inter-fractional changes, such as tissue redistributions or slow variations in the patient size, are common for breast cancer patients. This could influence the quality of the proton dose delivery and therefore compromise the planned dose, especially for the targets and organs-at-risk (OAR) located in the distal edge of the proton beam. Cone-beam CT (CBCT) imaging may be used for daily proton dose evaluation. However, image artefacts