ESTRO 2021 Abstract Book

S1432

ESTRO 2021

Conclusion The proposed daily treatment delivery QA workflows confirmed the daily treatment integrity with respect to file transfer verification and treatment fraction and course dose accumulation. Its clinical adoption can provide valuable QA measures to prevent potential critical failures during treatment. PO-1705 Evaluation of a markerless SGRT-only workflow for breast cancer patients T. Sauer 1 , D. Popp 1 , O.J. Ott 1 , C. Bert 1 1 Universitätsklinikum Erlangen, Friedrich-Alexander-Universität Erlangen-Nürnberg, Department of Radiation Oncology, Erlangen, Germany Purpose or Objective A markerless SGRT-only workflow for the treatment of breast cancer patients has been introduced clinically. The goal of this study was to investigate treatment time savings resulting from the omission of skin markings and the reduction of CBCT scans used for daily positioning. In addition, the decrease in imaging dose and the accuracy of the SGRT-based positioning compared to CBCT were evaluated. Materials and Methods As part of the new clinical workflow on two Versa HD linacs (Elekta, Stockholm), patients were pre-positioned with indexed positioning devices and the position corrected by using the AlignRT system (VisionRT, London). During the first week of treatment, the position was additionally corrected with a CBCT scan. An individual positioning concept was decided on the basis of the CBCT shifts of the first week: in case of shifts ≤5 mm a CBCT image was taken weekly with positioning based on SGRT-only on all other treatment days. In case of larger deviations, CBCT imaging was continued on a daily basis. The accuracy of the SGRT-based positioning and the treatment times (from log data of AlignRT) of patients treated according to the new concept were compared to patients treated with an old concept involving daily CBCTs (100 patients each group). Results Approximately 40% of the patients showed CBCT shifts within clinical tolerances and were considered for treatment with weekly CBCT. Treatment times for these patients have been reduced by approximately 150 s and non-therapeutic dose was decreased by up to 1.5 cGy, compared to patients treated with the old concept involving daily CBCTs. For SGRT-only fractions, treatment times decreased by approx. 230 s. Independently of the individual concept, treatment times have been reduced by approx. 90 s on average for all patients treated with the new scheme. Conclusion A clinically feasible workflow for the treatment of breast cancer patients has been introduced. It is based on markerless prepositioning and an individual positioning concept depending on the accuracy of SGRT based positioning during the first week of treatment. Compared to a daily CBCT positioning concept, significant time and imaging dose saving have been observed. PO-1706 Stereotactic body radiotherapy for bone metastases: Initial lessons learned regarding setup F. Gaard-Petersen 1 , M. van Overeem Felter 1 , M. Josipovic 2 , E. Serup-Hansen 1 , C.F. Behrens 1 , G. Persson 1,3 1 Herlev and Gentofte Hospital University of Copenhagen, Department of Oncology, Herlev, Denmark; 2 Rigshospitalet University of Copenhagen, Department of Oncology, Copenhagen, , Denmark; 3 Faculty of Health Sciences, University of Copenhagen, Department of Clinical Medicine, Copenhagen, Denmark