ESTRO 2022 - Abstract Book

S721

Abstract book

ESTRO 2022

Results The 647 pts included in the analysis had a G1+ SI rate at 2 years of 29.4%. 281 variables were considered: 127 published SNPs (GWAS literature), 40 clinical factors, 93 treatment factors and 21 dosimetric variables (for each volume and a/b). For volume thresholds <200cc, no dosimetric feature was selected by the wrapper method. Therefore, we derived a predictive model (16 features, no dosimetric variable) for use before RT planning (Model 1). At sub-DVH_200cc, for a/b=3.6Gy only Dmin was selected (Model 2) as dosimetric variable, while for a/b=1.8Gy, EUD (n=0.5) and Dmin entered the FNN (Model 3). Fig 2 reports the selected features and performance of the 3 models.

Conclusion A pre-planning SI model was derived that included information on genetics (6 SNPs), treatment (6 RT, 1 oncology) and clinical factors. Largest volume (200cc) sub-DVH allowed selection of dosimetric features, particularly with a/b=1.8Gy and EUD with n=0.5. Following validation, the model could be used to personalise use of new RT schedules, such as ultrahigh- hypofractionation, to minimise risk of SI.

MO-0802 Five-year oncological outcomes after two different APBI techniques; a prospective cohort study

M. Mast 1 , D. Jacobs 2 , N. Horeweg 2 , G. Speijer 3 , A. Petoukhova 1 , M. Straver 4 , E. Coerkamp 5 , H.M. Hazelbag 6 , J. Merkus 7 , E. Roeloffzen 8 , L. Zwanenburg 8 , J. van der Sijp 4 , M. Fiocco 9 , C. Marijnen 10 , P. Koper 1 1 Haaglanden Medical Center, Radiotherapy, Leidschendam, The Netherlands; 2 Leiden University Medical Center, Radiotherapy, Leiden, The Netherlands; 3 Haga Hospital, Radiotherapy, The Hague, The Netherlands; 4 Haaglanden Medical Center, Surgery, Leidschendam, The Netherlands; 5 Haaglanden Medical Center, Radiology, Leidschendam, The Netherlands; 6 Haaglanden Medical Center, Pathology, Leidschendam, The Netherlands; 7 Haga Hospital, Surgery, The Hague, The Netherlands; 8 Isala, Radiotherapy, Zwolle, The Netherlands; 9 Leiden University Medical Center, Statistics, Leiden, The Netherlands; 10 The Netherlands Cancer Institute, Radiotherapy, Amsterdam, The Netherlands Purpose or Objective To evaluate the ipsilateral breast tumour recurrence (IBTR) rate after two different accelerated partial breast irradiation (APBI) techniques (intraoperative electron radiotherapy, IORT and external-beam APBI, EB-APBI) in patients ≥ 60 years with early stage breast cancer.