ESTRO 2021 Abstract Book

S569

ESTRO 2021

Materials and Methods OligoCare is a pragmatic prospective observational cohort study of the E²-RADIatE project, a collaboration between ESTRO and EORTC. Patients are eligible irrespective of the OMD state (de-novo, repeat or induced) without restrictions with respect to local or systemic therapy, if all cancer lesions are treated with radical intent. Radical radiotherapy must be a component of treatment, without a limit regarding the maximum number of oligometastases. Results Between July 2019 and February 2021, a total of 19 international institutions enrolled 467 patients into the OligoCare cohort. Median number of patients enrolled per institution was 15 (range 1 – 71). The following results are preliminary and based on available data in February 2021: a total of 328 patients with information on primary disease, history of metastatic disease and current OMD lesions form the basis of this analysis. Prostate cancer was the most frequent primary tumor (42%) followed by colorectal cancer (23%), NSCLC (18%) and breast cancer (17%). Diagnosis of OMD included PET-imaging in 77% and MRI imaging in 16% of the patients. Patients were treated for de-novo, repeat or induced OMD in 58%, 30% or 12% of the cases, respectively. Metachronous oligo-recurrence was the most frequently observed OMD state (34%). Patients were treated with SBRT for a solitary metastasis in 67% of the cases. Most frequently irradiated metastasis locations were lung, non-vertebral bones and non-regional lymph nodes in 22%, 19% and 16% of the cases, respectively. The most commonly used radiotherapy delivery device, image guidance technology and treatment delivery techniques were C-arm linacs (84%), Cone-beam CT image guidance (82%) and VMAT treatment delivery (77%), respectively. Oligometastases were treated with a median of 4 radiotherapy fractions (range 1 – 12) and a median dose of 10 Gy per fraction (median of the planned mean CTV/ITV dose per fraction, maximum 39 Gy), resulting in a median BED of 74 Gy (α/β=10, maximum 220 Gy). Conclusion Feasibility of the OligoCare prospective registry trial has been demonstrated to assess real-world patterns of practice of radical radiotherapy for oligometastatic disease. PD-0741 Application of the ESTRO/EORTC oligometastatic disease classification system to current evidence D. Nevens 1 , A. Jongen 2 , I. Kindts 3 , C. Billiet 4 , P. Deseyne 5 , I. Joye 6 , Y. Lievens 7 , M. Guckenberger 8 1 Iridium Netwerk, Radiotherapy Department, Center for Oncological Research (CORE), Integrated Personalized and Precision Oncology (IPPON), University of Antwerp, Antwerp, Belgium; 2 University Hospital Zurich, University of Zurich, Department of Radiation Oncology, Zurich, Switzerland; 3 Cancer Centre, General Hospital Groeninge, Department of Radiotherapy, Kortrijk, Belgium; 4 Irdium Netwerk, Radiotherapy Department, Center for Oncological Research (CORE), Integrated Personalized and Precision Oncology (IPPON), University of Antwerp, Antwerp, Belgium; 5 Ghent University Hospital, Department of Radiation Oncology, Ghent, Belgium; 6 Iridium Netwerk, Center for Oncological Research (CORE), Integrated Personalized and Precision Oncology Network (IPPON), University of Antwerp, Antwerp, Belgium; 7 Ghent University Hospital, Ghent University, Department of Radiation Oncology, Ghent, Belgium; 8 University Hospital Zurich, University of Zurich, Department of Radiotherapy, Zurich, Switzerland Purpose or Objective With increasing interest in stereotactic body radiotherapy (SBRT) for treatment of oligometastatic disease (OMD) , E2-RADIATE/OligoCare, a joint ESTRO/EORTC prospective registry has been launched to collect real- world evidence. To support standardized data collection, analysis, and reporting within this project, a consensus for OMD classification has been established. This study aims to apply this new classification system to current evidence as identified in a systematic literature review . Materials and Methods A previously published systematic literature review, performed in Medline, Embase and Cochrane, was updated to include papers published until August 2019. We included prospective and retrospective studies using SBRT as a treatment component for OMD. The reporting of the OMD characteristics as described in the ESTRO/EORTC consensus was analyzed and a potential influence of the OMD classification on overall survival (OS) was evaluated. Results The systematic literature review identified 7415 potential publications, which resulted, after screening, in 95 studies for further analysis. Seventy-four of the of 95 studies (77.9%) were classified as retrospective and the remaining 21 (22.1%) as prospective studies. The median number of patients per study was 85. Regarding primary tumors, 54 studies reported on mixed disease-agnostic OMD cohorts, while 41 studies were based on homogeneous OMD cohorts with respect to primary tumor: prostate (n=16), lung (non-small cell; n=10), colorectal (n=8), renal (n=4), breast (n=1), cervix (n=1), and ovarian (n=1). Based on the five OMD classification questions of the ESTRO/EORTC consensus, we were able to accurately categorize 7/95 studies into one of the 9 categories (Table 1). Considering this small number, we also assessed whether studies could be categorized into one of the three higher-level OMD states: de novo, repeat, or induced OMD (Table 1). In addition to the 5 studies on metachronous oligorecurrence, and the one on synchronous OMD, an additional 14 studies were classified as “de novo OMD”, resulting in a total of 20 studies in this OMD state.