Department of Radiation Oncology, Catharina Hospital Eindhoven, The Netherlands Recommendations for prescribing and recording in lung SBRT according to the ACROP guideline and ICRU report 91. Evelyn E.C. de Jong1, Matthias Guckenberger 2, Nicolaus Andratschke 2, Karin Dieckmann 3, Mischa S. Hoogeman 4, Maaike Milder 4, Ditte Sloth Moller 5, Tine Bisballe Nyeng 5, Stephanie Tanadini-Lang 2, Eric Lartigau 6, Thomas Lacornerie 6, Suresh Senan 7, Wilko Verbakel 7, Dirk Verellen 8, Geert De Kerf 8, Coen W. Hurkmans 1 1Department of Radiation Oncology, Catharina Ziekenhuis, Eindhoven, the Netherlands; 2Department of Radiation Oncology, University Hospital Zürich, Switzerland; 3Department of Radiotherapy, Medical University of Vienna, Austria; 4Department of Radiation Oncology, Erasmus MC Cancer Institute, Rotterdam, the Netherlands; 5Department of Oncology, Aarhus University Hospital, Denmark; 6Department of Oncology, Centre Oscar Lambret, Lille, France; 7Department of Radiation Oncology, VU University Medical Center, Amsterdam, the Netherlands; 8Department of Radiotherapy, Iridium Kankernetwerk, Antwerp, Belgium Introduction and objectives In 2017 the ESTRO ACROP consensus guideline on implementation and practice of SBRT for periperherally located early stage NSCLC was published recommending to prescribe 3 x 15 Gy to the PTV as this results in a BED10Gy >100Gy. Later that year the ICRU published report 91 about prescribing, recording and reporting of stereotactic treatments. The purpose of this multicentre study is to quantify the current variation in prescription practice in the institutions that contributed to the ACROP guideline and to establish the link between ACROP and ICRU91 recommendations. Methods From each of the eight participating centres, 15 consecutive clinical treatment plans of patients with peripherally located early stage NSCLC were selected. Treatment plans were generated following the institutional protocol, centres A and B prescribed 3 x 13.5 Gy, centre C 3 x 15 Gy, centre E 3 x 17 Gy and centres D, F, G and H 3 x 18 Gy. Subsequently, dose parameters of the target volumes were reported as recommended by ICRU91 and also converted to BED10Gy. The centres employed different techniques for motion management, ITV concept, mid-ventilation concept, tracking or a mix of these. Results A B Figure 1: A) Boxplot of the minimum dose (D98%; red), Dmean Figure 2: GTV Dmean plotted as function of PTV D98%, the doses of (green) and the maximum dose (D2%; blue) of the PTV per centre. centres A and B are scaled to 3 x 15 Gy; physical doses are converted to BED doses using a α/β of 10. Discussion Based on our results we provided some recommendations for institutions starting with peripheral lung SBRT. • To prescribe 3 fractions of 15 Gy such that a minimum Conclusion PTV D98% of 100 Gy BED10Gy and minimum Prescription practice varied widely across the institutions. GTV/ITVmean dose of 150Gy BED10Gy is achieved. More detailed recommendations for dose planning and • To report the dose and other items like type of planning reporting of lung SBRT in line with the ICRU report 91 were system used and type of QA performed according to formulated, including a minimum PTV D98% of 100 Gy BED10 ICRU91 . and minimum GTV/ITV mean dose of 150 Gy BED10 and a • To report explicitly both PTV and GTV/ITV D98%, D2% D2% in the range of 60-70 Gy. and Dmean. • To report the high dose Conformity Index of the PTV (or GTV if prescribing to the GTV) based on V98% total body (and not on e.g. V95%). • To strive for a D2% in the range of 60-70 Gy, realising that it is patient dependent (lung density). ESTRO 2019, Abstract E38-0280 Corresponding author: E.E.C. de Jong, [email protected] PV-0103 Poster viewing 2: Advanced technologies Poster presented at: Evelyn De Jong DOI: 10.3252/pso.eu.ESTRO38.2019 ESTRO38.