ESTRO 36 Abstract Book

S353 ESTRO 36 _______________________________________________________________________________________________

Results RapidPlan DVH analysis of all 54 pt indicated that 4/9 patients with RP had the highest CL doses, and 3 had high IL doses(figure). 2/3 pt developing LH had the highest volumes of PBT receiving high doses >40Gy and Dmax>70Gy. For the 15 pt who developed ≥G3toxicity, the non-toxicity model showed that 5 of their plans had up to 2.5x higher CL mean dose than predicted, all these pt had RP. For 3 patients, the clinical plans had higher maximum PBT doses(70-82Gy) than the model,2 of these pt developed LH and 1 post-SABR atelectasis. For the other 8 pt, clinical plans were judged to be good. Conclusion A RapidPlan model identified the potential for plan improvements in nearly 50% of pt undergoing SABR for lung tumors ≥5cm, who developed G≥3 toxicity.Such plan quality checks are important for this type of higher-risk treatment. They could also help to improve quality of clinical studies. PO-0675 Evaluating commercial delineation software in routine clinical practice: analyzing time and quality. T. Lustberg 1 , W. Van Elmpt 1 , J. Van der Stoep 1 , J. Van Soest 1 , M. Gooding 2 , A. Dekker 1 1 Department of Radiation Oncology MAASTRO- GROW, School for Oncology and Developmental Biology- Maastricht University Medical Centre, Maastricht, The Netherlands 2 Mirada Medical Ltd, Science and Medical Technology, Oxford, United Kingdom Purpose or Objective Delineation of organs at risk (OAR) and target volumes is vital for treatment planning in radiation oncology. This process is very time consuming and quality of the delineation depends on the skill level of the observer. Automatic delineation software is commercially available but rarely used in clinical practice. The aim of this study to evaluate the quality of automatic delineation of OARs and the time that could potentially be gained by commissioning automatic delineation software for clinical use. Material and Methods Twenty stage I-III NSCLC patients were selected from routine clinical practice and their CT scans were used to delineate OARs. The following OARs were delineated: left lung, right lung, heart, spinal cord, esophagus, mediastinum, left brachial plexus, right brachial plexus and carina. Each OAR was delineated 3 times, once manually by a technician, once using commercial atlas- based delineation software and once by adjusting the software generated delineation to match clinical guidelines by the same technician. The time needed perform manual delineation and the adjustments to the automatically generated delineation were recorded. The atlas was derived from 10 stage I NSCLC patients collected from clinical practice. To compare the delineations, the maximum Hausdorff-distance was computed for each patient for each OAR in each CT slice between the manual delineation and the atlas, and between the manual delineation and the adjusted atlas. The mean of these maximums was calculated and presented as a boxplot for each OAR for the two comparisons together with the time required to perform the delineations. Results Delineation of the left lung, heart, esophagus, left and right brachial plexus and carina was quicker if the automatically generated delineation only needed minor adjustments (Figure 1B). The right lung, spinal cord and mediastinum show a time gain on average, but not for all cases (Figure 1B). The adjustment of the delineation created by the automatic delineation software resulted in a smaller mean maximum Hausdorff-distance for all OARs compared to the manual delineation (Figure 1A), but there was still a difference to the manual delineation.

Figure 1: A) Delineation mean maximum Hausdorff- distance for each OAR. B) Time needed to delineate the OARs. Conclusion Based on the results above, we conclude that automatically generated delineations save time for the majority of the cases and after minor adjustment meet clinical guidelines. Further investigation is needed into the quality of the automatic delineation software and inter-observer variability. PO-0676 outcomes of synchronous and metachronous pulmonary oligometastasis treated with SBRT A. Sharma 1 , M. Duijm 1 , E. Oomen-de Hoop 2 , J. Aerts 3 , C. Verhoef 4 , M. Hoogeman 1 , J. Nuyttens 1 1 Erasmus MC-Daniel den Hoed Cancer Center- Rotterdam- The Netherlands, Department of Radiation Oncology, Rotterdam, The Netherlands 2 Erasmus MC-Daniel den Hoed Cancer Center- Rotterdam- The Netherlands, Department of Medical Oncology, Rotterdam, The Netherlands 3 Erasmus MC-Daniel den Hoed Cancer Center- Rotterdam- The Netherlands, Department of Pulmonology, Rotterdam, The Netherlands 4 Erasmus MC-Daniel den Hoed Cancer Center- Rotterdam- The Netherlands, Department of Surgical Oncology, Rotterdam, The Netherlands Purpose or Objective The purpose of our study was to evaluate overall survival (OS) and identify factors associated with OS in patients diagnosed with inoperable pulmonary oligometastatic tumors. Material and Methods Between 2005 to 2015, 326 inoperable pulmonary oligometastasis in 206 patients with ≤ 5 metastasis in no more than two organs were treated with stereotactic body radiotherapy (SBRT). Synchronous metastases were defined as presence of metastases within 5 months of diagnosis of primary tumor, otherwise they were assigned to the metachronous group. Risk adapted SBRT was used to treat peripheral lung metastasis with 51 Gy or 54Gy or 60 Gy in 3 fractions or 30Gy in single fraction, central tumors received 50 Gy-55Gy in 5 fractions or 60Gy in 8 fractions and metastasis located close to esophagus or in mediastinum received 6x8 Gy, 7x7Gy or 8x7Gy. Dose to PTV was prescribed at the 70-90% isodose line (median 78%), covering at least 95% of PTV. OS was calculated from date of first SBRT session to date of death or date of last follow up for alive patients. The following variables were assessed for prognosis: age, gender, primary site, metachronous versus synchronous tumors, metastatic burden in body, metastatic burden in lungs, presence of extra pulmonary metastasis, delivery of pre SBRT chemotherapy, disease free interval, biological