ESTRO 36 Abstract Book

S548 ESTRO 36 2017 _______________________________________________________________________________________________

delineating method for delineating the CTV of the regional lymph nodes of breast cancer patients due to the increase of the CIgen combined with the shortest delineation time and the smallest standard deviation per delineating direction. We also recommend performing second reading to improve the concordance between radiation oncologists. Finally, further research is required because the CIgen did not reach a level higher than 0.8. PO-1002 Comparison of Best Commercial Model and Atlas based segmentation with CT and MR in brain cancer. J.Y. Woo 1 , T.Y. KIM 2 , J.Y. SEOK 3 , T.M. KIM 1 , Y.W. CHO 1 , S.Y. KIM 1 , J.G. BAEK 1 , J.H. KIM 1 , J.H. CHO 1 1 Yonsei Cancer Center, Radiation Oncology, Seoul, Korea Republic of 2 National Cancer Center, Radiation Oncology, Gyeonggi- do, Korea Republic of 3 Seoul National University Bundang Hospital, Radiation Oncology, Gyeonggi-do, Korea Republic of Purpose or Objective It is important to accurately delineate critical organ such as optic chiasm, pituitary gland and brainstem when radiation therapy is delivered in brain cancer. MR images were usually used to delineate critical organ accurately in most brain cases. But manually delineated contours by different users sometimes have different shape and region in the same planning CT. Even if different users delineate contours, we would expect to get more accurate and regular critical organ if using auto contouring method. Recently there are many commercial auto contouring softwares including model based segmentation (MBS) and atlas based segmentation (ABS) softwares even supporting MR images. This study aims to compare auto contouring methods to delineate critical organ accurately and to have certain shape and region. Material and Methods It is multi-center study. We selected 10 patients. We used three MBS software solutions and ABS software solution (MIM_software ver. 6.5.5.) to generate the automatic contouring on the planning CT. All MBS software just made contours without any preparation, and we chose the best result among 3 MBS solutions for comparison. But ABS software should have subjects (who are already registered for ABS to work on auto contouring and also they are not the patients involved in this study). We made two groups of atlas, 60 subjects of CT based and 20 subjects of MR based. We used two matching techniques for MR based ABS, Majority-vote and STAPLE. We analyzed auto contouring with 4 classified groups - best MBS (BM), CT based ABS for 60 subjects (CA), and MR based ABS using Majority-vote (MR_MV) and MR based ABS using STAPLE (MR_ST). We gained brain stem, optic chiasm, and pituitary gland contours. Average Dice Similarity Coefficients (DSC) was calculated for each structure to compare against 'gold” standard contours which are manually defined of 4 groups respectively. Values closer to 1 indicate higher accuracy. Results MR_ST was significantly more accurate than other group according to DSC of 0.646 ± 0.094 compared to 0.564 ± 0.102, 0.298 ± 0.109, 0.39 ± 0.254 respectively for MR_MV, CA and BM in optic chiasm. DCS scores in pituitary gland were following, 0.624 ± 0.055 in MR_ST, 0.582 ± 0.052 in MR_MV, 0.514 ± 0.140 in CA and 0.28 ± 0.24 in BM respetively. Brainstem was showed similar DSC score as 0.89 ± 0.021, 0.892 ± 0.017, 0.842 ± 0.038 and 0.73 ± 0.156 respectively for MR_ST, MR_MV, CA and BM. Conclusion Most of auto delineated contours was smoothened in advance. Among 4 groups, DSC of MR based was the highest. Even though auto contouring is conducted by different users, it shows certain shape and included similar region when we use same subject’s data. ABS

software takes more effort and time to use in the first place. However, MR based ABS would have better auto contouring accuracy compared with MBS and CT based ABS in brain cancer. In addition STAPLE has provided better results for smaller volumes based on my study. PO-1003 A analysis of safety of whole brain radiotherapy with Hippocampus avoidance in brain metastasis Y. Han 1 , J. Chen 1 , G. Cai 1 , X. Cheng 1 , Y. Kirova 2 , W. Chai 3 1 Shanghai Jiao Tong university-ruijin hospital, radiaton oncology, Shanghai, China 2 Institute Curie- Paris- France, Department of Radiation Oncology, Paris, France 3 Shanghai Jiao Tong university-ruijin hospital, Department of Radiology, Shanghai, China Purpose or Objective Purpose : Whole brain radiotherapy (WBRT) remains reference treatment in patients with brain metastasis (BM), especially with multiple lesions. Hippocampus avoidance in WBRT (HA-WBRT) offers the feasibility of less impaired cognitive function than conventional WBRT and better intracranial control than SBRT. Oncological safety is critical in defining the proper role of HA-WBRT. The study aims to investigate the frequency of intracranial substructure involvement based on large series of radiological data and to optimize the margin definition in treatment planning. Material and Methods Methods : Consecutive patients with diagnosis of BM from enhanced MRI between 03/2011 and 07/2016 diagnosed and treated in RuiJin Hospital were analyzed. Lesions of each patient were confirmed by a senior radiologist and the closest distances from tumor to the hippocampal area were measured and analyzed by radiation oncologist. Results Results : A total of 226 patients (pts) (115 males and 111 females) with 1080 metastatic measurable lesions have been studied. The distribution of the primary tumours was as following: 72.6% lung cancers (LC) (n=164), 19.9% breast cancer (BC) patients (n=45) and 7.5% from other malignancies (n=17). Seventy-one pts were diagnosed with BM before or simultaneously with their primary malignancy. In the case of others 155 pts, the latency of BM appearance was as following: 14 months in LC pts (n=100), 59 months in BC pts (n=42). Totally, 758 (70.2%) lesions were situated beyond the tentorium. The median diameter of the lesions was 10 mm (1.2mm-162mm). The situation of the lesions was as following: 322 (29.8%) in the cerebellum, 268 (24.8%) in the frontal lobe, 168 (15.6%) in the temporal lobe, 128(11.9%) in the parietal lobe, 131 (12.1%)in the occipital lobe, 45 (4.2%)in the thalamus and 18 (1.6%) in the brainstem. After measuring the closest between the lesions and the Hippocampus in every case, the pts with lesions close to this zone (n=45) were classifed into 3 catogories: 7 (3.1 %) at 5 mm or less, 13 (5.7%) within 10 mm or less and 19 (8.4%) at 20 mm or less (Fig1). 45 patients received WBRT only and 18 of 45 patients who had complete radiological follow-up after WBRT in the same hospital were founded progress of BM. The median follow-up was 11 months. Only one new lesion