ESTRO 36 Abstract Book

S552 ESTRO 36 _______________________________________________________________________________________________

Conclusion Inter- and intrafraction variations were analysed fo r three different cranial fixation systems. In trafraction translations were small for all systems, while interfraction rotations could be significant. The addition of an individual head support does not seem to decrease the interfraction rotations, and for intrafraction variations the results seem to even indicate a slight improvement when using a standard head support with a shape that provides good fixation for the head. Individual supports might have added value for patients with a deviating anatomy.

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Table 1. The differences of the CIgen between the three methods. CIgenDijkema et al. CIgenESTRO CIgenTool Average 0,58 0,57 0,64 Standard deviation (σ) 0,05 0,06 0,05 CIgen = Conformity Index generalized Conclusion Using the ‘Tool’ we found a significantly higher CIgen and a smaller CTV volume (compared with the method 'Dijkema et al.'). The advice is to use the ‘Tool’ as 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.

Poster: RTT track: Imaging acquisition and registration, OAR and target definition

PO-1001 Evaluation of target volume delineation of the regional lymph nodes in breast cancer patients M. Mast 1 , E. Gagesteijn 1 , T. Stam 1 , N. Knotter 2 , E. Kouwenhoven 1 , A. Petoukhova 1 , E. Coerkamp 3 , J. Van der Steeg 1 , J. Van Egmond 1 , H. Struikmans 1 1 Haaglanden Medical Centre Location Antoniushove, Radiation therapy, Den Haag, The Netherlands 2 Leiden University Medical Centre, Clinical oncology, Leiden, The Netherlands 3 Haaglanden Medical Centre Location Westeinde, Radiology, Den Haag, The Netherlands Purpose or Objective New ESTRO guidelines have been developed for the delineation of the Clinical Target Volumes (CTVs) of the regional lymph nodes of the breast. Until now we used the methods based on the article of ‘Dijkema et al.’. In response to these new insights, we decided to develop a tool to implement this new ESTRO guideline. The main question, which will be answered, is: “What are the differences between delineating the regional lymph nodes of breast cancer according to the method ‘Dijkema et al.’, ‘the ESTRO guidelines’ and ‘the Tool combined with ESTRO guidelines (‘Tool’)’?” Material and Methods In ten patients CTVs of the regional lymph nodes of the breast were delineated (in Pinnacle [1]) by three dedicated radiation oncologists, according to the two different guidelines and the ‘Tool’. The ‘Tool’ is a method where the subclavian and the axillary vessels are delineated by a radiation therapist and is expanded in all directions with 5 mm. This volume is than adjusted by the radiation oncologist on the basis of the prescribed anatomical boundaries of ‘the ESTRO guidelines’. After that, all CTVs were exported to MATLAB to calculate the Conformity Index generalized (CIgen ) [2]. In MATLAB the differences in the various directions on the axial coupes of the treatment planning-Computed Tomography scans were analysed. Also the volumes of the CTVs were calculated in Pinnacle. Finally, the required delineating times per patient, per guideline and per radiation oncologist were compared and analyses were carried out using SPSS [3]. [1]: Pinnacle Treatment Planning System, version 9.10 (Philips Healthcare) [2]: E. Kouwenhoven, 2009, Phys Med Biol. [3]: IBM SPSS Statistics for Windows, IBM Corp., Armonk, The MATLAB analyses showed that the ‘Tool’ had the highest CIgen (0.64 and σ = 0.05) relative to the other two methods ( p<0.04 ) (table 1) . Furthermore, the delineating time was shortest (13.6 min and σ = 2.4) by using the ‘Tool’. The use of the ESTRO guideline without the ‘Tool’ resulted in the smallest average CTV volume (150.6 cm 3 and σ = 41.0). Furthermore, we saw a clear decrease of the standard deviations in most delineating directions when using the ‘Tool’, except in the ventral NY, USA Results