ESTRO 37 Abstract book

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ESTRO 37

the CTVs and two VMAT (ECLIPSE v.13.7) and two IMPT (ECLIPSE v.10.0) plans were optimized for both patients. The VMAT plans consisted of two full coplanar arcs and two non-coplanar partial arcs. The IMPT plans made use of three beams with range shifters. A 4mm spot spacing were used. The prescription dose were 60Gy or 60Gy(RBE) mean to PTV. Results The conformity index defined by CI=V D /V PTV were calculated for all plans for dose levels D=50Gy, 40Gy, 30Gy, 20Gy and 10Gy. For the isotropic cases the population mean CI for the VMAT plans were respectively: 1.4[1.4;1.4]; 1.8[1.8;1,9]; 2.6[2.4; 2.8]; 3.9[3.5;4.3]; 6.6[6.5;6.7] and for IMPT: 1.4[1.4;1.5]; 1.9[1.8;1.9]; 2.3[2.2;2.5]; 2.9[2.6;3.1]; 3.6[3.0;4.1] For the anisotropic case the respective population mean CI is for VMAT: 1.6[1.6;1.6]; 2.1[2.1;2.2]; 3.0[2.7; 3.2]; 4.5[4.0;5.0]; 7.1[6.6;7.6] and for IMPT: 1.6[1,5;1.7]; 2.1[2.0;2.1]; 2.6[2.5;2.7]; 3.2[2.9;3.5]; 4.0[3.4;4.6]

Conclusion The number of layers in MFO plans can be reduced substantially more than in SFO plans without compromising the plan quality. The robustness is independent of the number of layers, and the SFO plans are significantly more robust than the MFO plans. Combining the two conclusions, however, shows that if the level of robustness is acceptable or enforced via robust optimization, MFO plans could be candidates for treatment time reductions via energy layer reductions as neither the plan quality nor robustness is compromised. PV-0204 Comparison of IMPT and VMAT for diffusion tensor image guided treatment planning of gliomas J.B. Petersen 1 , S. Lukacova 2 , M. Jensen 1 , T. Guldberg 2 , A. Harbøll 1 , J. Kallehauge 1 1 Aarhus University Hospital, Medical Physics- Department of Oncology, Aarhus C, Denmark 2 Aarhus University Hospital, Department of Oncology, Aarhus C, Denmark Purpose or Objective Recently, the use of clinical target volume (CTV) driven by the differential migrations patterns of gliomas in grey (GM) and white matter WM has shown promising results in predicting the location of marginal recurrences. The resulting CTVs however have also been shown to be more irregular in shape and will thus require a more highly modulated radiation treatment technique. The aim of this pilot study was to compare the dose distributions from Intensity Modulated Proton Therapy (IMPT) and Volume Modulated Arc Therapy (VMAT) for both anisotropic and isotropic migration driven CTVs. Both techniques are supposed to deliver highly conformal dose distributions to complex targets. Material and Methods Two high grade glioma patients were scanned using Diffusion Tensor Imaging (DTI) on a 1.5T Philips Ingenia MR scanner. Their brains were segmented into GM, WM and Cerebral Spinal Fluid (CSF). The extent of the microscopic spread (CTV) was estimated using the gross tumor volume (GTV) as starting point and the subsequent migration was different in the three segmented regions. In the isotropic case the migration of tumor cells was 10 times greater in WM compared to GM. No migration was allowed in CSF and across other known anatomical barriers: brainstem wall, falx, and tentorium. The anisotropic case extends this solely by using the DTI information about the WM fiber tract directions and adds this as the preferential direction of the migration. A 3mm Planning Target Volume (PTV) was added isotopically to

Conclusion Targets generated using differential migration patterns in glioma tends to be highly irregular. VMAT and IMPT produce equally and highly conformal plans with regards to high dose levels, while for low and medium-low dose levels IMPT plans are more conformal. PV-0205 Optimization of combined proton-photon treatments J. Unkelbach 1 , M. Bangert 2 , K. De Amorim Bernstein 3 , N. Andratschke 1 , M. Guckenberger 1 1 Universitätsspital Zürich, Radiation Oncology, Zürich, Switzerland 2 German Cancer Research Center, Medical Physics in Radiation Oncology, Heidelberg, Germany 3 Massachusetts General Hospital, Radiation Oncology, Boston, USA Purpose or Objective Proton therapy is a limited resource. Especially centers with a single-room proton machine, integrated into a standard radiotherapy clinic along with several linacs, face the question how to best allocate proton treatment slots over the patient population. In that context,