ESTRO 36 Abstract Book

S231 ESTRO 36 2017 _______________________________________________________________________________________________

prostate patients by acquiring the conversion algorithms within and outside an automatically contoured bone outline. The quality of the produced sCT images was quantified by HU and dose distribution comparisons against standard CT images. The treatment planning was conducted with VMAT. Results Figure 1 shows examples of the constructed sCTs with the original MR images of each scanner. The mean HU difference for the sCTs was 11 HUs and 90 HUs in the soft and bone tissue volumes, respectively (n=9). The target volume dose differences compared to the CTs were within 0.8% in all cases (0.2±0.5% [average±SD, n=9]). Table 1 presents the HU and dose distribution differe nces between the sCTs and the actual CT images.

Figure 2

Conclusion DPF can be estimated and constructed adaptively voxel- by-voxel in human tumor using multiple FDG-PET imaging obtained during the treatment course. DPF provides a potential quantitative objective for adaptive DPbN to plan the best clinical dose, escalate or de-escalate, in human tumor based on its own radiosensitivity or radioresistance. OC-0442 Intensity based synthetic CT generation from standard T2-weighted MR images with three MR scanners L. Koivula 1 , L. Wee 2 , J. Dowling 3 , P. Greer 4 , T. Seppälä 1 , J. Korhonen 1 1 Comprehensive Cancer Center- Helsinki University Central Hospital, Department of radiation oncolocy, Helsinki, Finland 2 Danish Colorectal Cancer Center South, Vejle Hospital, Vejle, Denmark 3 Commonwealth Scientific and Industrial Research Organisation CSIRO, CSIRO ICT Centre, Brisbane, Australia 4 Calvary Mater Newcastle Hospital, Radiation Oncology, Newcastle, Australia Purpose or Objective Recent studies have shown feasibility t o conduct the entire radiotherapy treatment planning workflow relying solely on magnetic resonance imaging (M RI). Yet, few hospitals have implemented the MRI-only workflow into clinical routine. One limiting issue is the requisite construction of a synthetic computed tomography (sCT) image. The majority of published sCT generation methods necessitate inclusion of extra sequences into the simulation imaging protocol. This study aims to develop an intensity-based sCT generation method that relies only on image data from standard T2-weighted sequence. The work includes images derived from three different manufacturers’ MR scanners. The primary target group was prostate, for which T2-weighted images are already used as standard target delineation images. Material and Methods The study utilized a total of 30 standard T2-weighted images acquired for prostate target delineation in three different clinics. The imaging was conducted with MR scanners (GE Optima 1.5T, Philips Ingenia 1.5T, and Siemens Skyra 3.0T) of each participating clinic by using their typical clinical settings. Intensity value variations of the obtained images were studied locally, and compared to corresponding Hounsfield units (HUs) of a standard CT image. The data of 21 of the 30 prostate patients was used to generate conversion models for bony and soft tissues to transform the MR image into sCT. The models were optimized separately for the images obtained by each MR platform. The sCT generation was tested for 9 of the 30

Conclusion This study revealed the feasibility of generating high quality sCTs directly from intensity values of standard T2- weighted MR images. The applied sCT generation method is adjustable for images applied by multiple manufacturers’ scanners with different clinical settings. This work can further contribute to wider clinical implementation of MRI-only based radiotherapy treatment planning.

Proffered Papers: Optimatisation algorithms for treatment planning

OC-0443 Robust optimization of VMAT in head and neck patients D. Wagenaar 1 , R.G.J. Kierkels 1 , J. Free 1 , J.A. Langendijk 1 , E.W. Korevaar 1 1 UMCG University Medical Center Groningen, Department of Radiation Oncology, Groningen, The Netherlands