ESTRO 37 Abstract book

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ESTRO 37

and 4DMRI. Entire liver and lung volumes below T8 vertebral level were contoured on inspiratory and expiratory phases of 4DMRI. Change in lung volumes were calculated between maximal inspiratory and expiratory bins. In addition, Euclidian distance was used to measure liver motion. Results To date, five patients and three volunteers have been scanned. Results of patient tumour movement are shown in Table 1. The mean amplitude of movement seen on 4DCT and 4DMRI was 1.36cm (range 0.28-2.59cm) and 1.36cm (range 0.53-2.19cm) respectively. Tumour delineation appeared equivalent or superior on the 4DMRI compared to 4DCT (see Figure 1). All 4DMRI sequences were <7minutes in duration and were well tolerated. In three healthy volunteers, AC reduced amplitude of liver movement and lung volumes as seen on 4DMRI.

Conclusion Results suggest that accurate MR-based dose calculation using a 2D cGAN for sCT generation is feasible for prostate cancer patients. An additional advantage of using this network is the short time needed to generate the sCT, which would be beneficial for MR-guided RT application. Future investigations will evaluate dose to clinically relevant volumes as well as the use of a 3D network. OC-0295 The feasibility of volumetric 4DMRI in upper abdominal radiation therapy treatment planning A. Oar 1 , R. Rai 1 , M. Jameson 1 , S. Deshpande 1 , G. Liney 1 , E. Juresic 1 , J. Veneran 1 , G. Dinsdale 1 , D. Elwadia 1 , S. Kumar 1 , M. Lee 1 1 Liverpool Hospital, Department Radiation Oncology, Liverpool, Australia Purpose or Objective 4DCT is widely used in radiation therapy (RT). 4DCT uses additional radiation exposure and has limitations in soft tissue delineation. Although 2DMRI ( MRIcine ) has been utilised in tumour tracking, there is very little published data utilising 3D volumetric acquired 4DMRI to detect tumour motion. 4DMRI provides motion information with improved volumetric tumour definition and without additional radiation exposure. Here we explore the movement of tumour and surrogates of tumour position in five patients undergoing upper abdominal RT on 4DCT and volumetric 4DMRI. Also, we explore the feasibility of abdominal compression (AC) in three healthy volunteers undergoing 4DMRI. AC reduces respiratory amplitude and liver movement. AC in combination with volumetric 4DMRI may benefit patients having liver SBRT. Material and Methods Patients underwent standard RT simulation including 3D and 4D CT and MRI simulation in the treatment position. The 4DMRI sequence is a prototype T1 weighted 3D gradient echo (VIBE) with radial self-gating (Siemens, Erlangen, Germany). For each patient, tumour or a surrogate of tumour position was selected and the range of motion on 4DCT and 4DMRI was compared. Volumes were contoured (MIM Software Inc, Cleveland, USA) on maximal inspiratory and expiratory phases for both 4DCT and 4DMRI. The total distance between centroids was calculated using Euclidian distances. Ability to delineate tumour and image quality were graded as per following: tumour-edge or image very clear (1), tumour-edge or image slightly blurred (2), considerable blurring of tumour-edge or image (3) and unable to delineate tumour or image not useable (4). Furthermore, three healthy volunteers were scanned using 4DMRI, with and without AC to confirm the feasibility of the combination of AC

Conclusion Further evaluation of motion, artefact and image quality is under way in a larger cohort of patients. Superior soft tissue delineation and reduced radiation exposure may mean 4DMRI is a suitable replacement for 4DCT. AC combined with 4DMRI is a feasible technique and may benefit patients having liver SBRT. OC-0296 High-field MR-linac treatment plans for hypoxia dose escalation in head and neck cancer D. Mönnich 1 , M. Nachbar 1 , E. Neuhaus 1 , C. Gani 2 , S. Boeke 1,2 , S. Welz 2 , D. Zips 2,3 , D. Thorwarth 1,3 1 University Hospital Tübingen, Section for Biomedical Physics- Department of Radiation Oncology, Tübingen, Germany 2 University Hospital Tübingen, Department of Radiation Oncology, Tübingen, Germany 3 German Cancer Research Center DKFZ, German Cancer Consortium DKTK partner site Tübingen, Heidelberg, Germany