ESTRO 36 Abstract Book

S930 ESTRO 36 2017 _______________________________________________________________________________________________

the radiotherapy treatment planning ( localised) and diagnostic (non-localised) DSA’s to the MR, the feeding arteries and the draining veins were delineated on the localised and non-localised imaging sets. An analysis of the accuracy of the registrations was calculated using the Hausdorff distance metric.

Results The phantom vessels were divided into two sets, the upper loop (UL) and the lower loop (LL) for analysis. The UL consisted of a single vessel traversing the X,Y & Z planes while the LL traversed the X & Z planes only. Using the Hausdorff distance metric a result of 0.41 mm and 0.85 mm displacement for the UL and LL respectively was calculated. A similar result was found for two clinical cases analysed, a Hausdorff distance of <0.8 mm for the feed artery and drain vein.

Conclusion The use of motion compensation in the delineation of oesophageal cancers reduced delineated volumes in 2 out of 4 patients and would be of benefit to spare surrounding organs at risk. EP-1719 Diagnostic DSA's, a resource for radiotherapy treatment planning of AVM's P. Davenport 1 , M. Javadpour 2 1 St Luke's Radiation Oncology Center, Physics, Dublin, Ireland 2 Beaumont Hospital, Neurosurgery, Dublin, Ireland Purpose or Objective To validate the use of diagnostic digital subtraction angiograms (DSA) for the radiotherapy treatment planning of arterial venous malformations (AVM) using a specialised registration software package. Material and Methods A CT, MRI & DSA compatible phantom was constructed which was used to assist with the calculation of geometric accuracy of the DSA-MRI registration software, SmartBrush Angio supplied by Brainlab. This phantom was imaged using the standard AVM patient care-path for CT, MRI and DSA. The CT and DSA imaging in this case was imaged with a stereotactic localisation frame in place which allowed the scaling of the DSA’s to the CT images. An additional set of DSA’s were acquired without the localisation frame. In each case the phantom vessels were contoured on DSA, MR and CT, the latter being the reference image set. Clinical validation of the registration software was completed for two patients. After the registration of both

Conclusion Based on the results of both the phantom study and the clinical data, the use of non-localised diagnostic DSA’s could be used to assist with the radiotherapy treatment planning of AVM’s. This negates the need to perform an invasive localised DSA in the majority of cases thereby reducing risks associated with this procedure. EP-1720 Framework for Statistical Cone-Beam CT Reconstruction with Prior Monte-Carlo Scatter Estimation J. Mason 1 , M. Davies 1 , W. Nailon 2 1 University of Edinburgh, Institute for Digital Communications, Edinburgh, United Kingdom 2 Oncology Physics Department, Edinburgh Cancer Centre, Edinburgh, United Kingdom Purpose or Objective Scatter from the patient and detector leads to significant inaccuracies and artefacts in cone-beam computed (CBCT). Monte-Carlo (MC) methods may allow the scatter signal to be accurately estimated based on a prior scan, but this must be matched and calculated for the new cone- beam measurements, and incorporated appropriately into a reconstruction method. We investigate a framework for statistical reconstruction with these prior MC estimates, under various work-flows. Material and Methods