ESTRO 36 Abstract Book

S943 ESTRO 36 _______________________________________________________________________________________________

Ireland 2 Beaumont Hospital, Neurosurgery, Dublin, Ireland

GTV delineations on motion compensated images of four patients were then compared to those performed according to the SCOPE protocol, in which the GTV is delineated on the inhale, mid-ventilation and exhale phases before being combined. Delineated volumes were evaluated as a surrogate for inter-observer uncertainty, as higher certainty leads to smaller volumes. In addition, the volume delineated on the motion compensated image is compared with the average volume of the SCOPE structures. Results In all cases the volume of the GTV delineated on the motion compensated image was smaller than the average SCOPE volume (figure 1). For two of the four patients, the reduction in volume is significant, however for PT1, the volume delineated on the motion compensated image was slightly greater than the mean volume delineated in the three phases. For the final patient (PT4), the difference is marginal mainly because an extra tumour extension was observed on the higher quality motion compensated image (figure 2), indicating a potential clinical benefit.

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 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,

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