ESTRO 36 Abstract Book

S943

ESTRO 36

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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.

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

, M. Javadpour

St Luke's Radiation Oncology Center, Physics, Dublin,

Ireland

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

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

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