ESTRO 2022 - Abstract Book

S1268

Abstract book

ESTRO 2022

Conclusion According to our results, the dose deformable CBCT registration could report that smaller bladder volume than planned is allowed until 3 times with permissible dose tolerance in bladder and rectum also a correct CTV’s coverage. Futures applications of our results will be the creation of a specific offline protocol.

PO-1492 Characterising anatomical changes of head and neck cancer patients during radiotherapy treatment

P. Nikou 1 , A. Nisbet 1 , A. Thompson 2 , S. Gulliford 3 , J. McClelland 1

1 University College London, Department of Medical Physics, London, United Kingdom; 2 University College London Hospital, Department of Radiotherapy , London, United Kingdom; 3 University College London Hospital, University College London, Department of Radiotherapy Physics, Department of Medical Physics, London, United Kingdom Purpose or Objective Inter-fractional anatomical changes can lead to uncertainties in the delivered dose distribution. To address this, there is an interest in modelling the anatomical changes which occur over the course of treatment. To inform the choice and complexity of the model, this project aimed to identify and quantify the inter-fractional anatomical changes of head and neck (H&N) cancer patients. Materials and Methods A cohort of 20 H&N cancer patients treated with IMRT were studied. Each patient had a planning CT (pCT), a rescan CT (rCT) and a series of CBCTs (4-10). A diffeomorphic deformable image registration aligned each CBCT to the pCT. The transformation was used to warp the pCT structures to each CBCT. To test the accuracy of the DIR, two independent geometric validation tests were performed. The warped contours were compared to (1) the rCT contours, (2) contours which were manually delineated on CBCTs. A longitudinal volumetric analysis was performed on each structure. A leave one out cross validation analysis determined the best function to parameterise the changes.

Results