ESTRO 2024 - Abstract Book

S5567

RTT - Patient care, preparation, immobilisation and IGRT verification protocols

ESTRO 2024

8. Gaudreault, M., Siva, S., Kron, T. and Hardcastle, N. (2022) 'Assessing organ at risk position variation and its impact on delivered dose in kidney SABR', Radiation Oncology, 17(1) p.112. Available at: https://doi.org/10.1186/s13014-022 02041-2 9. Slevin, F., Beasley, M., Needham, A., Lilley, J., Speight, R., Murray, L.J. and Henry, A.M. (2019) 'Image quality of cone beam CT used as image-guidance for pelvic Stereotactic Ablative Radiotherapy', Radiotherapy and Oncology, 133, Supplement 1, pp. S303-S303. Available at: https://eprints.whiterose.ac.uk/147776/3/1-s2.0-S0167814019309983 main.pdf (Accessed 4 December 2022)

1985

Digital Poster

Visibility of pelvic lymph nodes: CBCT versus iCBCT, a quantitative study

Tom Harthoorn 1 , Inge Jacobs 1 , Patricia Brouwers 1 , Barbara Wachters 1 , Isabelle De Marco 1 , Frank Van den Heuvel 1,2

1 Zuidwest Radiotherapeutisch Instituut, Oncology, Vlissingen, Netherlands. 2 University of Oxford, Oncology, Oxford, United Kingdom

Purpose/Objective:

In radiotherapy there is a shift towards ultra hypofractionation (UHF). When using UFH, high doses and tight margins are used, due to the very low number of fractions, it is even more important that dose is delivered to the right place. Therefore, a number of preconditions must be met before UHF can be implemented. One important precondition for implementation of UHF is target visibility. It is known that the contrast resolution in the pelvic region on a standard CBCT, is of inferior quality. Therefore, Varian Medical Systems has introduced the iterative CBCT. In theory this type of CBCT had a better contrast resolution, but a slight increase in noise.

This study investigates the added value of the iCBCT, in terms of reproducibility of delineation of the lymph nodes in the pelvic area, compered to the standard CBCT.

Material/Methods:

In total six lymph nodes are delineated in 72 (i)CBCT’s (36 CBCT’s/36 iCBCT’s). In total there are 252 unique contours. Five patients with oligometastatic lymph nodes are retrospectively selected. All five patients had six or more clinical CBCT’s. All CBCT’s are reconstructed with the iterative algorithm (iCBCT) on the linear accelerators. Two radiation oncologist and one RTT with focus on urological patients, had delineate the oligometastatic lymph nodes on the standard CBCT’s and the iCBCT’s. The delineations on the standard CBCT’s and de iCBCT’s are compared with each other. An in-house written script has calculated the dice-score and the Hausdorff block-distance between the scans. First, the dice-score and the Hausdorff distance of each patient per operator, per type of CBCT, are calculated. Subsequently, the dice-score and Hausdorff distance of the different operators are compered. The average, standard deviation, range and interquartile range (IQR) of both scores are calculated. Significance was tested with the Wilcoxon Signed Rank Test.