ESTRO 2024 - Abstract Book

S5564

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

ESTRO 2024

1967

Proffered Paper

Renal SABR: can the organ at risk position be assessed on the treatment CBCT?

Lisa Elliott 1 , Nick West 1 , Rachel A Pearson 1,2 , Ahmed Hashmi 1 , Karen Pilling 1 , Rachel Brooks-Pearson 1

1 Newcastle upon Tyne NHS Foundation Trust, Northern Centre for Cancer Care, Newcastle upon Tyne, United Kingdom. 2 Newcastle University, Translational and Clinical Research Institute, Newcastle upon Tyne, United Kingdom

Purpose/Objective:

Stereotactic ablative body radiotherapy (SABR) is high dose, hypo-fractionated radiotherapy delivered to small extra cranial lesions 1 . This highly conformal technique has recently been reported as beneficial in treating both primary and oligometastatic renal cell carcinoma 2,3,4,5 . One of the main challenges in planning and delivering renal SABR is the proximity of organs at risk (OARs) such as the small bowel and duodenum to the target. Strict dose planning limits to OARs, can mean that the dose to the target is compromised 6 . This reduction in dose to the target may have a detrimental clinical impact in renal cell carcinoma as the high ablative doses used in SABR are considered essential in overcoming the inherent radio-resistance of these cells 2 . Although cone beam computed tomography (CBCT) is the current gold standard image modality for image guided radiotherapy (IGRT) to assess target and OAR position, it does have limitations. The movement of the target due to respiration or internal organ motion can create artefacts which reduce image quality 7 . This makes visualisation of the soft tissue, and the small bowel more challenging, particularly as gas in the bowel creates streak artefacts which can obscure the images 8,9 . Bowel motion is well reported, however, limited published evidence on small bowel and duodenal position in renal SABR exists. Literature on the extent of OAR motion could assist the planning process and in clinical decision making during online image analysis. Therefore, methods of quantifying the extent of this motion are required to ensure that renal SABR is delivered safely. Therefore, before any CBCTs can be used to assess small bowel and duodenal motion, it is necessary to establish whether CBCTs are adequate in their quality to allow for further analysis to occur. The aim of this study is to investigate if CBCTs can be used to accurately visualise duodenum and small bowel in renal SABR.

Material/Methods:

Thirty-three CBCTs from 14 patients were retrospectively reviewed. Fractionations used were 26Gy/1#, 30Gy/3# and 42Gy/3#. Pre-treatment and intrafraction CBCTs were analysed in Raystation treatment planning system. The duodenum and small bowel were outlined on the CBCT to assess the visibility of these structures. A single observer rated the image quality scoring on a Likert scale the ability to contour each structure on each CBCT. Data was also recorded pertaining to the volume of gas present in each CBCT and lateral patient separation.

Results: