Underwood, Louise, Forshaw, M, Rankin, N, Turtle, Louise, Ioannou, T, Willett, A, Wong, H and Kirby, Mike 
ORCID: 0000-0001-9765-5641
(2026)
A service evaluation of three degrees of freedom (3DoF) versus six degrees of freedom (6DoF) for liver SABR patients, are 3DoF corrections sufficient in producing clinically acceptable matches in this patient group?
[Poster]
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Description
Background Liver stereotactic ablative radiotherapy (SABR) relies on image-guided radiotherapy (IGRT) to ensure treatment precision. Local protocol presently mandates six degrees of freedom (6DoF) corrections for liver SABR treatment. As a result, liver SABR cannot be treated on local novel technologies such as HalcyonTM with HyperSight (Varian, Palo Alto, CA), due to the 3DoF limitation, despite the potential clinical advantages of increased efficiency and improved image quality. Evaluating the necessity of 6DoF corrections for liver SABR could support a local change in protocol. Aims The aims of the service evaluation were to assess whether 3DoF only corrections produce clinically acceptable matches for liver SABR patients and whether there were differences in the magnitude of translational shifts between 3DoF and 6DoF matches. Inter-observer variability between a standard level radiographer and an advanced SABR radiographer was also studied. Methods The study included liver SABR patients treated for oligometastatic disease or hepatocellular carcinoma (HCC) over a five-year period (2019-2024). Doses varied from 30Gy-50Gy with all treatment being delivered over 5 fractions. 125 cone beam CT (CBCT) scans were retrospectively re-matched using an automatic 3DoF match with ROI around liver contour and reviewed by a single Hepatobiliary SABR consultant for clinical acceptability. Paired t-tests were used to compare the translational shifts between 3DoF and 6DoF corrections. Results Key findings include: 109 out of 125 CBCTs (87.2%) were deemed clinically acceptable with a 3DoF only match. Inter-observer variability was most prominent in the lateral axis. A statistically significant difference in translational shifts was observed in the longitudinal axis (t(124)=4.78, p<0.01) when comparing 3DoF and 6DoF matches. Discussion The majority of CBCTs were considered clinically acceptable with an automatic 3DoF match, suggesting the potential for liver SABR to be delivered without the need for 6DoF corrections. Acceptance rates may have been higher had manual adjustments been made to the automatic match. A significant difference was observed only in the longitudinal axis, suggesting that for liver SABR, 6DoF corrections do not have a significant impact on translational corrections in vertical and lateral axes. Inter-observer variability between therapeutic radiographers with differing experience highlights the requirement of robust training programmes for specialist treatment techniques. Conclusion This service evaluation has highlighted the potential for a change in protocol for SABR liver patients to 3DoF only treatment machines. Further investigation is required to determine the dosimetric effect of 3DoF only corrections instead of 6DoF corrections.
| Item Type: | Poster |
|---|---|
| Divisions: | Faculty of Health & Life Sciences Faculty of Health & Life Sciences > Inst. Population Health Faculty of Health & Life Sciences > Inst. Population Health > School of AHPs and Nursing |
| Depositing User: | Symplectic Admin |
| Date Deposited: | 16 Feb 2026 14:32 |
| Last Modified: | 16 Feb 2026 14:32 |
| DOI: | 10.13140/RG.2.2.19554.18887 |
| URI: | https://livrepository.liverpool.ac.uk/id/eprint/3197044 |
| Disclaimer: | The University of Liverpool is not responsible for content contained on other websites from links within repository metadata. Please contact us if you notice anything that appears incorrect or inappropriate. |
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