Taylor, Luke and Kirby, Mike 
ORCID: 0000-0001-9765-5641
(2025)
Quantifying and evaluating intrafractional motion and on-line repositioning for liver and adrenal SABR: a service evaluation
[Poster]
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Description
INTRODUCTION On-treatment image verification is essential for target localisation for abdominal stereotactic ablative body radiotherapy (SABR) with steep dose gradients. Linac-based image guided radiotherapy (IGRT) strategies involve 3D and 4D kV volumetric cone beam computed tomography (CBCT) imaging, with imaging just before treatment delivery and then repeated mid-treatment for evaluating any need for patient repositioning. Due to the lack of national guidelines, workflows vary across UK radiotherapy departments, with some omitting mid-treatment image verification entirely. The aim of this radiographer-led service evaluation was to quantify and assess patient positioning mid-treatment, to evaluate the current workflows and assess the potential to streamline the current process whilst maintaining treatment accuracy. METHODS Thirty patients, treated in a full-body vac bag with arms above their heads, undergoing liver or adrenal SABR were evaluated. Intra-fractional set-up error data was obtained retrospectively in 6 degrees of freedom (DoF). The absolute values of 139 CBCT images, acquired midway through treatment, were used to attain the absolute values in each DoF to represent the magnitude and direction of intra-fractional motion. The rate of intra-fractional motion was also considered using the maximum angle and 3D translation vector over the recorded treatment time. RESULTS Key findings: (1) The translational (+/-0.2cm) action level was achieved in 88%, 79% and 94% of measurements for vertical, longitudinal and lateral directions respectively—only one instance breached +/-0.5cm action level. (2) The rotational (+/-1o) action level was achieved in 89%, 82% and 86% of measurements for pitch, roll and yaw respectively. (3) Across all fractions, the mean overall treatment time was 15.7 (±4.7) minutes; range 9.5-41.4 minutes. The longest times involved exhale breath hold (EBH), with a mean of 21.0 (±6.7) minutes. (4) From statistical analysis, the Pearson (r, p-value) correlation coefficient for the 3D translational vector and rotation maximum angle, in relation to time, was (r = 0.166, p <0.051) and (r = 0.276, p < 0.001) respectively, revealing a weak positive correlation between movement and time. CONCLUSION This service evaluation quantified intra-fractional motion in 6 DoF for patients who underwent liver and adrenal SABR. Our chosen immobilisation seems effective for limiting intra-fractional motion. However, some inconsistencies in motion are still present. Although further dosimetric analysis would be helpful, the overall results here, and the relationship between the rate of intra-fractional motion and couch corrections, are promising in considering a move towards a more streamlined IGRT workflow; where no mid-treatment imaging is undertaken.
| Item Type: | Poster |
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| Divisions: | Faculty of Health & Life Sciences Faculty of Health & Life Sciences > Inst. Population Health |
| Depositing User: | Symplectic Admin |
| Date Deposited: | 17 Mar 2025 16:32 |
| Last Modified: | 17 Mar 2025 16:32 |
| DOI: | 10.13140/RG.2.2.23364.13446 |
| URI: | https://livrepository.liverpool.ac.uk/id/eprint/3190852 |
| 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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