ESTRO 2024 - Abstract Book

S5613

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

ESTRO 2024

not explicitly examined, however rotational error was measured separately and found 99.5% of rotations fell within 1°. Although this study is novel and useful in identifying the magnitude of residual errors at each couch position because couch corrections were applied at each couch angle, a new ‘baseline position’ is set at each couch angle, intra-fractional setup error cannot be directly determined.

Conclusion:

There is scant evidence for patient setup error for HyperArc. Whilst it is acknowledged that the additional imaging increases fraction delivery time, which contributes to the positional errors detected, this is the first data we are aware that examines patient position at each arc. The data collected in this study is novel and indicates that whilst the mean set up error may be minor compared with the PTV margin (and consistent with published literature), there is value in examining institutional patient residual error. Patient setup error during HyperArc is small, but significant, for a small number of patients, when considering the small margins employed. This data evidences minimal movement throughout most treatments, therefore, an evidence-based method to change imaging protocol should be considered. However, the complete removal of kV imaging is not currently viable as further work needs to be done to discern the cause patient setup error, notably at arc 3, as well as continue to reduce intra-fraction motion seen during treatments.

Whilst the institution's aim is to move to employ the default Varian image verification protocol for the HyperArc solution, it is crucial that this is done in an evidence-based manner.

We recommend testing your own set up error (as per On Target 2, 2019) as the positional certainty is heavily reliant on the immobilisation, which introduces interobserver variability in the mask manufacturing process.

Keywords: Hyperarc, positional, uncertainty

2843

Digital Poster

Factors affecting bony anatomy setup errors for lung Stereotactic Ablative Body Radiotherapy (SABR)

Emily Quinn 1 , Erica Bennett 2 , Laura Barry 2 , Dr.Andrew England 1 , Annemarie Devine 1 , Prof. Mark McEntee 1 , Theresa O'Donovan 1 , Dr. Paul Kelly 2 1 University College Cork, Medical Imaging and Radiation Therapy, School of Medicine, Cork, Ireland. 2 Bons Secours Radiotherapy, in Partnership with UPMC Hillman Cancer Centre, Cork, Ireland

Purpose/Objective: