ESTRO 2023 - Abstract Book

S2041

Digital Posters

ESTRO 2023

Conclusion Assessment of bladder filling using a bladder scan acquired before planning CT simulation or radiotherapy treatments showed a high rate of reproducibility. Routine implementation of this technology in the clinical practice is expected to improve the reproducibility of daily treatments, reduce daily imaging burden, and improve patient’s compliance.

PO-2270 Accuracy of a skull based automatic 6D match with kV-kV imaging on a Truebeam

S. Hoek 1

1 Amsterdam UMC, Radiotherapy, Amsterdam, The Netherlands

Purpose or Objective Set-up of brain indications at our department consisted of orthogonal kV-kV imaging with a 4D manual bone match based on the skull. On the Truebeam (Varian Medical systems), it is technically possible to use an automatic 6D bone match with kV-kV set-up though this was not tested yet. For a 6D set-up, CBCT could also be considered. This would expose patients to a higher imaging radiation dose and cost more time compared to kV-kV imaging. The necessity to see soft tissue with brain indications is mostly negligible: CBCT image quality rarely suffices to differentiate the PTV from other brain tissue. If the accuracy of an automatic 6D kV-kV match is comparable to a CBCT match on the skull, it would improve a manual 4D match. Matches would be faster and more accurate without using more radiation for imaging. Materials and Methods For this study 19 brain and sinus patients with 411 fractions in a 5-points thermoplastic mask(MacroMedics) were included as well as 102 intracranial stereotactic patients with 304 fractions in a frameless mask(Brainlab). An automatic 6D kV-kV match was applied followed by a 6D CBCT automatch. The data from 6D match on CBCT was analyzed to verify any accuracy differences of the 6D kV-kV match. All matches were based on skull structures only. Literature suggests that 6D couch usage can result in residual errors. A significant correlation between performed roll and lateral residual errors and to a lesser extent a performed pitch and longitudinal residual errors is proven. This can be minimized through fixation (Guckenberger et al. 2007). Since frameless masks are more rigid, these were examined separately from the 5-points masks in order to filter out any stability differences. Results Fig. 1 shows lateral residual errors >1.5 mm with 5-points masks are only seen when roll >1° is applied, this correlation is significant(r = -0.74). With frameless masks these residual errors are not that prominent nor significant(r = -0.21). The aim of this study is to compare the accuracy of a 6D kV-kV vs 6D CBCT automatch on the bony structures of the skull.