ESTRO 2024 - Abstract Book

S3977

Physics - Inter-fraction motion management and offline adaptive radiotherapy

ESTRO 2024

Mikkel Skaarup, Bettina Roche, Vibeke N Hansen, Nikolaj K G Jensen

Rigshospitalet, Department of Oncology, Centre for Cancer and Organ Diseases, Copenhagen, Denmark

Purpose/Objective:

To investigate the accuracy and reproducibility of a surface guided system for pre-positioning of patients across multiple treatment sites in radiotherapy. This is part of a larger study of surface guided radiotherapy (SGRT) to transition to tattooless treatments to reduce the associated, long-term, mental burden for patients as well as reduce the physical workload for the treatment staff.

Material/Methods:

In our clinic, we have 6 linear accelerators (Truebeam, Varian Medical systems, Palo Alto, USA) with ExacTrac Dynamic systems installed (Brainlab, Munich, Germany). ExacTrac Dynamic consists of three positional systems, a structured light emitter plus two optical cameras, a thermal camera, and a pair of x-ray tubes with flat panel detectors. For pre positioning, the optical light cameras create a 3D surface of the patient’s current position. This surface is matched against the body outline from the planning CT and translational and rotational shifts are calculated. Translational shifts are sent to the couch for automatic correction while rotational deviations must be corrected manually. Before treatment, imaging was performed, either paired 2D kV-kV images via the on-board imager (OBI) or a cone-beam CT (CBCT), to verify target position and make final adjustments based on internal anatomy. We used surface guided pre-positioning for all patients treated isocentrically with MV x-rays on these machines, except patients that were gated. We split patients into the following treatment sites: pelvic, thoracic (incl. breast), head & neck, bone, and other soft tissue. To investigate the accuracy of the SGRT pre-positioning, we collected the online match parameters in 6D for each of these fractions, i.e., the residual shift required based on x-ray imaging to match the target within local clinical tolerances. We also recorded the number of imaging procedures for each fraction, to investigate if SGRT had an impact on the number of patients that could not be aligned within tolerances based on initial pre-positioning. For comparison, we gathered equivalent historical control data from the year prior to this study where patients were pre-positioned with tattooed dots aligned with lasers in the treatment room. Again, we collected residual online match parameters and the number of imaging procedures used.

Results:

We collected data from a total of 5844 fractions pre-positioned with SGRT (460 patients) and 7167 fractions pre positioned with laser/tattoo (468 patients). The two groups had a similar distribution of age, sex, and treatment indication, except for a surplus of head & neck and prostate cancer patients in the control group. Specifically, the number of fractions for each treatment site was, 719 SGRT- and 1224 laser/tattoo-fractions for pelvic sites, 2307 SGRT- and 2246 laser/tattoo-fractions for thoracic sites, 1663 SGRT- and 2590 laser/tattoo-fractions for head & neck sites, 419 SGRT- and 392 laser/tattoo-fractions for bone, and 736 SGRT- and 715 laser/tattoo-fractions for other soft tissue targets.