ESTRO 2024 - Abstract Book

S3994

Physics - Inter-fraction motion management and offline adaptive radiotherapy

ESTRO 2024

817

Digital Poster

Surface-guided setup and intrafraction motion in free-breathing breast cancer radiation therapy

Trine O Kirkegaard 1 , Ingelise Jensen 1 , Thomas O Kristensen 1 , Marie Louise H Milo 2 , Martin S Nielsen 1,3

1 Aalborg University Hospital, Department of Medical Physics, Aalborg, Denmark. 2 Aalborg University Hospital, Department of Oncology, Aalborg, Denmark. 3 Aalborg University, Department of Clinical Medicine, Aalborg, Denmark

Purpose/Objective:

Surface guided radiation therapy (SGRT) presents the possibility to set up patients based on a 3D surface compared to the conventional setup method using skin markers. The primary aim of this study was to investigate the feasibility of SGRT for setup of breast cancer patients treated in free breathing compared to setup using skin markers. A secondary aim was to investigate intrafraction motion, with respiratory motion excluded, using surface-tracking data.

Material/Methods:

Twenty-one breast cancer patients receiving radiation therapy in free-breathing (3D conformal planning technique) were included in the study; 15 whole-breast (3 with sequential boost) and 6 partial-breast. The patients were prepositioned using either skin markers (135 frac) or SGRT (201 frac) from ExacTrac Dynamic (ETD) v1.1 (Brainlab, München, Germany). The skin markers indicated the plan isocenter and was setup in the room lasers. For SGRT, reflections of an optical structured light identified the patient surface and compared it to the corresponding external structure from the CT-scan (figure 1). All patients were set up using both setup-methods for different fractions in randomized order. After initial patient setup with either method our standard IGRT (orthogonal MV-kV for whole breast and kV-kV for partial-breast and boost plans) was applied, and the subsequent 3D couch shift was used for evaluating the patient prepositioning. Data was analyzed using unpaired t-test and F-test with 5% significance level. Intrafraction motion, excluding respiration, was evaluated using the log-files from ETD, where surface data was logged per monitor unit (MU) delivered. Data from 194 fractions was analyzed. For each main field (MU > 50) a mean surface displacement from baseline was found, and the difference between the two main fields for each fraction represented the intrafraction movement. The average time between delivery of the main fields was recorded. Intrafraction movement was reported as systematic and random variations as well as the mean population error (t-test).