ESTRO 2024 - Abstract Book

S4085

Physics - Inter-fraction motion management and offline adaptive radiotherapy

ESTRO 2024

2264

Digital Poster

Validation of a dedicated surface- and image-guidance system for breast deep inspiration breath hold

Thierry Gevaert, Cristina Teixeira, Racell Nabha, Marlies Boussaer, Adrian Gutierrez, Thomas Mulliez, Sven Van Laere, Mark De Ridder

UZ Brussel, Vrije Universiteit Brussel, Radiotherapy, Brussels, Belgium

Purpose/Objective:

Left-sided breast cancer patients often receive deep inspiration breath-hold (DIBH) radiotherapy (RT) to reduce the relative risk of heart disease mortality. The purpose of this study is to validate the ExacTrac DIBH (Brainlab, Munchen, Germany) workflow, a surface-guided RT (SGRT) system combined with real-time stereoscopic x-rays image-guided RT (IGRT), against our reference, Respiratory Gating for Scanners (RGSC) (Varian, CA, USA) in combination with a gated CBCT, and to analyze intra-breath-hold stability and reproducibility in clinical practice.

Material/Methods:

20 left-sided breast cancer patients treated with 40 Gy with a simultaneous integrated boost of 48 Gy in 15 fractions were included. Both a free-breathing (FB) and DIBH CT simulation were acquired, and appropriate skin was delineated to quantify the rise of the surface due to DIBH. Automated gating control (beam on/off) was performed using an audio-visual patient feedback system. Once the patient is within the DIBH gate, stereoscopic x-rays are taken for positioning. This workflow was compared to our standard: RGSC in combination with a gated CBCT. Patients were positioned and gated for 7 consecutive fractions with our standard CBCT workflow and residual setup errors with stereoscopic x-rays were measured. For another 7 consecutive fractions, the new ExacTrac Dynamic workflow (i.e. stereoscopic x-rays) was used and residual setup was analyzed with gated CBCT. Firstly; intra-breath-hold stability and reproducibility across all fractions of the entire treatment course were analyzed per patient. Secondly, a direct comparison between stereoscopic x-rays and gated CBCT was made in terms vertical directions, longitudinal directions, lateral directions, yaw, pitch, and roll. This analysis was performed in a paired design where the median values were used (to not bias estimates through outlying measures) for respectively the first seven fractions (RGSC workflow) and the last 7 fractions (ExacTrac workflow) within one patient. The statistical analysis performed was performed via Wilcoxon Signed-Rank tests. The statistical significance level was set at α = 0.05.

Results:

The mean and standard deviation of the absolute value of the residual setup errors after gated CBCT, verified with stereoscopic x-rays were 0.26 (0.23) mm, 0.26 (0.21) mm, and 0.31 (0.25) mm for vertical, longitudinal, and lateral directions, respectively, and 0.74 (0.58)°, 0.93 (0.92)° and 1.23 (1.03)°, respectively, for yaw, pitch, and roll. The mean absolute residual setup errors of stereoscopic x-rays was analyzed based on gated CBCT, 0.19 (0.22) mm, 0.23 (0.23) mm, and 0.25 (0.23) mm for vertical, longitudinal, and lateral directions, respectively, and 0.59 (0.59)°, 0.93 (0.91)° and 1.00 (0.93)°, respectively, for yaw, pitch, and roll. Average intra-breath-hold stability was 1.1 (0.7) mm and 2.3 (1.3) mm for ExacTrac and RGSC, respectively.