ESTRO 2024 - Abstract Book

S3196

Physics - Detectors, dose measurement and phantoms

ESTRO 2024

371

Poster Discussion

Integrating Cine EPID and Off-Axis Winston-Lutz Test for Multiple Brain Metastases RTS

Paul RETIF 1,2 , Abdourahamane DJIBO SIDIKOU 1 , Alexandre WALTENER 1 , Romain LETELLIER 1 , Anwar ALSALAH 1 , Estelle PFLETSCHINGER 1 , Fabian TAESCH 1 , Emilie VERRECCHIA-RAMOS 1 , Xavier MICHEL 3 1 CHR Metz-Thionville, Medical Physics Unit, Metz, France. 2 Université de Lorraine, CRAN, Nancy, France. 3 CHR Metz Thionville, Radiation Therapy Department, Metz, France

Purpose/Objective:

Stereotactic radiotherapy (SRT) has transformed cancer treatment, especially for brain metastases. Ensuring accurate SRT delivery is crucial, with the Winston-Lutz test being an important quality control tool. Off-axis Winston-Lutz (OAWL) tests are designed for accuracy assessment, but most are limited to fixed angles and hampered by local-field shifts caused by suboptimal Multi-Leaf Collimator (MLC) positioning. This study introduces a new OAWL approach for quality control in multi-brain-metastases SRT. Utilizing cine Electronic Portal Imaging Device (EPID) images, it can be used with dynamic conformal arc (DCA) therapy. However, dynamic OAWL (DOAWL) is prone to more local-field shifts due to dynamic MLC movements. A two-step DOAWL is proposed: step 1 calculates local-field shifts using dynamic MLC movements in the beam-eye view data from the Treatment Planning System (TPS), and step 2 processes cine EPID images with an OAWL algorithm to isolate true deviations.

Material/Methods:

The proposed methodology was validated with an anthropomorphic head phantom containing three metallic ball bearings, a set of six coplanar and non-coplanar DCA beams that were delivered by a Varian TrueBeam STx accelerator, cine EPID, and the OAWL analysis algorithm implemented in ImageJ.

Results:

The mean inherent local-field shift vectors, which ran from the center of the target to the center of its local field, ranged from 0.11 to 0.49 mm for the six beams. The maximums ranged from 0.22 to 1.11 mm. After inherent-shift correction, the mean and maximum EPID-measured displacement of the six beams were 0.34 and 1.03 mm, respectively and only 6.6% and 0.2% of all points exceeded the 0.75-and 1.0-mm thresholds, respectively.

Conclusion: