ESTRO 2024 - Abstract Book

S5462

RTT - Patient care, preparation, immobilisation and IGRT verification protocols

ESTRO 2024

the positional reproducibility of the Philips Ingenia Ambition 1.5T MR system using an MR-RT simulation protocol for head and neck patients employing a 5-point thermoplastic shell.

Material/Methods:

In a prospective study, 18 patients underwent MR-SIM procedures using 5-point thermoplastic shells and a phantom bottle for better fiducial visibility. The MR-RT Couchtop with Flex-D&L coils, including an anterior coil and a fixed posterior coil, was employed. An External Laser Position System (ELPS) collected positional reproducibility data during MR-RT sequences. Patient shells were realigned based on ELPS data using the Isotropic T2-3D Sequence. Variations in positional reproducibility were observed at the isocenter level in the transversal plane (L-R & A-P), coronal plane (L R & H-F), and sagittal plane (A-P & H-F).

Results:

The study found notable variations in positional reproducibility across different planes. In the transversal plane, standard deviations (SD) were 0.57 mm (L-R) and 0.45 mm (A-P). In the coronal plane, SDs were 0.57 mm (L-R) and 0.34 mm (H-F). In the sagittal plane, SDs were 0.45 mm (A-P) and 0.34 mm (H-F). The observed ranges of deviation in the transversal plane (L-R & A-P), coronal plane (L-R & H-F), and sagittal planes were (-1 mm to 1.3 mm & -0.6 mm to 0.6 mm), (-1.1 mm to 1.3 mm & -0.4 mm to 0.4 mm), and (-0.6 mm to 0.7 mm & -0.4 mm to 0.5 mm).

Conclusion:

This study demonstrates that it is feasible to achieve a high level of positional consistency on an MR-simulation system for intended offline MR-guided radiotherapy (MRgRT), with systematic errors measuring less than 1 millimeter in translation.

Keywords:

Position Reproducibility, MR-RT, MR-Guided Radiotherapy (MRgRT) External Laser Position System (ELPS), T2-3D Sequence, Geometric Efficiency.

Keywords: MRgRT , Position Reproducibility ,MR only SIM