ESTRO 2024 - Abstract Book

S5442

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

ESTRO 2024

21

Digital Poster

Development of MR-compatible immobilization device and initial experience of MRgRT for CNS tumors

Joongyo Lee 1 , Na Young Shin 1 , Seo Jin Lee 2 , Yoon Jin Cho 1 , In Ho Jung 1 , Ji won Sung 1 , Sei Joon Kim 1 , Jun Won Kim 1

1 Gangnam Severance Hospital, Radiation Oncology, Seoul, Korea, Republic of. 2 Yonsei Cancer Center, Radiation Oncology, Seoul, Korea, Republic of

Purpose/Objective:

There are currently no MR-guided RT (MRgRT) devices for brain tumors, and few treatment cases have been reported. In this study, we investigate the positional reproducibility using our own fixation device (Unity Brain tumor Immobilization Device, UBID) in brain tumor patients receiving MRgRT with 1.5T MR-LINAC (linear accelerator) to evaluate its feasibility in clinical practice and report the representative cases of central nervous system (CNS) tumor patient.

Material/Methods:

Quantitative analysis was performed by comparing images of placing only the MR phantom on the couch and images of placing the UBID next to the MR phantom. Twenty patients who received RT for CNS tumor using 1.5T MR-LINAC between June 2022 and October 2022 were retrospectively analyzed. Of the total patients, 5 patients did not use UBID and 15 patients used UBID. The positional reproducibility of UBID was evaluated through the median interfractional and intrafractional errors in the first 10 fractions.

Results:

Each MR image quality factors of the MR phantom with UBID satisfied the criteria presented by Elekta. Median values of median shifts in the mediolateral, anteroposterior, and craniocaudal axes for interfractional errors were 2.98-mm, 2.35-mm, and 1.40-mm, and for intrafractional errors were 0.05-mm, 0.03-mm, and 0.06-mm respectively. Median values of median rotations in the pitch, roll, and yaw for both interfractional and intrafractional were all 0.00°. One patient diagnosed with optic nerve sheath meningioma received definitive RT with motion monitoring during the irradiation. In the case of the other two patients, changes in the tumor cavity or residual lesions were observed in the MR images obtained with 1.5T MR-LINAC on the day of first treatment and immediately before irradiation of the 21st fraction, respectively, and therefore offline/online adaptation was performed.

Conclusion:

The reproducibility and immobility of using UBID in CNS tumor patients receiving RT with 1.5T MR-LINAC is clinically feasible. Based on our initial experience, we developed a workflow of 1.5T MR-LINAC treatment for CNS tumors.