An exploratory analysis of MR-guided fractionated stereotactic radiotherapy in patients with brain metastases

Shouliang Ding; Biaoshui Liu; Shiyang Zheng; Daquan Wang; Mingzhi Liu; Hongdong Liu; Pengxin Zhang; Kangqiang Peng; Haoqiang He; Rui Zhou; Jinyu Guo; Bo Qiu; Xiaoyan Huang; Hui Liu

doi:10.1016/j.ctro.2023.100602

An exploratory analysis of MR-guided fractionated stereotactic radiotherapy in patients with brain metastases

Clin Transl Radiat Oncol. 2023 Feb 23:40:100602. doi: 10.1016/j.ctro.2023.100602. eCollection 2023 May.

Authors

Affiliations

¹ Department of Radiation Oncology, State Key Laboratory of Oncology in South China, Sun Yat‑sen University Cancer Center, Guangzhou, China.
² Department of Radiology, State Key Laboratory of Oncology in South China, Sun Yat‑sen University Cancer Center, Guangzhou, China.

Abstract

Purpose: To assess the feasibility and potential benefits of online adaptive MR-guided fractionated stereotatic radiotherapy (FSRT) in patients with brain metastases (BMs).

Methods and materials: Twenty-eight consecutive patients with BMs were treated with FSRT of 30 Gy in 5 fractions on the 1.5 T MR-Linac. The FSRT fractions employed daily MR scans and the contours were utilized to create each adapted plan. The brain lesions and perilesional edema were delineated on MR images of pre-treatment simulation (Fx0) and all fractions (Fx1, Fx2, Fx3, Fx4 and Fx5) to evaluate the inter-fractional changes. These changes were quantified using absolute/relative volume, Dice similarity coefficient (DSC) and Hausdorff distance (HD) metrics. Planning target volume (PTV) coverage and organ at risk (OAR) constraints were used to compare non-adaptive and adaptive plans.

Results: A total of 28 patients with 88 lesions were evaluated, and 23 patients (23/28, 82.1%) had primary lung adenocarcinoma. Significant tumor volume reduction had been found during FSRT compared to Fx0 for all 88 lesions (median -0.75%, -5.33%, -9.32%, -17.96% and -27.73% at Fx1, Fx2, Fx3, Fx4 and Fx5, p < 0.05). There were 47 (47/88, 53.4%) lesions being accompanied by perilesional edema and the inter-fractional changes were significantly different compared to those without perilesional edema (p < 0.001). Patients with multiple lesions (13/28, 46.4%) had more significant inter-fractional tumor changes than those with single lesion (15/28, 53.6%), including tumor volume reduction and anatomical shift (p < 0.001). PTV coverage of non-adaptive plans was below the prescribed coverage in 26/140 fractions (19%), with 12 (9%) failing by more than 10%. All 140 adaptive fractions met prescribed target coverage. The adaptive plans also had lower dose to whole brain than non-adaptive plans (p < 0.001).

Conclusions: Significant inter-fractional tumor changes could be found during FSRT in patients with BMs treated on the 1.5 T MR-Linac. Daily MR-guided re-optimization of treatment plans showed dosimetric benefit in patients with perilesional edema or multiple lesions.

Keywords: Adaptive radiotherapy; Brain metastases; Fractionated stereotactic radiotherapy; Inter-fractional changes; MR-Linac.