Preliminary study of clinical application of respiratory navigator-guided stereotactic body radiation therapy of liver malignancies on magnetic resonance linear accelerator / 中华放射肿瘤学杂志

ABSTRACT

Objective:To investigate the workflow, feasibility and advantages of respiratory navigator-guided stereotactic body radiation therapy (SBRT) of liver malignancies on the magnetic resonance linear accelerator (MR-linac).Methods:Clinical data of 10 patients with liver cancer treated with respiratory navigator-guided SBRT on the MR-linac from September to December 2021 were analyzed retrospectively. All patients underwent CT and MR simulated localization, and plain, enhanced and 4D CT scan, and T 1 3D MR and T 2 3D MR images were collected. The expiratory 4D CT was chosen to design the reference plan. The T 2 3D navigator MR image (end-exhalation) was collected before treatment, the target position was adjusted or the target shape was modified in combination with the real-time monitoring 2D MR image and appropriate online adaptive planning process was selected. Then, the ability of CT, T 2 3D and T 2 3D navigator MR images to display the tumor was evaluated by naked eye. The changes of target volume were calculated. Dosimetric differences between the adaptive and reference plans were compared. The efficacy and adverse reactions of patients were evaluated. Results:In the free breathing state, the T 2 3D navigator MR image was significantly better than T 2 3D MR image to clearly display the tumor and its boundary. The adaptive plans of adapt-to-position (ATP) and adapt-to-shape (ATS) adopted by 10 patients was 37 times and 22 times respectively. The tumor subsided significantly in 3 patients. The average target conformal index (CI) of the adaptive plans was no different from that of the reference plans, but the gradient index (GI) was higher ( P<0.05), especially in the ATS plans. Compared to the reference plans, the normal liver V 5 Gy, V 10 Gy and D mean were almost the same, but the average MU was increased with a significant difference in the ATP adaptive plans ( P<0.05). The average of MU, segments and normal liver D mean and V 10 Gy in the ATS adaptive plans were lower than those in the reference plans, and the liver V 5 Gy was slightly increased. Seven patients were evaluated after 1 month and 3 months. The local control of lesions was promising. Toxicities were mild and no grade 3 or higher toxicities were observed. Conclusion:Respiratory navigator on MR-linac improves the visual clarity of tumors and online MR images, and shows its advantages to guide the adaptive precision radiotherapy of liver tumors, especially in SBRT.