The use of a permanent magnetic resonance imaging system for radiotherapy treatment planning of bone metastases

Abstract Purpose: To evaluate the usefulness of magnetic resonance (MR) imaging–based radiotherapy treatment planning (RTTP) for bone metastases in clinical applications. Methods and Materials: MR imaging–based RTTP was carried out for 28 patients with bone metastases using a permanent magnetic MR unit. Twenty-three patients received MR imaging–assisted X-ray simulation, and five underwent MR simulation. In MR imaging–assisted X-ray simulation, the radiation fields defined by an X-ray simulator were modified based on MR information scanned in the exact treatment position using MR skin markers. In MR simulation, both isocenter position and field size were determined on MR images and projected onto the patient’s skin. Results: All lesions unclear on other imaging modalities could be clearly identified on MR imaging. Of the 23 patients receiving MR imaging–assisted X-ray simulation, modification of the original radiation field was necessary in 14 patients (extended in 9, reduced in 4, and completely changed in 1). In MR simulation, appropriate radiation fields could be easily and quickly determined using MR imaging. Conclusion: Methods for MR imaging–based RTTP were developed and clinically implemented for patients with bone metastases, and they were shown to be useful for improving the accuracy of the tumor location. They would provide better therapeutic/palliative benefit to particular patients with bone metastases and could also be applied to other lesions in the future.