MRI-based Immobilization and Planning: A Feasibility Study of a Novel Inverse Method for CNS Radiotherapy

All patients referred for radiotherapy have had a previous diagnostic imaging study (CT-scan or more commonly MRI) showing the disease at the central nervous system (CNS). Moreover, after surgical biopsy or resection, many Centers perform repeated post-operative imaging. Despite all prior imaging, when radiotherapy treatment is decided, all patients undergo another imaging study (CT simulation [CT-sim]) in which patient's head is placed in a reproducible position, and endure a moulding procedure to create a personalized plastic mask for securing the patient's head in a fixed position during the CT acquisition, and reproduced at the subsequent radiation treatment sessions. Typical wait times between moulding, CT-sim and the first radiation treatment is 3-7 days. If a method would be available to accurately recreate the patient's position during diagnostic imaging and reproduce it during radiation treatments without the need for a moulding session or CT-sim, the treatment process can be streamlined and wait times shortened for patients.

Previous studies using 3D printing technology in radiotherapy (such as brachytherapy applicators) have shown that these employed materials are safe for use in clinical settings, and 3D printers can accurately produce devices of various shapes and sizes for clinical use.

In this study, we propose a novel workflow in which patient's position at diagnostic imaging is reproduced with a 3D-printed patient-specific immobilization device, enabling the use of the same diagnostic imaging for planning purposes in lieu of dedicated simulation and moulding sessions, to decrease wait times for patients between diagnostic imaging and start of radiation treatment.