Purpose: To realize real-time automatic patient head motion correction during radiation therapy with non-magnetic and non-radiation attenuating actuators. Contrary to current methods, this (i) removes need for frames or thermoplastic masks; (ii) corrects the complex intra/inter-fractional geometric uncertainties; (iii) and is compatible with standalone MRIs or combined MRI-Linac systems.
Methods: Following our recent investigation, we now present the real-time deformation framework of a soft actuator within the erstwhile-fabricated mechanism and describe the sensing and closed-loop pneumatic control system. We clamp fabricated actuators using 3D-printed PLA holders and fit the planar actuator with a pipe fitting connector. Compressed air at low pressure (~3-10 psi) is supplied through a firm polyurethane air tubing into a pressure transducer connection, whose outlet conveys the airflow into a proportional solenoid valve, which in turn leads to the pipe fitting connection of the soft. We construct a standard current source electronic regulator that varies the air flow into the solenoid valve. Finally, a flex sensor, meshed laterally along the center of the actuator during curing measures deformation.
Results: Effective closed-loop deformation of the actuator chamber is now realized as a result of the designed mechanism. By measuring the deformation of the actuator with an integrated flex sensor, we can proportionally adjust the airflow into the solenoid valves thereby allowing accurate regulation of the head motion.
Conclusion: This work shows the potential of real-time head motion correction with non-magnetic and a radiation-transparent soft actuator, arranged in systematic fashion around a patient’s head. This mechanism is useful in emerging hybrid MRI-Linear accelerators. Its inherent actuation medium (air) eliminates the risk of electronic/metallic parts that are unsuitable for the MRI’s magnetic fields and assures safe human-robot interaction.