Micromotors deliver precision for radiotherapy treatment

Provided to more than a quarter of cancer patients, today’s targeted radiotherapy has come a long way from its experimental, and Nobel Prize winning, origins. When administering the treatment, shaping of the beam is an important way of minimising the absorbed radiation in healthy tissue and delivering an accurate dose. In our latest article, EMS managing director Stewart Goulding explains how multileaf collimators (MLC) deliver accuracy in radiotherapy.

Until a few years ago, delivering precision during radiotherapy was challenging. Particularly when targeting areas such as the head and neck, doctors had to proceed with caution and deliver lower doses of radiation in order to protect areas like the spinal cord. Delivering too much could impact healthy areas surrounding the tumour, too little could render the treatment ineffective.

Thankfully, several technologies have improved the precision of radiotherapy treatment. A widely-used form of treatment today is intensity-modulated radiation therapy (IMRT). It uses multiple small photon or proton beams of varying intensities to irradiate a tumour, delivering precise control of individual rays within beams of radiation to enable better targeting, especially for tumours with complex shapes.

With IMRT, or any other form of radiotherapy, shaping of the beam is of extreme importance. It must target the treatment area without damaging any healthy tissue. Conventional collimator jaws are often used for shaping a rectangular treatment field but, as usually the treatment volume is not rectangular, additional shaping is required. One option is to use a Multi Leaf Collimator (MLC)

An MLC is a device that’s affixed onto the collimator of the linear accelerator system, which delivers radiation to the treatment area. It contains several sets of metallic “leaves” that, when opened and closed, can shape the beam of radiation as it exits the linear accelerator. Using an MLC to precisely shape the beams from multiple angles makes it possible to deliver a radiation dose that closely matches the volume of the tumour. The MLC also facilitates IMRT by using its adjustable leaves to shape the beam and by controlling exposure times, clinicians can deliver a different dose to different parts of the tumour.

Consequently, technicians can administer a higher dose to most aggressive areas of the tumour, and a lower dose where the beam risks passing through healthy tissue areas.

To deliver the accuracy and control an MLC requires, DC motors move the leaves in and out of place. Motors need to be designed for durability, so they can withstand continual use in a busy clinic. An MLC can need over 100 motors packed into a small space, and so motors must be lightweight and capable of delivering high torque in a small package.

Handling high torque and speed is essential if the motors are to manage the quick, accurate shape changes an MLC delivers. Motor torque must be at a level where the leaves can operate in a tight formation, and must account for the friction that occurs when the leaves brush against each other. Powerful rare earth magnets inside the motors can help achieve this high torque. To maintain motor control and adjust motor speed when necessary, it may also be wise to attach an encoder to each motor.

The FAULHABER SR series’ compact size means a large number of the motors can fit into the MLC. With no cogging torque and precise speed control, the SR series supports steady yet high-powered MLC operations and torque can be further increased by implementing a planetary gearhead.

Since the discovery of the X-ray, radiotherapy technology has come a long way. Today, thanks to the precision and accuracy an MLC can deliver, patients can benefit from a better controlled, more effective form of treatment.

Want to know more about the applications of DC micromotors in med-tech? Get in touch with a member of the EMS team today.