Precision frequency controller enhances radiation targeting accuracy in cancer treatment

Discover how a leading medical device manufacturer developing next-generation tomotherapy equipment used NI and Cyth technology to build a high-precision X-ray pulse controller.

Project Summary

Cyth developed a precision timing and control system using sbRIO, CircaFlex, and LabVIEW to automate radiation pulse generation and improve positional accuracy for tumor targeting while minimizing collateral damage to healthy tissue.

System Features & Components

• Deterministic control down to 250μs loop rates with beam power pulses up to 400μs improving radiation targeting precision.

• 40 KHz pulse rate handling and analog readback from pulsing subsystem.

• Parallel control of three stepper motors for frequency, power, and focus adjustment.

Outcomes

• Accelerated the product’s prototyping and design validation phase by 4-6 months.

• Minimized system integration costs by providing onsite bring-up support, including documentation, training, and calibration.

Technology-at-a-glance

• NI sbRIO-9606 running 20MHz FPGA control loop

• CircaFlex for I/O system integration and control loop design

• LabVIEW control and automation framework

• Precision stepper motors

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Tomotherapy as Medical Technology

Tomotherapy is a cancer therapy modality that directs radiation doses directly to tumor sites intending to minimize exposure to healthy tissue. During operation, the surgical team performs a 3D CT scan to image the cancerous sites, transmitting data wirelessly to the tomotherapy device which orchestrates the delivery of pulsed radiation, typically in the X-ray band of the RF spectrum. A multi-leaf collimator acts in unison with the pulsing stage to permit or block radiation beams based on the imaging data. The overall effect is to provide precise, personalized treatment to the patient.

A medical equipment company sought to develop a new tomotherapy device that pushed the envelope of pulsed radiation control and localization. In the early phases of the engineering design cycle, they needed to prototype and refine a mixed I/O system capable of microsecond-level pulse control. They also needed to validate the performance of this innovative medical device relating back to the overall effectiveness of treatment and patient recovery outcomes.

Engineering Challenge

The customer faced a complex real-time control challenge. They needed to coordinate the intensity-modulated radiation therapy (IMRT) pulser delivering the X-ray energy with positional feedback control based on CT imagery and the surgeon’s touch. These system requirements translated to microsecond-level synchronization across multiple parallel control loops managing:

• Pulsed radiation power

• Stepper motor positioning

• Other system components

These requirements exceeded the capabilities of standard programmable automation controllers (PACs), while developing custom circuitry would have consumed significant schedule time and budget resources. They evaluated using a system-on-chip (SoC), but integrating the electromechnical components of the systemwould be a challenge, nor did they have the in-house FPGA development expertise. The development team needed a solution that could bridge these gaps to provide high-performance control capabilities of FPGAs or custom hardware while keeping keeping the project on track.

• Closed feedback loop running up to 20MHz capable of 400us beam pulses

• Pulse processing: 40 KHz pulse rate handling from pulsing subsystem

• Automation control framework capable of triggering and analog readback digitization

• 3-axis stepper motor control

Cyth Solution

Control System Design: After refining the project requirements, the Cyth engineering team designed a control system capable of delivering the high-speed I/O and programmable control required for microsecond-level precision. The core hardware architecture included:

• NI Single-Board RIO (sbRIO-9606) containing a Xilinx FPGA and a CPU capable of 400MHz real-time processing

• CircaFlex mezzanine board with signal conditioning and connectivity to analog, digital, and stepper motor I/O

• Communication interfaces to other system components

The FPGA on the sbRIO, programmed in LabVIEW, enabled the primary control loop to run up to 20MHz, while the CircaFlex extended the sbRIO’s I/O capabilities through high-accuracy analog readback from the beam pulser and other system components. To achieve the required positional accuracy, the solution digitized and analyzed a high-speed pulsetrain used for triggering capability and feedback control for three stepper motors that direct frequency, power, and focus parameters.

Software Development: Built on the LabVIEW system design platform, the automated frequency controller (AFC) was extensible from the start. Working first to prototype the controller, the Cyth team used CircaFlex to quickly interface with various system I/O and leveraged their experience with automation frameworks to refine the algorithm, closing the multivariable feedback loop on the FPGA.

Software features included:

• Control paradigm defined in software and compiled to the sbRIO’s onboard FPGA

• Hardware-triggered safety interlocks

• Real-time system monitoring and user interface

• Diagnostic capabilities for system bring-up and calibration

Mechanicals and System Integration: Once the system components and architecture were sufficeintly validated, the Cyth team designed and built an enclosure with connectors for the various I/O in the system. As such, they were able to deliver a functional box that abstracted away the complexities of the controller so that the product team could continue integrating and validating the AFC into their end product.

It should be noted that the flexible nature of the LabVIEW-based architecture supported further software design iterations all the way down to the FPGA should the need arise based on system validation in subsequent engineering phases.

System Delivery and Bring-Up

Design Validation and Deployment: Following a 10-week design and build period, the Cyth team successfully delivered a working system delivered during a 2-day on-site visit focused on downstream system integration and usability. The Cyth team continued to support bring-up of the final product, including documentation, operator training, and calibration.