Developing a highly accurate and precise proton beam control solution to deliver a prescribed radiological dose to a specific location within a tumor.
Implementing intensity modulated pencil beam scanning in the ProNova SC360 by using Single-Board RIO solutions to meet the monitoring and control requirements to safely and effectively deliver the radiological dose to treat a tumor.
More than 1.6 million people will be diagnosed with cancer this year in the United States, with 320,000 of those cases eligible for proton therapy. However, with just 24 existing proton therapy centers, only 5 percent of eligible patients can receive this treatment. ProNova aims to make proton therapy a widely available cancer treatment option by delivering a lower cost, smaller, and more energy efficient proton therapy system without sacrificing clinical capabilities.
We designed the SC360 proton therapy system to provide the flexibility required to support 1 to 5 treatment rooms, allow for different treatment room configurations, meet individual customer needs, and enable easy integration with future R&D projects. This modular approach lends itself nicely to the design of a distributed control system with NI reconfigurable I/O (RIO) technology. This technology, in conjunction with the LabVIEW Real-Time Module and the LabVIEW FPGA Module, provide the hardware flexibility and programming capabilities needed to rapidly develop advanced embedded monitoring and control solutions for the SC360 without sacrificing the performance requirements of a proton therapy system. Consequently, we used CompactRIO and Single-Board RIO solutions extensively throughout the SC360 for magnet control, vacuum control, beamline diagnostics, and dose delivery. The SC360 offers a highly accurate and precise method for targeting tumors by using intensity modulated proton therapy (IMPT) with pencil beam scanning (PBS). This technology helps doctors treat large, non-contiguous targets with improved local control; thus, sparing sensitive organs and normal tissue from unnecessary radiation exposure. This allows proton therapy to provide a dosimetric advantage in more than 80 percent of all external beam radiation treatment cases.
The Dose Delivery System, or DDS, is the SC360 subsystem that accurately and precisely delivers protons from the beamline to a specific target in the patient. We implemented IMPT with PBS in the DDS using three sbRIO-9626 embedded controllers. The individual controller responsibilities include: dose monitoring, beam control, and beam position monitoring (Figure 2). A PBS treatment plan contains a set of locations, or spots, in 3D space (horizontal-X, vertical-Y, depth-Z) that are each prescribed a specific radiological dose. The spot produced by the proton beam is between 4–8 mm depending on depth and must be delivered within 1 mm of the prescribed location. Modulating the intensity of the proton beam adds a time dimension to the treatment plan by controlling the beam current to deliver each spot in ~5 ms. We used the Single-Board RIO FPGA and LabVIEW FPGA Module for each of these applications to meet the timing requirements for spot delivery and the response times required to safely remove the beam from the treatment room during spot transitions or following a safety interlock. Additionally, hard-wired signals pass between the FPGAs of each of the control components to trigger spot completion, spot advancement, and treatment faults. Each DDS module uses LabVIEW Real-Time to receive treatment plans, process spot treatment results, and report treatment results back to the treatment room master control component.
We control the vertical and horizontal position of the proton beam from the beamline to the patient using specialized scanning magnets. The Single-Board RIO device dedicated to beam control is responsible for controlling the magnetic fields required to deflect the proton beam to the desired spot location. Additionally, this controller provides the beam intensity set point required to maintain spot durations of 5 ms. We can sample the analog I/O available on the sbRIO-9626 at 10 kHz to continuously monitor critical feedback signals (control signals, load voltages, currents, fields, temperatures, and water flow) related to vertical, horizontal, and intensity control. The beam control system safely removes the proton beam from the treatment room if any of the monitored signals fall outside set point tolerances. The beam control module is triggered to adjust the magnet fields for the next spot when the dose has been delivered for the current spot. Upon verification that the monitored signals have settled at the new set point, the treatment can continue. We can complete and verify this spot transition process in <800 µs.
We monitor the amount of charge collected on two redundant dose planes located between the output of the beamline and the patient to control the dose delivered to a spot. We used the sbRIO-9626 to meet the analog I/O and digital I/O requirements for sampling the dose plane signal conditioning circuits. Additionally, we use the onboard FPGA to monitor the delivered dose at frequencies up to 1 MHz, and provide the response time required to safely remove the proton beam from the treatment room upon fulfilling the prescribed dose or in the event the delivered dose falls outside of treatment tolerances. This level of precise control makes it possible to deliver a radiological dose within 1 percent of the prescribed dose. The dose monitoring module also synchronizes spot advancement with other DDS modules upon the delivery of a prescribed dose. We accomplish this by 1) removing the beam from the room when the prescribed amount of dose is delivered, 2) triggering the beam control and beam position monitoring modules once the spot has been completed, 3) receiving notification from the beam control and beam positioning monitoring modules upon successful spot transition, and 4) completing the spot by verifying the delivered dose is within treatment tolerances. Once the spot transition has completed (<1 µs), the treatment plan resumes on the next spot if all components are confirmed ready for safe beam delivery. This process incrementally advances the control components through a treatment plan until a dose has been delivered to all prescribed spots.
The proton beam position is monitored using an ionization chamber that contains a grid of 64 horizontal and 64 vertical ion strips with 2.5 mm spacing. The large amount of digital I/O available on the sbRIO-9626 high-density RIO Mezzanine Card connector is critical for sampling the signal conditioning circuits used to measure the 128 analog inputs from the ion chamber. We use the Single-Board RIO controller’s FPGA to sample ion chamber signals in synchronization with dose delivery and analyze the incoming data in <100 µs. LabVIEW FPGA powered rapid prototyping and the development of advanced analysis, monitoring, and diagnostic routines for calculating spot position and size; verifying ion chamber performance; checking environmental conditions; and implementing safety interlocks. This module removes the proton beam from the treatment room if the beam analysis determines the spot position and size are not within 0.5 mm, or if other issues are diagnosed that jeopardize the accuracy or precision of the treatment.
ProNova received FDA approval for the SC360 earlier this year and plans to start treating the first patients later this year at the Provision Center for Proton Therapy in Knoxville, Tennessee. We have planned future SC360 installations for cities across the United States, Europe, and Asia. ProNova strives to improve upon the clinical advantages of proton therapy and introduce advanced technologies that help make this treatment option a reality for more cancer patients.
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