Real-Time Management and Control of Dose Distribution Released on a Tumor During Hadron Therapy

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"We use high-performance, reliable, commercial technology to acquire and process the particle detector data in a deterministic and safe way. The system, which is composed of the PXI platform combined with the LabVIEW Real-Time and LabVIEW FPGA modules, meets our specifications and interacts in parallel with other systems for the most critical part of the real-time control and drive of the dose delivered during irradiation."

- Simona Giordanengo, INFN - Istituto Nazionale di Fisica Nucleare

The Challenge:
Creating a real-time processing system that controls and drives therapeutic proton beams (or carbon ions) and integrates with a complex therapy machine.

The Solution:
Using the NI LabVIEW Real-Time Module and LabVIEW FPGA Module on the PXI platform to quickly, safely, and deterministically acquire and process data in parallel with other systems for dose distribution to tumors.

Author(s):
Simona Giordanengo - INFN - Istituto Nazionale di Fisica Nucleare
Marco Donetti - Centro Nazionale di Adroterapia Oncologica
Maria Adelaide Garella - Centro Nazionale di Adroterapia Oncologica

The Centro Nazionale di Adroterapia Oncologica (National Center for Oncological Hadron therapy, or CNAO), an Italian center of excellence, treats cancerous tumors using beams of charged particles called hadrons that have a mass greater than or equal to protons. A scan technique is used to release the particles and requires a precise, fast, and deterministic system for measurement and control of the beam characteristics. This system, called dose distribution (DD), must also synchronize and interface with different subsystems of the complex therapy machine and ensure high standards of reliability, robustness, and availability of materials used.

The CNAO, the Istituto Nazionale di Fisica Nucleare (Italian Institute of Nuclear Physics), and the University of Turin worked together to build the beam monitor and all the hardware and software interfaces to integrate the DD system into the CNAO machine.

System Architecture Description

The CNAO DD system comprises a pair of magnets for the transverse scan of the beam as well as a series of ionization chambers with differently segmented anodes for the measurement of the beam’s fluence, position, and size.

We use high-performance, reliable, commercial technology to acquire and process the particle detector data in a deterministic and safe way. The system, which is composed of the PXI platform combined with the LabVIEW Real-Time and LabVIEW FPGA modules, meets our specifications and interacts in parallel with other systems for the most critical part of the real-time control and drive of the dose delivered during irradiation.

The particle detectors measuring the beam intensity and position collect the real-time ionization charge. The first function of the DD system is to use this charge to control the displacement of the beam and release the dose, which is the unit mass energy translated into the number of particles that reach the tumor. The second function of the DD system is to intervene in the event of hardware component failure or detection of parameters outside clinical tolerance and then communicate the error to external systems that interrupt the irradiation.

System Detectors Description

The detectors that characterize the CNAO DD system consist of five ionization chambers filled and flushed with nitrogen at atmospheric pressure and ambient temperature. In particular, the signals generated come from:

  • Two chambers with an integral anode and sensitive area of 24 cm by 24 cm2 to measure the beam intensity at a frequency of 1 MS/s
  • Two chambers identical to the above, but rotated by 90 degrees with the anode segmented into 128 strips
  • One pixel chamber with the anode segmented into 32 pixels by 32 pixels

By calculating the center of gravity of the charges collected along the 256 strips  spaced apart by 1.65 mm, the strip chambers reconstruct the position of the beam in X and Y at a frequency of 20 kHz and with an accuracy of about 100 mm. The pixel chamber is divided into 1,024 pixels (6.5 mm-wide)  spaced apart by 0.1 mm and is used for redundant position and size control of the beam at a frequency of 10 kHz. We base the acquisition of the charge collected by the detectors on an ASIC (TERA06-TERA08 chip) with 64 independent channels (IF converters, 20 MHz to 100 MHz clock, with no idle time).

System Description: Fast and Slow Control

Control of the whole system, including the front end of the detectors, the gas distribution system, and the interface with the interlock system, resides in a cabinet that houses two PXI chassis. One chassis includes a controller running a real-time OS, NI PXI modules with FPGAs on board, four memory cards, one additional network card, and three custom PXI modules. The second chassis contains one controller, three industry digital cards, an additional network adapter, a serial card, and a custom PXI module.

The first chassis delegates the critical operations and decisions during irradiation to the FPGA. The four memory cards support the four FPGAs and they make the data/command exchange between the CPU and the adjacent FPGA even more robust. The FPGA and memory cards finally connect via external cable.

For each patient, the DD system receives a text file of the treatment plan with particle number sequences, positions of the beam, and more information used by the state machine of the DD. This is implemented on the fast control subsystem of the real-time controller, which manages the input/output via data bus through PXI modules as well as via Ethernet through external systems.

Control of the temperature, pressure, and flow of the gas inside of the detectors, as well as the voltage applied between the anode and cathode, is essential for a correct dose release. A subsystem of the DD called slow control manages these and checks for proper setup and initial conditions of the system prior to each treatment. The second chassis is dedicated to the slow control of the DD system.

The figure shows a diagram of the CNAO dose distribution system. Scanning magnets direct the beam on the tumor, monitors measure the characteristics of the beam, and the control system is contained in the cabinet at the bottom left. Two NI PXI chassis run the fast control (top) and the slow control (bottom) of the DD system. The fast control is performed using an NI PXI controller, five NI PXI FPGA modules, four NI PXI high-speed digital modules, one NI PXI network module, and three custom PXI modules. The slow control is carried out through one NI PXI controller, three NI PXI industrial DIO modules, one NI PXI network module, one NI PXI RS-232 module, and one custom PXI module.

Reliable High-Performance Results

We have used the distribution system for two years with 100 percent uptime. The certifications of the various components and software are in progress. In addition, the Austrian hadron therapy center, EBG MedAustron, has purchased a copy of the complete system. 

Author Information:
Simona Giordanengo
INFN - Istituto Nazionale di Fisica Nucleare

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