Heavy Ion Medical Machine Research Articles

An integrated system for measuring 3D dose distributions of carbon-ion pencil beams in regular QA practice

The accurate measurement of three-dimensional (3D) dose distribution of carbon-ion pencil beams in water is crucial for regular quality assurance (QA) practice. Although ionization chambers scanned in a water tank is conventionally used for this purpose, these measuring methods are time-consuming and labor-intensive. In addition, the beam of Heavy Ion Medical Machine (HIMM) changes continuously in each extracted duration, these methods cannot obtain the accurate 3D dose distribution. To solve these problems, an integrated system (PBDOSE) is conceived and established, which employs multi-strip ionization chambers (MSICs) to measure 2D lateral profile dose distributions. The lateral profile dose distribution in the context of various depths is measured by a mobile MSIC and normalized by the measurement of a reference MSIC to reduce the effect of beam instability. On this basis, a 3D dose distribution is created by stacking those profiles in depth direction. By conducting a single depth scan within 3 min at HIMM, information such as the 3D dose distribution, lateral contour images, the Bragg curve, beam spot size, beam position, incident direction, and energy of the beam can be obtained. The Bragg curve acquired from PBDOSE with statistical uncertainties of 1.5% was almost identical to those measured by a commercial water phantom. Besides that, the lateral profiles revealed a remarkable agreement with Gafchromic EBT3 film measurements within differences less than 0.1 mm. PBDOSE shows great prospects in the accurate and efficient measurement of 3D dose distribution for carbon-ion therapy, and the clinical application of this system will improve the efficiency of regular QA procedures to a great extent.

A dedicated in-beam PET system with a modular dual-head for radiotherapy imaging in HIMM

This paper presents a heavy-ion in-beam PET, referred to as ibPET with a specifically custom designed data acquisition system, which was constructed and tested at the Heavy Ion Medical Machine (HIMM) beam-line, HICTC in Wuwei. The data acquisition system of ibPET has undergone several upgrades during the years, And its data processing capability now exceeds one million events per second per channel. To achieve optimal performance of the ibPET under existing conditions, we tested coincident events and noise equivalent count (NEC) under different time coincidence windows.The results show that the signal-to-noise ratio of the reconstructed image data reaches its peak when the time window is around 3 ns, indicating that the ibPET performance is optimal at this point. In order to determine the size of the time window, we measured the system's time resolution FWHM to be 1.63 ns, and ultimately chose a time window size of twice the time resolution FWHM, which is 3.25 ns. Meanwhile, we demonstrate the capability of our ibPET to monitor the dose range with various irradiation. The results demonstrate that the system exhibits the expected exponential decay in counting rate after irradiation, and accurately provides penetration depth positions at different energy levels.

Progress in heavy ion cancer therapy at IMP and future development

AbstractBasic research on heavy ion cancer therapy such as radiobiology, medical physics, and therapeutic technique has been conducted at the Institute of Modern Physics (IMP), Chinese Academy of Sciences since 1995. Based on the achievements acquired in the basic research and the requirements for a heavy ion accelerator for radiotherapy purposes, a dedicated heavy ion therapy facility named Heavy Ion Medical Machine (HIMM) was designed at IMP and constructed in Wuwei, China. The HIMM facility consists of two electron cyclotron resonance ion sources, one cyclotron as the injector and one synchrotron as the main accelerator, and four different treatment rooms equipped with passive or active beam delivery systems, and accelerates carbon ions up to 400 MeV/u. After the performance inspection of HIMM organized by the National Medical Device Inspection Center, preclinical tests like cell and animal radiobiological experiments and dosimetric verification using anthropomorphic phantoms for elucidating the biophysical properties of the carbon ion beams provided by HIMM were carried out. According to the Chinese medical device regulations, a clinical trial in which 46 tumor patients were recruited and two hospitals participated was conducted in the HIMM facility, aiming at evaluating the treatment safety and short‐term efficacy of the medical device. The success of the clinical trial helped the HIMM facility be authorized by the Chinese government as a class III medical device. In this paper, all the aspects mentioned above are introduced and discussed, and implications for future improvements are also given.

Carbon ion radiography with a composite ionization chamber detector

Range uncertainty in carbon ion therapy can diminish treatment efficacy because it may cause deviation from the planned dose distribution. The precise and accurate determination of relative stopping power (RSP) maps of carbon ions in the patient is a direct solution to this problem. To obtain RSP maps in patients undergoing carbon ion radiography, our team developed a preliminary prototype of a composite ionization chamber detection (CICD) system. The CICD prototype employs synchronously gated integral electronics with the ability to measure the depth-to-dose curve and the beam profile simultaneously. Carbon ion radiography experiments were performed on hemispherical, sloped, and stepped phantoms using the Heavy Ion Medical Machine (HIMM) beam. The beam energy was 190.19 MeV/μ and the beam spot full width at half maximum (FWHM) was 7.42 mm. The radiographic image of the sloped phantom, the thickness prediction accuracy of each pixel (2 mm) is 88.25%, its absolute mean error (AME) is 1.07 mm, and the maximum absolute deviation (MAD) is 2.64 mm. The prediction accuracy of the CICD prototype is mainly affected by electronic noise, with a noise-to-signal ratio (NSR) of about 14.36 dB. Carbon ion radiography simulations were performed in this study using Geant4 software to eliminate the effect of the electronic noise. The thickness prediction accuracy is 98.54%, 98.62%, and 99.07% per pixel for hemispherical, sloped and stepped phantoms, respectively, with AME of 0.09 mm, 0.27 mm, and 0.48 mm. Carbon ion radiography utilizing the CICD prototype scheme has the ability to refine the accuracy and resolution of radiographic images, consequently establishing a scientific foundation for diminishing the effects of range uncertainty and fully exploiting the advantages of precision particle therapy.

Real-time digital signal processing implementation for in-beam PET of radiotherapy imaging in HIMM

The in-beam positron emission tomography (ibPET) is dedicated to radiotherapy imaging of the heavy-ion medical machine (HIMM), which requires precise online measurement, as well as real-time signal processing capability of the electronics. In this paper, we present the implementation of real-time digital signal processing in the data acquisition unit (DAQU) for an ibPET system based on the photomultiplier tube (PMT) readout of lutetium-yttrium oxyorthosilicate (LYSO) scintillator crystals. We have designed 10-channel customized signal processing circuit on a high-performance FPGA, which supports 3 working modes (single event processing mode, self-calibration mode and raw ADC data mode), position calculation, crystal locating, event sorting, and etc. Moreover, the implementation of real-time corrections is capable of dealing with photon peak correction to 511 keV and crystal ID-based time correction. The implemented real-time ibPET system can achieve 46% data compression and beyond 1,000,000 events/sec/channel signal processing capabilities. A series of initial tests is conducted, and the results indicate that this design meets the application requirement on online processing.

Monte Carlo study of the neutron ambient dose equivalent at the heavy ion medical machine in Wuwei

Monte Carlo study of the neutron ambient dose equivalent at the heavy ion medical machine in Wuwei

A System for Magnetic Measurement of the Triplet Quadrupoles for DTL

The Institute of Modern Physics (IMP) has developed a magnetic measurement system of the triplet quadrupoles in drift tube linac (DTL), based on the rotating coil method. The most important measurement requirement of the triplet in DTL is the deviation between the machinery axis of the cavity and the magnetic axis of the triplet quadrupoles, which is less than 0.1 mm, the angle deviation is less than 1 mrad. The magnetic field quality is also measured. There are two aspects to be considered when designing the system, one is the mechanical adjustment mechanisms for the three quadrupoles respectively, another is the specialized compensated coil consisting of two sets of windings which can be connected to measure the magnetic center and the high order harmonic errors. Simultaneously, optimizing the testing process is also crucial. Based on the results obtained on the two triplets in two tanks for a Heavy Ion Medical Machine with Linear Accelerator (HIMM-LINAC), the magnetic measurement system could meet the requirements

The influence of beam delivery uncertainty on dose uniformity and penumbra for pencil beam scanning in carbon-ion radiotherapy.

The dose uniformity and penumbra in the treatment field are important factors in radiotherapy, which affects the outcomes of radiotherapy. In this study, the integrated depth-dose-distributions (IDDDs) of 190 MeV/u and 260 MeV/u carbon beams in the active spot-scanning delivery system were measured and calculated by FLUKA Monte Carlo simulation based on the Heavy Ion Medical Machine (HIMM). Considering the dose distributions caused by secondary particles and scattering, we also used different types of pencil beam (PB) models to fit and compare the spatial distributions of PB. We superposed a bunch of PB to form a 20×20 cm2 treatment field with the double Gaussian and double Gaussian logistic beam models and calculated the influence of beam delivery error on the field flatness and penumbra, respectively. The simulated IDDDs showed good agreement with the measured values. The triple Gaussian and double Gaussian logistic beam models have good fitness to the simulated dose distributions. There are different influences on dose uniformity and penumbra resulting from beam uncertainties. These results would be helpful for understanding carbon ion therapy, and physical therapists are more familiar with beam characteristics for active scanning therapy, which provides a reference for commissioning and optimization of treatment plans in radiotherapy.

Performance of the Secondary Electrons Profile Monitor for the scanning gantry in the Heavy Ion Medical Machine

A Secondary Electrons Profile Monitor (SEPM) is developed as part of the beam dose delivery system in a clinical gantry of the Heavy Ion Medical Machine (HIMM). With the purpose of less disturbance to the beam, a thin foil with a thickness of 0.7μm and an accelerating grid with a diameter of 15μm are employed to produce and accelerate the secondary electrons, and two microchannel plates (MCPs) are used to multiply the electrons. Providing the real-time information of beam size, position, flatness, and symmetry in front of the scanning magnet, the beam monitor features an active area of 989 mm2, beam intensities between 1.0 ×103 to 1.0 ×108 particles per pulse (ppp) and a wide range of beam energies. A prototype is tested at the horizontal treatment room of the HIMM. Using different beam positions, sizes, and energies of 12C6+ beams, test experiments show that the beam monitor maintains good consistency with a Multi-Strip Ionization Chamber (MSIC). Compared to the MSIC, the SEPM shows a better signal-to-noise ratio (SNR) and higher sensitivity to the variation of the beam.

Performances of the beam monitoring system and quality assurance equipment for the HIMM of carbon-ion therapy.

PurposeThe heavy‐ion medical machine (HIMM), which is the first commercial medical accelerator designed and built independently by the institute of modern physics (IMP) in Wuwei, Gansu Province, China, had officially completed clinical trials at the time of this article's writing. Three types of detector systems were developed based on the ionization‐chamber principle to monitor the beam parameters during treatment in real time, quickly verify the beam performance during a routine checkup, and ensure patient safety.Methods and materialsThe above‐mentioned detector systems were used for beam monitoring and quality assurance in the treatment system. The beam‐monitoring system is composed of three integral ionization chambers (ICs) and two multistrip ionization chambers (MSICs) as a redundant design. The irradiation dose, beam position, and homogeneity of a lateral profile are monitored online by the beam‐monitoring system, and safety interlocks are established to keep the test results under the predefined tolerance limitation. The quality‐assurance equipment was composed of one MSIC and one IC stack. The IC stack was used for energy verification.ResultsThe off‐axis response of ICs is within a tolerance of 2%, and the dose interlock system (DIS) response time is less than 7 ms during the treatment process. The positioning resolution of MSICs reached 73 µm. The IC stack can verify the beam range within one spill and the measurement resolution is less than 0.2 mm.ConclusionsThe beam‐monitoring system (BMS) and quality‐assurance equipment (QAE) have been installed and run successfully within HIMM for two years and are associated with the HIMM treatment system to deliver the right dose to the correct position precisely. Furthermore, the daily QA task is simplified by it. Above all, the system has passed the performance test of the China Food and Drug Administration (CFDA).

Closed orbit correction of the HIMM synchrotron

In this paper the closed orbit correction of the Heavy Ion Medical Machine (HIMM) synchrotron is described. Results of simulations and measurements are presented. Consistently with simulations, it is possible to correct the maximum closed orbit distortion of the HIMM synchrotron down to 2.4mm in the horizontal direction and 0.7mm in the vertical one. The errors of dipole magnets, especially the longitudinal alignment errors (Δs), have large impact on the horizontal correction results. A Singular Value Decomposition (SVD) algorithm is adopted for computing the correction. The residual orbits and the effects of reducing the number of singular values are analytically expressed and simulated. In addition, the influences of BPM reading errors as well as corrector setting errors are analyzed. For further optimization, the method to estimate the dipole errors is studied. In the commissioning, the maximum closed orbits at BPMs can also be well corrected to within 1mm through SVD algorithm.

Intense carbon beams production with an all permanent magnet electron cyclotron resonance ion source for heavy ion medical machine.

LAPECR3 (Lanzhou All Permanent magnet Electron cyclotron Resonance ion source No. 3) had been developed as an ion injector of Heavy Ion Medical Machine (HIMM) accelerator facility since 2009. The first HIMM accelerator facility was built in Wuwei city in 2015, and the LAPCER3 ion source has delivered C5+ ion beam to HIMM for more than 1000 days in the past four years. In order to improve the performance of the LAPECR3 ion source for intense carbon beams production, continuous research and development work has been made. The recently developed LAPECR3 ion source together with the new low-energy beam transportation can provide better performance in terms of both beam intensity and quality. This paper will generally review the LAPECR3 ion source operation status for HIMM, and the recent improvement will be presented, especially the stable beams production of C4+ and C5+.

Transverse emittance measurement for the heavy ion medical machine cyclotron

The transverse emittance of the extracted beam from the heavy ion medical machine cyclotron is measured and then optimized for injection into the synchrotron. For the purposes of cross-validation, three methods, i.e., slit–grid, Q-scan, and 3-grid, are used to measure the emittance. In the slit–grid technique, an automatic selection of the region of interest is adopted to isolate the major noise from the beam phase space, which is an improvement over the traditional technique. After iterating over the contour level, an unbiased measurement of the emittance can be obtained. An improvement in the thin lens technique is implemented in the Q-scan method. The results of these measurements are presented.

A new alignment method for HIMM magnetic field measurement system

Abstract The Heavy Ion Medical Machine (HIMM) is China’s first heavy ion accelerator specifically for cancer treatment. To minimize the uncontrollable beam orbit and beam loss, the HIMM accelerator magnets require the condition of stringent field uniformity. The best way to examine whether the actual field is consistent with the design or not is to perform an accurate and reliable measurement on the magnetic field, which requires the accurate alignment of the magnetic field measurement system as the prerequisite. This research adopts the alignment of a Hall probe mapping system, long coil integral system and harmonic coils system. Firstly, the preliminary test launched at the HIMM is described. Then, a new alignment method is developed to improve the positioning accuracy and performance of magnetic field measurement system. The experimental results show that the alignment accuracy (maximum deviations) of all components of each magnetic field measurement system is higher than 0.1 mm, which satisfies the requirements for the positioning accuracy of high-precision magnetic field measurement system.

RF design of radio-frequency quadrupole accelerator for heavy ion medical machine

Abstract A 162.5 MHz, 7.2 MeV Radio Frequency Quadruples (RFQ) is being designed for the injector of a heavy ion medical machine, which is promoted by the Institute of Modern Physics (IMP), Chinese Academy of Science (CAS). The proposed RFQ will adopt the conventional 4-rod structure, which is most commonly used for the heavy ion linac at low energy section. RF design was based on a new fast-bunching beam dynamics design. Comparing with the conventional beam dynamics design, this design strategy makes the structure more compact and need less power consumption. To meet the requirements of beam dynamics, various methods were used to optimize the electric field distribution. The electric field fluctuation under 3.5% and the dipole field ratio under 3% were obtained simultaneously. Water temperature rise and cavity thermal deformation were also simulated based on the special water-cooling system design. Under the setting of the cooling parameters, the temperature rise of cooling water was kept below 2 °C in theory. Considering the possible frequency shift during assembling and operation, the tuning range of the movable plungers is 500 kHz to compensate frequency shift.

Alignment technology of heavy ion medical machine

Heavy ion medical machine (HIMM) is built by the Institute of Modern Physics, Chinese Academy of Sciences, with a high-energy beam transport line with a height of 18 m, and its complex space mounting structure increases the difficulty of installation and alignment. The aim of this paper is to provide methods to install all accelerator components efficiently and to ensure that the alignment accuracies of all installed components are within the designed values. We accomplished the fiducialization and pre-alignment of complex modules by combining the laser tracker and the alignment telescope. By analyzing various elements that affect the accuracy of alignment, a method of alignment for high-energy beam transport line was proposed based on high-precision three-dimensional control network. All components have been installed and aligned in a short time, alignment position accuracy of magnets is less than 0.1 mm, and the treatment components alignment accuracy is no more than 0.4 mm. On the basis of error analysis, all alignment results are better than the required precisions, and all of these guaranteed the successful operation of HIMM.

The design and implementation of the beam diagnostics control system for HIMM

The Heavy Ion Medical Machine (HIMM) is a compact synchrotron based facility built by the Institute of Modern Physics (IMP) in China. This facility delivers carbon ion beams with kinetic energies up to 400 MeV/u for clinical applications. The beam diagnostics system for HIMM is based on 18 different types of monitors and is used to measure all relevant beam parameters from the ion source to the irradiation therapy terminals which are critical for the commissioning of the accelerator as well as during the regular operation to ensure high up-time of the machine. The control system for all the monitors is designed, developed and implemented globally based on a 3-tier architecture with the aim to achieve a clear separation between front-end devices and their controllers. This paper presents the architecture, the design principle and the implementation of this control system. The beam parameters measured based on the detectors′ motion control and data acquisition control system are analyzed in detail. Furthermore, this beam diagnostics control system (BDCS) will be transplanted to the next heavy ion medical machine in Lanzhou city on account of the successful application in Wuwei city, the precise beam parameters measurement, and long term operation with high stability and reliability.

Heavy ion medical machine (HIMM) slow extraction commissioning

Heavy ion medical machine (HIMM) is the first Chinese heavy ion accelerator facility developed for cancer therapy. After commissioning, the slow extraction efficiency reached nearly 90% for all energies from 120 to 400 MeV/u. The spill duty factor exceeded 90% at a sample rate of 10 kHz. This paper reports the results of the HIMM’s slow extraction commissioning.

Research Progress on Accurate Pencil Beam Model for Heavy Ion Cancer Therapy

The heavy ion treatment planning system of Institute of Modern Physics(IMP), Chinese Academy of Sciences adopts single Gaussian model to depict the lateral dose distribution of pencil beam currently. Without taking secondary particles produced by heavy-ion pencil beam in medium into full consideration, the single Gaussian model is not accurate enough to describe the lateral dose distribution. In fact, an accurate pencil beam model should include the description of low dose envelope contributed by secondary particles. This work summarized the cause of formation, property, dose contribution, mathematic models and measuring methods of the low dose envelope laterally far away from the incident axis of a pencil beam. Moreover, the lateral dose distribution of heavy ion pencil beams with different energies were calculated by means of the Monte Carlo simulation method, based on the horizontal nozzle of the demonstration facility of heavy ion medical machine in the Wuwei heavy-ion therapy center, and thus the degree of coincidence between the simulated data and different mathematic models was investigated. The results verified that the triple Gaussian model was better than the single and double Gaussian models to depict the lateral dose distribution of heavy ion pencil beams, mentioned from existing papers. Thus, this work provides a basis for further developing practical and accurate pencil beam model for heavy ion cancer therapy.

Design of a NIM-based DAQ system

In order to satisfy the requirements of beam measurement in the heavy ion medical machine and other small nuclear physics experiments, we designed and built a nuclear instrumentation module-based data acquisition system. This is composed of a set of functional modules and a purpose-built bus. One of the modules operates as a master, collecting data from the other slave modules. It then sends the data to the back-end computer via Ethernet. In addition to the hardware, dedicated software has been designed and implemented. In this paper, we provide a detailed description of the architecture of the system, the data frame, and the software. The bus is the central part of the system. It can transmit data from the slave modules to the master at 33 MB/s. The frame used to transmit the data also ensures its integrity and monitors the hardware architecture. The client software is designed to process data in real time and store data on a hard disk for later analysis.