Medical Electron Linear Accelerators Research Articles

Technical Status and Development Trend of Medical Electron Linear Accelerators

More than 70% of tumor patients require radiotherapy. Medical electron linear accelerators are important high-end radiotherapy equipment for tumor radiotherapy. With the application of artificial intelligence technology in medical electron linear accelerator, radiotherapy has evolved from ordinary radiotherapy to today's intelligent radiotherapy. This study introduces the development history, working principles and system composition of medical electron linear accelerators. It outlines the key technologies for improving the performance of medical linear electron accelerators, including beam control, multi-leaf collimator, guiding technology and dose evaluation. It also looks forward to the development trend of major radiotherapy technologies, such as biological guided radiotherapy, FLASH radiotherapy and intelligent radiotherapy, which provides references for the development of medical electron linear accelerators.

Production Risk Analysis and Key Points for Field Inspection of Medical Electron Linear Accelerator

The medical electron linear accelerator（LINAC） has the characteristics of complex system structure, many core components and high precision control requirements, which puts forward higher requirements for product quality control and regulation. This study puts forward the main points of field inspection through the analysis of the technical characteristics and production risk of LINAC, combined with the requirements of the good manufacturing practice of medical devices. It has certain reference significance for quality management personnel and field inspectors.

Formulation of tissue maximum ratio for high energy photons using a medical electron linear accelerator

In Radiation Therapy efficiency and precision should be conserved so, there is a need to consider the parameters such as PDD and TMR. TMR is an important dosimetric function which can be measured experimentally and can be calculated from PDD by considering scatter factors. The purpose of this study was to compare and verify the accuracy of TMR data calculated using PDD with measured TMR data for 6 MV and 15 MV photon beams. The PDD values were measured at Source to Surface Distance, 100 cm for various radiation field sizes and depths. For the same field size, depth and energy, the TMR values were measured at Source to Axis Distance of 100 cm. The verification of the calculated TMR data was achieved by comparing it with the measured TMR data. The results had shown that; At the initial depths upto 7 cm, both the calculated and measured TMR were in good agreement, but the deviation increases as a function of depth, especially for the smaller field sizes. It can be concluded that; The calculated TMR values and RFA measured TMR data are having a good agreement and significant variations are indicated at increased depths of smaller field sizes.

Loss of NEIL3 activates radiotherapy resistance in the progression of prostate cancer.

Objective:To explore the genetic changes in the progression of castration-resistant prostate cancer (CRPC) and neuroendocrine prostate cancer (NEPC) and the reason why these cancers resist existing therapies.Methods:We employed our CRPC cell line microarray and other CRPC or NEPC datasets to screen the target gene NEIL3. Lentiviral transfection and RNA interference were used to construct overexpression and knockdown cell lines. Cell and animal models of radiotherapy were established by using a medical electron linear accelerator. Flow cytometry was used to detect apoptosis or cell cycle progression. Western blot and qPCR were used to detect changes in the protein and RNA levels.Results:TCGA and clinical patient datasets indicated that NEIL3 was downregulated in CRPC and NEPC cell lines, and NEIL3 was correlated with a high Gleason score but a good prognosis. Further functional studies demonstrated that NEIL3 had no effect on the proliferation and migration of PCa cells. However, cell and animal radiotherapy models revealed that NEIL3 could facilitate the radiotherapy sensitivity of PCa cells, while loss of NEIL3 activated radiotherapy resistance. Mechanistically, we found that NEIL3 negatively regulated the expression of ATR, and higher NEIL3 expression repressed the ATR/CHK1 pathway, thus regulating the cell cycle.Conclusions:We demonstrated that NEIL3 may serve as a diagnostic or therapeutic target for therapy-resistant patients.

Optimal Design of the Control System of Medical Electron Linear Accelerator Treatment Bed

Optimal Design of the Control System of Medical Electron Linear Accelerator Treatment Bed

Design of Uniformity Correction System for Medical Electron Linear Accelerator

Design of Uniformity Correction System for Medical Electron Linear Accelerator

Analysis of quality control test results of medical electron linear accelerators in Guangxi Province 2017—2019

Objective To understand the level of quality control in medical linear accelerator in Guangxi, and to provide technical support for the health administrative department to make related standards. Methods To select medical linear accelerators in Guangxi by random sampling method. Results A total of 118 accelerators were checked in 2017—2019, the initial inspection pass rates of medical linear accelerators were 56.8% and re-inspect pass rate were 96.6%. Conclusion The quality control level of the radiology institutions needs to be improved. The health administrative department should strengthen routine management, it is necessary to implement quality control in medical linear accelerator. 摘要： 目的 了解广西省医用电子直线加速器设备性能的质量控制水平, 为卫生行政部门研宄制定医用电子直线加 速器卫生标准和质量控制检测规范提供技术支持。 方法 采用随机抽样方法, 对广西省部分医用电子直线加速器进 行质控检测。 结果 2017—2019 年累计检测 118 台次加速器, 加速器质控检测(包括 X 射线和电子束)总初检合格率 为 56.8%, 总复检合格率为 96.6%; 二级、三级医院加速器质控检测初检合格率分别为 32.0%、62.2%, 差异有统计学意 义 ( P < 0.05), 初检合格率最低的指标是辐射剂量示值误差, 其次是辐射野均整度。 结论 广西省医用电子直线加速器 质量控制水平有待提高;卫生行政部门应进一步加强对加速器质控检测的监督, 定期开展加速器质控检测。

High-precision measurements of half‐lives for 69Ge, 73Se, 83Sr, 85mSr, and 63Zn radionuclides relevant to the astrophysical p-process via photoactivation at the Madison Accelerator Laboratory

The ground state half-lives of 69Ge, 73Se, 83Sr, 63Zn, and the half-life of the 1/2− isomer in 85Sr have been measured with high precision using the photoactivation technique at an unconventional bremsstrahlung facility that features a repurposed medical electron linear accelerator. The γ-ray activity was counted over about 6 half-lives with a high-purity germanium detector, enclosed into an ultra low-background lead shield. The measured half-lives are: T1/2(69Ge) = 38.82 ± 0.07 (stat) ± 0.06 (sys) h; T1/2(73Se) = 7.18 ± 0.02 (stat) ± 0.004 (sys) h; T1/2(83Sr) = 31.87 ± 1.16 (stat) ± 0.42 (sys) h; T1/2(85mSr) = 68.24 ± 0.84 (stat) ± 0.11 (sys) min; T1/2(63Zn) = 38.71 ± 0.25 (stat) ± 0.10 (sys) min. These high-precision half-life measurements will contribute to a more accurate determination of corresponding ground-state photoneutron reaction rates, which are part of a broader effort of constraining statistical nuclear models needed to calculate stellar nuclear reaction rates relevant for the astrophysical p-process nucleosynthesis.

The influence of shielding reinforcement in a vault with limited dimensions on the neutron dose equivalent in vicinity of medical electron linear accelerator.

BackgroundHigh energy electron linear accelerators (LINACs) producing photon beams with energies higher than 10 MeV are widely used in radiation therapy. In these beams, fast neutrons are generated, which results in undesired contamination of the therapeutic beam. In this study, measurements and Monte Carlo (MC) simulations were used to obtain neutron spectra and dose equivalents in vicinity of linear accelerator.Materials and methodsLINAC Siemens Oncor Expression in Osijek University Hospital is placed in vault that was previously used for 60Co machine. Then, the shielding of the vault was enhanced using lead and steel plates. Measurements of neutron dose equivalent around LINAC and the vault were done using CR-39 solid state nuclear track detectors. To compensate energy dependence of detectors, neutron energy spectra was calculated in measuring positions using MC simulations.ResultsThe vault is a source of photoneutrons, but a vast majority of neutrons originates from accelerator head. Neutron spectra obtained from MC simulations show significant changes between the measuring positions. Annual neutron dose equivalent per year was estimated to be less than 324 μSv in the measuring points outside of the vault.ConclusionsSince detectors used in this paper are very dependent on neutron energy, it is extremely important to know the neutron spectra in measuring points. Though, patient dosimetry should include neutrons, estimated annual neutron doses outside the vault were far below exposure limit of ionizing radiation for workers.

OA025] Response of ionization chambers in the presence of magnetic fields

Purpose The next generation of medical electron linear accelerators will integrate Magnetic Resonance Tomography (MRI). Therefore it will be possible to take direct images of the moving tumor during radiotherapy treatment. However serious consideration must be given to the strong magnetic field, which has an impact on the trajectories of the produced secondary electrons, because of the Lorentz force. This force affects both the dose distribution in water and the dose response of used detectors. For an accurate patient dosimetry these effects must be taken into account. Methods Monte Carlo methods correctly describe the radiation transport in different media, even in presence of magnetic fields and are therefore the gold standard for the evaluation of the impact of magnetic fields on clinical dosimetry. In this present study, the beam quality correction factors Kq and the relative response in magnetic fields of different ion chambers (PTW-31013, PTW-31021, EXRADIN-1ASL, NE2571) were investigated with Monte Carlo simulations, using the code EGSnrc. The chambers were modelled in detail according to the information given by the manufacturer and placed in a water phantom (30 × 30 × 30 cm3). The chambers were irradiated under reference conditions, following the recommendations of present dosimetry protocols, such as IAEA TRS-398: i.e. the field size at the phantom surface was 10 × 10cm2; the focus-surface-distance 100 cm and the depth of the chamber’s reference point was 10 cm. The source of the photons were several spectra of clinical medical accelerators applying nominal energies between 4 and 24 MV-X. The magnetic field was applied in different directions relative to the beam axis (z-direction) and the chamber’s symmetry axis and was varied between 0 and 3T. Results All chambers successfully passed the Fano test, the response of all chambers varied up to about 8% depending on the magnetic field strength and the field directions. Conclusions The response of the chambers with the magnetic fields, has a complex dependence on chamber radius, magnetic field strength, the orientation between radiation beams, chamber axis and magnetic field, and lastly the energy spectrum. Those variables consequently played a major role in the increase or decrease of correction factor, Kq.

医用电子直线加速器电子枪的典型故障与维护

医用电子直线加速器电子枪的典型故障与维护

Реконструкция действующего спектра тормозного излучения медицинских линейных ускорителей электронов по глубинным распределениям дозы в водном фантоме

Purpose: Development of the bremsstrahlung spectrum reconstruction method of medical electron linear accelerators (ELA) with different field sizes on the base of the deep dose distributions in a water phantom and determination of photon spectra for Varian Trilogy accelerator 6 MV. &#x0D; Material and methods: The proposed methodology is based on the use of dose kernels algorithm of point monoenergetic monodirectional source (pencil beam (PB)) for the deep dose distribution calculation, created different cross-section beams of in a water phantom, and experimental measurements of these distributions. For solving the inverse problem is applied Toolbox routines 'ptimtool knowing mathematical package MATLAB to solve.&#x0D; Results: Bremsstrahlung energy spectrum generated medical accelerator Varian Triology with different sizes of square fields from 3×3 up to 40×40 cm and average energy photons, depending on the size of the fields were received. Dose kernels for a set of defined energies PB were calculated. Depth dose distribution in a water phantom, calculated using the obtained spectra and dose kernels agree well with measurement dose distributions. &#x0D; Conclusion: The proposed technique reconstruction of bremsstrahlung spectrum of electron linear accelerator is adequate. Average energy spectra of bremsstrahlung photons for Varian Trilogy Accelerator in regime 6 MV varies from 1.71 to 1.43 MeV depending on the field size.

Monte Carlo simulation of a medical linear accelerator for filtered and FFF systems

In order to simulate radiation transport, various algorithms, codes, and programs have been developed. In this study Monte Carlo N-particle code is used to simulate a medical electron linear accelerator gantry for research purposes. Detailed geometry of the LINAC head and water phantom are modeled and simulated for calculations. Analyses are made for filtered and flattening filter-free (FFF) systems. Percent depth dose and dose profile measurements are calculated with Monte Carlo simulations and compared with experimental and theoretical values for quality assurance of the model. Flux, dose, and spectrum analyses are performed for filtered and FFF systems separately. In this study, it was aimed to run the linear accelerator in a computer environment for different purposes, and this aim was achieved.

Analysis of neutron flux around medical electron linear accelerator placed in the room reconstructed after decommissioning of 60Co units using monte carlo simulation

Introduction Increased neutron flux around high energy medical electron linear accelerators placed in the rooms reconstructed after decommissioning of 60Co unit has been reported before. Purpose The main limitation of the reported room was the space. Extremely short maze was used and walls were strengthened by lead. In this study, Monte Carlo simulation is used to analyze the reasons for increased neutron flux. Materials and methods A model of 18 MV photon beam linear accelerator with the room was built using the MCNP611 code. Points at several locations and different accelerator orientations were used to evaluate the neutron and photon ambient dose equivalent to which medical personnel could be exposed. Also, the different maze lengths was used in simulation to evaluate its significance for neutron protection. Then neutron sources, spectra, flux and dose equivalent were analyzed. Results Calculated neutron dose equivalent was not negligible from the aspect of personal dosimetry with almost 2 mSv/year per person in area occupied by staff (conservative estimation). The wall enhancement by lead was new source of photoneutrons. Simulated longer mazes significantly decreased neutron flux near the room door. Both, the lead enhancements and different lengths of mazes changed neutron spectra significantly in chosen points. Conclusion The study confirms that shielding from neutron radiation should be thoroughly analyzed if high energy linear accelerators are put in the room where the space constraints exist. The lead enhancement of walls and short mazes should be avoided. If this is not possible, lower energy photon beams should be used.

Sampling and inspection of dose and mechanical properties of medical linear accelerators in grass-roots radiotherapy units in Sichuan Province, China

Objective To investigate the dose and mechanical properties of medical electron linear accelerators in grass-roots radiotherapy units in Sichuan Province, China via sampling and inspection. Methods A total of eight radiotherapy units in Sichuan Province were selected by sampling, and the tests were performed for the dose and mechanical properties of the medical electron linear accelerators in use. Among these accelerators, there were 5 imported accelerators and 3 domestic accelerators. The test items and methods were determined according to the requirements in GB15213-94. Results Among the 14 test items, the items related to the flatness, symmetry, and overlap of radiation field. The other tests of dose accuracy and mechanical precision achieved good results. Conclusions There is a need to strengthen the daily quality control work for dose and mechanical accuracy of medical electron linear accelerators in grass-roots radiotherapy units in Sichuan Province and perfect the allocation of professional equipment and personnel and training of related personnel. With the support of Sichuan Radiotherapy Quality Control Center, quality control supervision and guidance should cover the whole province. Key words: Accelerator; Radiotherapy dose; Mechanics mechanism; Quality control

Prevalence study of tumor radiotherapy in the Xinjiang Uygur Autonomous Region

Objective To investigate the development status of tumor radiotherapy in the Xinjiang Uygur Autonomous Region. Methods A questionnaire survey we used last time was conducted by letter, Email, telephone or fax to investigate all the medical institutions in the Xinjiang Uygur Autonomous Region for researching the current status of radiotherapy academic settings, human resources, allocation of radiotherapy facilities and standardization of medical practices. Results Up to the end of January 2015, there were 30 medical electron linear accelerators, 21 simulated locators, 10 breach-loading brachytherapy machines, 31 treatment planning systems and 5 γ or X knives in Xinjiang. Radiotherapy was carried out in 20 medical institutions, including 14 three-dimensional conformal radiotherapy and 9 intensity modulated radiation therapy, 8 breach-loading brachytherapy, 3 stereotactic radiotherapy, and 2 volumetric modulated arc therapy. There were 280 radiation personnel (except nurses), including 159 radiation oncologists, 40 radiotherapy physicists and 81 radiotherapy technologists. There were 1167 hospital beds and 855 cancer patients received radiotherapy on average every day. Conclusions Although radiation personnel has increased, radiotherapy facilities have been improved, hospital beds and patients received radiotherapy also have become more, the improvements are needed for cause of imbalance in precise radiation therapy development. Key words: Neoplasms/RT; Data collection

Determination of gamma-ray energies and half lives of platinum radio-isotopes by photon activation using a medical electron linear accelerator: a feasibility study

In this study, we attempted to determine the gamma-ray energies and half lives of platinum radio-isotopes produced by photo-neutron reactions. Platinum was irradiated with bremsstrahlung of a clinical electron linear accelerator (c-linac). To determine characteristic gamma-ray energies and half lives of platinum radio-isotopes high resolution spectroscopy was applied. Gamma energies and half lives were measured and compared with reliable literature values for 191Pt, 195mPt and 197Pt.

Status of medical electron linear accelerator for cancer treatment in Iran

Status of medical electron linear accelerator for cancer treatment in Iran

SU‐E‐T‐560: Monte Carlo Simulation of the Neutron Radiation Field Around a Medical 18 MV Linac

Purpose:Today the majority of radiation therapy treatments are performed at medical electron linear accelerators (linacs). The accelerated electrons are used for the generation of bremsstrahlung photons. The use of higher electron respectively photon energies has some advantages over lower energies such as the longer dose build‐up. However photons with energies higher than ∼7 MeV can additionally to the interaction with bound electrons undergo inelastic reactions with nuclei. These photonuclear reactions lead to the emission of fast neutrons which contaminate the primary photon field. The neutrons might penetrate through the collimators and deliver out‐of‐field dose to the patient. Furthermore the materials inside the linac head as well as the air inside the treatment room get activated which might deliver dose to the medical employees even when the linac is not in operation. A detailed knowledge of these effects is essential for adequate radiation protection of the employees and an optimal patient treatment.Methods:It is a common method to study the radiation fields of such linacs by means of Monte Carlo simulations. For the investigation of the effects caused by photonuclear reactions a typical linac in high energy mode (Varian Clinac 18 MV‐X) as well as the surrounding bunker were modelled and simulated using the Monte Carlo code FLUKA which includes extensive nuclear reaction and neutron transport models additional to electron‐photon transport as well as capabilities for a detailed study of effective dose distributions and activation yields.Results:Neutron spectra as well as neutron effective dose distributions within the bunker were obtained, reaching up to some mSv/Gy in the patient's plane. The results are normalized per Gy in the depth dose maximum at 10×10 cm2 field size. Therefore an absolute interpretation is possible.Conclusion:The obtained data gives a better understanding of the photonuclear reaction caused effects.

Performance characteristics of mobile MOSFET dosimeter for kilovoltage X-rays used in image guided radiotherapy

The main objective of this study was to investigate the characteristics of metal oxide semiconductor field effect transistor (MOSFET) dosimeter for kilovoltage (kV) X-ray beams in order to perform the in vivo dosimetry during image guidance in radiotherapy. The performance characteristics of high sensitivity MOSFET dosimeters were investigated for 80, 90, 100, 110, 120, and 125 kV X-ray beams used for imaging in radiotherapy. This study was performed using Clinac 2100 C/D medical electron linear accelerator with on-board imaging and kV cone beam computed tomography system. The characteristics studied in this work include energy dependence, angular dependence, and linearity. The X-ray beam outputs were measured as per American Association of Physicists in Medicine (AAPM) TG 61 recommendations using PTW parallel plate (PP) ionization chamber, which was calibrated in terms of air kerma (Nk) by the National Standard Laboratory. The MOSFET dosimeters were calibrated against the PP ionization chamber for all the kV X-ray beams and the calibration coefficient was found to be 0.11 cGy/mV with a standard deviation of about ±1%. The response of MOSFET was found to be energy independent for the kV X-ray energies used in this study. The response of the MOSFET dosimeter was also found independent of angle of incidence for the gantry angles in the range of 0° to 360° in-air as well as at 3 cm depth in tissue equivalent phantom.