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@#Multi-leaf collimators are devices to block rays from medical linear accelerators, which directly affect doses to targets and organs at risk by adjusting field shape and dose distribution in radiation therapy. As multi-leaf collimators are diversified in structure, there has been growing research on dosimetric comparison of various multi-leaf collimators. In this paper, we introduced the classifications of multi-leaf collimators according to their basic components, as well as the hardware structure and design features of the products of main accelerator manufacturers, including Varian’s Millennium MLC, HD120 MLC, and Halcyon, Elekta’s MLCi/i2 and Agility, and Accuray’s InCise 2 MLC and TomoTherapy. In terms of clinical application evaluation, focusing on radiotherapy plans for nasopharyngeal carcinoma, we reviewed comparative studies on the dosimetry performance of multi-leaf collimators and the effects of relevant parameters on dose distribution. We hope this review on the design and application evaluation of multi-leaf collimators can provide a reference for more innovative design and accelerator selection and parameter setting in clinical individualized treatment.
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@#<b>Objective</b> To investigate the current situation of quality control in medical linear accelerators in Hebei Province, China. <b>Methods</b> The main performance indices of some medical linear accelerators in Hebei Province, 2019—2021 were tested according to the current relevant effective standards GB 15213—2016 <i>Medical Electron Accelerators-Functional Performance Characteristics and Test Methods</i> and WS 674—2020 <i>Specification for Testing of Quality Control in Medical Linear Accelerator</i>. <b>Results</b> A total of 175 medical linear accelerators were tested from 2019 to 2021, and the annual pass rates were 72.4% in 2019, 75.9% in 2020, and 79.4% in 2021. The overall pass rate of initial inspection was 76.0%, and the pass rate of reinspection was 100.0%. The index with the lowest pass rate in the initial inspection was square X radiation field uniformity, followed by dose deviation and square X radiation field symmetry. <b>Conclusion</b> Medical institutions should strengthen quality control management, conduct regular testing of medical linear accelerators, and timely correct dose deviation, so as to ensure the treatment effect of patients.
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@#Abstract: Objective To evaluate the key quality control and protective performance test of Halcyon medical linear accelerator. Methods WS 674-2020Specification for Testing of Quality Control in Medical Linear Accelerator（ According to the hereinafter WS 674-2020） ， referred to and the manufacturer´s manual the performance of the first Halcyon medical linear accelerator in Results ， ， Hunan Province was tested. The results showed that all ten indicators of the accelerator including dose deviation ， ， （ ， ， ， - repeatability linearity daily stability and symmetry the results were 0.10% 0.03% 0.04% 0.50% and 100.50% 100.80% ）， - - respectively met the requirements of WS 674 2020. The results of manufacturer quality control indicators such as dose rate ， ， stability in beam gantry rotation isocenter and mechanical position accuracy megavolt image parameters and cone beam computer tomography image parameters met the requirements of the manufacturer´s regulations. Due to the special structure and ， - ： function of the accelerator it is difficult to detect the parameter required by WS 674 2020 as below the radiation leakage - ， ， ， ， outside the M zone the uniformity the indicators related to the light field the offset of the radiation beam axis the zero scale Conclusion - position of the rotating motion scale and others. It is difficult to carry out complete testing according to WS 6742020 for Halcyon medical linear accelerator and it is urgent for the state to issue relevant testing standards to standardize and strengthen the quality control testing of various accelerators.
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Objective To analyze the deployment of medical linear accelerators at 26 hospitals in China, and suggest on the deployment of such accelerators. Methods From June 2017 to November 2018, a total of 26 hospitals were surveyed by stratified random sampling. Descriptive analysis of the deployment and staffing of medical linear accelerators at 26 hospitals, and the deployment appropriateness of the medical linear accelerator was evaluated using the TOPSIS method. Results The number of medical linear accelerators in different types of hospitals was significantly different. The proportion of imported equipment at tertiary hospitals was 80% (12/15) and the proportion of imported equipment at secondary hospitals was 9% (1/11). The professional staff was deployed basically reasonable, and there was a shortage of physicists at some hospitals. The suitability of medical linear accelerators at tertiary hospitals was better than that of secondary hospitals, 80% (12/15) of tertiary hospitals received " good" and above ratings, while 91% (10/11) of the secondary hospitals received " general" and below ratings. Conclusions Hospitals should carry out the allocation of large-scale medical equipment based on their own situations and requirements. Efforts should be paid on training of professional technicians for radiotherapy. It is important to strengthen the management of planning, access and supervision of medical equipment.
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Objective: To monitor the protecting effect of lead apron of accelerator staff against radiation in treatment room (dose and damage of residual radiation). Methods: In the protection experiment about lead apron, thermoluminescence dosimeter (TLD) was applied to monitor the dose corresponding various point of inside and outside of lead apron. Under the same condition of radiation, the first test aimed at un-metal dressing (the work pants without metal zipper and metal button) and the second test aimed at jeans (those with one metal zipper and one metal button). At front of the apron, there were 3 points (Left, Middle and Right) of inside and outside were monitored, respectively. And at behind, the body without shelter from apron were tested at 3 points of wearing, and then the average effective dosage were calculated. Results: ①The averagely effective dosage of inside of lead apron was significantly higher than that of outside at the first test (t=0.0002, P<0.01). And the average effective dosage of inside of lead apron was still significantly higher than that of outside at the second test (t=0.0158, P<0.05).②The averagely effective dosage of various points behind body of second test was significantly higher than that of the first test (t=0.0005, P<0.01). ③The differences of averagely effective dosages of inside and outside of lead apron between the second test and the first test were no significantly (t=0.0991, t=0.0537, P>0.05), respectively. Conclusion: Only using lead apron can't achieve prospective protection effect and it even can increase the radiation dosage for accelerator staffs, especially for woman of childbearing age. Hospital should strictly implement relevant stipulations of ICRP, IBSS and CBSS and staff should not wear any accessory with metal material. Besides, the relevant method that can reduce radiation dosage and protect health should be written in operation instruction or guidelines.
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Objective: To evaluate the performance of morning check device by comparing the dosimetric parameters of medical linear accelerators measured by radiation dosimeter, 3D water phantom and morning check device. Methods:The dosimetric parameters of the linear accelerator were measured and adjusted by using dosimeter and 3D water phantom so as firstly to ensure the stability of the beam system of accelerators. After the baseline was established, the dosimeter, 3D water phantom and morning check device were applied to measure central axis output dosage, and flatness and symmetry of the field, respectively. And then the data were collected and differences of the results were compared. And compared the results of morning check device with the baseline to evaluate performance of morning check device. Results: The results measured of morning check device were close to those measured by 3D water phantom. The maximum deviations of central axis output (CAX), flatness along LR direction, flatness along GT direction, symmetry along LR direction and symmetry along GT direction measured by morning check device were 0.87%, 0.96%, 0.48%, 0.40% and 0.59%, respectively, which were in the range of 3% and could meet the requirement of AAPM TG-142 report. Conclusion: It shows that the morning check device is effective and feasible to be used for daily quality control of linear accelerators, and it can be used as tool of daily quality control.
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Objective:To explore the configuration of air conditioner and ventilating system of large medical equipment in comprehensive hospital so as to meet the normal operation of various large medical equipment of hospital.Methods: Facing to the characteristics, that the requirements of large medical equipment on air conditioner and ventilating system were higher than that of common equipment and the configuration requirements of different large medical equipment on air conditioner and ventilating system were different, the allocation according to the demands was adopted.Results:Depended on the equipment parameter and requirement of actual operation of linear acceleration, magnetic resonance imaging (MRI), computed tomography (CT) and the machine room of digital subtraction angiography (DSA) in the items of new medical technique building of hospital to design the configuration plan of air conditioner and ventilating system of large medical equipment so as to ensure their normal operation. Conclusion: In the planning programming and construction management of air conditioner and ventilating system of large medical equipment, the different characteristics of them should be considered so as to establish better basis for installation, debugging and operation of equipment in later period. At the same time, these can provide better medical environment for patients and medical staff.
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Objective:To analyze the attenuation of immobilization baseplate of carbon fiber for ray and the change of dose verification results for enhanced radiation field of MatriXX. And to primarily research the influence of this immobilization baseplate for the dose distribution of radiation field of radiotherapy.Methods: 20 patients with cervical cancer were enrolled in the research. The angle of gantry was 180°in the enhanced plan of immobilization field, and the corresponding verification plans were designed. When the verification plan was implemented on the Varian Clinac iX of accelerator, the two-dimensional ionization chamber array (MatriXX) was used to measure dose distributions of the plan. The immobilization baseplate of carbon fiber (ORFIT AIO) was used in the research. The situations of no baseplate (A group), one baseplate (B group), two baseplates (C group)and three baseplates (D group)between the handpiece of accelerator and Matri XX were researched, respectively. The data of the 4 groups were obtained by using software (OminiPro I'mRT), and the largest dose point and passing rate of Gamma in plane of radiation field were counted and analyzed.Results: Compared with A group, the average attenuation factors for ray on the largest dose point of B, C and D group in the plane of radiation field were (1.73±0.11)％, (3.44±0.36)％, and (5.48±0.44)％, respectively. The passing rates of Gamma in the 4 groups were (94.87±2.31)％, (99.18±0.61)％, (99.79±0.27)％ and (96.24±1.99)％, respectively. And the differences of passing rate between each group and A group were statistical significance (t=9.788,t=9.261,t=2.256,P<0.05).Conclusion:The immobilization baseplate of carbon fiber has influence for the attenuation of high-energy X-rays and it can affect the dose distribution of radiation field which has passed baseplate in some degrees. And when physicists calculates the dose, they should consider the effect of immobilization baseplate of carbon fiber for dose distribution of radiation field.
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Objective The ionization chamber of ELEKTA medical linear accelerator monitoring is open to environmental factors such as temperature, air pressure, and humidity that may affect the stability of absolute dose output .The article aimed to ana-lyze the morning and evening absolute dose output stability at different energies of ELEKTA SYNERGY medical linear accelerator . Methods The absolute doses at different energies of medical linear accelerators were calibrated according to the IAEA TRS -277 re-port, and WI3 type solid water was used to perform repeated measurements in the morning and in the evening for 52 consecutive days under the same measurement conditions , during which a water tank measurement was conducted at random intervals per week to verify the accuracy of WI3 solid water measurements. Results The maximum deviation of WI3 solids water and tank measurement at all en -ergies was 0.5％ and the maximum deviations of daily energy stability at different energies were : -2.0％ (6MV), 1.9％ (15MV), 1.8％ (6MeV), -2.4％ (8MeV), -2.3％ (10MeV), -2.0％ (12MeV), 2.1％ (15MeV).The differences of 6MV, 15MV, 8MeV, and 10MeV energies in morning and evening paired t tests were statistically significant (P<0.05) without clinical significance, while no statistic significance was found in the differences of 6MeV, 12MeV, and 15MeV energies ( P >0.05). Conclusion Elekta Synergy medical linear accelerator shows excellent stability in absolute dose output.
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Objective To provide a solution to improve the radiation shielding for medical accelerator room with clay bricks.Methods According to the basic shielding equations provided by the relevant national standards and international reports,equations for shielding reconstruction calculation were derived to calculate the required thickness of clay bricks wall,which reached the reference dose rate control level.The dose rates at reference points after reconstruction were also estimated based on the measured dose rates at reference points before reconstruction of accelerator room,calculated distance correction factors and transmission factors of added clay bricks wall.Results The measured dose rates satisfied the requirement of reference dose rate control level.The estimated dose rates were slightly higher than the measured values.Conclusion The radiation shielding requirement of medical accelerator room is fulfilled with the presented shielding reconstruction method by building clay bricks wall,measured dose rates could be conservatively predicted with the dose rates calculated by derived equations.
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Objective:To verify the dose of static and dynamic intensity modulated radiotherapy (IMRT) through 2-dimension ionization chamber matrix after external electrically-driven multi-leaf collimator (MLC) was installed in KB1800 medical linear accelerator. Methods: 40 patients who need receive IMRT were divided into static IMRT group (20cases) and dynamic IMRT group (20cases) as the random number table. The ionization chamber was applied to implement scale dose, and solid water and 2-D ionization chamber matrix was applied to verify dose. Besides, the feasibility of static and dynamic IMRT were compared and researched.Results: The verification results of plane dosage of static IMRT plan and dynamic IMRT plan showed that the passing rates both of them were above 90.0%, and the verification of intensity modulated dosimetry of medical electric linear accelerator KB1800 with external electric MLC was consistent with standard.Conclusion:After the external electrically-driven MLC is installed on the accelerator, the dosage of IMRT can achieve the verification standard, and it can be applied to clinical treatment and can satisfy the requirement of clinical radiotherapy.
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Objective To provide a solution to improve the radiation shielding for medical accelerator room with clay bricks.Methods According to the basic shielding equations provided by the relevant national standards and international reports,equations for shielding reconstruction calculation were derived to calculate the required thickness of clay bricks wall,which reached the reference dose rate control level.The dose rates at reference points after reconstruction were also estimated based on the measured dose rates at reference points before reconstruction of accelerator room,calculated distance correction factors and transmission factors of added clay bricks wall.Results The measured dose rates satisfied the requirement of reference dose rate control level.The estimated dose rates were slightly higher than the measured values.Conclusion The radiation shielding requirement of medical accelerator room is fulfilled with the presented shielding reconstruction method by building clay bricks wall,measured dose rates could be conservatively predicted with the dose rates calculated by derived equations.
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Objective:To analyze and compare the dose monitoring and control systems of two types of medical linear accelerator systematically from the view of mechanical and electrical engineering, and establish the method of the quality assurance of the dosimetry system and the solution in the routine maintenance.Methods: To systematically compare and analyze the system of dose monitoring and control for two types of linear accelerators (Precise Elekta and C-series of Varian Medical Systems) from twofold aspects that included machine physics and electric engineering of medical linear accelerators.Results:The monitoring system that took ionization chamber as center was established between connotation of machine physics and concrete realization of electromechanical engineering, and explained the difference and similarity between open type and sealed type of ionization chamber, and the theory that Precise series needn't be serviced by PFN.Conclusion: Based on the analysis of ionization chambers structure of medical linear accelerators on the principle of quality assurance system, proposed dosimetric testing and adjustment method, and provide reference for the establishment of quality assurance system and technical procedures of the maintenance engineering.
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Objective To discuss the detail design of medical linear accelerator room to optimize the layout of radiation shield.Methods According to the optimization principle for medical exposure protection and national radiation protection related documents,the influence of detail design on room quality was analyzed.Optimization design was executed from theaspects of spatial layout,protection,shielding wall,decorating materials,labyrinth,control cabin,protective door,occupancy factor,purification ventilation,tennperature humidity control and etc.Results The design and layout of the roomwere optimized to eliminate hidden risksand reduce the design flaws to prevent adverse consequences due to design errors.Conclusion Detail design contributes to stable operation,enhanced quality and efficiency of medical linear accelerator room.
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Objective:To discuss the influence factor of induced radioactivity radiation field of high-energy medical linear accelerator and its safeguard measures.Methods: The simulation test was applied to research the radiation level of the induced radioactivity for high-energy medical linear accelerator; and to research the influences of different factors, such as radiation dose, range of exposure and site of exposure and so on, on the changes of radiation field.Results: The research showed that the high-energy X-ray radiation field strength would increase with the increasing of radiation dose, while reduce with the increasing of radiation time; and the obviously reductive trend appeared after radiated 5minutes. Meanwhile, radiation intensity would reduce with the increasing of irradiated area, but the reductive trend was not totally proportional in accordance with the increasing of irradiated area. Additionally, the head part of linear accelerator could produce the most intensity of radiation field on exposure site, and the farther away the head part of linear accelerator, the intensity the lower; and the reductive trend would increase when the distance exceeded 150cm.Conclusion: The induced radioactive radiation field intensity of high-energy medical linear accelerator has some characteristics of change. The effective safeguard measures were to reduce the work time in equipment room, reduce the adjustment time of patient position and choose reasonable exposure site and dose, and all of these measures can reduce the radiation injury.
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Objective:To verify the dose of static and dynamic intensity modulated radiotherapy (IMRT) through 2-dimension ionization chamber matrix after external electrically-driven multi-leaf collimator (MLC) was installed in KB1800 medical linear accelerator. Methods: 40 patients who need receive IMRT were divided into static IMRT group (20cases) and dynamic IMRT group (20cases) as the random number table. The ionization chamber was applied to implement scale dose, and solid water and 2-D ionization chamber matrix was applied to verify dose. Besides, the feasibility of static and dynamic IMRT were compared and researched.Results: The verification results of plane dosage of static IMRT plan and dynamic IMRT plan showed that the passing rates both of them were above 90.0%, and the verification of intensity modulated dosimetry of medical electric linear accelerator KB1800 with external electric MLC was consistent with standard.Conclusion:After the external electrically-driven MLC is installed on the accelerator, the dosage of IMRT can achieve the verification standard, and it can be applied to clinical treatment and can satisfy the requirement of clinical radiotherapy.
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Objective:Through getting acknowledge of the High-voltage of medical linear accelerator, it makes it possible for the relative medical workers to do a quick reaction to the repairmen and maintenance to the accelerator, and to maintain the machine to a good performance efficiently. While through understanding the application situation and development of accelerator, we could do a better choice at the terms of choosing an accelerator for hospital which meet the basic requirements and accuracy.Methods: Using the block diagram to introduce the main part of High-voltage of medical linear accelerator, and especially introduce the charging pinciple of charging transformer and the charge and discharge of PFN. The accelerator plays a vital fuction at radiation therapy, and we introduce the accelerator application in various fields and the development situation of technology application.Results: It’s significant to know the working principle of High- voltage as it’s helpful to ensure whether the machine works normal or not and to diagnose faults in it.Conclusion: In addition, through understanding the application situation and the development of accelerator, we could choose an appropriate accelerator for our hospital.
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Objective To investigate the impact of gantry angles on the position accuracy of buildin multi-leaf collimator (MLC) during static (step & shoot) intensity modulated radiotherapy (IMRT).Methods The position accuracy of MillenniumTM 60 pairs multi-leaf collimator (MLC) in Varian 23EX medical linear accelerator during 10 fractions of treatments with static intensity modulated radiotherapy (IMRT) was retrospectively analyzed by resolving dynamic therapy log files and MLC planning files.The single leaf position deviation and gap deviation of each MLC pairs were compared between expected values and actual outcomes.The impact of gantry angle on MLC position accuracy was also investigated with paired t-test between vertical and horizontal beams.Results All the MLC position deviations ranged within ± 1.0 mm,while the gap deviations were at the range of ± 1.5 mm.The statistical standard deviation of MLC position deviations among fractions was less than 0.06 mm.After all the 60 pairs of MLC leaves were taken into account,the M LC position deviation in the field of 103° was smaller than in the field of 0° (t =58.74,P ＜ 0.01),but there was no significant difference between 257° and 0°,while only the moving leaves were put into consideration,the MLC position deviation in the field of 103° was still smaller than in the field of 0°,but the MLC position deviation in the field of 257° was slightly higher than in thefield of 0° (t =41.95、-4.47,P ＜ 0.01).Conclusions The MillenniumTM 60 pairs MLC in Varian 23EX medical linear accelerator meets the mechanical quality assurance requirement during static IMRT treatments.The MLC positioning showed stable repeatability among treatment fractions.Although the MLC position accuracy is slightly affected by gravity from different gantry angles,but still meets the mechanical QA requirements for medical linear accelerator.This dynamic analysis method is expected to be a novel strategy which may improve the existing QA protocols.
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Objective To study the calculational method for the radiotherapy facilities of the medical linear accelerator' s useful beam towars its maze.Methods The shielding calculation was made under the relevant national standards for a radiotherapy treatment room and compared with the test results.Results The dose rates at the maze entrance as calculated and measured were 89 and 86 μSv/h inside the maze door,as well as 5.7 and 6.2 μSv/h outside the maze door,respectively.The calculated results were consistent with measured results.Conclusions By comparison of calculated results with measured results,the accuracy of the theoretical calculation method could be verified.