Medical Linear Electron Accelerator Research Articles

Оценка функционирования дозиметрического оборудования при проведении измерений в полях импульсного микросекундного фотонного излучения с известными характеристиками

This paper continues the series of articles [1,2,3] devoted to the determination of the main dosimetric characteristics of the fields of high-energy pulsed microsecond photon radiation generated by medical linear electron accelerator (LINAC for short) and assessment of the possibility of using LINAC as a source of reference radiation field for calibration of dosimetric equipment. This publication presents the results of evaluation of the portable dosimeter DKSAT1123 and detection unit BDKG-206 when measuring in such fields under different modes of LINAC operation. The possibility of this dosimetric equipment operation in the fields was assessed by comparing dosimeter readings with reference values of dosimetric characteristics of these fields, namely: average ambient dose equivalent rate H*(10), measured with the help of high-precision reference dosimeter DKS-AT5350. It was found that the deviation of H*(10) measurements conducted with the help of the DKS‑AT1123 and BDKG-206 from the reference values strongly depends on the radiation properties, namely the H*(10) value in the pulse. It is shown that at the H*(10) value in the pulse less than 0,2 mSv/s the deviation does not exceed 10%, at the H*(10) value in the pulse 0,2–0,4 mSv/s the deviation does not exceed 33%, and at the H*(10) value in the pulse more than 0,5 mSv/s the deviation can reach 72%.

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.

Оценка характеристик полей фотонного излучения медицинских линейных ускорителей электронов различных производителей

The article presents an assessment of the characteristics of pulsed photon radiation fields generated by medical linear electron accelerators (or CLINAC for short), namely: Varian Clinac iX, Elekta Infinity, Varian VitalBeam. Their technical characteristics, namely: average radiation energy, pulse duration and repetition rate, ambient dose equivalent rate in a single pulse are studied from the point of view of using a CLINAC as a source of pulsed photon radiation field suitable for calibration of dosimetric equipment. The average photon radiation energy is calculated using Monte Carlo modeling. Measurement of the ambient dose equivalent rate generated by the CLINAC at a given point is performed by the reference dosimeter DKS-AT5350/1. Determination of single pulse duration and pulse repetition rate is performed by direct measurements using the pulsed photon radiation detection unit BDKG-206.

Влияние свинцового фильтра на среднюю энергию фотонного излучения медицинского линейного ускорителя электронов

The article considers the change in the average energy of photon radiation with the upper limit of the spectrum of 6 MeV, generated by a medical linear electron accelerator (or LINAC for short), when radiation passes through a lead filter of various thicknesses. The calculation of the spectrum and average energy of photon radiation is carried out using Monte Carlo modelling. Additionally, the coefficients of attenuation of photon radiation by a lead filter are calculated. Particular attention is paid to the influence of the filter on the shape of the spectrum. The validation of the calculation is determined by comparing the model and experimentally obtained attenuation coefficients for kerma.

Hardware implementation of dynamic radiation therapy verification

The effectiveness of the use of modern technologies and methods of radiation treatment depends on the means of quality control of the operational parameters of the radiotherapy equipment. The development of technical means for verification of the radiation therapy plan, allowing accurate assessment of the three-dimensional dose distribution in the target, is a priority task when introducing innovative methods of radiation treatment. The aim of the work is to develop tools for assessing the three-dimensional dose distribution of radiation therapy plans with intensity modulation using the magnitude of the absolute radiation dose. The authors analyzed the existing technical means and methods for verifying radiation therapy plans on medical linear electron accelerators, and also identified their shortcomings. It is shown that these techniques for verifying the three-dimensional dose distribution do not give an accurate idea of the absolute values of the radiation dose in the target. A system and a method are proposed that allows improving the accuracy of the verification of the radiation therapy plan by using the obtained cross-calibration coefficient determined taking into account the value of the radiation output of the medical linear accelerator immediately at the time of the implementation of both this procedure and the radiation therapy session, as well as a method for verifying the plan radiation therapy with their use.

Тhe effect of cancer patients’ positioning accuracy during radiation therapy sessions using medical linear electron accelerators on the parameters of their individual 3D dose distribution

Due to the rapid development and further improvement of radiation treatment technologies oncologists have an opportunity to precisely deliver individual dose distributions to the tumor, minimizing the doses obtained by critical organs and healthy structures. For the correct and successful application of these complex methods of radiation therapy, it was necessary to enforce the requirements for the technical and dosimetric parameters of the radiotherapy equipment. The purpose of the research is to determine the magnitude of the possible error for patients’ positioning during their radiotherapy treatments using medical linear accelerators by modeling the impact of the patient’s body on the treatment couch. To determine the values of a possible error, the authors have considered the design and characteristics of a typical treatment couch, developed a model of the “average” patient’s body (phantom), which allowed changing the load to the treatment couch with a step of 1 kg. The position parameters of treatment couches were determined for the main types of localization of radiation therapy for malignant tumors: head and neck tumors, breast tumors and pelvic tumors. Numerical values of the treatment coach deviations from prescribed horizontal position were experimentally established for a load from 40 to 180 kg for a treatment couch used at the N.N. Alexandrov National Cancer Centre of Belarus. Based on the obtained experimental data, the necessity to correct the patient's treatment conditions at the stage of treatment planning were confirmed in order to ensure the delivery accuracy of individual dose distributions as required by the radiation therapy protocols. Authors stated that an analysis of the dependence of the deviations in the dose delivered to the patients on the deviation of the radiotherapy table from its horizontal position should be carried out for each radiotherapy table used in clinical practice. The development and implementation of a mechanism that will allow considering this information when choosing the parameters of the patient’s treatment session and prescribing the dose for any localization of malignant neoplasms is needed.

Влияние малых доз гамма-излучения на оптические свойства наноструктурированного кремния, полученного методом металл-стимулированного химического травления in situ

Влияние малых доз гамма-излучения на оптические свойства наноструктурированного кремния, полученного методом металл-стимулированного химического травления in situ

Effects of Ionizing Radiation Detector Characteristics on the Results of Measurements of Percent Depth Doses in Small Photon Fields

Studies of the dosimetric parameters of small fields of ionizing radiation are extremely important in current clinical dosimetry. This article considers analysis of plots of percent depth dose in small photon fields obtained using an Elekta Synergy medical linear electron accelerator with energies of 6 and 10 MeV using ionization chambers with different active volumes and a semiconductor detector. Comparative data for the following parameters are presented: depth of maximum dose, surface dose, dose at a depth of 10 cm, and various other aspects of the plots. These data were found to depend on the type of detector used in identical measurement conditions. The main features of the detection of dose distributions by different detectors are noted and conclusions are drawn regarding the advantages of using detectors with the smallest available active volumes in clinical dosimetry.

Determination of Effective Spectrum of Medical Linear Electron Accelerators from Depth Dose Distributions

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Challenges in X-Ray Medical Diagnosis

This article analyzes current challenges in medical X-ray diagnosis. The design of a tunnel-type ionization chamber for recording dose and dose power over a wide range of bremsstrahlung radiation energies is discussed. We address questions related to the standardization of apparatus and the creation of a universal digital platform for X-ray radiotherapy instruments as the basis for building state-of-the-art, productive, safe, and reliable radiotherapy instruments with different operating modes in terms of power supply voltage and power, from kilowatts to tens of kilowatts. The article also considers the state of X-ray diagnosis in general and the quality of X-ray apparatus; the challenge of measuring technogenic radiation doses to patients; the use of digital technologies providing digital images of quality no less than and even greater than that of film-based images combined with significant reductions in effective doses during investigations, and the advantages of computer processing; the treatment of nosological groups of diseases by radiotherapy; the needs for radiotherapy systems based on medical linear electron accelerators; radiation safety for staff and the population; small-scale, mobile devices for X-ray investigations in patients; and legal and technical aspects. A special program for assessing the detective quantum efficiency of dynamic digital X-ray image detectors is proposed.

Calculation of X-Ray Protection for Medical Linear Electron Accelerators with Energy Higher than 10 MeV

In this article we analyze the process of calculation of combined radiation protection of medical linear acceler� ators of electrons with Xray energy above 10 MeV. Aspects of radiation protection calculation are now wide� ly discussed in the context of therapy of cancer patients. Highenergy accelerators are often used in radiation ther� apy departments. Accommodation of highenergy accel� erators to radiation therapy departments is not a trivial problem. In practice, the radiation protection of the room where the accelerator is installed is limited due to insufficient area of the room. Combinations of heavy and light materials (steel, lead, concrete, polyethylene, etc.) are used for radiation protection. In combined protection

Computing Efficiency Improvement in Monte Carlo Simulation of a 12 MV Photon Beam Medical LINAC

Variance reduction techniques (VRTs) have been tremendously successful when applied to Monte Carlo radiation transport codes for which the computation time constitutes an important and a problematic parameter. In fact, many Monte Carlo calculations absolutely require variance reduction methods to achieve practical computation times. The MCNPX code has a fairly rich set of variance reduction techniques; the most known are transport cutoffs, interaction forcing, Bremsstrahlung splitting and Russian roulette. Also, the use of a phase space seems to be appropriate to reduce enormously the computing time. This work deals with the use of VRTs provided by MCNPX code for the simulation of a clinical linear electron accelerator (LINAC). Differences between various sets of VRTs are investigated. Combination between VRTs and PS is also analyzed during this study. Analysis showed that the use of VRTs and PS improve the simulation efficiency by a factor greater than 700. Finally, experimental curves of depth-dose and dose profile performed in a homogeneous water phantom are compared to dose distributions computed by use of MCNPX Monte Carlo code.

Set-up of a passive Bonner sphere system for neutron spectrometry at mixed fields with predominant photon component based on activation detector

A passive Bonner sphere system (BSS), based on thermal neutron activation detectors, was developed to perform neutron spectrometry in pulsed and very intense (n-gamma) fields with predominant photon component, as those produced by high energy (>10 MV) medical linear electron accelerators. In this paper, a description of the new system is presented together with an experimental characterisation of a portable Sodium Iodide (NaI) detector and a fixed high-purity Germanium one, both used to measure the induced gamma-activity of the activated materials, respectively, in situ and in the laboratory. The choice of the activated materials is justified according to pre-established practical considerations and physical criteria. The response functions of the entire passive BSS were calculated using the MCNPX code. A preliminary experimental validation with a bare (252)Cf source is given as well.

The electron energy dependence of the TL response for CVD diamonds

The thermoluminescent (TL) response of CVD diamond is investigated after bombarding a sample with monoenergetic electrons (at 6 and 21 MeV). Irradiations are performed at room temperature with a medical linear electron accelerator PRIMUS (KD2-Siemens). The TL curve shows a peak at approximately 540 K. The area of this peak as a function of fluence exhibits saturation behaviour at high energies. Moreover, there is no significant difference between the TL response at 21 MeV electrons and that at 6 MeV. In order to explain these experimental results, calculations of the ionising dose have been performed with the code MCNPX (Monte Carlo N-Particle) for various incident energies from 0.1 MeV up to 100 MeV.

Monte Carlo simulation of a medical linear accelerator for radiotherapy use

A Monte Carlo code MCNPX (Monte Carlo N-particle) was used to model a 25 MV photon beam from a PRIMUS (KD2-Siemens) medical linear electron accelerator at the Centre Antoine Lacassagne in Nice. The entire geometry including the accelerator head and the water phantom was simulated to calculate the dose profile and the relative depth-dose distribution. The measurements were done using an ionisation chamber in water for different square field ranges. The first results show that the mean electron beam energy is not 19 MeV as mentioned by Siemens. The adjustment between the Monte Carlo calculated and measured data is obtained when the mean electron beam energy is approximately 15 MeV. These encouraging results will permit to check calculation data given by the treatment planning system, especially for small fields in high gradient heterogeneous zones, typical for intensity modulated radiation therapy technique.

A double focusing magnet system for a medical linear electron accelerator

A double achromatic magnet system is described which bends electrons of moderate to high clinical energy (2 MeV to 30 MeV) through 112.5° onto a target. The X-ray or electron beam emerging from the target is used for medical therapy. By providing quadrupole and sextupole corrections to the bending magnets, a spot size of 2 × 2 mm 2 at the target is obtained as well as double achromatic behaviour, for electron beams with a large relative energy spread of 10%, an initial width and height of 5 mm, and with an initial divergence spread of ± 1 mrad. The corrections have been introduced on the basis of field measurements in the median plane of the bending system, and subsequent trajectory calculations. The effects agree with numerical results obtained by running a second-order particle transport code on the predicted magnet shape.

Experimental evaluation of the physical characteristics of a 45-MEV medical linear electron accelerator.

T He Specific components designed for the therapeutic application of the 45-MEV linear electron accelerator installed at Michael Reese Hospital and the general principles of operation of this apparatus have previously been reported (1). An electron beam was first released from the accelerator tube on March 6,1954, but measurements of the physical characteristics of the entire system could be carried out only after the magnet system had been designed, manufactured, and installed. Theoretically, a linear electron accelerator could be designed in such a manner as to produce a practically monoenergetic electron beam of definite size with energy controlled by the amount of input power or frequency. In the present stage of development, however, an external magnet system is required for the control of the energy and other physical properties of the output electron beam. The performance of the entire system depends as much on the magnets as on the accelerator. In this paper, some basic characteristics of the acce...