MV Medical Linear Accelerator Research Articles

Effects of Irradiation on Biology and Mating Behaviour of Wild Males of Brown Marmorated Stink Bug Using a 6 MV Medical Linear Accelerator

The brown marmorated stink bug, Halyomorpha halys, is a pentatomid bug of Eastern Asian origin that became an economically relevant pest in the Eurasian and American continents. Management of this species is limited to use of chemical insecticides: an inefficient method due to the strong adaptability of the target pest. The sterile insect technique (SIT) is potentially a valid tactic in the search for nontoxic alternatives. In this work, we investigated the suitability of mass-trapped overwintering males, collected during the aggregation phase before the winter diapause, for their release as competitive sterile males in an SIT programme. Differently from previous studies, irradiation was applied with a linear accelerator device that produced high-energy photons. Following a similar scientific protocol with newly emerged irradiated males, the effects of X-ray irradiation on physiological parameters (longevity, fecundity and fertility) were assessed. In addition, behavioural bioassays were carried out in no-choice conditions to evaluate if irradiation interferes with mating processes. The results are very encouraging; the effects of the irradiation at 32 Gy did not differ from the controls in the longevity or fecundity of the exposed overwintering adults. The hatching rate of the eggs laid by the fertile females that had mated with the irradiated males was less than 5%. The results of behavioural bioassays showed that the irradiation did not cause a significant impact on the quality of the sterile males. More research is warranted to evaluate the mating competitiveness of sterile males in semi-field and field conditions.

Innovative utilization of compact disc for measuring fast neutron generated from a 10 MV medical linear accelerator

Background: High-energy photons produced from a medical linear accelerator (LINAC) have long been used as one of the most effective ways for treating cancers. During the treatment process, some photo neutrons are unavoidably created by [γ,n] reactions, imposing additional and undesirable dose on a patient. This amount of unplanned dose from photo neutrons can potentially harm the patient as well as medical personnel during the treatment. This study is aimed to develop a methodology for measuring fast neutron dose generated from 10 MV LINAC by employing polycarbonate from base material of compact disk (CDs) and a fast neutron converter. Materials and methods: The polycarbonate base layer of CDs has been applied to fast neutron dosimetry with nuclear track method by combining with polymethyl methacrylate (PMMA) converter for fast neutrons. A number of CDs badges were irradiated with high energy photon from 10 MV Elekta Synergy LINAC in the solid water phantom at depth of 0, 2.5, 5, 10, 15 and 20 cm then etched with potassium hydroxide ethanol water (PEW) solution that containing with potassium hydroxide, ethanol and water with ratio of 15:45:40. The optimal condition for the chemical etching were found at 60±2 °C, for 14 hr. Results: Comparison of neutron equivalent doses from measurement of CD track detector and CR-39 track detector has shown that the maximum fast neutron dose equivalent was at depth of 5 cm of phantom. This agreement has confirmed that the CD track detector can be employed to measure fast neutron doses produced from LINAC in an accurate and affordable fashion. Conclusion: It is confirmed that the CD track detector can be employed to measure fast neutron doses produced from LINAC in an accurate and affordable fashion.

Monte Carlo Simulation-Based BEAMnrc Code of a 6 MV Photon Beam Produced by a Linear Accelerator (LINAC)

In radiotherapy, high energy ionizing radiation , such as X-rays, gamma rays and electron beams , is used. The dose in the tissue is often approached with the dose in the medium of the body which is 80 % of human soft tissue. It is often difficult to determine the dose because the interaction of materials in a medium is very random. Measurement is also quite difficult because there are almost no detectors that are tissue equivalent. Measurement using an ion chamber requires a lot of correction to obtain a dose in the tissue , which is done using phantom and not directly in humans . This research aim ed to compare the absorbed dose between modelling using Monte Carlo simulation and experiments. The simulation of dose distribution produced by a 6 MV medical linear accelerator has been performed using BEAMnrc code running on Linux-based 2 processor system arranged in parallel. BEAMnrc was used to model and simulate the linac head with an SSD of 100 cm and Field size of 10x10 cm 2 . A phase-space file is obtained as input to a DOSXYnrc code to produce Percent Depth Dose (PDD) in water and polymethyl methacrylate ( PMMA ) phantoms. New particles formed (electrons: 0.2 %, photon: 0.17 %; and positron: 0.08 %) were far from the contamination threshold of 2 %. The range of the correction factor of the depth of a maximum dose compared to the experimental data was 0.0 4 -0.15.

Monte Carlo evaluation of out-of-field dose in 18 MV pelvic radiotherapy using a simplified female MIRD phantom

This study was devoted to determining the unwanted dose due to scattered photons to the out-of-field organs and subsequently estimate the risk of secondary cancers in the patients undergoing pelvic radiotherapy. A typical 18 MV Medical Linear Accelerator (Varian Clinac 2100 C/D) was modeled using MCNPX® code to simulate pelvic radiotherapy with four treatment fields: anterior-posterior, posterior-anterior, right lateral, left lateral. Dose evaluation was performed inside Medical Internal Radiation Dose (MIRD) revised female phantom. The average photon equivalent dose in out-of-field organs is 8.53 mSv Gy−1, ranging from 0.17 to 72.11 mSv Gy−1, respectively, for the organs far from the Planning Treatment Volume (Brain) and those close to the treatment field (Colon). Evidence showed that colon with 4.3049% and thyroid with 0.0020% have the highest and lowest risk of secondary cancer, respectively. Accordingly, this study introduced the colon as an organ with a high risk of secondary cancer which should be paid more attention in the follow-up of patients undergoing pelvic radiotherapy. The authors believe that this simple Monte Carlo (MC) model can be also used in other radiotherapy plans and mathematical phantoms with different ages (from childhood to adults) to estimate the out-of-field dose. The extractable information by this simple MC model can be also employed for providing libraries for user-friendly applications (e.g. ‘.apk’) which in turn increase the public knowledge about fatal cancer risk after radiotherapy and subsequently decrease the concerns in this regard among the public.

Skin and build up dose determination for a 2.5 MV medical linear accelerator imaging beam.

The 2.5 MV Imaging beam produced by a Varian TrueBeam linear accelerator produces a dose build up effect at the beam entrance similar to other high energy photon beams. The surface dose values were found to range from 39% of maximum dose at a 5cm × 5cm field size up to 69% of maximum at a 40cm × 40cm field. The depth of maximum dose deposition was found to range from 5mm at smaller field sizes to 4mm at larger field sizes. Whilst large absorbed doses will not be delivered utilizing these beams, the data provided will allow the medical physics community to assess and estimate doses to patient's skin and subcutaneous tissue from low energy MV imaging beams.

Analysis of Photo Neutron Dose to Patient from a 15 MV Linear Accelerator

Medical Linear Accelerator produces high-intensity bremsstrahlung beam, with typical energy ranges from 4 to 18MV for treatment purposes. The materials including patient exposed to this high energy spectrum lead to a photonuclear reaction in them. In these Photon energy domains, photo neutron production (n, p, and γ, n) is the major reaction channel. This is important as Carbon, Oxygen, Hydrogen, and Nitrogen are the predominant elements in a typical human being and having low photon neutron threshold. Apart from this, the equipment involved in a radiation treatment including Head, Couch, immobilization accessories, etc contributes to photo neutron production. The present study was recorded and analyzed the photo neutron spectra due to 15 MV medical linear accelerator using CR-39 Solid State Nuclear Track Detector and image processing software.

Monte Carlo simulation and experimental evaluation of dose distributions produced by a 6 MV medical linear accelerator.

The purpose of this work was to quantify the differences in dose distributions computed by Monte Carlo simulations against experimental measurements from an Elekta Synergy™ linear accelerator. The study was done using PRIMO, a PENELOPE-based Monte Carlo code. The dose calculation algorithm was compared under static field irradiations at 6 MV in a virtual water phantom for field sizes 10 × 10, 5 × 5 and 3 × 3 cm2. Experimental depth doses and profiles were obtained using a pair of CC13 iba® ionization chambers at a SSD = 100 cm in an iba Blue phantom™. Simulations and experimental data were compared in terms of point by point differences. Gamma analysis was also used in order to evaluate dose- differences and distance to agreement (2%, 2mm respectively) of calculated and experimental dose distributions. The evaluation of depth dose distributions indicated that differences increased by decreasing the field size. In all cases the mean dose difference was below 1%. Lateral profiles differences were also below 1% for all field sizes. Gamma analysis results were in an agreement of 99% for almost all the dose distributions for the chosen criteria. The performed Monte Carlo simulation using PRIMO showed good agreement compared to experimental measurements for both, depth dose and dose profiles for the evaluated fields sizes, largely used in commonly radiotherapy treatments.

Evaluation of neutron fluence in the treatment room and along the maze of an 18 MV linear accelerator

Neutron fluence and dose equivalent rate in the treatment room and along the maze of an 18 MV medical linear accelerator was evaluated using Monte Carlo code MCNP5. Scope of the study was to test the hypothesis that a simple accelerator head model can adequately estimate the neutron fluence in the treatment room and along the maze without the requirement of a detailed modeling of the complex accelerator head configuration. The accelerator head was modeled either as a spherical cell source of 10 cm in radius or as a point source in the centre of a spherical cell of 10 cm internal and 20 cm external radious, both made of tungsten. The calculations were compared against measurements performed using gold and indium activation foils. A good agreement between calculated and experimental results was observed in the treatment room. However, the calculations at the maze entrance overestimated the neutron fluence by a factor of 3. The results of the study contribute towards the development of a simple and computationally cost effective methodology for the calculation of neutron dose in the treatment room and the maze of high energy medical accelerators providing a representative simulation of the complex accelerator, bunker and maze configurations that cannot be described by presently used analytical expressions.

Monte Carlo Investigation of Photon Beam Characteristics and its Variation with Incident Electron Beam Parameters for Indigenous Medical Linear Accelerator.

Purpose:A Monte Carlo model of a 6 MV medical linear accelerator (linac) unit built indigenously was developed using the BEAMnrc user code of the EGSnrc code system. The model was benchmarked against the measurements. Monte Carlo simulations were carried out for different incident electron beam parameters in the study.Materials and Methods:Simulation of indigenously developed linac unit has been carried out using the Monte Carlo based BEAMnrc user-code of the EGSnrc code system. Using the model, percentage depth dose (PDD), and lateral dose profiles were studied using the DOSXYZnrc user code. To identify appropriate electron parameters, three different distributions of electron beam intensity were investigated. For each case, the kinetic energy of the incident electron was varied from 6 to 6.5 MeV (0.1 MeV increment). The calculated dose data were compared against the measurements using the PTW, Germany make RFA dosimetric system (water tank MP3-M and 0.125 cm3 ion chamber).Results:The best fit of incident electron beam parameter was found for the combination of beam energy of 6.2 MeV and circular Gaussian distributed source in X and Y with FWHM of 1.0 mm. PDD and beam profiles (along both X and Y directions) were calculated for the field sizes from 5 cm × 5 cm to 25 cm × 25 cm. The dose difference between the calculated and measured PDD and profile values were under 1%, except for the penumbra region where the maximum deviation was found to be around 2%.Conclusions:A Monte Carlo model of indigenous linac (6 MV) has been developed and benchmarked against the measured data.

Structural Shielding Design of a 6 MV Flattening Filter Free Linear Accelerator: Indian Scenario.

Detailed structural shielding of primary and secondary barriers for a 6 MV medical linear accelerator (LINAC) operated with flattening filter (FF) and flattening filter free (FFF) modes are calculated. The calculations have been carried out by two methods, one using the approach given in National Council on Radiation Protection (NCRP) Report No. 151 and the other based on the monitor units (MUs) delivered in clinical practice. Radiation survey of the installations was also carried out. NCRP approach suggests that the primary and secondary barrier thicknesses are higher by 24% and 26%. respectively, for a LINAC operated in FF mode to that of a LINAC operated in both FF and FFF modes with an assumption that only 20% of the workload is shared in FFF mode. Primary and secondary barrier thicknesses calculated from MUs delivered on clinical practice method also show the same trend and are higher by 20% and 19%, respectively, for a LINAC operated in FF mode to that of a LINAC operated in both FF and FFF modes. Overall, the barrier thickness for a LINAC operated in FF mode is higher about 20% to that of a LINAC operated in both FF and FFF modes.

New aspect determination of photoneutron contamination in 18 MV medical linear accelerator

In this study, the neutron contamination due to the 2300C/D Varian medical linac has been calculated by using the long counter. In doing so, the energy response of the long counter in wide energy ranges (1keV–7MeV) of the neutron has been flattened and its effective center and directional sensitivity has been determined. All calculations have been performed by using the simulation of the measurable arrangement with the Monte Carlo N-Particle MCNPX code at isocenter for different photon field sizes. The obtained results showed that the inverse square formula for determining the neutron fluence needs to be corrected so that in the power value of d, the distance from the source to the point of interest, the value 1.88 ± 0.08 is substituted with 2 at inverse square law in the field size 10 × 10 cm2. Therefore, the values of the neutron strength, neutron fluence and the ambient dose equivalent, H*(10) have been obtained by using the above correction. Finally, the obtained results have been compared with other published results. On the other hand, it is found that the flattening filter caused to sharp the energy fluence at the center of the beam by using the point detector tally and consequently the high dose delivered to the patient.

Photon activation analysis of large metallurgical slag samples using a 23 MV medical linear accelerator

The potential of large sample photon activation analysis for multi-element, non-destructive analysis of metallurgical tap smelting slag using a 23 MV medical linear accelerator as photon source was investigated. An absolute quantification method was developed. The results of the analysis were compared against values obtained by instrumental neutron activation analysis with a satisfactory agreement. Advantages of the technique include improved representativeness of results by analysis of larger samples, elimination of reference samples, irradiation versatility and convenience. The technique will be applied to examine early bronze age copper ore reduction practices between islands of the Aegean.

A simple and fast physics-based analytical method to calculate therapeutic and stray doses from external beam, megavoltage x-ray therapy

State-of-the-art radiotherapy treatment planning systems provide reliable estimates of the therapeutic radiation but are known to underestimate or neglect the stray radiation exposures. Most commonly, stray radiation exposures are reconstructed using empirical formulas or lookup tables. The purpose of this study was to develop the basic physics of a model capable of calculating the total absorbed dose both inside and outside of the therapeutic radiation beam for external beam photon therapy. The model was developed using measurements of total absorbed dose in a water-box phantom from a 6 MV medical linear accelerator to calculate dose profiles in both the in-plane and cross-plane direction for a variety of square field sizes and depths in water. The water-box phantom facilitated development of the basic physical aspects of the model. RMS discrepancies between measured and calculated total absorbed dose values in water were less than 9.3% for all fields studied. Computation times for 10 million dose points within a homogeneous phantom were approximately 4 min. These results suggest that the basic physics of the model are sufficiently simple, fast, and accurate to serve as a foundation for a variety of clinical and research applications, some of which may require that the model be extended or simplified based on the needs of the user. A potentially important advantage of a physics-based approach is that the model is more readily adaptable to a wide variety of treatment units and treatment techniques than with empirical models.

Ionizing radiation detectors based on Ge-doped optical fibers inserted in resonant cavities.

The measurement of ionizing radiation (IR) is a crucial issue in different areas of interest, from environmental safety and industrial monitoring to aerospace and medicine. Optical fiber sensors have recently proven good candidates as radiation dosimeters. Here we investigate the effect of IR on germanosilicate optical fibers. A piece of Ge-doped fiber enclosed between two fiber Bragg gratings (FBGs) is irradiated with gamma radiation generated by a 6 MV medical linear accelerator. With respect to other FBG-based IR dosimeters, here the sensor is only the bare fiber without any special internal structure. A near infrared laser is frequency locked to the cavity modes for high resolution measurement of radiation induced effects on the fiber optical parameters. In particular, we observe a variation of the fiber thermo-optic response with the radiation dose delivered, as expected from the interaction with Ge defect centers, and demonstrate a detection limit of 360 mGy. This method can have an impact in those contexts where low radiation doses have to be measured both in small volumes or over large areas, such as radiation therapy and radiation protection, while bare optical fibers are cheap and disposable.

Measurement of activity distribution using photostimulable phosphor imaging plates in decommissioned 10 MV medical linear accelerator.

Photonuclear reactions generate neutrons in the head of the linear accelerator. Therefore, some parts of the linear accelerator can become activated. Such activated materials must be handled as radioactive waste. The authors attempted to investigate the distribution of induced radioactivity using photostimulable phosphor imaging plates. Autoradiographs were produced from some parts of the linear accelerator (the target, upper jaw, multileaf collimator and shielding). The levels of induced radioactivity were confirmed to be non-uniform within each part from the autoradiographs. The method was a simple and highly sensitive approach to evaluating the relative degree of activation of the linear accelerators, so that appropriate materials management procedures can be carried out.

X-ray storage performance of KCl:Eu2+ with high cumulated dose

The effects of high cumulative radiation dose on the luminescence properties of KCl:Eu2+ are investigated. Pellet samples of KCl:Eu2+ were given doses of up to 200kGy at the Louisiana State University Synchrotron facility. After synchrotron irradiation, samples were optically bleached and given a clinical dose of 2Gy from a 6 MV medical linear accelerator. Optical properties were evaluated using photostimulated luminescence (PSL), photoluminescence (PL), and temperature-dependent PSL measurements. For a cumulated dose of up to 5–10kGy, the PSL emission intensity increased by 15% compared to the PSL signal with no radiation history. For doses higher than 10kGy, the PSL emission intensity retained at least 70% of the original intensity. Spatial correlation of the charge storage centers increased for doses up to 5kGy and then decreased for higher cumulative doses. Emission band at 975nm was attributed to transitions of Eu1+. PL spectra showed an intense peak centered at 420nm for all cumulative doses. The results of this work show that KCl:Eu2+ storage phosphors are excellent reusable materials for radiation therapy dosimetry.

Monte Carlo estimation of photoneutrons spectra and dose equivalent around an 18 MV medical linear accelerator

A fully detailed Monte Carlo geometrical model of an 18MV Varian Clinac 2100C medical linear accelerator, lodged at Blida Anti-Cancer Centre in Algeria, was developed during this study to estimate the photoneutrons spectra and doses at the patient table in a radiotherapy treatment room, for radiation protection purposes.Subsequently, thanks to this model, extensive M.C. calculations of neutron fluences and ambient dose equivalent were carried out at three selected locations on the patient table in the medical facility for a reference field size of 10×10cm2 and a Source to Surface Distance (SDD) of 100cm. At the patient table, the calculated neutron ambient doses equivalent were 3.50, 0.89 and 0.62mSvGy−1 at isocenter, 40cm and 100cm from the isocenter.Thereafter, a sensitivity analysis was performed to investigate the effect of variation of some pertinent parameters (source term model, Multi-Leaf Collimators and the shielding walls of the treatment room) on the production of the photoneutrons doses at the patient table.Finally, a full comparative study has been performed, in order, to estimate the consistency of the author's results. Therefore, the obtained M.C. results were compared, firstly, to a few measurements acquired, for the same irradiation facility using CR-39 Nuclear Track Detectors (NTDs), at the isocenter assuming different field sizes, and secondly, to both theoretical and experimental results available in the literature for the same medical facility and for different irradiation conditions. From these comparisons, a mean difference (for all the locations and field sizes considered) of about 15% was found.Despite, the possible differences in the accelerator modeling, including variations in the accelerator head and room geometries and differences in the computational tools and photoneutrons cross-sections data used in the literature, the results obtained through this investigation are encouraging, highlighting thereby the consistency of the geometrical M.C. model assumed in this work.

Design and Optimization of a Novel Bored Biplanar Permanent-Magnet Assembly for Hybrid Magnetic Resonance Imaging Systems

We present a novel design for a biplanar permanent-magnet assembly suitable for use in hybrid magnetic resonance imaging (MRI) systems. The key feature of our design is a large cylindrical hole that is longitudinally bored through the entire magnet assembly. The presence of the bore permits the potential inclusion of additional peripheral devices within or near the magnet structure that may benefit from being placed along, or oriented parallel to, the main magnetic field. In particular, the magnet assembly can be considered for use in an integrated system consisting of a 6 MV medical linear accelerator (linac) coupled to an MRI system for state-of-the-art real-time image-guided adaptive radiotherapy. We use magnetic field calculations based on the finite-element method (FEM) to quantify the detrimental effects of the bore on the field homogeneity in the imaging volume for pole-piece designs found commonly in industry. We then demonstrate that shape optimization of the pole pieces yields novel pole designs that lead to suitable levels of field homogeneity. We examined the resultant magnetic field within the bore for the optimized design and found that it has maximum field homogeneity.

Measurements of the photonuclear neutron yield of 15 MV medical linear accelerator

High energy medical linear accelerators (>10 MV) are increasingly used in radiotherapy. At such high photon energies neutron production via photonuclear reactions in the heavy elements which compose the linac head is inevitable. Neutrons from linacs can contribute to an additional dose to staff, patients and the general public. Our intention is two-fold; to provide shielding against the neutron contamination and to establish the depthdose curve of thermal neutrons within human tissue, with an aim to utilise linacs in boron neuron capture therapy (BNCT). In our studies neutron measurements were undertaken, with a Varian Clinac 2100C/D linear accelerator operating at 15 MV nominal energy, by irradiating 18 cm thick 30×30 cm2 block of tissue equivalent material. Measurements were taken using indium and aluminum activation foil at the centre of the block. Our results show that by leaving the linac jaws open neutron production is increased compared to the case when these are shut, for one minute exposure at 400MU. In this work we present a comparison between our results and existing literature and attempt to explore some sharp contrasts.

On the Development of the VIPAR Polymer Gel Dosimeter for Three-Dimensional Dose Measurements

Summary: The new polymer gel dosimeter, based on the modification of the VIPAR gel composition, is described for the purpose of radiation dose distribution measurement in radiotherapy. It features increased concentration of the two VIPAR substrates: N-vinylpyrrolidone (8%) and gelatine (7.5%) (N,N′-methylenebisacrylamide was maintained at 4%), and the addition of copper sulphate (0.0008%) and ascorbic acid (0.007%) in order to facilitate the preparation through elimination of the need for deoxygenation of the gel. Following the exposure to ionizing radiation, polymerisation and cross-linking of the new gel monomers occurs retaining the spatial distribution of absorbed dose and causing opacity of the gel. Quantitative parameters of the new gel dose response were studied using magnetic resonance imaging to relate polymerisation induced physicochemical changes of the gel to dose. The dose threshold is found significantly lower than that of the original VIPAR gel. The linear part of measured spin-spin relaxation rate R2(D) ( = 1/T2(D)) reaches up to 35 Gy. Its slope and an intercept are slightly higher relative to the original VIPAR. The efficiency of the new polymer gel-magnetic resonance imaging dosimeter was also tested for dose verification of a 3D dose distribution planned by a commercially available treatment planning software (Eclipse External Beam v.6.5) and delivered by a 6 MV medical linear accelerator. The new polymer gel is proposed to be called, VIPARnd (after VIPAR-normoxic-double).