Linac natW target close-in geometry photoneutron study by nuclear track distribution function

Introduction: One of scientific concern is increasing of unwanted neutron dose to the patient, in head and neck radiation therapy due to the presence of some isotopes in dental restorations and head of medical linac. The aim of this study is to measure the equivalent dose of thermal and fast neutron due to head of Siemens Primus Linac and a healthy tooth, Amalgam, Ni-Cr alloy and Ceramco irradiated by 15 MV photon beams. Materials and Methods: To evaluation of production of secondary neutrons due to the various dental restorations and head of medical linac in in 15 MV photon beam of Siemens Primus linac (Siemens AG, Erlangen, Germany), three commercial dental materials were used. This dental phantom configuration was consisted of combination of two healthy teeth, a tooth filled with Amalgam, a Ni-Cr alloy and Ceramco which they were collected randomly from dentistry clinics. The dental phantom was placed in depth of 1 cm in PMMA. In order to score of thermal and fast neutron equivalent doses, CR-39 detector was used. All the results of equivalent dose are considered to the delivery of 100 cGy dose at the maximum depth of 3.1 cm in the PMMA phantom with 15 MV photon beam and 10 × 10 cm2 field. Results: It is found out the maximum fast neutron dose was scored on the phantom surface which is related to head of Siemens primus linac. About the dental restorations, maximum fast neutron equivalent dose is related to amalgam, Ceramco and Ni-Cr alloy with amount of 0.19 mSv, 1.04 mSv, and 0.97 mSv at depth of 1.8 cm, respectively and then they decrease as the depth increases. The minimum amount of thermal neutron dose was measured on the surface of phantom. In case of denture samples, after dental phantom, the trend of the thermal neutron dose is reduced. The results indicated that maximum amount of thermal equivalent dose is related to Amalgam, Ceramco and Ni-Cr alloy and is equal to 1.45 mSv, 1.38 mSv, and 1.32 mSv, respectively. Conclusion: This study indicates an interpretation about photoneutron production in presence of the various dental restorations and head of Siemens primus medical linac. Presence of some elements in metallic dentures and head of medical linac, on the path of high photon beam can leads to the additional dose in the patient body. According to these results, thermal and fast neutron equivalent dose are started with an increase then they are reduced at depths after the dental restorations. Therefore, according to these results, it is recommended that some attempt should be carried out to make sure that the dental restorations are not in the path of primary photon beam with high energy.

Objective To establish a novel Monte Carlo simulation method for reconstruction of medical accelerator model and X-ray energy spectrum based on IAEA Varian 6 MV X-ray phase-space file and photon energy spectrum of the target accelerator. Methods The verified 6 MV X-ray phase-space files were preprocessed to elevate the energy of each particle. Particles were saved in different Phase-Space-Let (PSL) files according to their position and energy, yielding an initial photon energy spectrum for Monte Carlo simulation of accelerator under an initial target energy. The initial photon energy spectrum was fit to a photon energy spectrum of an accelerator (Elekta Precise 10 MV X-ray accelerator) under an unknown target energy to yield a fitting coefficient, which was the weight of each PSL. Finally, an accelerator model under an unknown target energy was reconstructed using the initial PSL files and the weight information. The percentage depth dose (PDD) distribution was calculated in different square open fields. The effectiveness of this method was verified using one dimensional gamma passing rate. Results The peak position and overall distribution of the reconstructed 10 MV photon energy spectrum were in accordance with those of the verified 10 MV photon energy spectrum. The PDD calculated from the reconstructed 10 MV accelerator model agreed well with the measured PDD. The one-dimensional gamma passing rate was above 96%(1%/1 mm, threshold=0%). Conclusion The Monte Carlo reconstruction method proposed in this study is reliable, accurate, and effective. Key words: X-ray energy spectrum; Linac head beamreconstruction; Phase-Space-Let files; Monte Carlo simulation

Applicability of the two-angle differential method to response measurement of neutron-sensitive devices at the RCNP high-energy neutron facility

Neutron flux measurements in the Gran Sasso national laboratory and in the Slanic Prahova Salt Mine

Neutron spectral fluence and dose distribution inside a NYLON 6 phantom irradiated with pencil beam of high energy protons

The purpose of this study is to characterize the stray neutron radiation field in scanning proton therapy considering a pediatric anthropomorphic phantom and a clinically-relevant beam condition.Using two extended-range Bonner sphere spectrometry systems (ERBSS), Working Group 9 of the European Radiation Dosimetry Group measured neutron spectra at ten different positions around a pediatric anthropomorphic phantom irradiated for a brain tumor with a scanning proton beam. This study compares the different systems and unfolding codes as well as neutron spectra measured in similar conditions around a water tank phantom.The ten spectra measured with two ERBSS systems show a generally similar thermal component regardless of the position around the phantom while high energy neutrons (above 20 MeV) were only registered at positions near the beam axis (at 0°, 329° and 355°). Neutron spectra, fluence and ambient dose equivalent, H *(10), values of both systems were in good agreement (<15%) while the unfolding code proved to have a limited effect. The highest H *(10) value of 2.7 μSv Gy−1 was measured at 329° to the beam axis and 1.63 m from the isocenter where high-energy neutrons (E ⩾ 20 MeV) contribute with about 53%. The neutron mapping within the gantry room showed that H *(10) values significantly decreased with distance and angular position with respect to the beam axis dropping to 0.52 μSv Gy−1 at 90° and 3.35 m. Spectra at angles of 45° and 135° with respect to the beam axis measured here with an anthropomorphic phantom showed a similar peak structure at the thermal, fast and high energy range as in the previous water-tank experiments. Meanwhile, at 90°, small differences at the high-energy range were observed.Using ERBSS systems, neutron spectra mapping was performed to characterize the exposure of scanning proton therapy patients. The ten measured spectra provide precise information about the exposure of healthy organs to thermal, epithermal, evaporation and intra-nuclear cascade neutrons. This comprehensive spectrometry analysis can also help in understanding the tremendous literature data based rem-counters while also being of great value for general neutron shielding and radiation safety studies.

Purpose:Photons from a modern high‐energy therapeutic linear accelerator used in X‐ray radiotherapy causes photonuclear reactions in an accelerator or patient's body. The aim of this study is to evaluate the biological effectiveness including these particles by Microdosimetric Kinetic Model (MKM) based on microdosimetry.Methods:A linear accelerator operating at 15 MV was used. CR‐39 was used to obtain LET spectra of secondary ions selectively, as CR‐39 is regarded insensitive to photons. CR‐39 was put on the central axis of the X‐ray beam at depths of 0, 5 and 10 cm in plastic phantom at a source to detector distance of 100 cm. Pits formed by the traversal of ions were etched then analyzed to obtain restricted LET distribution. Frequency‐mean and dose‐mean lineal energy was evaluated from the relationship between the restricted LET and the lineal energy required to evaluate the biological effectiveness by MKM. The relationship was calculated by Monte Carlo simulations with GEANT4.Results:Restricted LET distributions of secondary particles showed broad distributions that decreases exponentially with increasing LET. Frequency‐mean and dose‐mean lineal energy were determined uniquely within the scope of the energies of secondary particles generated from photons of 15 MeV. The frequency‐mean lineal energies at the depth of 0, 5 and 10 cm were 15.1, 16.0 and 19.7 keV/μm respectively, and the dose‐mean lineal energies were 18.6, 20.5 and 19.6 keV/μm, respectively. RBE of secondary particles for HSG cell evaluated by MKM was about 2.0 at all depths, and RBE of all particles including photons was evaluated 1.0.Conclusion:We investigated the biological effectiveness of secondary particles by photonuclear reactions. The method to evaluate RBE by MKM was established with measurements and simulations. However, the influence of these secondary ions on RBE was found negligible in the entire biological effectiveness of the high‐energy X‐ray.This study has been supported by JSPS KAKENHI Grant Number 25861144.

High energy x-rays from a medical linear accelerator (LINAC) is used to treat cancer patients in radiotherapy department. The medical linac can produce bremsstrahlung x-rays from 4MV to 18MV and the commonly used linac produces 6MV, 10 MV and 15MV photons for treating major parts of the cancer patients. The photo neutron production during the radiation treatment is one of the major issues which have to be addressed with high impact because of the high LET nature associated with it. Photo neutrons are produced from several high atomic number (Z) elements present in the linac head mostly by the (ɣ, n) reaction. The flattening filter used in medical linac to produce uniform intensity distribution (made up of either tungsten, steel, lead, uranium, aluminum or a combination) is one of the photo neutron sources in the linac head. Advanced radiotherapy treatments like Intensity Modulated Radiotherapy (IMRT) and Volumetric Arc Therapy (VMAT) doesn't require a flat radiation field, and hence the flattening filter could be removed. This is called flattening filter free beam (FFF beam)1, 2. The removal of the filter will result in a forward peaked photon beam, which is very advantageous for these kinds of treatments3, 4. The purpose of this work was to find out the difference in the percentage of photo neutron production in a flattening filter free (FFF) and flattening filter (FF) beam using CR39 Solid State Nuclear Track Detector (SSNTD) from an Elekta Versa HD machine. The neutron fluence was measured at different positions with FFF and FF mode and the results were tabulated. The neutron fluence was lower for the FFF mode of operation than the FF mode. The reduction ranges from 2.27% to 44.22%.

A semiempirical method to characterize the pencil-beam dose kernel is presented. Results from measurements are described by mathematical models of the applicable physical processes. The measurements were made with 6 and 25 MV x-ray beams from a linear accelerator. Broad-beam notations were used consistently, and the pencil-beam quantities were obtained by differentiation. The results were compared to pencil-beam kernels calculated by Monte Carlo techniques. The analysis of the measured data included a number of approximations. It was assumed that all the constituent pencil beams in the field are parallel, i.e., the divergence is ignored. Furthermore, the lateral variations of the incident photon fluence and the energy spectrum were disregarded. Monte Carlo calculations, on the other hand, are based on an average energy spectrum over the field, and are free from divergence and variations in the incident photon fluence. Measured and Monte Carlo calculated pencil beams nevertheless agreed well, and the approximations mentioned caused at maximum 2.7% discrepancies for the largest field size at 6 MV.

Background: Boron neutron capture therapy (BNCT) is a potential radiation therapy for treating refractory cancers. Measuring the neutron energy spectrum is important to evaluate the biological effect of BNCT. We have developed a novel low-energy neutron spectrometer with a 3He position-sensitive proportional counter. The effectiveness of this spectrometer remained unvalidated due to the inadequate response function.Materials and Methods: The response function of this spectrometer was evaluated by Monte Carlo simulation to perform the validation experiment of this spectrometer. The 3He(n,p)3H reaction rate for each monochromatic neutron (energy range, 0.5 eV–10 keV) was calculated. Numerical experiments were conducted to investigate the performance of this spectrometer. Several estimated values of the energy spectrum were obtained and compared with a calculated energy spectrum at the exit of the epithermal column by the Monte Carlo simulation by preparing several candidates for signals. The Bayesian estimation algorithm was utilized for the estimation.Results and Discussion: The results indicate that the spectrometer and the evaluated response functions can be utilized to measure the energy spectrum of neutrons in the low-energy range. However, the energy spectrum could not be well represented &gt;4 keV due to the poor response function, including uncertainties in response function calculation as well as the poor energy resolution of this detector in the high-energy region.Conclusion: The response function of the low-energy neutron spectrometer for the epithermal energy region can be assessed by the Monte Carlo simulation. The numerical experiments reveal that the effectiveness of this spectrometer can be shown in the range of 0.5 eV.

Introduction: Previous studies have shown that a Monte Carlo method for the transportations photon beam in medical linear accelerator is a good way. Strip of simulation can be used to measure the dose distribution in phantoms and patients' body. EGSnrc Code is the only code written for use in the field of radiation therapy that has many subset codes that BEAMnrc code is an important one, in which transferred electrons and photons simulation takes place in the head of medical device. DBS technique (Directional Bremsstrahlung Splitting) is a technique that applies a braking radiation in collision. In this study will be discussed to evaluate the effect of this technique on simulation time and particle number of phase-space data and its effect on output spectrum photon beam (6MV) Siemens accelerator Primus model Materials and Methods: : Beginning the geometry of accelerator was stimulated according to its specifications by using the appropriate combination code BEAMnrc. Scoring plane that get phase-space data, in parts of the device such as: target, it was determined the flattening filter by using BEAMDP program to extract their average energy and output spectra in these parts. Also the other side of the research, simulation parameters and output spectra were compared by changing the amount of DBS. Results: Due to the importance of time in fast Mont Carlo, in the simulation with low history of DBS. Considering the time and quality of the spectrum, DBS can be useful. Conclusion: The results show that by changing the number of DBS from 1 to 1000, the amount of simulation time (Elapsed Time) and CPU time and number of particles into phase- space file, respectively have been 7.1, 7 and 36.9 times.

This study describes the modeling and the experimental verification and clinical implementation of the alpha release of Pinnacle3 Monte Carlo (MC) electron beam dose calculation algorithm for patient-specific treatment planning. The MC electron beam modeling was performed for beam energies ranging from 6 to 18 MeV from a Siemens (Primus) linear accelerator using standard-shaped electron applicators and 100 cm source-to-surface distance (SSD). The agreement between MC calculations and measurements was, on average, within 2% and 2 mm for all applicator sizes. However, differences of the order of 3%-4% were noted in the off-axis dose profiles for the largest applicator modeled and for all energies. Output factors were calculated for standard electron cones and square cutouts inserted in the 10 x 10 cm2 applicator for different SSDs and were found to be within 4% of measured data. Experimental verification of the MC electron beam model was carried out using an ionization chamber and film in solid-water slab and anthropomorphic phantoms containing bone and lung materials. Agreement between calculated and measured dose distributions was within +/-3%. Clinical comparison was performed in four patient treatment plans with lesions in highly irregular anatomies, such as the ear, face, and breast, where custom-designed bolus and field shaping blocks were used in the patient treatments. For comparison purposes, treatment planning was also performed using the conventional pencil beam (PB) algorithm with the Pinnacle3 treatment planning system. Differences between MC and PB dose calculations for the patient treatment plans were significant, particularly in anatomies where the target was in close proximity to low density tissues, such as lung and air cavities. Concerning monitor unit calculations, the largest differences obtained between MC and PB algorithms were between 4.0% and 5.0% for two patients treated with oblique beams and involving highly irregular surfaces, i.e., breast and cheek. Clinical results are reported for overall uncertainty values (averaged over voxels with doses >50% dosemax) ranging from 2% to 0.3% and calculations were performed using cubic voxels with side 0.3 cm. Timing values ranged from 2 min to 24.5 h, depending on the field size, beam energy, number, and thickness of computed tomography slices used to define the patient's anatomy for the overall uncertainty values mentioned above.

Simulated response of a multi-element thick gas electron multiplier-based microdosimeter to high energy neutrons

We report the experimental procedure and data that establishes the correlation between natural boron (B <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">10</sup> ) concentration and thermal neutron soft error rate (SER) in an advanced 28nm high-k/metal gate (HK/MG) technology node. Thermal neutron induced singe event upsets (SEU) depend on the concentration of B <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">10</sup> in the contact process adopted for boosting SRAM performance. However, as technology rapidly evolves in terms of transistor feature size and overall design complexity, B <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">10</sup> concentration needs to decrease so as to reduce thermal neutron SER risk. Optimization of contact and eSiGe process can provide a technology profile that is robust against thermal and high energy neutron SER.

To study the scatter factors during I-131 thyroid scintigraphic studies with a pinhole collimator (5mm hole) was developed a Monte Carlo (MC) simulation using GAMOS code. First, to check the accuracy of the Monte Carlo model, simulated and measured data using a thyroid phantom were compared. The accuracy of the Monte Carlo model was verified by the good agreement between measured and simulated energy spectra and the maximum discrepancies of 2% in the counts/sec/MBq. Next, simulations to investigate scatter were performed for different tissue thickness between the thyroid and collimator (5-15mm). The image’s scatter contribution was significant in the 5mm pinhole, being between 27-40%. On the basis of the separated scatter from direct count included in window energy spectra, a preliminary evaluation of multiple window energy correction methods was performed. For the simulated thyroid geometry with pinhole, the reduce inferior double energy window methods (15% on 364keV photopeak window) provides a reasonable correction for scatter. This study is the first approach; we recommend including real thyroid geometry with different thyroid depth-thickness and mass.