Primus Linac Research Articles

Sensitivity Analysis of a 6 MeV Photon Beam Monte Carlo Model.

This study aimed to optimize efficiency in Monte Carlo (MC) simulation using sensitivity analysis of a beam model. The BEAMnrc-based model of 6 MV beam of a Siemens Primus linac was developed. For sensitivity analysis, the effect of the electron source, treatment head, and virtual phantom specifications on calculated percent depth dose (PDD) and lateral dose profiles was evaluated. The optimum mean energy (E) and the full width at half maximum (FWHM) of the intensity distribution of the electron beam were calculated as 6.7 MeV and 3 mm, respectively. Increasing E from 6.1 to 6.7 MeV, increased the PDD in the fall-off region by 4.70% and decreased the lateral profile by 8.76%. Changing the FWHM had a significant effect on the buildup region of PDD and the horns and out-of-field regions of the lateral profile. Increasing the collimators opening by 0.5 mm, PDD increased by 2.13% and the central and penumbra regions of profiles decreased by 1.98% and 11.40% respectively. Collimator properties such as thickness and density were effective in changing the penumbra (11.32% for 0.25 cm increment) and the out-of-field (22.82% for 3 g/cm3) regions of the lateral profiles. Analysis of a 6 MV model showed that PDD profiles were more sensitive to changes in energy than to FWHM of the electron source. The lateral profiles were sensitive to E, FWHM, and collimator opening. The density of the collimator affected only the out-of-field region of lateral profiles. The findings of this study may be used to make benchmarking of an MC beam model more efficient.

Simulation Of Neutron Contamination In 6, 8, 10, 15, 18 and 25 MV Voltage Linac Device Using The Monte Carlo Method

<p>A research on neutron contamination in LINAC device has been carried out using a Monte Carlo method. The simulation is based on the Siemens Primus LINAC machine model whose component consists of target, primary collimator, flattening filter and secondary collimator as its main components. A neutron contamination examination was carried out using a 10 x 10 cm radiation field and a 100 cm SSD. Subsequently, at a distance of 100 cm from the X-ray source, a water phantom is placed. Investigation of the presence of contaminants was carried out the LINAC operating voltages of 6, 8, 10, 15, 18 and 25 MV. The simulation results show that neutron contamination occurs due to the interaction of photons with the components of the LINAC device, namely the primary collimator, flattening filter and secondary collimator. The operating voltages that can produce neutron contaminant start at 10 MV. Increase in the voltage of the LINAC device causes consequent increase in neutron flux. Such increase in neutron flux has the potential to increase therapeutic dose.</p>

Validation of Monte Carlo-based calculations for megavolt electron beams for IORT and FLASH-IORT

In Intra-Operative Radiation Therapy (IORT) the tumour site is surgically exposed and normal tissue located around the tumour may be avoided. Electron applicators would require large surgical incisions; therefore, the preferred mechanism for beam collimation is the IORT cone system. FLASH radiotherapy (FLASH-RT) involves the treatment of tumours at ultra-high dose rates and the IORT cone system can also be used. This study validates the Monte Carlo-based calculations for these small electron beams to accurately determine the dose characteristics of each possible cone-energy combination as well as custom-built alloy cutouts attached to the end of the IORT cone. This will contribute to accurate dose distribution and output factor calculations that are essential to all radiation therapy treatments. A Monte Carlo (MC) model was modelled for electron beams produced by a Siemens Primus LINAC and the IORT cones. The accelerator was built with the component modules available in the BEAMnrc code. The phase-space file generated by the BEAM simulation was used as the source input for the subsequent DOSXYZnrc simulations. Percentage Depth Dose (PDD) data and profiles were extracted from the dose distributions obtained with the DOSXYZnrc simulations. These beam characteristics were compared with measured data for 6, 12, and 18 MeV electron beams for the IORT open cones of diameters 19, 45, and 64 mm and irregularly shaped cutouts. The MC simulations could replicate electron beams within a criterion of 3%/3 mm. Applicator factors were within 0.7%, and cone factors showed good agreement, except for the 9 mm cone size.Based on the successful comparisons between measurement and MC-calculated dose distributions, output factors for the open cones and for small irregularly shaped IORT beams, it may be concluded that the Monte Carlo based dose calculation could replicate electron beams used for IORT and FLASH-IORT.

Modeling and Analysis of Percentage Depth Dose (PDD) and Dose Profile of X-Ray Beam Produced by Linac Device with Voltage Variation

The Percentage Depth Dose (PDD) and dose profile of X-Ray output from a LINAC therapy device have been modeled and analyzed. The research was conducted by simulation method through the use of Particle and Heavy Ion Transport code System (PHITS) program. The LINAC therapy device modeled in this work refers to the Siemens Primus LINAC therapy device, which is operated at 6 MV, 10 MV and 18 MV voltages. Determination of PDD was carried at a depth of 0-30 cm and dose profile at a depth of 0-20 cm in a water phantom, placed at 100 cm from the source, which is exposed to a radiation field area of 10×10 cm 2 . Results from the modeling of the LINAC therapy device agrees with the actual X-ray apparatus and has produced Bremsstrahlung X-ray. It was found from the analysis of the PDD curve that the maximum doses are at the depth of 1.5 cm, 2.5 cm and 3.4 cm. The value of build up factor for each LINAC voltage agrees with the reference. Additionally,  the results of the analysis of the doses profile suggest that the X-ray output has good degree of uniformity. The flatness of dose profile occurs at the depth of 20 cm with percentage value of flatness at 1.6 %, 1.9 % and 1.2 %. The flatness values are all less than 2%. The flatness values shows ≤ 2 % deviation from reference value, which is below the tolerance range required in a measurement.

Investigation the trend of different magnetic fields types on linac photon beam mode by Monte Carlo method using Geant4 toolkit

The present study is aimed at investigating the behavior of the secondary particles due to the photon beam interaction at the presence of the longitudinal, radial, tangential (angles), and uniformly springy magnetic fields with different intensities. The photon mode of a 15 MV Siemens Primus linac is used as an example. On the validity of the accelerator simulation, the percentage of depth dose and dose profile were also measured in the water phantom in 5-Azar hospital. The simulation has been performed by the Geant4.10.3 version in order to assess investigate the effect of different magnetic fields with a variety of intensity on dose profiles. Based on the profile dose distribution obtained for magnetic fields with different types and intensities it can be realized that the field of 3 T has the optimal condensation of the dose profile distribution. The striking feature the flux of electrons dramatically decreases for the tangential field compared to other magnetic fields, as in the dose profile graphs of this filed were shown.

Validation of Monte Carlo Model for Dose Evaluation outside the Treatment Field for Siemens 6MV Beam

Introduction: There has been a concern about the unintended doses to critical structures outside the treatment field due to the increased risk of radiation-induced second cancer following radiotherapy treatments. Today, Monte Carlo (MC) simulation is considered the most accurate method for dose calculations in different domains of medical physics. Material and Methods: The Geant4 Application for Tomographic Emission (GATE) code was used to create an MC model of 6MV Siemens Primus linac. Measurements were taken in a water phantom using an ion chamber to validate the MC model. Dose profiles outside the treatment field at 1.5 (dmax), 5.0 and10.0 cm depths for field sizes from 5×5 to 20×20 cm2 were measured in the present study. Out-of-field percentage depth dose (PDD) curves at 0.0, 5.0, and 7.5 cm off axis for field size 10×10 cm2 were investigated for both measurements and simulation. However out-of-field PDDs from 10 to 15 cm off axis for field size 10×10 cm2 were studied only by simulation. Results: The comparisons showed agreement between the measured and simulated doses for the out-of-field profiles along the in-plane direction for all considered field sizes and depths, as well as for the PDDs at 0.0 and 5.0 cm off axis, but with less agreement at 7.5 cm off axis. All the simulated out-of-field PDDs at distances ≥ 10 cm off axis had similar trend shapes. Conclusion: The developed MC model is considered a good representation of 6 MV Siemens Primus linac for the out-of-field dose calculation in lieu of measurements.

Characterization of Wedge Factors and Dose Distributions in Radiotherapy with Symmetric and Asymmetric Physical Wedged Beams of 6 MV Photon Beam

Introduction: Physical wedge by modify photon beam shape and intensity has been utilized in radiotherapy to obtain uniformly dose distribution in tumor site with reduced hot spots. Calculation of dosimetric parameters for both symmetric and asymmetric wedged fields is proved necessary during linear accelerator (Linac) commissioning. The present study aimed to achieve output factors and dose profiles for symmetric and asymmetric wedged fields of 6 MV beams. Material and Methods: The Siemens PRIMUS Linac head for 6 MV beam was simulated by BEAMnrc and all dose calculations were performed by DOSXYZnrc code. Percentage depth dose (PDD) and profiles for open and wedged (15° and 45°) fields were compared with corresponding measurements. Wedge factors for 10 x 10 cm2 field were obtained as a function of lateral distance as well for half beam wedged fields. Results: Based on the results of the present study, the calculated doses were in agreement with the measured data. The output factors on the central axis of symmetric wedged beams decreased to 0.693 and 0.307 for 15˚, and 45˚ wedges. The total photon fluence of 15˚ and 45˚ physical wedged fields reduced to 71.6% and 27.7% of open field, respectively. Conclusion: The output factor for asymmetric wedged fields was found to be lower than corresponding symmetric open and wedged fields, particularly at field edges. Lack of scattering photons near the half beam edges resulted in dose fall-off in these regions possible to be overestimated by treatment planning system and consequently caused cold spots at target volume.

Assessment of skin dose in breast cancer radiotherapy: on-phantom measurement and Monte Carlo simulation.

The main purpose of the present study is assessment of skin dose in breast cancer radiotherapy. Accurate assessment of skin dose in radiotherapy can provide useful information for clinical considerations. A RANDO phantom was irradiated using a 6 MV Siemens Primus linac with medial and tangential radiotherapy fields for simulating breast cancer treatment. Dosimetry was also performed on various positions across the fields using an EBT3 radiochromic film. Similar conditions of measurement on the RANDO phantom including field size, irradiation angle, number of fields, etc. were subsequently simulated via the Monte Carlo N-Particle Transport code (MCNP). Ultimately, dose values for corresponding points from both methods were compared. Considering dosimetry using radiochromic films on the RANDO phantom, there were points having underdose and overdose based on the prescribed dose and skin tolerance levels. In this respect, 81.25% and 18.75% of the points had underdose and overdose, respectively. In some cases, several differences were observed between the measurement and the MCNP simulation results associated with skin dose. Based on the results of the points which had underdose, it was suggested that a bolus should be used for the given points. With regard to overdose points, it was advocated to consider skin tolerance dose in treatment planning. Differences between the measurement and the MCNP simulation results might be due to voxel size of tally cells in simulations, effect of beam's angle of incidence, validation time of linac's head, lack of electronic equilibrium in the build-up region, as well as MCNP tally type.

Dental Materials Effect in Neutron Contamination: Electron Mode of a Linac.

Background: Neutron contamination is produced in electron beams of linac when tooth or dental materials are located in the path of beam.Objective: This study aims to determine the neutron dose contamination from different dental restoration materials in electron mode of a linac.Material and Methods: In this experimental study, the neutron dose contamination was calculated in the presence of tooth and tooth restored by Ceramco C3 veneer, Eclipse or amalgam. The electron mode included 8, 12, and 14 MeV electron beams of Siemens Primus linac at different depths before and after tooth. MCNPX code was used to simulate the linear accelerator and dental restoration materials. Tooth and tooth restoration materials were located in the beams’ central axis and the neutron dose was scored in 3 × 3 × 1 cm3 voxels at different depths before and after the tooth.Results: The highest neutron dose contamination was observed for the combination of the tooth and Eclipse in 12 and 14 MeV beams and the maximum calculated relative neutron dose was 1.53 for tooth and Eclipse for 14 MeV electron beam.Conclusion: Tooth and dental materials lead to neutron dose contamination production, therefore, in order to avoid having harmful effects on normal tissues due to the neutron beam in head and neck cancer, it is recommended that treatment planning performed should not place tooth with dental restoration materials in the path of the beam and lower energy electron beams be used.

Experimental study of the influence of dental restorations on thermal and fast photo-neutron production in radiotherapy with a high-energy photon beam

In head and neck radiation therapy, the presence of dental restorations can increase unwanted neutron dose to the patient. This study aimed at the measurement of secondary neutron production induced by irradiation of a healthy tooth, Amalgam, Ni-Cr alloy and Ceramco with a photon beam generated in the treatment head of a Siemens Primus linac at a voltage of 15 MV. The irradiation field amounted to 10 × 10 cm2. The measurements of thermal and fast-neutron equivalent doses were performed by means of CR-39 detectors positioned in various depths of a Perspex (polymethyl methacrylate) phantom as at open field as at presence of corresponding dental restorations. The general trend of thermal neutron as well as fast-neutron equivalent dose behind the denture samples reveals their reduction with increasing depth. The maximum values of thermal-neutron dose related to Amalgam, Ceramco and Ni-Cr alloy amount to 1.45 mSv/100 MU, 1.38 mSv/100 MU and 1.32 mSv/100 MU, whereas the corresponding maximum values of fast-neutron dose at the depth of 1.8 cm amount to 0.19 mSv/100 MU, 1.04 mSv/100 MU and 0.97 mSv/100 MU, respectively. The present study investigates the neutron dose accompanied with radiotherapy. It is recommended that attempts have to be made to ensure that dental restorations are not in the path of the primary high-energy photon beam. Considering treatment planning, the guidelines of radiation protection should be improved.

A Monte Carlo study on dose perturbation due to dental restorations in a 15 MV photon beam.

The main purpose of this study is to evaluate the effect of dose perturbation due to common dental restoration materials in the head and neck radiotherapy with a 15 MV external photon beam. Teeth with three dental restorations such as tooth filled with Amalgam, Ni-Cr alloy, and Ceramco were simulated by MCNPX Monte Carlo code. In this simulation, the dental materials were exposed by a 15 MV photon beam from a Siemens Primus linac, inside a water phantom. A Siemens Primus linear accelerator and a phantom including: tooth only, tooth with Amalgam, tooth with Ni-Cr alloy, and tooth with Ceramco were simulated by MCNPX Monte Carlo code, separately. The percentage dose change was evaluated relative to dose in water versus depth for these samples on the beam's central axis. The absolute dose by prescription of 100 cGy dose in water phantom at 3.0 cm depth was calculated for water, tooth, tooth with Amalgam, tooth with Ni-Cr alloy, and tooth with Ceramco. The maximum percentage dose change is related to tooth with Ni-Cr alloy, tooth, tooth with Ceramco, and tooth with Amalgam with amounts of 7.73%, 6.95%, 4.7%, and 3.06% relative to water at 0.75 cm depth, respectively. When 100.0 cGy dose was prescribed at 3.1 cm, the maximum absolute dose was 201.0% in the presence of tooth with Ni-Cr alloy at 0.75 cm. Introduction of the compositions of dental restorations can improve the accuracy of dosimetric calculations in treatment planning and protect the healthy tissues surrounding teeth from a considerable overdose.

The comparison between 6 MV Primus LINAC simulation output using EGSnrc and commissioning data

Introduction: Monte Carlo calculation method is considered to be the most accurate method for dose calculation in radiotherapy. The purpose of this research is comparison between 6 MV Primus LINAC simulation output with commissioning data using EGSnrc and build a Monte Carlo geometry of 6 MV Primus LINAC as realistically as possible. The BEAMnrc and DOSXYZnrc (EGSnrc package) Monte Carlo model of the LINAC head was used as a benchmark. Materials and Methods In the first part, the BEAMnrc was used for the designing of the LINAC treatment head. In the second part, dose calculation and for the design of 3D dose file were produced by DOSXYZnrc. The simulated PDD and beam profile obtained were compared with that calculated using commissioning data. Good agreement was found between calculated PDD (1·1%) and beam profile using Monte Carlo simulation and commissioning data. After validation, TPR20,10, TMR and Sp values were calculated in five different field. Results Good agreement was found between calculated values by using Monte Carlo simulation and commissioning data. Average differences for five field sizes in this approach is about 0·83% for Sp. For TPR20,10 differences for field sizes 10 × 10 cm2 is 0·29% and for TMR in five field sizes, the average value is ~ 1·6%. Conclusion: In conclusion, the BEAMnrc and DOSXYZnrc codes package have very good accuracy in calculating dose distribution for 6 MV photon beam and it can be considered as a promising method for patient dose calculations and also the Monte Carlo model of primus linear accelerator built in this study can be used as method to calculate the dose distribution for cancer patients.

Quantification the dosimetric parameters of asymmetric physical wedged-6MV photon beam

Introduction: Physical wedge as a useful tool has been utilized in radiotherapy to modify photon beam shape and intensity such that it distributes dose uniformly in tumor site and reduces hot points. Since during Linac commissioning dosimetric parameters like output factors and lateral dose profiles are measured only for symmetric open and wedged fields, so calculation the parameters for asymmetric wedged fields become necessary. The study aims to achieve output factors and dose profiles for symmetric and asymmetric wedged fields of 6 MV photon beams. Materials and Methods: The Siemens PRIMUS Linac head for 6 MV photon beam was simulated by BEAMnrc and all dose calculations were performed by DOSXYZnrc code. Percentage depth dose (PDD) and profiles for open and wedged (15° and 45°) fields were compared with corresponding measurements. Wedge factors for 10 x 10 cm2 field size as a function of lateral distance from central axis were obtained as well for half beam (negative or positive Y jaws were closed) wedged fields. All mesurments were carried out using 0.125 cm3 Farmer type ionization chamber with DOSE1 electrometer (FC65G, Scanditronix-Wellhofer, Germany) at the depth of 10 cm with source to surface distance (SSD) of 100 cm in 50 cm3 PTW-Blue water phantom and processed by dosimetry software RFAplus (Version 5.2, Scanditronix-Wellhofer, Germany). Results: The calculated doses were in agreement with measured data that confirmed the simulated MC model. The output factors on the central axis of symmetric wedged beams decreased to 0.693 and 0.307 for 15˚ and 45˚ wedges, respectively. The total photon fluence of 15˚ and 45˚ physical wedged fields reduced to 71.6% and 27.7% of fluence for open field, respectively. It was found that the output factor for asymmetric wedged fields is lower than ones from symmetric fields, particularly at field edges. Conclusion: The presences of physical wedge across the beamline decrease the photon fluence and cases beam hardening both for symmetric and asymmetric wedged fields. Lack of scattering photons near the half beam edges in asymmetric wedged field causes a dose fall off in these regions where have potential to overestimate the calculated dose by treatment planning system and consequent cold spots at target volume. Our calculated correction coefficients are recommended to calculate doses by TPS in case of asymmetric wedged fields.

Assessment of secondary neutron dose due to dental restorations in head and neck radiation therapy

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.

The comparison between 6 MV Primus LINAC simulation output using EGSnrc and commissioning data – ERRATUM

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Benchmarking of Siemens Linac in Electron Modes: 8-14 MeV Electron Beams

Radiation therapy using electron beams is a promising method due to its physical dose distribution. Monte Carlo (MC) code is the best and most accurate technique for forespeaking the distribution of dose in radiation treatment of patients. We report an MC simulation of a linac head and depth dose on central axis, along with profile calculations. The purpose of the present research is to carefully analyze the application of MC methods for the calculation of dosimetric parameters for electron beams with energies of 8-14 MeV at a Siemens Primus linac. The principal components of the linac head were simulated using MCNPX code for different applicators. The consequences of measurements and simulations revealed a good agreement. Gamma index values were below 1 for most points, for all energy values and all applicators in percent depth dose and dose profile computations. A number of states exhibited rather large gamma indices; these points were located at the tail of the percent depth dose graph; these points were less used in in radiotherapy. In the dose profile graph, gamma indices of most parts were below 1. The discrepancies between the simulation results and measurements in terms of Zmax, R90, R80 and R50 were insignificant. The results of Monte Carlo simulations showed a good agreement with the measurements. The software can be used for simulating electron modes of a Siemens Primus linac when direct experimental measurements are not feasible.

Accuracy evaluation of distance inverse square law in determining virtual electron source location in Siemens Primus linac.

The aim of this study is to evaluate the accuracy of the inverse square law (ISL) method for determining location of virtual electron source (SVir) in Siemens Primus linac. So far, different experimental methods have presented for determining virtual and effective electron source location such as Full Width at Half Maximum (FWHM), Multiple Coulomb Scattering (MCS), and Multi Pinhole Camera (MPC) and Inverse Square Law (ISL) methods. Among these methods, Inverse Square Law is the most common used method. Firstly, Siemens Primus linac was simulated using MCNPX Monte Carlo code. Then, by using dose profiles obtained from the Monte Carlo simulations, the location of SVir was calculated for 5, 7, 8, 10, 12 and 14MeV electron energies and 10cm×10cm, 15cm×15cm, 20cm×20cm and 25cm×25cm field sizes. Additionally, the location of SVir was obtained by the ISL method for the mentioned electron energies and field sizes. Finally, the values obtained by the ISL method were compared to the values resulted from Monte Carlo simulation. The findings indicate that the calculated SVir values depend on beam energy and field size. For a specific energy, with increase of field size, the distance of SVir increases for most cases. Furthermore, for a special applicator, with increase of electron energy, the distance of SVir increases for most cases. The variation of SVir values versus change of field size in a certain energy is more than the variation of SVir values versus change of electron energy in a certain field size. According to the results, it is concluded that the ISL method can be considered as a good method for calculation of SVir location in higher electron energies (14MeV).

The comparison between 6 MV Primus LINAC simulation output using EGSnrc and commissioning data

AbstractIntroductionMonte Carlo calculation method is considered to be the most accurate method for dose calculation in radiotherapy. The purpose of this research is comparison between 6 MV Primus LINAC simulation output with commissioning data using EGSnrc and build a Monte Carlo geometry of 6 MV Primus LINAC as realistically as possible. The BEAMnrc and DOSXYZnrc (EGSnrc package) Monte Carlo model of the LINAC head was used as a benchmark.MethodsIn the first part, the BEAMnrc was used for the designing of the LINAC treatment head. In the second part, dose calculation and for the design of 3D dose file were produced by DOSXYZnrc. The simulated PDD and beam profile obtained were compared with that calculated using commissioning data. Good agreement was found between calculated PDD (1·1%) and beam profile using Monte Carlo simulation and commissioning data. After validation, TPR20,10, TMR and Spvalues were calculated in five different field.ResultsGood agreement was found between calculated values by using Monte Carlo simulation and commissioning data. Average differences for five field sizes in this approach is about 0·83% for Sp. for TPR20,10differences for field sizes 10×10 cm2is 0·29% and for TMR in five field sizes, the average value is ~1·6%.ConclusionIn conclusion, the BEAMnrc and DOSXYZnrc codes package have very good accuracy in calculating dose distribution for 6 MV photon beam and it can be considered as a promising method for patient dose calculations and also the Monte Carlo model of primus linear accelerator built in this study can be used as method to calculate the dose distribution for cancer patients.

Dosimetric characteristics of LinaTech DMLC H multi leaf collimator: Monte Carlo simulation and experimental study.

This study evaluated the basic dosimetric characteristics of a Dynamic Multi Leaf Collimator (DMLC) using a diode detector and film measurements for Intensity Modulated Radiation Therapy Quality Assurance (IMRT QA). The EGSnrc Monte Carlo (MC) simulation system was used for the determination of MLC characteristics. Radiation transmission and abutting leaf leakage relevant to the LinaTech DMLC H were measured using an EDGE detector and EBT3 film. In this study, the BEAMnrc simulation code was used for modeling. The head of Siemens PRIMUS linac (6 MV) with external DMLC H was entered into a BEAMnrc Monte Carlo model using practical dosimetry data. Leaf material density, as well as interleaf and abutting air gaps were determined according to the computed and measured dose profiles. The IMRT QA field was used to evaluate the dose distribution of the simulated DMLC H. According to measurements taken with the EDGE detector and film, the total average measured leakage was 1.60 ± 0.03% and 1.57 ± 0.05%, respectively. For these measurements, abutting leaf transmission was 54.35 ± 1.85% and 53.08 ± 2.05%, respectively. To adapt the simulated leaf dose profiles with measurements, leaf material density, interleaf and abutting air gaps were adjusted to 18 g/cm3, 0.008 cm and 0.108 cm, respectively. Thus, the total average leakage was estimated to be about 1.59 ± 0.02%. The step‐and‐shoot IMRT was implemented and 94% agreement was achieved between the film and MC, using 3%‐3 mm gamma criteria. The results of this study showed that the dosimetric characteristics of DMLC H satisfied international standards.

Developing equations to predict surface dose and therapeutic interval in bolused electron fields: A Monte Carlo Study

In this research, we aim to investigate the influence of different materials, as a bolus, on the low-energy electron beam dose distributions and to develop equations for predicting surface dose based on bolus thickness, as well as the therapeutic interval based on surface dose.All the Monte Carlo (MC) calculations and measurements were conducted on a Siemens PRIMUS linac. Based on EGSnrc MC code, BEAMnrc system was used to model a Siemens linac and generate phase-space files for three electron beams (6, 8, and 10MeV). The particles were transported from the phase-space files to the bolus materials and the simulated water phantom using DOSXYZnrc. Various materials with different thicknesses were examined as a bolus, and appropriate equations were determined for each material and electron beam.The comparison of percent depth dose (PDD) curves and beam profiles, using MC, with the measured data demonstrated that the calculated values properly matched with the measurements. The results indicated that the use of bolus materials with the density of higher than soft tissue can increase both surface dose and therapeutic interval simultaneously. This finding arises from the fact that the required bolus thickness for achieving the therapeutic surface dose decreases in the case of high-density materials.Two series of prediction equations were proposed for predicting the surface dose based on bolus thickness and the therapeutic interval based on surface dose. These equations are able to calculate properly the bolus thickness required for producing a therapeutic surface dose (above 90%) for any therapeutic interval.