Electron Beam Dose Distributions Research Articles

Development and verification of an electron Monte Carlo engine for applications in intraoperative radiation therapy.

In preparation of future clinical trials employing the Mobetron electron linear accelerator to deliver FLASH Intraoperative Radiation Therapy (IORT), the development of a Monte Carlo (MC)-based framework for dose calculation was required. To extend and validate the in-house developed fast MC dose engine MonteRay (MR) for future clinical applications in IORT. MR is a CPU MC dose calculation engine written in C++ that is capable of simulating therapeutic proton, helium, and carbon ion beams. In this work, development steps are taken to include electrons and photons in MR are presented. To assess MRs accuracy, MR generated simulation results were compared against FLUKA predictions in water, in presence of heterogeneities as well as in an anthropomorphic phantom. Additionally, dosimetric data has been acquired to evaluate MRs accuracy in predicting dose-distributions generated by the Mobetron accelerator. Runtimes of MR were evaluated against those of the general-purpose MC code FLUKA on standard benchmark problems. MR generated dose distributions for electron beams incident on a water phantom match corresponding FLUKA calculated distributions within 2.3% with range values matching within 0.01mm. In terms of dosimetric validation, differences between MR calculated and measured dose values were below 3% for almost all investigated positions within the water phantom. Gamma passing rate (1%/1mm) for the scenarios with inhomogeneities and gamma passing rate (3%/2mm) with the anthropomorphic phantom, were>99.8% and 99.4%, respectively. The average dose differences between MR (FLUKA) and the measurements was 1.26% (1.09%). Deviations between MR and FLUKA were well within 1.5% for all investigated depths and 0.6% on average. In terms of runtime, MR achieved a speedup against reference FLUKA simulations of about 13 for 10 MeV electrons. Validations against general purpose MC code FLUKA predictions and experimental dosimetric data have proven the validity of the physical models implemented in MR for IORT applications. Extending the work presented here, MR will be interfaced with external biophysical models to allow accurate FLASH biological dose predictions in IORT.

4D in vivo dosimetry for a FLASH electron beam using radiation-induced acoustic imaging

Objective. The primary goal of this research is to demonstrate the feasibility of radiation-induced acoustic imaging (RAI) as a volumetric dosimetry tool for ultra-high dose rate FLASH electron radiotherapy (FLASH-RT) in real time. This technology aims to improve patient outcomes by accurate measurements of in vivo dose delivery to target tumor volumes. Approach. The study utilized the FLASH-capable eRT6 LINAC to deliver electron beams under various doses (1.2 Gy pulse−1 to 4.95 Gy pulse−1) and instantaneous dose rates (1.55 × 105 Gy s−1 to 2.75 × 106 Gy s−1), for imaging the beam in water and in a rabbit cadaver with RAI. A custom 256-element matrix ultrasound array was employed for real-time, volumetric (4D) imaging of individual pulses. This allowed for the exploration of dose linearity by varying the dose per pulse and analyzing the results through signal processing and image reconstruction in RAI. Main Results. By varying the dose per pulse through changes in source-to-surface distance, a direct correlation was established between the peak-to-peak amplitudes of pressure waves captured by the RAI system and the radiochromic film dose measurements. This correlation demonstrated dose rate linearity, including in the FLASH regime, without any saturation even at an instantaneous dose rate up to 2.75 × 106 Gy s−1. Further, the use of the 2D matrix array enabled 4D tracking of FLASH electron beam dose distributions on animal tissue for the first time. Significance. This research successfully shows that 4D in vivo dosimetry is feasible during FLASH-RT using a RAI system. It allows for precise spatial (∼mm) and temporal (25 frames s−1) monitoring of individual FLASH beamlets during delivery. This advancement is crucial for the clinical translation of FLASH-RT as enhancing the accuracy of dose delivery to the target volume the safety and efficacy of radiotherapeutic procedures will be improved.

Planar dose calculation of electron therapy

Purpose. The aim of this study is to determine the planar dose distribution of irregularly-shaped electron beams at their maximum dose depth (z max) using the modied lateral build-up ratio (LBR) and curve-fitting methods. Methods. Circular and irregular cutouts were created using Cerrobend alloy for a 14 × 14 cm2 applicator. Percentage depth dose (PDD) at the standard source-surface-distance (SSD = 100 cm) and point dose at different SSD were measured for each cutout. Orthogonal profiles of the cutouts were measured at z max. Data were collected for 6, 9, 12, and 15 MeV electron beam energies on a VERSA HDTM LINAC using the IBA Blue Phantom2 3D water phantom system. The planar dose distributions of the cutouts were also measured at z max in solid water using EDR2 films. Results. The measured PDD curves were normalized to a normalization depth (d 0) of 1 mm. The lateral-buildup-ratio (LBR), lateral spread parameter (σ R (z)), and effective SSD (SSD eff ) for each cutout were calculated using the PDD of the open applicator as the reference field. The modified LBR method was then employed to calculate the planar dose distribution of the irregular cutouts within the field at least 5 mm from the edge. A simple curve-fitting model was developed based on the profile shapes of the circular cutouts around the field edge. This model was used to calculate the planar dose distribution of the irregular cutouts in the region from 3 mm outside to 5 mm inside the field edge. Finally, the calculated planar dose distribution was compared with the film measurement. Conclusions. The planar dose distribution of electron therapy for irregular cutouts at z max was calculated using the improved LBR method and a simple curve-fitting model. The calculated profiles were within 3% of the measured values. The gamma passing rate with a 3%/3 mm and 10% dose threshold was more than 96%.

Investigation of the possibility of shaping an electron dose field of a clinical accelerator with 3D printed polymer products

The improvement of existing dose delivery techniques is a constant goal in cancer radiation therapy, since it increases the treatment efficiency. For example, the use of so-called boluses and compensators offers ways to correct for surface irregularities or tissue inhomogeneities in some irradiated areas. While compensators are usually inserted along the radiation beam at a certain distance from the patient, boluses are located directly on the surface of the patient's body and follow its contours. Depending on their thickness and shape, these beam modifiers enable a shift of the depth of the dose maximum and control the depth-dose distribution. However, an accurate production of beam modifiers often requires complex procedures, thus limiting their use in the clinic. This study suggests the fused filament fabrication technique to produce polymer-based beam modifiers for shaping the dose of clinical electron beams. The feasibility of this approach was studied through a series of experiments and simulations using the Monte Carlo method. The results show that therapeutic electron beams with energies of 6–12 MeV can be effectively modified using such polymer samples. The numerical model can also be used to evaluate the dose distribution of electron beams shaped by plastic absorbers prior to production, thereby making it possible to select the compensator geometry for specific purposes.

Fundamental evaluation of dose and dose distribution under applied topical agents and dressings used for skin care in radiotherapy

PurposeRadiation dermatitis is a common adverse event in radiotherapy and is treated using topical agents or dressings; however, it may be exacerbated by increasing the skin dose during irradiation. This study investigated the effects on the dose and dose distribution assuming irradiation without wiping the agent off. MethodsFive types of topical products and dressings available in clinical settings were used in this study. These products were applied to a tough water phantom, and the dose and dose distributions of photon and electron beam were measured using an ionization chamber and an EBT3 Gafchromic film, respectively. For dose measurements, topical products were applied to thicknesses of 0, 1, 2, 3, 4, 5, and 10 mm, and 100 monitor units (MU) were irradiated. The dressings were pasted onto the phantom. For dose distribution measurements, the Gafchromic film was placed parallel to the radiation flux. The thicknesses of the topical products were 0, 1, and 5 mm. ResultsThe doses of 6 and 10 MV X-rays increased 0.35–0.82% and 0.25–0.55% with topical product thicknesses of 4 or 5 mm, respectively. In contrast, the electron beam dose decreased by 10.67% at 6 MeV and 2.11% at 12 MeV with a topical product thickness of 5 mm. The applied topical products shifted the X-ray and electron beam dose distributions toward the surface. However, the dressings did not affect the dose and dose distributions. Specifically, dose changes were less than 0.3% for all employed dressings. ConclusionBased on the results of this study, we suggest that topical agents and dressings do not affect the dose and dose distribution except when topical agents are applied particularly thickly. However, the actual dose received by the skin needs to be investigated in the future.

Characteristics of Dose Distributions of Electron Beams Used in the Radiation Processing of Food Products

Characteristics of Dose Distributions of Electron Beams Used in the Radiation Processing of Food Products

Characteristics of very high-energy electron beams for the irradiation of deep-seated targets.

Driven by advances in accelerator technology and the potential of exploiting the FLASH effect for the treatment of deep-seated targets (>5cm), there is an active interest in the construction of devices to deliver very high-energy electron (VHEE) beams for radiation therapy. The application of novel VHEE devices, however, requires an assessment of the tradeoffs between the different beam parameter choices including beam energies, beam divergences, and maximal field sizes. This study systematically examines the dosimetric beam properties of VHEE beams, determining their clinical usefulness while marking their limits of applications for different beam configurations. We performed Monte Carlo simulations of the dose distributions of electron beams for different energies (25-250MeV), source-to-surface distances (SSD) (50cm, 100cm, parallel), and field sizes (2cm2 ×2cm2 to 15cm2 ×15cm2 ) in water using a research version of the RayStation treatment planning system (RaySearch Labs 9A IONPG). The beam was simulated using a monoenergetic point source and perfect collimation. Central axis percentage depth dose (PDD) and transverse dose profiles at multiple depths were evaluated and compared to those of MV photon beams. Profile characteristics including therapeutic range (TR) at 90%, proximal fall-off (PFO) at 90%, lateral penumbra (LP) at 90%-10%, and field width (FW) at 90% were obtained. Very high-energy electrons beams with SSD 100cm and parallel beams (infinite SSD) exhibit a linear to near-linear increase of TR as a function of energy in the simulated energy range and reach values well beyond the typical depths of lesions encountered in clinics (<20cm). Their TR show a marked field size dependence only for field sizes <10cm2 ×10cm2 . For VHEE beams with SSD 50cm, TR are largely reduced (4-8cm). For beam energies >150MeV with large SSD (>100cm), for many configurations, there is no substantial difference in PDD when adding an opposed beam. This may potentially reduce the number of VHEE beams needed for treatment by a factor of two compared to a treatment using lower energies and lower SSD. In order to cover deep-seated targets homogeneously, VHEE devices with a parallel beam must provide a maximum field size up to several centimeters larger than the tumor size. For the investigated diverging beams, there is not such a significant field width reduction with depth for larger fields as it is compensated by divergence. Penumbrae of VHEE beams are smaller than those of clinical MV photon beams for lower depths (<5cm) but increase quickly for larger depths. There is only a relatively small dependence of penumbra on the SSD of the beam. The findings presented in this study assess the performance of VHEE beams and offer a first estimate of treatment indications and tradeoffs for a given design of a VHEE device. SSD >100cm results in clinically more favorable PDD. Beam energies of 100MeV and above are needed to cover common tumors (5-15cm in-depth) conformally. Higher energies provide an additional benefit specifically for small and deep-seated lesions due to their reduced lateral penumbrae.

Measurements of Electron Beam Dose Distributions in Perspex Block for Different Field Size

The linear accelerator is used in radiotherapy to treat tumors whether it was benign or malignant. The megavoltage electron beam is used to treat superficial tumors that do not exceed 5cm depth. In this work the dose distribution before irradiating the patient to check whether the prescribed dose is matched with the irradiated dose to help the physicist to fix the errors or deviations if it is detected. The quality assurance (QA) measured of electron beam with energy 12 MeV at common different depths and field sizes using StarTrack 2D detector and to ensure that it does not exceed the recommended limits. The equipped QA device is a StarTrack 2D detector under the linear accelerator infinity from Elekta at 100 cm from source-to surface distance SSD. The tested energy 12 MeV at depths 0.5 cm and 1.5 cm for field sizes 6cm×6cm, 10cm×10 cm and 14cm×14cm as limits measured according to the International Electrotechnical Commissioning (IEC) protocols. Results show that the revealed an error in the output dose at 6cm×6cm and 10cm×10 cm field sizes for 1.5 cm depth but for 14cm×14cm field size at 0.5 cm depth, the dose found to be above the tolerance. Also it’s found that the output dose is highly reached to 1.5 cm depth than the 0.5 cm. Furthermore, all the rotation axis of the collimator are within the limits with a few noises in the signal at the inline and the crossline axis. We conclude that there was an error in the output does need to be recalibrated before irradiating the patients to electron beam therapy at 12 MeV to assure that the treatment is qualified and efficient.

Investigation of the properties changes observed for plastic samples made by fused deposition modelling under radiation exposure

This work shows investigation of the transmission dynamics of polymer samples made of PLA plastic (polylactide) by fused deposition modelling for electron beam. Besides, results of tests for mechanical destruction (compression) of plastic samples with radiation exposure and without are shown. Article demonstrates that properties of plastic samples are stable up to 1.5 kGy, that proves the suitability of this material for sample production intended for depth dose distributions of electron beams.

Development and validation of an analytical model allowing accurate predictions of gamma and electron beam dose distributions in a water medical phantom.

The aim of this work was to study photon and electron dose distributions in a phantom filled with water using the Monte Carlo Geant4 tool for electron energies ranging from 1 to 21MeV and for photon energies ranging from 1.25MeV to 25MeV, corresponding to conventional radiotherapy Linac energies. The results of the Geant4 calculations were validated based on the relevant experimental data previously published. The results obtained were fitted and analytical models of dose distributions were developed for gamma radiation and electrons. For each of these models, one-dimensional (including dose depth profiles as a function of the depth inside the phantom) and two-dimensional (including the dose distribution as a function of depth and lateral position inside the phantom) dose distributions have been considered. Results are presented for photons and electrons of various energies. The coefficient of determination [Formula: see text] illustrates an excellent match between the developed analytical model and the Geant4 results. It is demonstrated that the analytical models developed in the present study can be applied in various fields such as those used for calibration applications and radiation therapy. It is concluded that the analytical models developed allow for quick, easy and reliable clinical dose estimates and offer promising alternatives to the standard tools and methods used in radiotherapy for treatment planning.

Theoretical study of the dose measurements reliability with longitudinally arranged dosimetry films in materials with different densities

Investigation purpose. Theoretical study of the depth dose measurements for therapeutic electron beam with longitudinally arranged dosimetry films in materials with different densities. Materials and methods. The work studies how the density of the medium, in which electrons propagate, affects the measured percentage depth dose and its reliability (PDD) . For that, we calculate the distribution of the electron beam dose distribution in homogeneous materials with different densities and in a dosimetry film placed in materials with these densities. The density of material in the calculation varies from 0.4 to 2.3 g/cm3 with a 0.1 g/cm3 step. The coincidence of the PDD within the experimental measurement accuracy, that equals 4% for dosimetry film and 2% for measurements without it, is chosen as the data fitting criterion. Results. The PDD calculated for two geometries and for different media densities is the result of this work. The calculation shows that PDD difference is negligible when the density of the film is equal to the media one. With decreasing of the media density the difference appears in the regions of both shallow and great depth. The PDD is lower for the geometry with film than for geometry without it in case of these densities. When the media density is rising the opposite effect is observed: the PDD in the film is higher than in geometry without film. The maximum range and therapeutic range in both geometries coincide for the calculated curves throughout the range under study. Discussion. The work shows applicability of the investigated method for measurement of the electron beam percentage depth dose in media with densities ranging from 0.9 to 1.8 g/cm3. The results show that PDD measurement method with longitudinally arranged dosimetry films can be applied to determine the maximum range and therapeutic range for media with densities of 0.4 to 2.3 g/cm3, and to measure the half-value depth for media with densities ranging from 0.7 to 2.1 g/cm3.

Estimation of the three-dimensional (3D) dose distribution of electron beams from medical linear accelerator (LINAC) using plastic scintillator plate

Measurements of three-dimensional (3D) dose distribution of electron-beams in water are important for high-energy electron beams from medical linear accelerators (LINAC). Although ionization chambers are commonly used for this purpose, measurements take a long time for precise 3D dose distribution. To solve the problem, we tried the measurements of the 3D dose distributions using a scintillator plate combined with a mirror. After we placed a 1 mm thick plastic scintillator plate at the upper inside of a black box, a water phantom was set above the plastic scintillator plate outside the black box, and electron beam was irradiated to the water phantom from the upper side. The attenuated electron-beam by the water in the phantom was detected by the plastic scintillator plate and the scintillation image was formed in the plate. The image was reflected by a surface mirror set below the plastic scintillator plate and detected by a cooled charge coupled device (CCD) camera from the side. We changed the depths of the water in the phantom, obtained the scintillation images, and calculated a 3D scintillation image using the measured images. Measurements were made for 9 MeV and 12 MeV electron-beams using the imaging system. From the images, we could successfully form 3D scintillation images. The depth profiles measured from the 3D images showed almost identical distribution with those calculated by the planning system within the difference of 5%. The lateral profiles also showed almost identical within the difference of the widths less than 2.5 mm. We conclude that the proposed method is promising for 3D dose distribution measurements of electron-beams.

EP-1771 Measuring the influence of magnetic fields on the dose distributions of clinical electron beams

EP-1771 Measuring the influence of magnetic fields on the dose distributions of clinical electron beams

Comparing experimental assessment of the peripheral dose outside the applicator in electron beams of ELEKTA with Treatment planning system

Introduction: The use of electrons in the electron therapy to destroy tumoral tissue is dedicated significant contribution of different methods of radiation therapy. Scattered radiation due to exited electrons of the applicator affect the dose out of the field in the patient's normal tissue. The aim of this study is to determine the peripheral dose outside the applicator in the electron beams of Elekta accelerator. Materials and Methods: In this study the peripheral dose outside the applicator in electron beams was measured using linear accelerator Elekta Synergy Plateform and it was compared with the obtained results from the treatment planning system (TPS) Isogray model. The peripheral dose profiles were measured and compared Using the solid water phantom set and the film dosimetry system of EBT3 at energy levels 6, 10 and 18 MeV in the applicators with the different dimensions and at different angles of 0, 10 and 20 at the depth 0 and 0.5 and 1cm and for each energy level at depth of maximum dose (Dmax). The peripheral dose Profiles has been normalized to the edge of the field. Results: The highest Peak dose was observed in 18 MeV beam outside the applicator. Peak dose was reduced with increasing the electron beam energy. Using the applicator 20 × 20 cm2 for energy 18 MeV, a dose peak of 1.6% was observed on the surface at a distance of 2 cm from the outer edge of applicator and also for energy 6 MeV, 1.15% at the same distance from the edge of the applicator. It was found that the dose peak decreases with increasing depth and increases with increasing field size. Also the dose peak increased with increasing gantry angle from zero to 20 degrees. The result of measured peripheral dose outside the applicator by using TPS of Clarkson algorithm showed that the dose Calculation can be evaluated only up to distance of 3cm from the edge of the field. Conclusion: Totally, anticipation of dose distribution of the electron beams in collision with matter is different and difficult in various accelerators because of the complexity of the behavior of electrons. However, according to the results of this study in Elekta accelerator, noticeably dose peak was observed in use of high-energy electron beams because of more incidence of bremsstrahlung radiation outside the treatment field. The radiotherapy team can have prevented from damage to organs at risk outside the applicator by awareness of the value and location of peripheral dose outside the treatment field with applying the principles of radiation protection like shields. The evaluated TPS is not a good way to measure the peripheral dose outside the field.

Experimental validatıon of peripheral dose distribution of electron beams for eclipse electron Monte Carlo algorithm

AbstractAimThe accuracy of two calculation algorithms of the Varian Eclipse treatment planning system (TPS), the electron Monte Carlo algorithm (eMC) and general Gaussian pencil beam algorithm (GGPB) for calculating peripheral dose distribution of electron beams was investigated.MethodsPeripheral dose measurements were carried out for 6, 9, 12, 15, 18 and 22 MeV electron beams using parallel plate ionisation chamber and EBT3 film in the slab phantom. Measurements were performed for 6×6, 10×10 and 25×25 cm2 cone sizes at dmax of each energy up to 20 cm beyond the field edges. The measured and TPS calculated data were compared.ResultsThe TPS underestimated the out-of-field doses. The difference between measured and calculated doses increase with the cone size. For ionisation chamber measurement, the largest deviation between calculated and measured doses is &lt;4·29% using the eMC, but can increase up to 8·72% of the distribution using GGPB. For film measurement, the minimum gamma analysis passing rates between measured and calculated dose distributions for all field sizes and energies used in this study were 91·2 and 74·7% for eMC and GGPB, respectively.FindingsThe use of GGPB for planning large field treatments with 6 MeV could lead to inaccuracies of clinical significance.

Electron beam dose perturbations caused by diode detectors used for in vivo dosimetry: Gafchromic film dose measurements in a realistic pelvic prosthesis phantom

Background and purposeDiode detectors used for in vivo dosimetry could influence patient dose due to their shadow effect in radiation fields. This study measures the impact of in vivo diodes on therapeutic electron beam dose distributions in a realistic pelvic prosthesis phantom. Materials and methodsTwo commercially available electron in vivo diodes (the IBA Dosimetry EDP-53G and Sun Nuclear QED 1112000) were studied. Depth dose measurements for 8 × 8, 10 × 10 and 11 × 11 cm2 15 MeV electron fields for open beams and with the diodes placed on the central axis (CAX) of the beam were acquired using Gafchromic EBT3 films in a realistic pelvic phantom that contains Ti hip prosthesis and bony structures. Deviations between dose data obtained with and without the diodes in the electron fields were used to evaluate the impact of the diodes on the electron dose inside the phantom. ResultsCAX depth dose distributions measured using Gafchromic EBT3 film with the diodes in the electron fields on the prosthesis and non-prosthesis sides of the phantom showed dose reductions in the shadow of the diodes compared to dose data acquired in open fields. The average dose reductions recorded along the CAX at depths ≤ 4.0 cm ranged from 6% to 8% and 10% to 13% for the QED and EDP diodes, respectively. In the treatment of epithelial skin cancer or scleredema of Buschke using 10 irradiation fractions, the diodes would reduce the electron dose by approximately 1% if only single IVD measurements are performed. For treatment regimes using 3–5 fractions a dose reduction ≥ 2% would be attained. ConclusionElectron in vivo diodes can induce strong perturbations on patient dose that could influence clinical outcome especially for single-fraction electron treatment of CD30+ lymphoproliferative disorders and accelerated partial breast irradiation delivered by intraoperative radiotherapy using a single dose after lumpectomy or a treatment regime using 3–5 fractions.

Modeling the influence of electron beam energy distribution on quality of radiation processing

The obtained values of most probable energy and practical range have been compared to values calculated according to the formula proposed by the internationally recognized documents. The presented results of the study are focused on the issue of the influence of electron beam energy spread on the depth dose distribution and practical range of electron beam in the irradiated material. The computational experiments have been performed using the Monte-Carlo simulation method for modeling the electron beam energy spectra and depth dose distributions of electrons in aluminum target. Obtained values of most probable energy Ep and practical range Rp have been compared to the values calculated according to formula proposed by the internationally recognized report. The value of a practical range of electrons Rp strongly depends on electron beam energy spread, even in case when value of most probable energy Ep of electrons in the beam is unchanged. Results of computer experiments show that in case of a large energy spread, and presence of asymmetry of electron energy distribution, the electrons energy can’t be determined properly by empirical formulas included to the international standards.

Measurement of the influence of titanium hip prosthesis on therapeutic electron beam dose distributions in a novel pelvic phantom

PurposeTo investigate the degree of 18 and 22MeV electron beam dose perturbations caused by unilateral hip titanium (Ti) prosthesis. MethodsMeasurements were acquired using Gafchromic EBT2 film in a novel pelvic phantom made out of Nylon-12 slices in which a Ti-prosthesis is embedded. Dose perturbations were measured and compared using depth doses for 8×8, 10×10 and 11×11cm2 applicator-defined field sizes at 95cm source-surface-distance (SSD). Comparisons were also made between film data at 100cm SSD for a 10×10cm2 field and dose calculations made on CMS XiO treatment planning system utilizing the pencil beam algorithm. The extent of dose deviations caused by the Ti prosthesis based on film data was quantified through the dose enhancement factor (DEF), defined as the ratio of the dose influenced by the prosthesis and the unchanged beam. ResultsAt the interface between Nylon-12 and the Ti implant on the prosthesis entrance side, the dose increased to values of 21±1% and 23±1% for 18 and 22MeV electron beams, respectively. DEFs increased with increasing electron energy and field size, and were found to fall off quickly with distance from the nylon-prosthesis interface. A comparison of film and XiO depth dose data for 18 and 22MeV gave relative errors of 20% and 25%, respectively. ConclusionThis study outlines the lack of accuracy of the XiO TPS for electron planning in highly heterogeneous media. So a dosimetric error of 20–25% could influence clinical outcome.

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.

Electron linear accelerator system for natural rubber vulcanization

Development of an electron accelerator system, beam diagnostic instruments, an irradiation apparatus and electron beam processing methodology for natural rubber vulcanization is underway at the Plasma and Beam Physics Research Facility, Chiang Mai University, Thailand. The project is carried out with the aims to improve the qualities of natural rubber products. The system consists of a DC thermionic electron gun, 5-cell standing-wave radio-frequency (RF) linear accelerator (linac) with side-coupling cavities and an electron beam irradiation apparatus. This system is used to produce electron beams with an adjustable energy between 0.5 and 4MeV and a pulse current of 10–100mA at a pulse repetition rate of 20–400Hz. An average absorbed dose between 160 and 640Gy is expected to be archived for 4MeV electron beam when the accelerator is operated at 400Hz. The research activities focus firstly on assembling of the accelerator system, study on accelerator properties and electron beam dynamic simulations. The resonant frequency of the RF linac in π/2 operating mode is 2996.82MHz for the operating temperature of 35°C. The beam dynamic simulations were conducted by using the code ASTRA. Simulation results suggest that electron beams with an average energy of 4.002MeV can be obtained when the linac accelerating gradient is 41.7MV/m. The rms transverse beam size and normalized rms transverse emittance at the linac exit are 0.91mm and 10.48πmm·mrad, respectively. This information can then be used as the input data for Monte Carlo simulations to estimate the electron beam penetration depth and dose distribution in the natural rubber latex. The study results from this research will be used to define optimal conditions for natural rubber vulcanization with different electron beam energies and doses. This is very useful for development of future practical industrial accelerator units.