Normal lung tissue complication probability in MR-Linac and conventional radiotherapy.

PURPOSE: To study normal lung tissue (NLT) complications in magnetic resonance (MR) image based linac and conventional radiotherapy (RT) techniques. MATERIALS AND METHODS: The Geant4 toolkit was used to simulate a 6 MV photon beam. A homogenous magnetic field of 1.5 Tesla (T) was applied in both perpendicular and parallel directions relative to the radiation beam.Analysis of the NLT complications was assessed according to the normal lung tissue complication probability (NTCP), the mean lung dose (MLD), and percentage of the lung volume receiving doses greater than 20 Gy (V20), using a sample set of CT images generated from a commercially available 4D-XCAT digital phantom. RESULTS: The results show that the MLD and V20 were lower for MR-linac RT. The largest reduction of MLD and V20 for MR-linac RT configurations were 5 Gy and 29.3%, respectively. CONCLUSION: MR-linac RT may result in lower NLT complications when compared to conventional RT.

Monte Carlo calculation of photo-neutron dose produced by circular cones at 18 MV photon beams.

AIM: The aim of this study is to calculate neutron contamination at the presence of circular cones irradiating by 18 MV photons using Monte Carlo code. BACKGROUND: Small photon fields are one of the most useful methods in radiotherapy. One of the techniques for shaping small photon beams is applying circular cones made of lead. Using this method in high energy photon due to neutron contamination is a crucial issue. MATERIALS AND METHODS: Initially, Varian linac producing 18 MV photons was simulated and after validating the code, various circular cones were also simulated. Then, the number of neutrons, neutron equivalent dose and absorbed dose per Gy of photon dose were calculated along the central axis. RESULTS: Number of neutrons per Gy of photon dose had their maximum value at depth of 2 cm and these values for 5, 10, 15, 20 and 30 mm circular cones were 9.02, 7.76, 7.61, 6.02 and 5.08 (n cm-2 Gy-1), respectively. Neutron equivalent doses per Gy of photon dose had their maximum at the surface of the phantom and these values for mentioned collimators were 1.48, 1.33, 1.31, 1.12 and 1.08 (mSv Gy-1), respectively. Neutron absorbed doses had their maximum at the surface of the phantom and these values for mentioned collimators sizes were 103.74, 99.71, 95.77, 81.46 and 78.20 (µGy/Gy), respectively. CONCLUSIONS: As the field size gets smaller, number of neutrons, equivalent and absorbed dose per Gy of photon increase. Also, neutron equivalent dose and absorbed dose are maximum at the surface of phantom and then these values will be decreased.

Is grid therapy useful for all tumors and every grid block design?

Grid therapy is a treatment technique that has been introduced for patients with advanced bulky tumors. The purpose of this study is to investigate the effect of the radiation sensitivity of the tumors and the design of the grid blocks on the clinical response of grid therapy. The Monte Carlo simulation technique is used to determine the dose distribution through a grid block that was used for a Varian 2100C linear accelerator. From the simulated dose profiles, the therapeutic ratio (TR) and the equivalent uniform dose (EUD) for different types of tumors with respect to their radiation sensitivities were calculated. These calculations were performed using the linear quadratic (LQ) and the Hug-Kellerer (H-K) models. The results of these calculations have been validated by comparison with the clinical responses of 232 patients from different publications, who were treated with grid therapy. These published results for different tumor types were used to examine the correlation between tumor radiosensitivity and the clinical response of grid therapy. Moreover, the influence of grid design on their clinical responses was investigated by using Monte Carlo simulations of grid blocks with different hole diameters and different center-to-center spacing. The results of the theoretical models and clinical data indicated higher clinical responses for the grid therapy on the patients with more radioresistant tumors. The differences between TR values for radioresistant cells and radiosensitive cells at 20 Gy and 10 Gy doses were up to 50% and 30%, respectively. Interestingly, the differences between the TR values with LQ model and H-K model were less than 4%. Moreover, the results from the Monte Carlo studies showed that grid blocks with a hole diameters of 1.0 cm and 1.25 cm may lead to about 19% higher TR relative to the grids with hole diameters smaller than 1.0 cm or larger than 1.25 cm (with 95% confidence interval). In sum-mary, the results of this study indicate that grid therapy is more effective for tumors with radioresistant characteristics than radiosensitive tumors.

Dose distribution verification for GYN brachytherapy using EBT Gafchromic film and TG-43 calculation.

AIM: Verification of dose distributions for gynecological (GYN) brachytherapy implants using EBT Gafchromic film. BACKGROUND: One major challenge in brachytherapy is to verify the accuracy of dose distributions calculated by a treatment planning system. MATERIALS AND METHODS: A new phantom was designed and fabricated using 90 slabs of 18 cm × 16 cm × 0.2 cm Perspex to accommodate a tandem and Ovoid assembly, which is normally used for GYN brachytherapy treatment. This phantom design allows the use of EBT Gafchromic films for dosimetric verification of GYN implants with a cobalt-60 HDR system or a LDR Cs-137 system. Gafchromic films were exposed using a plan that was designed to deliver 1.5 Gy of dose to 0.5 cm distance from the lateral surface of ovoids from a pair of ovoid assembly that was used for treatment vaginal cuff. For a quantitative analysis of the results for both LDR and HDR systems, the measured dose values at several points of interests were compared with the calculated data from a commercially available treatment planning system. This planning system was utilizing the TG-43 formalism and parameters for calculation of dose distributions around a brachytherapy implant. RESULTS: The results of these investigations indicated that the differences between the calculated and measured data at different points were ranging from 2.4% to 3.8% for the LDR Cs-137 and HDR Co-60 systems, respectively. CONCLUSION: The EBT Gafchromic films combined with the newly designed phantom could be utilized for verification of the dose distributions around different GYN implants treated with either LDR or HDR brachytherapy procedures.

Bystander Response Following High-Dose X-irradiation; Time-dependent Nature of GammaH2AX Foci and Cell Death Consequences.

Background: The paradigm shifts in target theory could be defined as the radiation-triggered bystander response in which the radiation deleterious effects occurred in the adjacent cells. Objective: This study aims to assess bystander response in terms of DNA damage and their possible cell death consequences following high-dose radiotherapy. Temporal characteristics of gH2AX foci as a manifestation of DNA damage were also evaluated. Material and Methods: In this experimental study, bystander response was investigated in human carcinoma cells of HeLa and HN5, neighboring those that received high doses. Medium transfer was performed from 10 Gy-irradiated donors to 1.5 Gy-irradiated recipients. GammaH2AX foci, clonogenic and apoptosis assays were investigated. The gH2AX foci time-point study was implemented 1, 4, and 24 h after the medium exchange. Results: DNA damage was enhanced in HeLa and HN5 bystander cells with the ratio of 1.27 and 1.72, respectively, which terminated in more than two-fold clonogenic survival decrease, along with gradual apoptosis increase. GammH2AX foci temporal characterization revealed maximum foci scoring at the 1 h time-point in HeLa, and also 4 h in HN5, which remained even 24 h after the medium sharing in higher level than the control group. Conclusion: The time-dependent nature of bystander-induced gH2AX foci as a DNA damage surrogate marker was highlighted with the persistent foci at 24 h. considering an outcome of bystander-induced DNA damage, predominant role of clonogenic cell death was also elicited compared to apoptosis. Moreover, the role of high-dose bystander response observed in the current work clarified bystander potential implications in radiotherapy.

Investigation of TG-43 Dosimetric Parameters for 192Ir Brachytherapy Source Using GATE Monte Carlo Code.

Purpose: According to the revised Task Group number 43 recommendations, a brachytherapy source must be validated against a similar or identical source before its clinical application. The purpose of this investigation is to verify the dosimetric data of the high dose rate (HDR) BEBIG 192Ir source (Ir2.A85-2). Materials and Methods: The HDR 192Ir encapsulated seed was simulated and its main dosimetric data were calculated using Geant4 Application for Tomographic Emission (GATE) simulation code. Cubic cells were used for the calculation of dose rate constant and radial dose function while for anisotropy function ring cells were used. DoseActors were simulated and attached to the respective cells to obtain the required data. Results: The dose rate constant was obtained as 1.098 ± 0.003 cGy.h - 1.U - 1, differing by 1.0% from the reference value reported by Granero et al. Similarly, the calculated values for radial dose and anisotropy functions presented good agreement with the results obtained by Granero et al. Conclusion: The results of this study suggest that the GATE Monte Carlo code is a valid toolkit for benchmarking brachytherapy sources and can be used for brachytherapy simulation-based studies and verification of brachytherapy treatment planning systems.

Evaluation of Capability and Relationship of Different Radiobiological Endpoints for Radiosensitivity Prediction in Human Tumor Cell Lines Compared with Clonogenic Survival.

Background: Establishing a predictive assay of radiosensitivity (as an appropriate, practical and cost-effective method) has been challenging. Objective: The purpose of this study is to evaluate the capability and relationship of various endpoints, including GammaH2AX, micronuclei; and apoptosis in determining the human tumor cell lines radiosensitivities compared with clonogenic survival. Material and Methods: In an experimental in-vitro study, the response of carcinoma cell lines of HN5 and HeLa to 2 Gy of 6 MV photon beam was investigated via various assays. Results: Survival fraction at 2 Gy (SF2) of HeLa and HN5 was indicated as 0.42 ± 0.06 and 0.5 ± 0.03 respectively, proposing more radioresistance of HN5. This finding was confirmed with "2 Gy apoptosis enhancement ratio" which was 1.77 and 1.42 in HeLa and HN5. The increased levels of DNA DSBs were observed after irradiation; significant in HeLa with enhancement rate of 19.24. The micronuclei formation followed an ascending trend post irradiation; but with the least difference between two cells. Although the relationship between micronuclei and clonogenic survival was moderate (R2 = 0.35), a good correlation was observed between apoptosis and clonogenic survival (R2 = 0.71). Conclusion: The results of studied endpoints agreed with the SF2, highlighting their capabilities in radiosensitivity prediction. In terms of the enhancement ratio, gammaH2AX foci scoring could be a valid indicator of radiosensitivity but not the exact surrogate marker of survival because no correlation was observed. Moreover, considering the chief determents comprising lack of time and money, the apoptotic induction might be an appropriate indicator with the best correlation coefficient.

Intensity-modulated brachytherapy for vaginal cancer.

This study aimed to evaluate the dose modulation potential of static and dynamic steel-shielded applicators using the Geant4 Application for Emission Tomography (GATE) Monte Carlo code for the treatment of vaginal cancer. The GATE TOOLKIT (version 9.0) was used to simulate vaginal cancer intensity-modulated brachytherapy (IMBT) in a pelvic water-equivalent phantom. IMBT performance of a multichannel static and single-channel dynamic steel-shielded applicator was compared to that of a conventional multichannel Plexiglas applicator. DoseActors were defined to calculate the absorbed dose and attached to the voxelized target and organs at risk (OARs). 60Co and 192Ir high-dose-rate seeds were used as irradiation sources. Dynamic IMBT decreased the D2cc of the rectum and bladder by 28.67 and 28.11% using the 60Co source and by 40.00 and 36.34% using the 192Ir source, respectively. Static IMBT decreased the D2cc for the rectum and bladder by 11.69 and 9.29% using the 60Co source and by 22.21 and 17.71% using the 192Ir source, respectively. In contrast, absorbed dose parameters (D5, D90, and D100) for the target in the three techniques showed a mean relative variation of 0.96% (0.00-7.49%) for both sources. Static and dynamic IMBT using steel-shielded applicators provided relatively better OAR protection while maintaining similar target coverage in the treatment of vaginal cancer.

BEBIG 60Co HDR brachytherapy source dosimetric parameters validation using GATE Geant4-based simulation code.

Purpose: This study aims to validate the dosimetric characteristics of High Dose Rate (HDR) 60Co source (Co0.A86 model) using GATE Geant4-based Monte Carlo code. According to the recommendation of the American Association of Physicists in Medicine (AAPM) task group report number 43, the dosimetric parameters of a new brachytherapy source should be verified either experimentally or by Monte Carlo calculation before clinical applications. The validated 60Co source in this study will be used for the simulation of intensity-modulated brachytherapy (IMBT) of vaginal cancer using the same GATE Geant4-based Monte Carlo code in the future. Materials and methods: GATE (version 9.0) simulation code was used to model and calculate the required TG-43U1 dosimetric data of the 60Co HDR source. DoseActors were defined for calculation of dose rate constant, radial dose function, and anisotropy function in a water phantom with an 80 cm radius. Results: The dose rate constant was obtained as 1.070 ± 0.008 cGy . h - 1 . U - 1 which shows a relative difference of 2.01% compared to the consensus value, 1.092  â€‹cGy . h - 1 . U - 1 . The calculated results of anisotropy and radial dose functions starting from 0.1 cm to 10 cm around the source showed excellent agreement with the results of published studies. The mean variation of the radial dose and anisotropy functions values from the consensus data were 1% and 0.9% respectively. Conclusion: Findings from this investigation revealed that the validation of the HDR 60Co source is feasible by the GATE Geant4-based Monte Carlo code. As a result, the GATE Monte Carlo code can be used for the verification of the brachytherapy treatment planning system.

Neutron contamination in radiotherapy processes: a review study.

Using high-energy photon beams is one of the most practical methods in radiotherapy treatment of cases in deep site located tumors. In such treatments, neutron contamination induced through photoneutron interaction of high energy photons (>8 MeV) with high Z materials of LINAC structures is the most crucial issue which should be considered. Generated neutrons will affect shielding calculations and cause extra doses to the patient and the probability of increase induced secondary cancer risks. In this study, different parameters of neutron production in radiotherapy processes will be reviewed.

Ipsilateral lung normal tissue complication probability parameters for different dose calculation algorithms in radiotherapy of breast cancer.

PURPOSE: Different dose calculation algorithms (DCAs) predict different dose distributions for the same treatment. Awareness of optimal model parameters is vital for estimating normal tissue complication probability (NTCP) for different algorithms. The aim is to determine the NTCP parameter values for different DCAs in left-sided breast radiotherapy, using the Lyman-Kutcher-Burman (LKB) model. MATERIALS AND METHODS: First, the methodology recommended by International Atomic Energy Agency TEC-DOC 1583 was used to establish the accuracy of dose calculations of different DCAs including: Monte Carlo (MC) and collapsed cone algorithms implemented in Monaco, pencil beam convolution (PBC) and analytical anisotropic algorithm (AAA) implemented in Eclipse, and superposition and Clarkson algorithms implemented in PCRT3D treatment planning systems (TPSs). Then, treatment planning of 15 patients with left-sided breast cancer was performed by the mentioned DCAs and NTCP of the left-lung normal tissue were calculated for each patient individually, using the LKB model. For the PB algorithm, the NTCP parameters were taken from previously published values and new model parameters obtained for each DCA, using the iterative least squares methods. RESULTS: For all cases and DCAs, NTCP computation with the same model parameters resulted in >15% deviation in NTCP values. The new NTCP model parameters were classified according to the algorithm type. Thus, the discrepancy of NTCP computations was reduced up to 5% after utilizing adjusted model parameters. CONCLUSIONS: This paper confirms that the NTCP values for a given treatment type are different for the different DCAs. Thus, it is essential to introduce appropriate NTCP parameter values according to DCA adopted in TPS, to obtain a more precise estimation of lung NTCP. Hence, new parameter values, classified according to the DCAs, must be determined before introducing NTCP estimation in clinical practice.

Enhanced response of radioresistant carcinoma cell line to heterogeneous dose distribution of grid; the role of high-dose bystander effect.

PURPOSE: The classical dogma that restricted the radiation effect to the directly irradiated cells has been challenged by the bystander effect. This off-target phenomenon which was manifested in adjacent cells via signaling of fully exposed cells might be involved in high-dose Grid therapy as well. Here, an in-vitro study was performed to examine the possible extent of carcinoma cells response to the inhomogeneous dose distribution of Grid irradiation in the context of the bystander effect. MATERIALS AND METHODS: Bystander effect was investigated in human carcinoma cell lines of HeLa and HN5 adjacent to those received high-dose Grid irradiation using 'medium transfer' and 'cell-to-cell contact' strategies. Based on the Grid peak-to-valley dose profile, medium transfer was exerted from 10 Gy uniformly exposed donors to 1.5 Gy uniformly irradiated recipients. Cell-contact bystander was evaluated after nonuniform dose distribution of 10 Gy Grid irradiation using cloning cylinders. GammaH2AX foci, micronucleus and clonogenic assays besides gene expression analysis were performed. RESULTS: Various parameters (ɑ/ß, D37, D50) extracted from survival curve which fitted to the Linear Quadratic model, verified more radioresistance of HN5. Survival fraction at 2 Gy (SF2) indicated as 0.42 ± 0.06 in HeLa and 0.5 ± 0.03 in HN5. The level of survival decrease, DNA damages and micronucleus of cells located in the Grid shielded areas (1.5 Gy cell-to-cell contact bystander cells) were significantly more than the values obtained from cells which were irradiated by merely uniform dose of 1.5 Gy. The gH2AX foci and micronuclei frequencies were enhanced in cell-contact bystander approximately more than 1.8 times. Relative expression of DNA damage repair pathway genes (Xrcc6 and H2afx) in bystander cells increased significantly. The most cell survival reduction (11.6 times) was revealed in the Grid bystander cells of radioresistant cell line (HN5). No statistically significant difference between 10 Gy uniform beam and Grid non-uniform beam was observed. CONCLUSIONS: Various endpoints confirmed an augmented response of cells in the valley dose region of the Grid block significantly (compared with the cells irradiated by identical dose of uniform beam), suggesting the role of high-dose bystander effect which was more pronounced in resistant carcinoma cell lines. These findings could provide a partial explanation for the Grid beneficial response seen in a number of pre-clinical and clinical studies.

Dosimetric evaluation of electron total skin irradiation using gafchromic film and thermoluminescent dosimetry.

AIM OF STUDY: The aim of this study is to evaluate some dosimetry parameters such as uniformity, surface dose, and max depth dose with thermoluminescent dosimetry (TLD) and EBT3 film in total skin electron beam therapy (TSEBT). METHODS: Stationary and rotary methods were set on Varian linear accelerator, Clinac 2100C. To create a radiation field large enough (168 cm × 60 cm) and uniform, the source skin distance was set 400 cm. Electron beam energy was 6 MeV. The skin dose values were obtained in 21 different points on the phantom surface. RESULTS: The results of dose uniformity in stationary technique were obtained as 10% and 2.6% by TLDs and 6% and 2.3% by films in longitudinal axis and transverse axis, respectively. The measurements at rotational technique by TLDs at the referred conditions showed a homogeneous total field with intensity variation of 10% in the longitudinal axis and 4% at horizontal axis. CONCLUSION: Based on the results of this study, stationary techniques are preferred for TSEBT. The main advantage of rotational techniques is reducing the time of treatment. The results also demonstrate that TLD should be routinely used in TSEBT treatment. Due to the high sensitivity of radiochromic films, this type of film was suitable for a wide therapeutic field. Comprehensive treatment to Rando phantom showed that the uniformity is better at the trunk than in the mobile parts of the body; the soles of the feet, perineum region, and scalp vertex should be treated in boost.

Determination of geometric accuracy of radiotherapy fields by port film and DRR using Matlab graphical user interface.

The purpose of this study is to determine and verify the exact location of radiation therapy fields by using port-film and digital reconstruction radiograph (DRR) as a low-cost tool. Initially, an appropriate algorithm was written for the application of port film in the megavoltage beam irradiation. Detectable contrast was created for the image and then by using appropriate markers and developed written program by MATLAB as DRrPortRegistartion. Semi-automatic and automatic registration between port-film and DRR images were performed for pelvic and chest phantoms. Then, results were compared with electronic portal imaging device (EPID) images in similar conditions. By using this software, DRR and port film as treatment verification tools, the precision of treatment verification and the accuracy of radiation therapy fields were achieved in the extent of the millimeter. Validation results with EPID demonstrated that the mean absolute average error in angle is equal to 0.59 degrees, 1.70 mm in the X-direction, and 2.42 mm in the Y-direction. The results of this study illustrated that using this software and suitable low-cost hardware in the machines without EPID can increase the precision of treatment verification to the millimeter and it can be introduced as a suitable alternative for EPID in centers for increasing treatment accuracy. Graphical abstract ᅟ.

Comparison of penumbra regions produced by ancient Gamma knife model C and Gamma ART 6000 using Monte Carlo MCNP6 simulation.

The accuracy of penumbral measurements in radiotherapy is pivotal because dose planning computers require accurate data to adequately modeling the beams, which in turn are used to calculate patient dose distributions. Gamma knife is a non-invasive intracranial technique based on principles of the Leksell stereotactic system for open deep brain surgeries, invented and developed by Professor Lars Leksell. The aim of this study is to compare the penumbra widths of Leksell Gamma Knife model C and Gamma ART 6000. Initially, the structure of both systems were simulated by using Monte Carlo MCNP6 code and after validating the accuracy of simulation, beam profiles of different collimators were plotted. MCNP6 beam profile calculations showed that the penumbra values of Leksell Gamma knife model C and Gamma ART 6000 for 18, 14, 8 and 4 mm collimators are 9.7, 7.9, 4.3, 2.6 and 8.2, 6.9, 3.6, 2.4, respectively. The results of this study showed that since Gamma ART 6000 has larger solid angle in comparison with Gamma Knife model C, it produces better beam profile penumbras than Gamma Knife model C in the direct plane.

Comparison of full width at half maximum and penumbra of different Gamma Knife models.

As a radiosurgical tool, Gamma Knife has the best and widespread name recognition. Gamma Knife is a noninvasive intracranial technique invented and developed by Swedish neurosurgeon Lars Leksell. The first commercial Leksell Gamma Knife entered the therapeutic armamentarium at the University of Pittsburgh in the United States on August 1987. Since that time, different generation of Gamma Knife developed. In this study, the technical points and dosimetric parameters including full width at half maximum and penumbra on different generation of Gamma Knife will be reviewed and compared. The results of this review study show that the rotating gamma system provides a better dose conformity.

Application of Geant4 Monte Carlo simulation in dose calculations for small radiosurgical fields.

The Geant4 toolkit was used to develop a Monte Carlo (MC)-based engine for accurate dose calculations in small radiation field sizes. The Geant4 toolkit (version 10.1.p02) was used to simulate 6-MV photon beam of a Varian2100C linear accelerator that is being used for stereotactic radiosurgery (SRS) treatment with small radiation fields. Geometric models of 3 in-house designed radiosurgical divergent cones, with the diameters of their projections at the isocenter being 10, 20, and 30 mm, were simulated. The accuracy of the MC simulation technique was examined by reproducing several different simulated dosimetric parameters of the primary beams with the experimental data. The dose distributions are first checked for single beams for each cone, then standard multiple field (SMF) techniques are applied. A sample set of DICOM files from computed tomography (CT) scan imaging of a patient's head was converted to the Geant4 geometry format to implement MC-based engine for a clinical test. To validate the accuracy of the MC-based calculations for SMF arrangements, the isodose lines from MC simulation in water phantom were compared with the measured isodose lines using EBT3 Gafchromic film in Solid Water phantoms. Agreements between measured and simulated depth dose values and beam profiles for SRS cones were generally within 2%/2 mm. For output factors, the largest discrepancy was observed for 10 mm SRS cone, which was 1.7%. For SMF techniques, in SRS cones, the MC simulation and EBT3 Gafchromic film dosimetry were in acceptable agreement (5%/5 mm). Excellent agreement between the results of the MC-based and measured dose values for both single and SMF techniques in SRS cones indicates the ability of the Geant4 toolkit to be applied as the platform for treatment planning of advanced radiotherapy techniques.

Dosimetric properties of new formulation of PRESAGE® with tin organometal catalyst: Development of sensitivity and stability to megavoltage energy.

AIM: Tin-base catalyst is one of the widely used organometallic catalysts in polyurethane technology. The purpose of this study was to evaluate the effect of tin organometallic catalyst in the radiation response and radiological properties of a new formula of PRESAGE®. MATERIALS AND METHODS: In the study, two types of PRESAGE were fabricated. A very little amount of dibutyltindillaurate (DBTDL) (0.07% weight) was used as a catalyst in the fabrication of new PRESAGE (i.e., PRESAGE with catalyst), which components were: 93.93% weight polyurethane, 5% weight tetrachloride, and 1% weight leucomalachite green (LMG). For PRESAGE without catalyst, 94% weight polyurethane, 4% weight tetrachloride, and 2% weight LMG were used. Radiochromic response and postirradiation stability of PRESAGEs were determined. Also, radiological characteristics of PRESAGEs, such as mass density, electron density, mass attenuation coefficient, and mass stopping power in different photon energies were assessed and compared with water. RESULTS: The absorption peak of new PRESAGE compared to PRESAGE without catalyst was observed without change. Sensitivity of new PRESAGE was higher than PRESAGE without catalyst and its stability after the first 1 h was relatively constant. Also, Mass attenuation coefficient of new PRESAGE in energy ranges <0.1 MeV was 10% more than water, whereas the maximum difference of mass stopping power was only 3%. CONCLUSIONS: Tin organometallic catalyst in very low concentration can be used in fabrication of radiochromic polymer gel to achieve high sensitivity and stability as well as good radiological properties in the megavoltage photon beam.

Measurement of neutron dose in the compensator IMRT treatment.

A radiation treatment delivery technique, intensity modulated radiation therapy (IMRT), has found widespread use in the treatment of cancers. One of IMRT implementing methods is IMRT compensator based, which the modulation are done by high Z materials. When photons with energies higher than 8MV interact with high Z material in path, Photoneutrons are produced. In this study, the effect of compensator on photoneutron production was investigated. The Monte Carlo code MCNPX was used to calculate the neutron dose equivalent as a function of the depth in phantom with and without compensator. Measurements were made using CR-39 track-etched detectors. CR-39 detectors, were cut in dimensions of 2.5×2.5 cm2 by laser, placed in different depths of slab phantom and then irradiated by 18MV photons. Same procedure was performed with the compensator present and absent. The measured data were compared with MCNP calculations. In both experimental and simulation results, neutron dose equivalent when compensator used, was less than non-compensator field. The calculated neutron dose equivalent was maximum at surface and decreased exponentially by increasing depth, but in experimental data, the neutron dose equivalent reached a maximum at approximately 3cm depth in the phantom and beyond which decreased with depth.CR-39 calibration was carried out in air, by considering that neutron energy spectrum changes toward thermal neutrons by depth in phantom increasing, it is suggested that for measuring equivalent neutron dose at phantom depth, should have proper neutron calibration in terms of energy spectrum.

Evaluation of the effect of temperature variation on response of PRESAGE® dosimeter.

INTRODUCTION: Many factors, such as PRESAGE ® composition, dose rate, energy, and type of radiation, temperature, etc., may effect on PRESAGE ® dosimeter response. The aim of this study was investigating the effect of temperature variation on response of PRESAGE ® solid dosimeter. MATERIALS AND METHODS: In this study, a PRESAGE ® solid detector was fabricated. Ninety-four percent weight polyurethane, 5% weight carbon tetrachloride, and 1% weight leucomalachite green were used. Radiological and physical characteristics of PRESAGEs ®, such as mass density, electron density, and effective number atomic were obtained and compared with water. Response of PRESAGE ® dosimeter in temperatures -4, 10, 25, 35, 45, 55, 65, 75, 85, and 90°C was evaluated. In addition, the absorption peak at various temperatures was investigated. RESULTS: The results showed that the absorption peak at different temperatures was in the range of 630-635 nm. For temperatures below 75°C, the results indicated that temperature variation has no effect on the response of PRESAGE ® dosimeter whereas at the temperatures> 75°C, temperature variation has an effect on PRESAGE ® dosimeter response. CONCLUSION: The finding showed that temperature changes have not impact on the absorption peak. In addition, the results related to the effect of temperature variation on the response of PRESAGE ® dosimeter showed that in the range of clinical applications (temperatures below 75°C), temperature variation has no effect on PRESAGE ® dosimeter response.