The high dose gradients and non-uniformity of dose distributions within the target lead to a chal... more The high dose gradients and non-uniformity of dose distributions within the target lead to a challenge in the dosimetry of the Grid radiation fields. The aim of this study is to perform a precise EBT3 Gafchromic film dosimetry for Grid therapy fields using a commercially available flatbed colour scanner. METHODS: In this project, samples of the EBT3 Gafchromic films are exposed to Grid radiation fields. The irradiated EBT3 films were read using a flatbed Microtek scanner. The responses of these films (i.e. films from the same batch) as functions of the absorbed dose values are calibrated by irradiation under a fixed standard technique (i.e. 10x10 cm 2 filed, 100 cm SSD, and depth of the maximum dose). These films are also read with the same scanner using the red, green, and blue channels. Four different approaches were used to evaluate film dosimetry for the Grid therapy applications: 1) single channel film dosimetry method (SCM), 2) dual channel film dosimetry method (DCM), 3) linearized dose-response curve method (LRCM), and 4) triple channel film dosimetry method (TCM). A dose of 20 Gy was delivered to the point along the central axis of the grid hole at the depth of maximum dose (dmax) for a 10 × 10 cm 2 Grid field size. Beam profiles and percentage depth dose distributions of the Grid radiation have been measured in water-equivalent phantom material, using EBT3 films. The accuracy of the relative and the absolute dosimetry of the films were examined by comparison of the TLD measured data with the Monte Carlo simulated values.
International Journal of Radiation Biology, Nov 12, 2020
Purpose: The classical dogma that restricted the radiation effect to the directlyirradiated cells... more Purpose: The classical dogma that restricted the radiation effect to the directlyirradiated 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 & 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-tovalley 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/β, 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 A c c e p t e d M a n u s c r i p t 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 nonuniform 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.
Journal of Applied Clinical Medical Physics, Jul 1, 2016
A new design of 125 I (Model IR-Seed2) brachytherapy source has been manufactured recently at the... more A new design of 125 I (Model IR-Seed2) brachytherapy source has been manufactured recently at the Applied Radiation Research School, Nuclear Science and Technology Research Institute in Iran. The source consists of six resin beads (0.5 mm diameter) that are sealed in a cylindrical titanium capsule of 0.7 mm internal and 0.8 mm external diameters. This work aims to evaluate the dosimetric parameters of the newly designed 125 I source using experimental measurements and Monte Carlo (MC) simulations. Dosimetric characteristics (dose rate constant, radial dose function, and 2D and 1D anisotropy functions) of the IR-Seed2 were determined using experimental measurements and MC simulations following the recommendations by the Task Group 43 (TG-43U1) report of the American Association of Physicists in Medicine (AAPM). MC simulations were performed using the MCNP5 code in water and Plexiglas, and experimental measurements were carried out using thermoluminescent dosimeters (TLD-GR207A) in Plexiglas phantoms. The measured dose to water in Plexiglas data were used for verification of the accuracy of the source and phantom geometry in the Monte Carlo simulations. The final MC simulated data to water in water were recommended for clinical applications. The MC calculated dose rate constant (Λ) of the IR-Seed2 125 I seed in water was found to be 0.992 ± 0.025 cGy h-1 U-1. Additionally, its radial dose function by line and point source approximations, g L (r) and g p (r), calculated for distances from 0.1 cm to 7 cm. The values of g L (r) at radial distances from 0.5 cm to 5 cm were measured in a Plexiglas phantom to be between 1.212 and 0.413. The calculated and measured of values for 2D anisotropy function, F(r, θ), were obtained for the radial distances ranging from 1.5 cm to 5 cm and angular range of 0°-90° in a Plexiglas phantom. Also, the 2D anisotropy function was calculated in water for the clinical application. The results of these investigations show that the uncertainty of the experimental data is within ± 7% between the measured and simulated data in Plexiglas. Based on these results, the MC-simulated dosimetric parameters of the new 125 I source model in water are presented for its clinical applications in brachytherapy treatments.
Purpose: The clinical efficacy of Grid therapy has been examined by several investigators. In thi... more Purpose: The clinical efficacy of Grid therapy has been examined by several investigators. In this project, the hole diameter and hole spacing in Grid blocks were examined to determine the optimum parameters that give a therapeutic advantage. Methods: The evaluations were performed using Monte Carlo (MC) simulation and commonly used radiobiological models. The Geant4 MC code was used to simulate the dose distributions for 25 different Grid blocks with different hole diameters and center-to-center spacing. The therapeutic parameters of these blocks, namely, the therapeutic ratio (TR) and geometrical sparing factor (GSF) were calculated using two different radiobiological models, including the linear quadratic and Hug–Kellerer models. In addition, the ratio of the open to blocked area (ROTBA) is also used as a geometrical parameter for each block design. Comparisons of the TR, GSF, and ROTBA for all of the blocks were used to derive the parameters for an optimum Grid block with the maximum TR, minimum GSF, and optimal ROTBA. A sample of the optimum Grid block was fabricated at our institution. Dosimetric characteristics of this Grid block were measured using an ionization chamber in water phantom, Gafchromic film, and thermoluminescent dosimeters in Solid WaterTM phantom materials. Results: The results of these investigations indicated that Grid blocks with hole diameters between 1.00 and 1.25 cm and spacing of 1.7 or 1.8 cm have optimal therapeutic parameters (TR > 1.3 and GSF~0.90). The measured dosimetric characteristics of the optimum Grid blocks including dose profiles, percentage depth dose, dose output factor (cGy/MU), and valley-to-peak ratio were in good agreement (±5%) with the simulated data. Conclusion: In summary, using MC-based dosimetry, two radiobiological models, and previously published clinical data, we have introduced a method to design a Grid block with optimum therapeutic response. The simulated data were reproduced by experimental data.
Introduction: In radiation therapy, the accuracy of dose calculations by a treatment planning sys... more Introduction: In radiation therapy, the accuracy of dose calculations by a treatment planning system (TPS) is important to achieve tumor control and to spare normal tissue. Treatment planning system calculations in the heterogeneous situation may present significant inaccuracies. In this study, three different dose calculation algorithms, pencil beam (PB), collapsed cone (CC), and Monte-Carlo (MC), provided by our planning system were compared to assess their impact on the three-dimensional planning of lung region. Materials and Methods: The methodology was based on IAEA TEC-DOC 1583. The phantom resembling the human thorax are used and all tests were planned on three- dimensional treatment planning systems (TPSs) and irradiated with photon beams of 6, and 18 MV X-ray energies. The doses in specific points were measured with an ionization chamber. The differences between the measured and calculated doses were reported. This study was tested using different algorithms/inhomogeneity correction methods implemented in Monaco treatment planning system. Results: The measurements were conducted for all test case datasets for two photon beam energies and calculation algorithms. The deviation between the measured and calculated values for all test cases made with advanced algorithms (MC and CC) were within the agreement criteria, while the larger deviations were observed for PB algorithm. Subsequently, there were discovered dose differences greater than 20% for some simple algorithms and high energy X-ray beams. The number of measurements with results outside the agreement criteria increased with the increase of the beam energy and decreased with TPS calculation algorithm sophistication. Also, a few errors in the basic dosimetry data in TPS were detected and corrected. Conclusion: Differences were found when comparing the calculation algorithms. The PB algorithm actually overestimated the dose compared with those calculated by the CC and MC algorithms. The MC algorithm showed better accuracy than the other algorithms. Therefore advanced dose calculation algorithms are suitable and should be used in clinical practice
Background: One major challenge in brachytherapy is to verify the accuracy of dose distribu ons c... more Background: One major challenge in brachytherapy is to verify the accuracy of dose distribu ons calculated by the treatment planning system. In this project, a new phantom design has been introduced for quality assurance of dose distribu ons in gynocological (GYN) brachytherapy implants using EBT GafChromic film. Materials and Methods: This phantom has been designed and fabricated from 90 slabs of 18×16×0.2 cm 3 Perspex to accommodate a tandem and ovoids assembly, which is normally used for GYN brachytherapy treatment. In addi on, this phantom design is allowing the use EBT GafChromic films for dosimetric verifica on of GYN implants with Cs-137 Selectron LDR system. With this assembly, GafChromic films were exposed using a plan designed to deliver 2.5 Gy dose to point "A" in Manchester system for tandem and ovoids configura ons and to deliver 1.5 Gy of dose to 0.5 cm distance from the lateral surface of ovoids for using ovoid-pair. The measured dose distribu ons with GafChromic films were compared with the TPS isodose lines both numerically and spa ally. For a quan ta ve analysis of the results, the measured doses values at several points of interest were evaluated with the treatment planning data and values obtained following the TG-43 dose calcula on formalism. Results: The results of these inves ga ons have indicated that the new phantom design enables us to measure differences of greater than ±6% for LDR brachytherapy GYN treatments. Conclusion: The new phantom design could be u lized for the QA procedure of the brachytherapy remote aCer loading systems to confirm the accuracy of dose distribu on in GYN implants.
With the advent of new complex but precise radiotherapy techniques, the demands for an accurate, ... more With the advent of new complex but precise radiotherapy techniques, the demands for an accurate, feasible three-dimensional (3D) dosimetry system have been increased. A 3D dosimeter system generally should not only have accurate and precise results but should also feasible, inexpensive, and time consuming. Recently, one of the new candidates for 3D dosimetry is optical computed tomography (CT) with a radiochromic dosimeter such as PRESAGE®. Several generations of optical CT have been developed since the 90s. At the same time, a large attempt has been also done to introduce the robust dosimeters that compatible with optical CT scanners. In 2004, PRESAGE® dosimeter as a new radiochromic solid plastic dosimeters was introduced. In this decade, a large number of efforts have been carried out to enhance optical scanning methods. This article attempts to review and reflect on the results of these investigations.
Introduction: Many factors, such as PRESAGE ® composition, dose rate, energy, and type of radiati... more 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.
Radiation oncology has been rapidly improved by the application of new equipment and techniques. ... more Radiation oncology has been rapidly improved by the application of new equipment and techniques. With the advent of new complex and precise radiotherapy techniques such as intensity modulated radiotherapy, stereotactic radiosurgery, and volumetric modulated arc therapy, the demand for an accurate and feasible three-dimensional (3-D) dosimetry system has increased. The most important features of a 3-D dosimeter, apart from being precise, accurate and reproducible, include also its low cost, feasibility, and availability. In 2004 a new generation of solid plastic dosimeters which demonstrate a radiochromic response to ionizing radiation was introduced. PRESAGE ® plastic dosimeter lacks the limitations of previous Ferric and polymer plastic 3-D dosimeters such as diffusion, sensitivity to oxygen, fabrication problems, scanning and read out challenges. In this decade, a large number of efforts have been carried out to enhance PRESAGE ® structure and scanning methods. This article attempts to review and reflect on the results of these investigations.
The aim of this study is to evaluate the application and accuracy of polymer gels for determining... more The aim of this study is to evaluate the application and accuracy of polymer gels for determining electron dose distributions in the presence of small heterogeneities made of bone and air. Different cylindrical phantoms containing MAGIC (Methacrylic and Ascorbic acid in Gelatin Initiated by Copper) normoxic polymer gel were used under the slab phantoms during irradiation. MR images of the irradiated gel phantoms were obtained to determine their R2 (spin-spin) relaxation maps for conversion to absorbed dose. One-and 2-dimensional lateral dose profiles were acquired at depths of 1 and 4 cm for 8 and 15 MeV electron beams. The results were compared with the doses measured by a diode detector at the same positions. In addition, the dose distribution in the axial orientation was measured by the gel dosimeter. The slope and intercept for the R2 versus dose curve were 0.509 ± 0.002 Gy −1 s −1 and 4.581 ± 0.005 s −1 , respectively. No significant variation in dose-R2 response was seen for the two electron energies within the applied dose ranges. The mean dose difference between the measured gel dose profiles was smaller than 3% compared to those measured by the diode detector. These results provide further demonstration that electron dose distributions are significantly altered in the presence of tissue inhomogeneities such as bone and air cavity and that MAGIC gel is a useful tool for 3-dimensional dose visualization and qualitative assessment of tissue inhomogeneity effects in electron beam dosimetry.
Aim of Study: The aim of this study is to evaluate some dosimetry parameters such as uniformity, ... more 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.
The Geant4 toolkit was used to develop a Monte Carlo (MC)-based engine for accurate dose calculat... more 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.
The electron benefit transfer (EBT) GAFCHROMIC films possess a number of features making them app... more The electron benefit transfer (EBT) GAFCHROMIC films possess a number of features making them appropriate for high-quality dosimetry in intensity-modulated radiation therapy (IMRT). Compensators to deliver IMRT are known to change the beam-energy spectrum as well as to produce scattered photons and to contaminate electrons; therefore, the accuracy and validity of EBT-film dosimetry in compensator-based IMRT should be investigated. Percentage-depth doses and lateral-beam profiles were measured using EBT films in perpendicular orientation with respect to 6 and 18 MV photon beam energies for: (1) different thicknesses of cerrobend slab (open, 1.0, 2.0, 4.0, and 6.0 cm), field sizes (5 Â 5, 10 Â 10, and 20 Â 20 cm 2), and measurement depths (D max , 5.0 and 10.0 cm); and (2) stepwedged compensator in a solid phantom. To verify results, same measurements were implemented using a 0.125 cm 3 ionization chamber in a water phantom and also in Monte Carlo simulations using the Monte Carlo N-particle radiation transport computer code. The mean energy of photons was increased due to beam hardening in comparison with open fields at both 6 and 18 MV energies. For a 20 Â 20 cm 2 field size of a 6 MV photon beam and a 6.0 cm thick block, the surface dose decreased by about 12% and percentage-depth doses increased up to 3% at 30.0 cm depth, due to the beam-hardening effect induced by the block. In contrast, at 18 MV, the surface dose increased by about 8% and depth dose reduced by 3% at 30.0 cm depth. The penumbral widths (80% to 20%) increase with block thickness, field size, and beam energy. The EBT film results were in good agreement with the ionization chamber dose profiles and Monte Carlo N-particle radiation transport computer code simulation behind the stepwedged compensator. Also, there was a good agreement between the EBT-film and the treatmentplanning results on the anthropomorphic phantom. The EBT films can be accurately used as a 2D dosimeter for dose verification and quality assurance of compensator-based C-IMRT.
Comparison of penumbra regions produced by ancient Gamma knife model C and Gamma ART 6000 using M... more Comparison of penumbra regions produced by ancient Gamma knife model C and Gamma ART 6000 using Monte Carlo MCNP6 simulation, Applied Radiation and Isotopes,
PURPOSE Whole-body photoneutron (PN) energy-specific dosimetry on phantom surfaces and 360°angula... more PURPOSE Whole-body photoneutron (PN) energy-specific dosimetry on phantom surfaces and 360°angular fast PN distribution dosimetry on and around polyethylene (PE) phantom organs for prostate cancer in 10 cm × 10 cm and 20 cm × 20 cm field sizes of 18 MV X-rays of Varian Clinac 2100C linear accelerator. METHODS Novel "Sohrabi neutron dosimetry methods" including "miniature passive neutron dosimeter/spectrometer" and "strip polycarbonate neutron dosimeters" were applied. Energy-specific PN dose equivalents on surface as well as 360°fast PN dose equivalent angular distributions on and around PE phantom organs; head, neck, thorax, arms, pelvis, thighs and legs were determined. RESULTS Matrix of surface (skin) energy-specific PN dose equivalents including total thermal, total epithermal, total fast, sum total thermal + epithermal and sum total thermal + epithermal + fast, and 360°angular fast PN dose equivalent responses were determined. The results indicate that data matrix of 20 cm × 20 cm field size provides higher PN dose equivalent values than those of 10 cm × 10 cm field size for surface points even remote from the central axis and for all 360°angular fast PN dose equivalent distributions on organs studied. CONCLUSIONS Matrix of energy-specific PN dose equivalents was obtained demonstrating that the Sohrabi neutron dosimetry methods applied are unique for energy-specific PN dose equivalent studies as well as for 360°angular PN dose equivalent distribution data for PN-SPC risk estimation. The dosimetry methods can be specifically applied to many other exotic applications in health physics, medical physics, space flight dosimetry, and nuclear science and technology.
The high dose gradients and non-uniformity of dose distributions within the target lead to a chal... more The high dose gradients and non-uniformity of dose distributions within the target lead to a challenge in the dosimetry of the Grid radiation fields. The aim of this study is to perform a precise EBT3 Gafchromic film dosimetry for Grid therapy fields using a commercially available flatbed colour scanner. METHODS: In this project, samples of the EBT3 Gafchromic films are exposed to Grid radiation fields. The irradiated EBT3 films were read using a flatbed Microtek scanner. The responses of these films (i.e. films from the same batch) as functions of the absorbed dose values are calibrated by irradiation under a fixed standard technique (i.e. 10x10 cm 2 filed, 100 cm SSD, and depth of the maximum dose). These films are also read with the same scanner using the red, green, and blue channels. Four different approaches were used to evaluate film dosimetry for the Grid therapy applications: 1) single channel film dosimetry method (SCM), 2) dual channel film dosimetry method (DCM), 3) linearized dose-response curve method (LRCM), and 4) triple channel film dosimetry method (TCM). A dose of 20 Gy was delivered to the point along the central axis of the grid hole at the depth of maximum dose (dmax) for a 10 × 10 cm 2 Grid field size. Beam profiles and percentage depth dose distributions of the Grid radiation have been measured in water-equivalent phantom material, using EBT3 films. The accuracy of the relative and the absolute dosimetry of the films were examined by comparison of the TLD measured data with the Monte Carlo simulated values.
International Journal of Radiation Biology, Nov 12, 2020
Purpose: The classical dogma that restricted the radiation effect to the directlyirradiated cells... more Purpose: The classical dogma that restricted the radiation effect to the directlyirradiated 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 & 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-tovalley 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/β, 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 A c c e p t e d M a n u s c r i p t 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 nonuniform 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.
Journal of Applied Clinical Medical Physics, Jul 1, 2016
A new design of 125 I (Model IR-Seed2) brachytherapy source has been manufactured recently at the... more A new design of 125 I (Model IR-Seed2) brachytherapy source has been manufactured recently at the Applied Radiation Research School, Nuclear Science and Technology Research Institute in Iran. The source consists of six resin beads (0.5 mm diameter) that are sealed in a cylindrical titanium capsule of 0.7 mm internal and 0.8 mm external diameters. This work aims to evaluate the dosimetric parameters of the newly designed 125 I source using experimental measurements and Monte Carlo (MC) simulations. Dosimetric characteristics (dose rate constant, radial dose function, and 2D and 1D anisotropy functions) of the IR-Seed2 were determined using experimental measurements and MC simulations following the recommendations by the Task Group 43 (TG-43U1) report of the American Association of Physicists in Medicine (AAPM). MC simulations were performed using the MCNP5 code in water and Plexiglas, and experimental measurements were carried out using thermoluminescent dosimeters (TLD-GR207A) in Plexiglas phantoms. The measured dose to water in Plexiglas data were used for verification of the accuracy of the source and phantom geometry in the Monte Carlo simulations. The final MC simulated data to water in water were recommended for clinical applications. The MC calculated dose rate constant (Λ) of the IR-Seed2 125 I seed in water was found to be 0.992 ± 0.025 cGy h-1 U-1. Additionally, its radial dose function by line and point source approximations, g L (r) and g p (r), calculated for distances from 0.1 cm to 7 cm. The values of g L (r) at radial distances from 0.5 cm to 5 cm were measured in a Plexiglas phantom to be between 1.212 and 0.413. The calculated and measured of values for 2D anisotropy function, F(r, θ), were obtained for the radial distances ranging from 1.5 cm to 5 cm and angular range of 0°-90° in a Plexiglas phantom. Also, the 2D anisotropy function was calculated in water for the clinical application. The results of these investigations show that the uncertainty of the experimental data is within ± 7% between the measured and simulated data in Plexiglas. Based on these results, the MC-simulated dosimetric parameters of the new 125 I source model in water are presented for its clinical applications in brachytherapy treatments.
Purpose: The clinical efficacy of Grid therapy has been examined by several investigators. In thi... more Purpose: The clinical efficacy of Grid therapy has been examined by several investigators. In this project, the hole diameter and hole spacing in Grid blocks were examined to determine the optimum parameters that give a therapeutic advantage. Methods: The evaluations were performed using Monte Carlo (MC) simulation and commonly used radiobiological models. The Geant4 MC code was used to simulate the dose distributions for 25 different Grid blocks with different hole diameters and center-to-center spacing. The therapeutic parameters of these blocks, namely, the therapeutic ratio (TR) and geometrical sparing factor (GSF) were calculated using two different radiobiological models, including the linear quadratic and Hug–Kellerer models. In addition, the ratio of the open to blocked area (ROTBA) is also used as a geometrical parameter for each block design. Comparisons of the TR, GSF, and ROTBA for all of the blocks were used to derive the parameters for an optimum Grid block with the maximum TR, minimum GSF, and optimal ROTBA. A sample of the optimum Grid block was fabricated at our institution. Dosimetric characteristics of this Grid block were measured using an ionization chamber in water phantom, Gafchromic film, and thermoluminescent dosimeters in Solid WaterTM phantom materials. Results: The results of these investigations indicated that Grid blocks with hole diameters between 1.00 and 1.25 cm and spacing of 1.7 or 1.8 cm have optimal therapeutic parameters (TR > 1.3 and GSF~0.90). The measured dosimetric characteristics of the optimum Grid blocks including dose profiles, percentage depth dose, dose output factor (cGy/MU), and valley-to-peak ratio were in good agreement (±5%) with the simulated data. Conclusion: In summary, using MC-based dosimetry, two radiobiological models, and previously published clinical data, we have introduced a method to design a Grid block with optimum therapeutic response. The simulated data were reproduced by experimental data.
Introduction: In radiation therapy, the accuracy of dose calculations by a treatment planning sys... more Introduction: In radiation therapy, the accuracy of dose calculations by a treatment planning system (TPS) is important to achieve tumor control and to spare normal tissue. Treatment planning system calculations in the heterogeneous situation may present significant inaccuracies. In this study, three different dose calculation algorithms, pencil beam (PB), collapsed cone (CC), and Monte-Carlo (MC), provided by our planning system were compared to assess their impact on the three-dimensional planning of lung region. Materials and Methods: The methodology was based on IAEA TEC-DOC 1583. The phantom resembling the human thorax are used and all tests were planned on three- dimensional treatment planning systems (TPSs) and irradiated with photon beams of 6, and 18 MV X-ray energies. The doses in specific points were measured with an ionization chamber. The differences between the measured and calculated doses were reported. This study was tested using different algorithms/inhomogeneity correction methods implemented in Monaco treatment planning system. Results: The measurements were conducted for all test case datasets for two photon beam energies and calculation algorithms. The deviation between the measured and calculated values for all test cases made with advanced algorithms (MC and CC) were within the agreement criteria, while the larger deviations were observed for PB algorithm. Subsequently, there were discovered dose differences greater than 20% for some simple algorithms and high energy X-ray beams. The number of measurements with results outside the agreement criteria increased with the increase of the beam energy and decreased with TPS calculation algorithm sophistication. Also, a few errors in the basic dosimetry data in TPS were detected and corrected. Conclusion: Differences were found when comparing the calculation algorithms. The PB algorithm actually overestimated the dose compared with those calculated by the CC and MC algorithms. The MC algorithm showed better accuracy than the other algorithms. Therefore advanced dose calculation algorithms are suitable and should be used in clinical practice
Background: One major challenge in brachytherapy is to verify the accuracy of dose distribu ons c... more Background: One major challenge in brachytherapy is to verify the accuracy of dose distribu ons calculated by the treatment planning system. In this project, a new phantom design has been introduced for quality assurance of dose distribu ons in gynocological (GYN) brachytherapy implants using EBT GafChromic film. Materials and Methods: This phantom has been designed and fabricated from 90 slabs of 18×16×0.2 cm 3 Perspex to accommodate a tandem and ovoids assembly, which is normally used for GYN brachytherapy treatment. In addi on, this phantom design is allowing the use EBT GafChromic films for dosimetric verifica on of GYN implants with Cs-137 Selectron LDR system. With this assembly, GafChromic films were exposed using a plan designed to deliver 2.5 Gy dose to point "A" in Manchester system for tandem and ovoids configura ons and to deliver 1.5 Gy of dose to 0.5 cm distance from the lateral surface of ovoids for using ovoid-pair. The measured dose distribu ons with GafChromic films were compared with the TPS isodose lines both numerically and spa ally. For a quan ta ve analysis of the results, the measured doses values at several points of interest were evaluated with the treatment planning data and values obtained following the TG-43 dose calcula on formalism. Results: The results of these inves ga ons have indicated that the new phantom design enables us to measure differences of greater than ±6% for LDR brachytherapy GYN treatments. Conclusion: The new phantom design could be u lized for the QA procedure of the brachytherapy remote aCer loading systems to confirm the accuracy of dose distribu on in GYN implants.
With the advent of new complex but precise radiotherapy techniques, the demands for an accurate, ... more With the advent of new complex but precise radiotherapy techniques, the demands for an accurate, feasible three-dimensional (3D) dosimetry system have been increased. A 3D dosimeter system generally should not only have accurate and precise results but should also feasible, inexpensive, and time consuming. Recently, one of the new candidates for 3D dosimetry is optical computed tomography (CT) with a radiochromic dosimeter such as PRESAGE®. Several generations of optical CT have been developed since the 90s. At the same time, a large attempt has been also done to introduce the robust dosimeters that compatible with optical CT scanners. In 2004, PRESAGE® dosimeter as a new radiochromic solid plastic dosimeters was introduced. In this decade, a large number of efforts have been carried out to enhance optical scanning methods. This article attempts to review and reflect on the results of these investigations.
Introduction: Many factors, such as PRESAGE ® composition, dose rate, energy, and type of radiati... more 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.
Radiation oncology has been rapidly improved by the application of new equipment and techniques. ... more Radiation oncology has been rapidly improved by the application of new equipment and techniques. With the advent of new complex and precise radiotherapy techniques such as intensity modulated radiotherapy, stereotactic radiosurgery, and volumetric modulated arc therapy, the demand for an accurate and feasible three-dimensional (3-D) dosimetry system has increased. The most important features of a 3-D dosimeter, apart from being precise, accurate and reproducible, include also its low cost, feasibility, and availability. In 2004 a new generation of solid plastic dosimeters which demonstrate a radiochromic response to ionizing radiation was introduced. PRESAGE ® plastic dosimeter lacks the limitations of previous Ferric and polymer plastic 3-D dosimeters such as diffusion, sensitivity to oxygen, fabrication problems, scanning and read out challenges. In this decade, a large number of efforts have been carried out to enhance PRESAGE ® structure and scanning methods. This article attempts to review and reflect on the results of these investigations.
The aim of this study is to evaluate the application and accuracy of polymer gels for determining... more The aim of this study is to evaluate the application and accuracy of polymer gels for determining electron dose distributions in the presence of small heterogeneities made of bone and air. Different cylindrical phantoms containing MAGIC (Methacrylic and Ascorbic acid in Gelatin Initiated by Copper) normoxic polymer gel were used under the slab phantoms during irradiation. MR images of the irradiated gel phantoms were obtained to determine their R2 (spin-spin) relaxation maps for conversion to absorbed dose. One-and 2-dimensional lateral dose profiles were acquired at depths of 1 and 4 cm for 8 and 15 MeV electron beams. The results were compared with the doses measured by a diode detector at the same positions. In addition, the dose distribution in the axial orientation was measured by the gel dosimeter. The slope and intercept for the R2 versus dose curve were 0.509 ± 0.002 Gy −1 s −1 and 4.581 ± 0.005 s −1 , respectively. No significant variation in dose-R2 response was seen for the two electron energies within the applied dose ranges. The mean dose difference between the measured gel dose profiles was smaller than 3% compared to those measured by the diode detector. These results provide further demonstration that electron dose distributions are significantly altered in the presence of tissue inhomogeneities such as bone and air cavity and that MAGIC gel is a useful tool for 3-dimensional dose visualization and qualitative assessment of tissue inhomogeneity effects in electron beam dosimetry.
Aim of Study: The aim of this study is to evaluate some dosimetry parameters such as uniformity, ... more 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.
The Geant4 toolkit was used to develop a Monte Carlo (MC)-based engine for accurate dose calculat... more 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.
The electron benefit transfer (EBT) GAFCHROMIC films possess a number of features making them app... more The electron benefit transfer (EBT) GAFCHROMIC films possess a number of features making them appropriate for high-quality dosimetry in intensity-modulated radiation therapy (IMRT). Compensators to deliver IMRT are known to change the beam-energy spectrum as well as to produce scattered photons and to contaminate electrons; therefore, the accuracy and validity of EBT-film dosimetry in compensator-based IMRT should be investigated. Percentage-depth doses and lateral-beam profiles were measured using EBT films in perpendicular orientation with respect to 6 and 18 MV photon beam energies for: (1) different thicknesses of cerrobend slab (open, 1.0, 2.0, 4.0, and 6.0 cm), field sizes (5 Â 5, 10 Â 10, and 20 Â 20 cm 2), and measurement depths (D max , 5.0 and 10.0 cm); and (2) stepwedged compensator in a solid phantom. To verify results, same measurements were implemented using a 0.125 cm 3 ionization chamber in a water phantom and also in Monte Carlo simulations using the Monte Carlo N-particle radiation transport computer code. The mean energy of photons was increased due to beam hardening in comparison with open fields at both 6 and 18 MV energies. For a 20 Â 20 cm 2 field size of a 6 MV photon beam and a 6.0 cm thick block, the surface dose decreased by about 12% and percentage-depth doses increased up to 3% at 30.0 cm depth, due to the beam-hardening effect induced by the block. In contrast, at 18 MV, the surface dose increased by about 8% and depth dose reduced by 3% at 30.0 cm depth. The penumbral widths (80% to 20%) increase with block thickness, field size, and beam energy. The EBT film results were in good agreement with the ionization chamber dose profiles and Monte Carlo N-particle radiation transport computer code simulation behind the stepwedged compensator. Also, there was a good agreement between the EBT-film and the treatmentplanning results on the anthropomorphic phantom. The EBT films can be accurately used as a 2D dosimeter for dose verification and quality assurance of compensator-based C-IMRT.
Comparison of penumbra regions produced by ancient Gamma knife model C and Gamma ART 6000 using M... more Comparison of penumbra regions produced by ancient Gamma knife model C and Gamma ART 6000 using Monte Carlo MCNP6 simulation, Applied Radiation and Isotopes,
PURPOSE Whole-body photoneutron (PN) energy-specific dosimetry on phantom surfaces and 360°angula... more PURPOSE Whole-body photoneutron (PN) energy-specific dosimetry on phantom surfaces and 360°angular fast PN distribution dosimetry on and around polyethylene (PE) phantom organs for prostate cancer in 10 cm × 10 cm and 20 cm × 20 cm field sizes of 18 MV X-rays of Varian Clinac 2100C linear accelerator. METHODS Novel "Sohrabi neutron dosimetry methods" including "miniature passive neutron dosimeter/spectrometer" and "strip polycarbonate neutron dosimeters" were applied. Energy-specific PN dose equivalents on surface as well as 360°fast PN dose equivalent angular distributions on and around PE phantom organs; head, neck, thorax, arms, pelvis, thighs and legs were determined. RESULTS Matrix of surface (skin) energy-specific PN dose equivalents including total thermal, total epithermal, total fast, sum total thermal + epithermal and sum total thermal + epithermal + fast, and 360°angular fast PN dose equivalent responses were determined. The results indicate that data matrix of 20 cm × 20 cm field size provides higher PN dose equivalent values than those of 10 cm × 10 cm field size for surface points even remote from the central axis and for all 360°angular fast PN dose equivalent distributions on organs studied. CONCLUSIONS Matrix of energy-specific PN dose equivalents was obtained demonstrating that the Sohrabi neutron dosimetry methods applied are unique for energy-specific PN dose equivalent studies as well as for 360°angular PN dose equivalent distribution data for PN-SPC risk estimation. The dosimetry methods can be specifically applied to many other exotic applications in health physics, medical physics, space flight dosimetry, and nuclear science and technology.
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Papers by Hassan Nedaie