Anthony Teran - Academia.edu (original) (raw)
Papers by Anthony Teran
Medical Physics, 2013
ABSTRACT Purpose: To evaluate the performance of a pixelated‐Silicon detector for proton radiosur... more ABSTRACT Purpose: To evaluate the performance of a pixelated‐Silicon detector for proton radiosurgery applications and determine a methodology for response correction as a function of proton energy/LET. Methods: Proton radiosurgery requires metrology apparatus that have a high spatial resolution and a stable (or well characterized) response to LET. To meet this need the dose magnifying glass or DMG was developed at the University of Wollongong. This device is a pixelated silicon strip detector comprising an array of 128 phosphor implanted n+ strips on a p‐type silicon wafer. A 100μm pitch device was tested with proton radiation to evaluate its performance. The DMG was mounted in a water tank and irradiated with various discrete energies to develop correction factors as a function of proton energy. Depth dose and lateral profiles of various proton radiosurgery beams were then collected for comparison with standard metrology techniques. Results: The DMG performed well providing realtime depth dose and lateral profile information. The device did over‐respond to proton dose especially below 100MeV resulting in over‐estimation in the spread‐out Bragg peak region of almost 30%. This over‐response could be accounted for using a power law correction, the parameters of which were established for a range of discrete proton energies down to 20MeV. Using the central channel of the DMG, accurate depth dose profiles proton fields to 1mm diameter were obtained without errors associated with partial volume sampling, while the full array could be used to provide real time profile information of fields below 1.5cm diameter without the need for detector scanning. Conclusion: The DMG is a potentially useful device for proton therapy, in particular in providing realtime data for small fields associated with SRS. Further work is required to better characterize the performance of the device as a function of depth/LET before it can be used clinically.
Medical Physics, 2013
ABSTRACT Purpose: Radiographic film dosimetry suffers from energy dependence in Proton dosimetry,... more ABSTRACT Purpose: Radiographic film dosimetry suffers from energy dependence in Proton dosimetry, and thus is not suitable for absolute dosimetry. In this study, we investigate film dosimetry for the constancy check of percentage depth dose (PDD) and beam profile measurements in proton beams. Methods: From PDD measured by film and ion chamber (IC), calibration factors as a function of depth (IC/film) was obtained. These factors imply variable slopes (with energy and depth) of linear characteristic curves that relate film response to dose. They were used to convert day‐to‐day film measurements into dose. Film dosimetry of a 186 MeV proton beam was performed to investigate this hypothesis. In addition, Monte Carlos simulation of a 250 MeV proton beam was performed calculating proton fluence spectrum along the off‐axis direction. By multiplying stopping powers of film emulsion and water, respectively, to the spectrum, doses to film and water were calculated. The ratio of film dose to water dose was evaluated across the off‐axis distance to understand film response. Results: The measured and calibrated PDD approached to that of IC, but near the end of spread‐out‐bragg‐peak (SBOP), a spurious peak is observed due to the mismatch of distal edge between calibration film and measurement film. The SBOP width was measurable within 1mm. The distal edge was reproducible within 1.5mm. Entrance dose was reproducible within 5.5%. The possible sources of such errors include developer uncertainty, film emulsion nonuniformity, and misalignment of film edge to the phantom surface. For off‐axis evaluation, the dose ratio varied within 3%, and thus film is shown to be accurate for dosimetry across off‐axis distance. Conclusions: Radiographic film can be suitable for beam profile measurements and may be suitable for PDD constancy check for proton beams. Routine use will confirm such error which will be presented in this study.
Physics in Medicine & Biology
Objective. To investigate the potential of using a single quadrupole magnet with a high magnetic ... more Objective. To investigate the potential of using a single quadrupole magnet with a high magnetic field gradient to create planar minibeams suitable for clinical applications of proton minibeam radiation therapy. Approach. We performed Monte Carlo simulations involving single quadrupole Halbach cylinders in a passively scattered nozzle in clinical use for proton therapy. Pencil beams produced by the nozzle of 10–15 mm initial diameters and particle range of ∼10–20 cm in water were focused by magnets with field gradients of 225–350 T m−1 and cylinder lengths of 80–110 mm to produce very narrow elongated (planar) beamlets. The corresponding dose distributions were scored in a water phantom. Composite minibeam dose distributions composed from three beamlets were created by laterally shifting copies of the single beamlet distribution to either side of a central beamlet. Modulated beamlets (with 18–30 mm nominal central SOBP) and corresponding composite dose distributions were created in ...
Radiotherapy and Oncology, 2020
Radiotherapy and Oncology, 2020
Journal of applied clinical medical physics / American College of Medical Physics, Jan 8, 2015
Radiographic film dosimetry suffers from its energy dependence in proton dosimetry. This study so... more Radiographic film dosimetry suffers from its energy dependence in proton dosimetry. This study sought to develop a method of measuring proton beams by the film and to evaluate film response to proton beams for the constancy check of depth dose (DD). It also evaluated the film for profile measurements. To achieve this goal, from DDs measured by film and ion chamber (IC), calibration factors (ratios of dose measured by IC to film responses) as a function of depth in a phantom were obtained. These factors imply variable slopes (with proton energy and depth) of linear characteristic curves that relate film response to dose. We derived a calibration method that enables utilization of the factors for acquisition of dose from film density measured at later dates by adapting to a potentially altered processor condition. To test this model, the characteristic curve was obtained by using EDR2 film and in-phantom film dosimetry in parallel with a 149.65 MeV proton beam, using the method. An ad...
We study the time dependence of the grain size distribution N(r,t) during crystallization of a d-... more We study the time dependence of the grain size distribution N(r,t) during crystallization of a d-dimensional solid. A partial differential equation including a source term for nuclei and a growth law for grains is solved analytically for any dimension d. We discuss solutions obtained for processes described by the Kolmogorov-Avrami-Mehl-Johnson model for random nucleation and growth (RNG). Nucleation and growth are set on the same footing, which leads to a time-dependent decay of both effective rates. We analyze in detail how model parameters, the dimensionality of the crystallization process, and time influence the shape of the distribution. The calculations show that the dynamics of the effective nucleation and effective growth rates play an essential role in determining the final form of the distribution obtained at full crystallization. We demonstrate that for one class of nucleation and growth rates the distribution evolves in time into the logarithmic-normal (lognormal) form d...
Bulletin of the American Physical Society, 2008
ABSTRACT The logarithmic-normal (lognormal) distribution is one of the most frequently observed d... more ABSTRACT The logarithmic-normal (lognormal) distribution is one of the most frequently observed distributions in nature and describes a large number of physical, biological and even sociological phenomena. However, a derivation of this distribution from first principles is lacking. We propose a differential equation governing the time development of grain size distribution in random nucleation and growth processes. The solution of this equation provides an analytical derivation of size distributions that has a form of the lognormal type. The resulting expression is used to discuss the grain size distribution of solid phase crystallized Si-films.
Physics in Medicine and Biology
Journal of applied clinical medical physics, Jan 18, 2017
As technology continues to develop, external beam radiation therapy is being employed, with incre... more As technology continues to develop, external beam radiation therapy is being employed, with increased conformity, to treat smaller targets. As this occurs, the dosimetry methods and tools employed to quantify these fields for treatment also have to evolve to provide increased spatial resolution. The team at the University of Wollongong has developed a pixelated silicon detector prototype known as the dose magnifying glass (DMG) for real-time small-field metrology. This device has been tested in photon fields and IMRT. The purpose of this work was to conduct the initial performance tests with proton radiation, using beam energies and modulations typically associated with proton radiosurgery. Depth dose and lateral beam profiles were measured and compared with those collected using a PTW parallel-plate ionization chamber, a PTW proton-specific dosimetry diode, EBT3 Gafchromic film, and Monte Carlo simulations. Measurements of the depth dose profile yielded good agreement when compared...
Journal of Applied Clinical Medical Physics, May 8, 2015
Radiographic film dosimetry suffers from its energy dependence in proton dosimetry. This study so... more Radiographic film dosimetry suffers from its energy dependence in proton dosimetry. This study sought to develop a method of measuring proton beams by the film and to evaluate film response to proton beams for the constancy check of depth dose (DD). It also evaluated the film for profile measurements. To achieve this goal, from DDs measured by film and ion chamber (IC), calibration factors (ratios of dose measured by IC to film responses) as a function of depth in a phantom were obtained. These factors imply variable slopes (with proton energy and depth) of linear characteristic curves that relate film response to dose. We derived a calibration method that enables utilization of the factors for acquisition of dose from film density measured at later dates by adapting to a potentially altered processor condition. To test this model, the characteristic curve was obtained by using EDR2 film and in-phantom film dosimetry in parallel with a 149.65 MeV proton beam, using the method. An additional validation of the model was performed by concurrent film and IC measurement perpendicular to the beam at various depths. Beam profile measurements by the film were also evaluated at the center of beam modulation. In order to interpret and ascertain the film dosimetry, Monte Carlos simulation of the beam was performed, calculating the proton fluence spectrum along depths and off-axis distances. By multiplying respective stopping powers to the spectrum, doses to film and water were calculated. The ratio of film dose to water dose was evaluated. Results are as follows. The characteristic curve proved the assumed linearity. The measured DD approached that of IC, but near the end of the spread-out Bragg peak (SOBP), a spurious peak was observed due to the mismatch of distal edge between the calibration and measurement films. The width of SOBP and the proximal edge were both reproducible within a maximum of 5 mm; the distal edge was reproducible within 1 mm. At 5 cm depth, the dose was reproducible within 10%. These large discrepancies were identified to have been contributed by film processor uncertainty across a layer of film and the misalignment of film edge to the frontal phantom surface. The deviations could drop from 5 to 2 mm in SOBP and from 10% to 4.5% at 5 cm depth in a well-controlled processor condition (i.e., warm up). In addition to the validation of the calibration method done by the DD measurements, the concurrent film and IC measurement independently validated the model by showing the constancy of depth-dependent calibration factors. For profile measurement, the film showed good agreement with ion chamber measurement. In agreement with the experimental findings, computationally obtained ratio of film dose to water dose assisted understanding of the trend of the film response by revealing relatively large and small variances of the response for DD and beam profile measurements, respectively. Conclusions are as follows. For proton beams, radiographic film proved to offer accurate beam profile measurements. The adaptive calibration method proposed in this study was validated. Using the method, film dosimetry could offer reasonably accurate DD constancy checks, when provided with a well-controlled processor condition. Although the processor warming up can promote a uniform processing across a single layer of the film, the processing remains as a challenge.
The micromorphology of solids impacts in an essential way their mechanical, electronic, optical o... more The micromorphology of solids impacts in an essential way their mechanical, electronic, optical or magnetic properties. Hence, it is an important task to characterize properly the granularity of materials. One central quantity providing such information is the grain size distribution. We propose an analytical derivation of this distribution during the random nucleation and growth crystallization process of a d-dimensional solid
Aps Meeting Abstracts, Mar 1, 2008
The logarithmic-normal (lognormal) distribution is one of the most frequently observed distributi... more The logarithmic-normal (lognormal) distribution is one of the most frequently observed distributions in nature and describes a large number of physical, biological and even sociological phenomena. However, a derivation of this distribution from first principles is lacking. We propose a differential equation governing the time development of grain size distribution in random nucleation and growth processes. The solution of this equation provides an analytical derivation of size distributions that has a form of the lognormal type. The resulting expression is used to discuss the grain size distribution of solid phase crystallized Si-films.
The micromorphology of solids impacts in an essential way their mechanical, electronic, optical o... more The micromorphology of solids impacts in an essential way their mechanical, electronic, optical or magnetic properties. Hence, it is an important task to characterize properly the granularity of materials. One central quantity providing such information is the grain size distribution. We propose an analytical derivation of this distribution during the random nucleation and growth crystallization process of a d-dimensional solid (d=1,2,3). We describe how the grain size distribution evolves from early stages of crystallization to its final form when complete crystallization is achieved. We also discuss the remarkable result that for certain classes of nucleation and growth rates the asymptotic limit of large times is a logarithmic-normal (lognormal) type distribution. Finally, we apply the theory to the time-evolution of the grain size distribution during solid-phase crystallization of Si-films.
Journal of applied clinical medical physics / American College of Medical Physics, 2015
The small fields and sharp gradients typically encountered in proton radiosurgery require high sp... more The small fields and sharp gradients typically encountered in proton radiosurgery require high spatial resolution dosimetric measurements, especially below 1-2 cm diameters. Radiochromic film provides high resolution, but requires postprocessing and special handling. Promising alternatives are diode detectors with small sensitive volumes (SV) that are capable of high resolution and real-time dose acquisition. In this study we evaluated the PTW PR60020 proton dosimetry diode using radiation fields and beam energies relevant to radiosurgery applications. Energies of 127 and 157 MeV (9.7 to 15 cm range) and initial diameters of 8, 10, 12, and 20mm were delivered using single-stage scattering and four modulations (0, 15, 30, and 60mm) to a water tank in our treatment room. Depth dose and beam profile data were compared with PTW Markus N23343 ionization chamber, EBT2 Gafchromic film, and Monte Carlo simulations. Transverse dose profiles were measured using the diode in "edge-on"...
Journal of applied clinical medical physics / American College of Medical Physics, 2015
The purpose of this study was to evaluate the effectiveness of full three-dimensional (3D) gamma ... more The purpose of this study was to evaluate the effectiveness of full three-dimensional (3D) gamma algorithm for spot scanning proton fields, also referred to as pencil beam scanning (PBS) fields. The difference between the full 3D gamma algorithm and a simplified two-dimensional (2D) version was presented. Both 3D and 2D gamma algorithms are used for dose evaluations of clinical proton PBS fields. The 3D gamma algorithm was implemented in an in-house software program without resorting to 2D interpolations perpendicular to the proton beams at the depths of measurement. Comparison between calculated and measured dose points was car-ried out directly using Euclidian distance in 3D space and the dose difference as a fourth dimension. Note that this 3D algorithm faithfully implemented the original concept proposed by Low et al. (1998) who described gamma criterion using 3D Euclidian distance and dose difference. Patient-specific proton PBS plans are separated into two categories, dependin...
The logarithmic-normal (lognormal) distribution is one of the most frequently observed distributi... more The logarithmic-normal (lognormal) distribution is one of the most frequently observed distributions in nature and describes a large number of physical, biological and even sociological phenomena. However, a derivation of this distribution from first principles is lacking. We propose a differential equation governing the time development of grain size distribution in random nucleation and growth processes. The solution of this equation provides an analytical derivation of size distributions that has a form of the lognormal type. The resulting expression is used to discuss the grain size distribution of solid phase crystallized Si-films.
MRS Proceedings, 2009
We analyze the grain size distribution during solid phase crystallization of Silicon thin films. ... more We analyze the grain size distribution during solid phase crystallization of Silicon thin films. We use a model developed recently that offers analytical expressions for the timeevolution of the grain size distribution during crystallization of a d-dimensional solid. Contrary to the usual fit of the experimental results with a lognormal distribution, the theory describes the data from basic physical principles such as nucleation and growth processes. The theory allows for a good description of the grain size distribution except for early stages of crystallization. The latter case is expected and discussed. An important outcome of the model is that the distribution at full crystallization is determined by the time-dependence of the nucleation and growth rates of grains. In the case under consideration, the theory leads to an analytical expression that has the form of a lognormal-type distribution for the fully crystallized sample.
Physical Review B, 2010
We study the time dependence of the grain size distribution N (r, t) during crystallization of a ... more We study the time dependence of the grain size distribution N (r, t) during crystallization of a d−dimensional solid. A partial differential equation including a source term for nuclei and a growth law for grains is solved analytically for any dimension d. We discuss solutions obtained for processes described by the Kolmogorov-Avrami-Mehl-Johnson model for random nucleation and growth (RNG). Nucleation and growth are set on the same footing, which leads to a time-dependent decay of both effective rates. We analyze in detail how model parameters, the dimensionality of the crystallization process, and time influence the shape of the distribution. The calculations show that the dynamics of the effective nucleation and effective growth rates play an essential role in determining the final form of the distribution obtained at full crystallization. We demonstrate that for one class of nucleation and growth rates the distribution evolves in time into the logarithmicnormal (lognormal) form discussed earlier by Bergmann and Bill [J. Cryst. Growth 310, 3135 (2008)]. We also obtain an analytical expression for the finite maximal grain size at all times. The theory allows for the description of a variety of RNG crystallization processes in thin films and bulk materials. Expressions useful for experimental data analysis are presented for the grain size distribution and the moments in terms of fundamental and measurable parameters of the model.
Medical Physics, 2013
ABSTRACT Purpose: To evaluate the performance of a pixelated‐Silicon detector for proton radiosur... more ABSTRACT Purpose: To evaluate the performance of a pixelated‐Silicon detector for proton radiosurgery applications and determine a methodology for response correction as a function of proton energy/LET. Methods: Proton radiosurgery requires metrology apparatus that have a high spatial resolution and a stable (or well characterized) response to LET. To meet this need the dose magnifying glass or DMG was developed at the University of Wollongong. This device is a pixelated silicon strip detector comprising an array of 128 phosphor implanted n+ strips on a p‐type silicon wafer. A 100μm pitch device was tested with proton radiation to evaluate its performance. The DMG was mounted in a water tank and irradiated with various discrete energies to develop correction factors as a function of proton energy. Depth dose and lateral profiles of various proton radiosurgery beams were then collected for comparison with standard metrology techniques. Results: The DMG performed well providing realtime depth dose and lateral profile information. The device did over‐respond to proton dose especially below 100MeV resulting in over‐estimation in the spread‐out Bragg peak region of almost 30%. This over‐response could be accounted for using a power law correction, the parameters of which were established for a range of discrete proton energies down to 20MeV. Using the central channel of the DMG, accurate depth dose profiles proton fields to 1mm diameter were obtained without errors associated with partial volume sampling, while the full array could be used to provide real time profile information of fields below 1.5cm diameter without the need for detector scanning. Conclusion: The DMG is a potentially useful device for proton therapy, in particular in providing realtime data for small fields associated with SRS. Further work is required to better characterize the performance of the device as a function of depth/LET before it can be used clinically.
Medical Physics, 2013
ABSTRACT Purpose: Radiographic film dosimetry suffers from energy dependence in Proton dosimetry,... more ABSTRACT Purpose: Radiographic film dosimetry suffers from energy dependence in Proton dosimetry, and thus is not suitable for absolute dosimetry. In this study, we investigate film dosimetry for the constancy check of percentage depth dose (PDD) and beam profile measurements in proton beams. Methods: From PDD measured by film and ion chamber (IC), calibration factors as a function of depth (IC/film) was obtained. These factors imply variable slopes (with energy and depth) of linear characteristic curves that relate film response to dose. They were used to convert day‐to‐day film measurements into dose. Film dosimetry of a 186 MeV proton beam was performed to investigate this hypothesis. In addition, Monte Carlos simulation of a 250 MeV proton beam was performed calculating proton fluence spectrum along the off‐axis direction. By multiplying stopping powers of film emulsion and water, respectively, to the spectrum, doses to film and water were calculated. The ratio of film dose to water dose was evaluated across the off‐axis distance to understand film response. Results: The measured and calibrated PDD approached to that of IC, but near the end of spread‐out‐bragg‐peak (SBOP), a spurious peak is observed due to the mismatch of distal edge between calibration film and measurement film. The SBOP width was measurable within 1mm. The distal edge was reproducible within 1.5mm. Entrance dose was reproducible within 5.5%. The possible sources of such errors include developer uncertainty, film emulsion nonuniformity, and misalignment of film edge to the phantom surface. For off‐axis evaluation, the dose ratio varied within 3%, and thus film is shown to be accurate for dosimetry across off‐axis distance. Conclusions: Radiographic film can be suitable for beam profile measurements and may be suitable for PDD constancy check for proton beams. Routine use will confirm such error which will be presented in this study.
Physics in Medicine & Biology
Objective. To investigate the potential of using a single quadrupole magnet with a high magnetic ... more Objective. To investigate the potential of using a single quadrupole magnet with a high magnetic field gradient to create planar minibeams suitable for clinical applications of proton minibeam radiation therapy. Approach. We performed Monte Carlo simulations involving single quadrupole Halbach cylinders in a passively scattered nozzle in clinical use for proton therapy. Pencil beams produced by the nozzle of 10–15 mm initial diameters and particle range of ∼10–20 cm in water were focused by magnets with field gradients of 225–350 T m−1 and cylinder lengths of 80–110 mm to produce very narrow elongated (planar) beamlets. The corresponding dose distributions were scored in a water phantom. Composite minibeam dose distributions composed from three beamlets were created by laterally shifting copies of the single beamlet distribution to either side of a central beamlet. Modulated beamlets (with 18–30 mm nominal central SOBP) and corresponding composite dose distributions were created in ...
Radiotherapy and Oncology, 2020
Radiotherapy and Oncology, 2020
Journal of applied clinical medical physics / American College of Medical Physics, Jan 8, 2015
Radiographic film dosimetry suffers from its energy dependence in proton dosimetry. This study so... more Radiographic film dosimetry suffers from its energy dependence in proton dosimetry. This study sought to develop a method of measuring proton beams by the film and to evaluate film response to proton beams for the constancy check of depth dose (DD). It also evaluated the film for profile measurements. To achieve this goal, from DDs measured by film and ion chamber (IC), calibration factors (ratios of dose measured by IC to film responses) as a function of depth in a phantom were obtained. These factors imply variable slopes (with proton energy and depth) of linear characteristic curves that relate film response to dose. We derived a calibration method that enables utilization of the factors for acquisition of dose from film density measured at later dates by adapting to a potentially altered processor condition. To test this model, the characteristic curve was obtained by using EDR2 film and in-phantom film dosimetry in parallel with a 149.65 MeV proton beam, using the method. An ad...
We study the time dependence of the grain size distribution N(r,t) during crystallization of a d-... more We study the time dependence of the grain size distribution N(r,t) during crystallization of a d-dimensional solid. A partial differential equation including a source term for nuclei and a growth law for grains is solved analytically for any dimension d. We discuss solutions obtained for processes described by the Kolmogorov-Avrami-Mehl-Johnson model for random nucleation and growth (RNG). Nucleation and growth are set on the same footing, which leads to a time-dependent decay of both effective rates. We analyze in detail how model parameters, the dimensionality of the crystallization process, and time influence the shape of the distribution. The calculations show that the dynamics of the effective nucleation and effective growth rates play an essential role in determining the final form of the distribution obtained at full crystallization. We demonstrate that for one class of nucleation and growth rates the distribution evolves in time into the logarithmic-normal (lognormal) form d...
Bulletin of the American Physical Society, 2008
ABSTRACT The logarithmic-normal (lognormal) distribution is one of the most frequently observed d... more ABSTRACT The logarithmic-normal (lognormal) distribution is one of the most frequently observed distributions in nature and describes a large number of physical, biological and even sociological phenomena. However, a derivation of this distribution from first principles is lacking. We propose a differential equation governing the time development of grain size distribution in random nucleation and growth processes. The solution of this equation provides an analytical derivation of size distributions that has a form of the lognormal type. The resulting expression is used to discuss the grain size distribution of solid phase crystallized Si-films.
Physics in Medicine and Biology
Journal of applied clinical medical physics, Jan 18, 2017
As technology continues to develop, external beam radiation therapy is being employed, with incre... more As technology continues to develop, external beam radiation therapy is being employed, with increased conformity, to treat smaller targets. As this occurs, the dosimetry methods and tools employed to quantify these fields for treatment also have to evolve to provide increased spatial resolution. The team at the University of Wollongong has developed a pixelated silicon detector prototype known as the dose magnifying glass (DMG) for real-time small-field metrology. This device has been tested in photon fields and IMRT. The purpose of this work was to conduct the initial performance tests with proton radiation, using beam energies and modulations typically associated with proton radiosurgery. Depth dose and lateral beam profiles were measured and compared with those collected using a PTW parallel-plate ionization chamber, a PTW proton-specific dosimetry diode, EBT3 Gafchromic film, and Monte Carlo simulations. Measurements of the depth dose profile yielded good agreement when compared...
Journal of Applied Clinical Medical Physics, May 8, 2015
Radiographic film dosimetry suffers from its energy dependence in proton dosimetry. This study so... more Radiographic film dosimetry suffers from its energy dependence in proton dosimetry. This study sought to develop a method of measuring proton beams by the film and to evaluate film response to proton beams for the constancy check of depth dose (DD). It also evaluated the film for profile measurements. To achieve this goal, from DDs measured by film and ion chamber (IC), calibration factors (ratios of dose measured by IC to film responses) as a function of depth in a phantom were obtained. These factors imply variable slopes (with proton energy and depth) of linear characteristic curves that relate film response to dose. We derived a calibration method that enables utilization of the factors for acquisition of dose from film density measured at later dates by adapting to a potentially altered processor condition. To test this model, the characteristic curve was obtained by using EDR2 film and in-phantom film dosimetry in parallel with a 149.65 MeV proton beam, using the method. An additional validation of the model was performed by concurrent film and IC measurement perpendicular to the beam at various depths. Beam profile measurements by the film were also evaluated at the center of beam modulation. In order to interpret and ascertain the film dosimetry, Monte Carlos simulation of the beam was performed, calculating the proton fluence spectrum along depths and off-axis distances. By multiplying respective stopping powers to the spectrum, doses to film and water were calculated. The ratio of film dose to water dose was evaluated. Results are as follows. The characteristic curve proved the assumed linearity. The measured DD approached that of IC, but near the end of the spread-out Bragg peak (SOBP), a spurious peak was observed due to the mismatch of distal edge between the calibration and measurement films. The width of SOBP and the proximal edge were both reproducible within a maximum of 5 mm; the distal edge was reproducible within 1 mm. At 5 cm depth, the dose was reproducible within 10%. These large discrepancies were identified to have been contributed by film processor uncertainty across a layer of film and the misalignment of film edge to the frontal phantom surface. The deviations could drop from 5 to 2 mm in SOBP and from 10% to 4.5% at 5 cm depth in a well-controlled processor condition (i.e., warm up). In addition to the validation of the calibration method done by the DD measurements, the concurrent film and IC measurement independently validated the model by showing the constancy of depth-dependent calibration factors. For profile measurement, the film showed good agreement with ion chamber measurement. In agreement with the experimental findings, computationally obtained ratio of film dose to water dose assisted understanding of the trend of the film response by revealing relatively large and small variances of the response for DD and beam profile measurements, respectively. Conclusions are as follows. For proton beams, radiographic film proved to offer accurate beam profile measurements. The adaptive calibration method proposed in this study was validated. Using the method, film dosimetry could offer reasonably accurate DD constancy checks, when provided with a well-controlled processor condition. Although the processor warming up can promote a uniform processing across a single layer of the film, the processing remains as a challenge.
The micromorphology of solids impacts in an essential way their mechanical, electronic, optical o... more The micromorphology of solids impacts in an essential way their mechanical, electronic, optical or magnetic properties. Hence, it is an important task to characterize properly the granularity of materials. One central quantity providing such information is the grain size distribution. We propose an analytical derivation of this distribution during the random nucleation and growth crystallization process of a d-dimensional solid
Aps Meeting Abstracts, Mar 1, 2008
The logarithmic-normal (lognormal) distribution is one of the most frequently observed distributi... more The logarithmic-normal (lognormal) distribution is one of the most frequently observed distributions in nature and describes a large number of physical, biological and even sociological phenomena. However, a derivation of this distribution from first principles is lacking. We propose a differential equation governing the time development of grain size distribution in random nucleation and growth processes. The solution of this equation provides an analytical derivation of size distributions that has a form of the lognormal type. The resulting expression is used to discuss the grain size distribution of solid phase crystallized Si-films.
The micromorphology of solids impacts in an essential way their mechanical, electronic, optical o... more The micromorphology of solids impacts in an essential way their mechanical, electronic, optical or magnetic properties. Hence, it is an important task to characterize properly the granularity of materials. One central quantity providing such information is the grain size distribution. We propose an analytical derivation of this distribution during the random nucleation and growth crystallization process of a d-dimensional solid (d=1,2,3). We describe how the grain size distribution evolves from early stages of crystallization to its final form when complete crystallization is achieved. We also discuss the remarkable result that for certain classes of nucleation and growth rates the asymptotic limit of large times is a logarithmic-normal (lognormal) type distribution. Finally, we apply the theory to the time-evolution of the grain size distribution during solid-phase crystallization of Si-films.
Journal of applied clinical medical physics / American College of Medical Physics, 2015
The small fields and sharp gradients typically encountered in proton radiosurgery require high sp... more The small fields and sharp gradients typically encountered in proton radiosurgery require high spatial resolution dosimetric measurements, especially below 1-2 cm diameters. Radiochromic film provides high resolution, but requires postprocessing and special handling. Promising alternatives are diode detectors with small sensitive volumes (SV) that are capable of high resolution and real-time dose acquisition. In this study we evaluated the PTW PR60020 proton dosimetry diode using radiation fields and beam energies relevant to radiosurgery applications. Energies of 127 and 157 MeV (9.7 to 15 cm range) and initial diameters of 8, 10, 12, and 20mm were delivered using single-stage scattering and four modulations (0, 15, 30, and 60mm) to a water tank in our treatment room. Depth dose and beam profile data were compared with PTW Markus N23343 ionization chamber, EBT2 Gafchromic film, and Monte Carlo simulations. Transverse dose profiles were measured using the diode in "edge-on"...
Journal of applied clinical medical physics / American College of Medical Physics, 2015
The purpose of this study was to evaluate the effectiveness of full three-dimensional (3D) gamma ... more The purpose of this study was to evaluate the effectiveness of full three-dimensional (3D) gamma algorithm for spot scanning proton fields, also referred to as pencil beam scanning (PBS) fields. The difference between the full 3D gamma algorithm and a simplified two-dimensional (2D) version was presented. Both 3D and 2D gamma algorithms are used for dose evaluations of clinical proton PBS fields. The 3D gamma algorithm was implemented in an in-house software program without resorting to 2D interpolations perpendicular to the proton beams at the depths of measurement. Comparison between calculated and measured dose points was car-ried out directly using Euclidian distance in 3D space and the dose difference as a fourth dimension. Note that this 3D algorithm faithfully implemented the original concept proposed by Low et al. (1998) who described gamma criterion using 3D Euclidian distance and dose difference. Patient-specific proton PBS plans are separated into two categories, dependin...
The logarithmic-normal (lognormal) distribution is one of the most frequently observed distributi... more The logarithmic-normal (lognormal) distribution is one of the most frequently observed distributions in nature and describes a large number of physical, biological and even sociological phenomena. However, a derivation of this distribution from first principles is lacking. We propose a differential equation governing the time development of grain size distribution in random nucleation and growth processes. The solution of this equation provides an analytical derivation of size distributions that has a form of the lognormal type. The resulting expression is used to discuss the grain size distribution of solid phase crystallized Si-films.
MRS Proceedings, 2009
We analyze the grain size distribution during solid phase crystallization of Silicon thin films. ... more We analyze the grain size distribution during solid phase crystallization of Silicon thin films. We use a model developed recently that offers analytical expressions for the timeevolution of the grain size distribution during crystallization of a d-dimensional solid. Contrary to the usual fit of the experimental results with a lognormal distribution, the theory describes the data from basic physical principles such as nucleation and growth processes. The theory allows for a good description of the grain size distribution except for early stages of crystallization. The latter case is expected and discussed. An important outcome of the model is that the distribution at full crystallization is determined by the time-dependence of the nucleation and growth rates of grains. In the case under consideration, the theory leads to an analytical expression that has the form of a lognormal-type distribution for the fully crystallized sample.
Physical Review B, 2010
We study the time dependence of the grain size distribution N (r, t) during crystallization of a ... more We study the time dependence of the grain size distribution N (r, t) during crystallization of a d−dimensional solid. A partial differential equation including a source term for nuclei and a growth law for grains is solved analytically for any dimension d. We discuss solutions obtained for processes described by the Kolmogorov-Avrami-Mehl-Johnson model for random nucleation and growth (RNG). Nucleation and growth are set on the same footing, which leads to a time-dependent decay of both effective rates. We analyze in detail how model parameters, the dimensionality of the crystallization process, and time influence the shape of the distribution. The calculations show that the dynamics of the effective nucleation and effective growth rates play an essential role in determining the final form of the distribution obtained at full crystallization. We demonstrate that for one class of nucleation and growth rates the distribution evolves in time into the logarithmicnormal (lognormal) form discussed earlier by Bergmann and Bill [J. Cryst. Growth 310, 3135 (2008)]. We also obtain an analytical expression for the finite maximal grain size at all times. The theory allows for the description of a variety of RNG crystallization processes in thin films and bulk materials. Expressions useful for experimental data analysis are presented for the grain size distribution and the moments in terms of fundamental and measurable parameters of the model.