Inhwan Yeo - Academia.edu (original) (raw)

Papers by Inhwan Yeo

Medical physics, 2016

A method is proposed to reconstruct a four-dimensional (4D) dose distribution using phase matchin... more A method is proposed to reconstruct a four-dimensional (4D) dose distribution using phase matching of measured cine images to precalculated images of electronic portal imaging device (EPID). (1) A phantom, designed to simulate a tumor in lung (a polystyrene block with a 3 cm diameter embedded in cork), was placed on a sinusoidally moving platform with an amplitude of 1 cm and a period of 4 s. Ten-phase 4D computed tomography (CT) images of the phantom were acquired. A planning target volume (PTV) was created by adding a margin of 1 cm around the internal target volume of the tumor. (2) Three beams were designed, which included a static beam, a theoretical dynamic beam, and a planning-optimized dynamic beam (PODB). While the theoretical beam was made by manually programming a simplistic sliding leaf motion, the planning-optimized beam was obtained from treatment planning. From the three beams, three-dimensional (3D) doses on the phantom were calculated; 4D dose was calculated by mean...

Physics in Medicine and Biology, Sep 1, 2009

A straightforward and accurate method was developed to verify the delivery of intensity-modulated... more A straightforward and accurate method was developed to verify the delivery of intensity-modulated radiation therapy (IMRT) and to reconstruct the dose in a patient. The method is based on a computational algorithm that linearly describes the physical relationship between beamlets and dose-scoring voxels in a patient and the dose image from an electronic portal imaging device (EPID). The relationship is expressed in the form of dose response functions (responses) that are quantified using Monte Carlo (MC) particle transport techniques. From the dose information measured by the EPID the received patient dose is reconstructed by inversely solving the algorithm. The unique and novel non-iterative feature of this algorithm sets it apart from many existing dose reconstruction methods in the literature. This study presents the algorithm in detail and validates it experimentally for open and IMRT fields. Responses were first calculated for each beamlet of the selected fields by MC simulation. In-phantom and exit film dosimetry were performed on a flat phantom. Using the calculated responses and the algorithm, the exit film dose was used to inversely reconstruct the in-phantom dose, which was then compared with the measured in-phantom dose. The dose comparison in the phantom for all irradiated fields showed a pass rate of higher than 90% dose points given the criteria of dose difference of 3% and distance to agreement of 3 mm.

Medical physics, 2016

To develop and evaluate a fast Monte Carlo (MC) dose calculation model of electronic portal imagi... more To develop and evaluate a fast Monte Carlo (MC) dose calculation model of electronic portal imaging device (EPID) based on its effective atomic number modeling in the XVMC code. A previously developed EPID model, based on the XVMC code by density scaling of EPID structures, was modified by additionally considering effective atomic number (Zeff) of each structure and adopting a phase space file from the EGSnrc code. The model was tested under various homogeneous and heterogeneous phantoms and field sizes by comparing the calculations in the model with measurements in EPID. In order to better evaluate the model, the performance of the XVMC code was separately tested by comparing calculated dose to water with ion chamber (IC) array measurement in the plane of EPID. In the EPID plane, calculated dose to water by the code showed agreement with IC measurements within 1.8%. The difference was averaged across the in-field regions of the acquired profiles for all field sizes and phantoms. Th...

Radiation Oncology, May 4, 2006

Purpose: To evaluate intensity-modulated radiation therapy (IMRT) as an alternative to conformal ... more Purpose: To evaluate intensity-modulated radiation therapy (IMRT) as an alternative to conformal radiotherapy (CRT) or 4-field box boost (4FB) in women with gynecologic malignancies who are unsuitable for brachytherapy for technical or medical reasons.

Journal of the Korean Institute of Electrical and Electronic Material Engineers, Mar 1, 2012

Limiting thermal exposure time using rapid thermal processing(RTP) has emerged as promising simpl... more Limiting thermal exposure time using rapid thermal processing(RTP) has emerged as promising simplified process for manufacturing of solar cell in a continuous way. This paper reports the simplification of co-firing using RTP. Actual temperature profile for co-firing after screen printing is a key issue for high-quality metal-semiconductor contact. The plateau time during the firing process were varied at 450℃ for 10∼16 sec. Glass frit in Ag paste etch anti-reflection layer with plateau time. Glass frit in Ag paste is important for the Ag/Si contact formation and performances of crystalline Si solar cell.

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.

Journal of the Korean Institute of Electrical and Electronic Material Engineers, 2010

Radiation oncology (London, England), Jan 24, 2015

Exploiting biologic imaging, studies have been performed to boost dose to gross intraprostatic tu... more Exploiting biologic imaging, studies have been performed to boost dose to gross intraprostatic tumor volumes (GTV) while reducing dose elsewhere in the prostate. Interest in proton beams has increased due to superior normal-tissue sparing they afford. Our goal was to dosimetrically compare 3D conformal proton boost plans with intensity-modulated radiation therapy (IMRT) plans with respect to target coverage and avoiding organs at risk. Treatment planning computer tomography scans of ten patients were selected. For each patient, two hypothetical but realistic GTVs each with a fixed volume were contoured in different anatomical locations of the prostate. IMRT and proton beam plans were created with a prescribed dose of 50.4 Gy to the initial planning target volume (PTV) including the PTV of the seminal vesicles (PSV), 70.2 Gy to the PTV of the prostate (PPS), and 90 Gy to the PTV of the gross tumor volumes (PGTVs). For proton plans, uncertainties of range and patient setup were accoun...

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...

Journal of applied clinical medical physics / American College of Medical Physics, 2011

The Stereotactic Alignment for Linear Accelerator (S. A. Linac) system is developed to convenient... more The Stereotactic Alignment for Linear Accelerator (S. A. Linac) system is developed to conveniently improve the alignment accuracy of a conventional linac equipped with stereotactic cones. From the Winston-Lutz test, the SAlinac system performs three-dimensional (3D) reconstruction of the quality assurance (QA) ball coordinates with respect to the radiation isocenter, and combines this information with digital images of the laser target to determine the absolute position of the room lasers. A handheld device provides near-real-time repositioning advice to enable the user to align the QA ball and room lasers to within 0.25 mm of the centroid of the radiation isocenter. The results of 37 Winston-Lutz tests over 68 days showed that the median 3D QA ball alignment error was 0.09 mm, and 97% of the time the 3D error was ≤ 0.25 mm. All 3D isocentric errors in the study were 0.3 mm or less. The median x and y laser alignment coordinate error was 0.09 mm, and 94% of the time the x and y las...

IFMBE Proceedings, 2007

An accurate method was developed to verify the beamlet weight of intensity modulated radiation th... more An accurate method was developed to verify the beamlet weight of intensity modulated radiation therapy (IMRT) and to reconstruct dose in a patient. The method utilizes linear relationship between beamlets and dose scoring voxels in a patient and electronic portal ...

Proceedings of the 22nd Annual International Conference of the IEEE Engineering in Medicine and Biology Society (Cat. No.00CH37143), 2000

The authors tested an imaging plate for the dosimetry of photon beams. This test involved measure... more The authors tested an imaging plate for the dosimetry of photon beams. This test involved measurements using imaging plates and additionally an X-ray film, an ion-chamber, and EGS4 Monte Carlo transport code. As a result, the imaging plate showed potential for portal dosimetry

Progress in Medical Physics, 2014

Journal of applied clinical medical physics / American College of Medical Physics, 2011

Almost 20 years ago, Emami et al. presented a comprehensive set of dose tolerance limits for norm... more Almost 20 years ago, Emami et al. presented a comprehensive set of dose tolerance limits for normal tissue organs to therapeutic radiation, which has proven essential to the field of radiation oncology. The paradigm of stereotactic body radiotherapy (SBRT) has dramatically different dosing schemes but, to date, there has still been no comprehensive set of SBRT normal organ dose tolerance limits. As an initial step toward that goal, we performed an extensive review of the literature to compare dose limits utilized and reported in existing publications. The impact on dose tolerance limits of some key aspects of the methods and materials of the various authors is discussed. We have organized a table of 500 dose tolerance limits of normal structures for SBRT. We still observed several dose limits that are unknown or not validated. Data for SBRT dose tolerance limits are still preliminary and further clinical trials and validation are required. This manuscript presents an extensive colle...

Radiation oncology (London, England), 2006

To evaluate intensity-modulated radiation therapy (IMRT) as an alternative to conformal radiother... more To evaluate intensity-modulated radiation therapy (IMRT) as an alternative to conformal radiotherapy (CRT) or 4-field box boost (4FB) in women with gynecologic malignancies who are unsuitable for brachytherapy for technical or medical reasons. Dosimetric and toxicity information was analyzed for 12 patients with cervical (8), endometrial (2) or vaginal (2) cancer previously treated with external beam pelvic radiotherapy and a CRT boost. Optimized IMRT boost treatment plans were then developed for each of the 12 patients and compared to CRT and 4FB plans. The plans were compared in terms of dose conformality and critical normal tissue avoidance. The median planning target volume (PTV) was 151 cm(3) (range 58-512 cm(3)). The median overlap of the contoured rectum with the PTV was 15 (1-56) %, and 11 (4-35) % for the bladder. Two of the 12 patients, both with large PTVs and large overlap of the contoured rectum and PTV, developed grade 3 rectal bleeding. The dose conformity was signifi...

Progress in Medical Physics, 2014

In gated radiation therapy (gRT), due to residual motion, beam delivery is intended to irradiate ... more In gated radiation therapy (gRT), due to residual motion, beam delivery is intended to irradiate not only the true extent of disease, but also neighboring normal tissues. It is desired that the delivery covers the true extent (i.e. clinical target volume or CTV) as a minimum, although target moves under dose delivery. The objectives of our study are to validate if the intended dose is surely delivered to the true target in gRT and to quantitatively understand the trend of dose delivery on it and neighboring normal tissues when gating window (GW), motion amplitude (MA), and CTV size changes. To fulfill the objectives, experimental and computational studies have been designed and performed. A custom-made phantom with rectangle-and pyramid-shaped targets (CTVs) on a moving platform was scanned for four-dimensional imaging. Various GWs were selected and image integration was performed to generate targets (internal target volume or ITV) for planning that included the CTVs and internal margins (IM). The planning was done conventionally for the rectangle target and IMRT optimization was done for the pyramid target. Dose evaluation was then performed on a diode array aligned perpendicularly to the gated beams through measurements and computational modeling of dose delivery under motion. This study has quantitatively demonstrated and analytically interpreted the impact of residual motion including penumbral broadening for both targets, perturbed but secured dose coverage on the CTV, and significant doses delivered in the neighboring normal tissues. Dose volume histogram analyses also demonstrated and interpreted the trend of dose coverage: for ITV, it increased as GW or MA decreased or CTV size increased; for IM, it increased as GW or MA decreased; for the neighboring normal tissue, opposite trend to that of IM was observed. This study has provided a clear understanding on the impact of the residual motion and proved that if breathing is reproducible gRT is secure despite discontinuous delivery and target motion. The procedures and computational model can be used for commissioning, routine quality assurance, and patient-specific validation of gRT. More work needs to be done for patient-specific dose reconstruction on CT images.

Nanoscale zero-valent iron (nZVI) has recently received much attention for remediation of soil an... more Nanoscale zero-valent iron (nZVI) has recently received much attention for remediation of soil and groundwater contaminated with trichloroethylene (TCE). But there have been many debates on the toxic or inhibitory effects of nZVI on the environment. The objective of this study was to investigate the effects of nZVI on the activity of Geobacter lovleyi and to determine the potent effect of combination of abiotic and biotic treatment of TCE dechlorination. TCE degradation efficiencies of Geobacter lovleyi along with nZVI were more increased than those when nZVI was solely used. The amount of total microbial protein was increased in the presence of nZVI and hydrogen evolved from nZVI was consumed as electron donor by Geobacter lovleyi. In addition, dechlorination of TCE to cis-DCE by Geobacter lovleyi along with nZVI in respiking of exogenous of TCE shows that the reactivity of Geobacter lovleyi was also maintained. These results suggest that the application of Geobacter lovleyi along ...

Progress in Medical Physics, 2013

ABSTRACT We evaluated the effect of two kinds of breathing biofeedback technique such as audio-in... more ABSTRACT We evaluated the effect of two kinds of breathing biofeedback technique such as audio-instruction and audio-visual biofeedback on breathing reproducibility and the CTV coverage during repeated treatment regimes in respiration-gated radiotherapy. In this study, the breathing data of nineteen lung cancer patients acquired from Medical College of Virginia (MCV) during five weeks were used. The dose evaluation algorithm was programmed in MATLAB. In the result, the CTV coverage was decreased as 30.0% due to the breathing irreproducibility for free-breathing. For audio-visual biofeedback, the CTV coverage was improved as 20.0% because patients can learn how control their breathing stably. And the audio-instruction was effective to preserve the breathing reproducibility.

The Journal of the …, 1998

Purpose : This study is intended to understand the sensitometric characteristics and the emulsion... more Purpose : This study is intended to understand the sensitometric characteristics and the emulsion properties of the commercially available CEA TVS film in comparison with the Kodak X-Omat V film. Materials and Methods : For this purpose, we have formulated an analytic expression of the characteristic curves for x-ray film exposed to mixed radiation of electrons, photons, and visible light. This mathematical expression was developed based on reaction-rate and target-hit theories. Unlike previous expressions, it relates optical density to emuls ion properties such as grain size and silver bromide content. We have also developed a quantity which characterizes the film response to visible light relative to that to photons and electrons. This quantity could be expressed as a function of grain area. Thus, we have developed mathematical expressions and quantities with which the emulsion properties of the films can be revealed based on the sensitometric characteristics. Demonstrating the use of this analytical study, we exposed CEA and Kodak verification films to the mixed radiation of electrons, photons, and visible light, and interpreted the experimental results accordingly. Results : We have demonstrated that: (1) the saturation density increases as the silver bromide content increases, (2) the time required to reach the threshold dose (to which the film begins to respond) when films are exposed to visible light decreases as the grain size increases, and (3) the CEA film contains more silver bromide, whereas the Kodak film contains larger grains. These findings were supported by the data provided by the manufacturers afterward. Conclusion : This study presented an analytical and experimental basis for understanding the response of X-ray film with respect to the emulsion properties.

Medical physics, 2016

A method is proposed to reconstruct a four-dimensional (4D) dose distribution using phase matchin... more A method is proposed to reconstruct a four-dimensional (4D) dose distribution using phase matching of measured cine images to precalculated images of electronic portal imaging device (EPID). (1) A phantom, designed to simulate a tumor in lung (a polystyrene block with a 3 cm diameter embedded in cork), was placed on a sinusoidally moving platform with an amplitude of 1 cm and a period of 4 s. Ten-phase 4D computed tomography (CT) images of the phantom were acquired. A planning target volume (PTV) was created by adding a margin of 1 cm around the internal target volume of the tumor. (2) Three beams were designed, which included a static beam, a theoretical dynamic beam, and a planning-optimized dynamic beam (PODB). While the theoretical beam was made by manually programming a simplistic sliding leaf motion, the planning-optimized beam was obtained from treatment planning. From the three beams, three-dimensional (3D) doses on the phantom were calculated; 4D dose was calculated by mean...

Physics in Medicine and Biology, Sep 1, 2009

A straightforward and accurate method was developed to verify the delivery of intensity-modulated... more A straightforward and accurate method was developed to verify the delivery of intensity-modulated radiation therapy (IMRT) and to reconstruct the dose in a patient. The method is based on a computational algorithm that linearly describes the physical relationship between beamlets and dose-scoring voxels in a patient and the dose image from an electronic portal imaging device (EPID). The relationship is expressed in the form of dose response functions (responses) that are quantified using Monte Carlo (MC) particle transport techniques. From the dose information measured by the EPID the received patient dose is reconstructed by inversely solving the algorithm. The unique and novel non-iterative feature of this algorithm sets it apart from many existing dose reconstruction methods in the literature. This study presents the algorithm in detail and validates it experimentally for open and IMRT fields. Responses were first calculated for each beamlet of the selected fields by MC simulation. In-phantom and exit film dosimetry were performed on a flat phantom. Using the calculated responses and the algorithm, the exit film dose was used to inversely reconstruct the in-phantom dose, which was then compared with the measured in-phantom dose. The dose comparison in the phantom for all irradiated fields showed a pass rate of higher than 90% dose points given the criteria of dose difference of 3% and distance to agreement of 3 mm.

Medical physics, 2016

To develop and evaluate a fast Monte Carlo (MC) dose calculation model of electronic portal imagi... more To develop and evaluate a fast Monte Carlo (MC) dose calculation model of electronic portal imaging device (EPID) based on its effective atomic number modeling in the XVMC code. A previously developed EPID model, based on the XVMC code by density scaling of EPID structures, was modified by additionally considering effective atomic number (Zeff) of each structure and adopting a phase space file from the EGSnrc code. The model was tested under various homogeneous and heterogeneous phantoms and field sizes by comparing the calculations in the model with measurements in EPID. In order to better evaluate the model, the performance of the XVMC code was separately tested by comparing calculated dose to water with ion chamber (IC) array measurement in the plane of EPID. In the EPID plane, calculated dose to water by the code showed agreement with IC measurements within 1.8%. The difference was averaged across the in-field regions of the acquired profiles for all field sizes and phantoms. Th...

Radiation Oncology, May 4, 2006

Purpose: To evaluate intensity-modulated radiation therapy (IMRT) as an alternative to conformal ... more Purpose: To evaluate intensity-modulated radiation therapy (IMRT) as an alternative to conformal radiotherapy (CRT) or 4-field box boost (4FB) in women with gynecologic malignancies who are unsuitable for brachytherapy for technical or medical reasons.

Journal of the Korean Institute of Electrical and Electronic Material Engineers, Mar 1, 2012

Limiting thermal exposure time using rapid thermal processing(RTP) has emerged as promising simpl... more Limiting thermal exposure time using rapid thermal processing(RTP) has emerged as promising simplified process for manufacturing of solar cell in a continuous way. This paper reports the simplification of co-firing using RTP. Actual temperature profile for co-firing after screen printing is a key issue for high-quality metal-semiconductor contact. The plateau time during the firing process were varied at 450℃ for 10∼16 sec. Glass frit in Ag paste etch anti-reflection layer with plateau time. Glass frit in Ag paste is important for the Ag/Si contact formation and performances of crystalline Si solar cell.

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.

Journal of the Korean Institute of Electrical and Electronic Material Engineers, 2010

Radiation oncology (London, England), Jan 24, 2015

Exploiting biologic imaging, studies have been performed to boost dose to gross intraprostatic tu... more Exploiting biologic imaging, studies have been performed to boost dose to gross intraprostatic tumor volumes (GTV) while reducing dose elsewhere in the prostate. Interest in proton beams has increased due to superior normal-tissue sparing they afford. Our goal was to dosimetrically compare 3D conformal proton boost plans with intensity-modulated radiation therapy (IMRT) plans with respect to target coverage and avoiding organs at risk. Treatment planning computer tomography scans of ten patients were selected. For each patient, two hypothetical but realistic GTVs each with a fixed volume were contoured in different anatomical locations of the prostate. IMRT and proton beam plans were created with a prescribed dose of 50.4 Gy to the initial planning target volume (PTV) including the PTV of the seminal vesicles (PSV), 70.2 Gy to the PTV of the prostate (PPS), and 90 Gy to the PTV of the gross tumor volumes (PGTVs). For proton plans, uncertainties of range and patient setup were accoun...

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...

Journal of applied clinical medical physics / American College of Medical Physics, 2011

The Stereotactic Alignment for Linear Accelerator (S. A. Linac) system is developed to convenient... more The Stereotactic Alignment for Linear Accelerator (S. A. Linac) system is developed to conveniently improve the alignment accuracy of a conventional linac equipped with stereotactic cones. From the Winston-Lutz test, the SAlinac system performs three-dimensional (3D) reconstruction of the quality assurance (QA) ball coordinates with respect to the radiation isocenter, and combines this information with digital images of the laser target to determine the absolute position of the room lasers. A handheld device provides near-real-time repositioning advice to enable the user to align the QA ball and room lasers to within 0.25 mm of the centroid of the radiation isocenter. The results of 37 Winston-Lutz tests over 68 days showed that the median 3D QA ball alignment error was 0.09 mm, and 97% of the time the 3D error was ≤ 0.25 mm. All 3D isocentric errors in the study were 0.3 mm or less. The median x and y laser alignment coordinate error was 0.09 mm, and 94% of the time the x and y las...

IFMBE Proceedings, 2007

An accurate method was developed to verify the beamlet weight of intensity modulated radiation th... more An accurate method was developed to verify the beamlet weight of intensity modulated radiation therapy (IMRT) and to reconstruct dose in a patient. The method utilizes linear relationship between beamlets and dose scoring voxels in a patient and electronic portal ...

Proceedings of the 22nd Annual International Conference of the IEEE Engineering in Medicine and Biology Society (Cat. No.00CH37143), 2000

The authors tested an imaging plate for the dosimetry of photon beams. This test involved measure... more The authors tested an imaging plate for the dosimetry of photon beams. This test involved measurements using imaging plates and additionally an X-ray film, an ion-chamber, and EGS4 Monte Carlo transport code. As a result, the imaging plate showed potential for portal dosimetry

Progress in Medical Physics, 2014

Journal of applied clinical medical physics / American College of Medical Physics, 2011

Almost 20 years ago, Emami et al. presented a comprehensive set of dose tolerance limits for norm... more Almost 20 years ago, Emami et al. presented a comprehensive set of dose tolerance limits for normal tissue organs to therapeutic radiation, which has proven essential to the field of radiation oncology. The paradigm of stereotactic body radiotherapy (SBRT) has dramatically different dosing schemes but, to date, there has still been no comprehensive set of SBRT normal organ dose tolerance limits. As an initial step toward that goal, we performed an extensive review of the literature to compare dose limits utilized and reported in existing publications. The impact on dose tolerance limits of some key aspects of the methods and materials of the various authors is discussed. We have organized a table of 500 dose tolerance limits of normal structures for SBRT. We still observed several dose limits that are unknown or not validated. Data for SBRT dose tolerance limits are still preliminary and further clinical trials and validation are required. This manuscript presents an extensive colle...

Radiation oncology (London, England), 2006

To evaluate intensity-modulated radiation therapy (IMRT) as an alternative to conformal radiother... more To evaluate intensity-modulated radiation therapy (IMRT) as an alternative to conformal radiotherapy (CRT) or 4-field box boost (4FB) in women with gynecologic malignancies who are unsuitable for brachytherapy for technical or medical reasons. Dosimetric and toxicity information was analyzed for 12 patients with cervical (8), endometrial (2) or vaginal (2) cancer previously treated with external beam pelvic radiotherapy and a CRT boost. Optimized IMRT boost treatment plans were then developed for each of the 12 patients and compared to CRT and 4FB plans. The plans were compared in terms of dose conformality and critical normal tissue avoidance. The median planning target volume (PTV) was 151 cm(3) (range 58-512 cm(3)). The median overlap of the contoured rectum with the PTV was 15 (1-56) %, and 11 (4-35) % for the bladder. Two of the 12 patients, both with large PTVs and large overlap of the contoured rectum and PTV, developed grade 3 rectal bleeding. The dose conformity was signifi...

Progress in Medical Physics, 2014

In gated radiation therapy (gRT), due to residual motion, beam delivery is intended to irradiate ... more In gated radiation therapy (gRT), due to residual motion, beam delivery is intended to irradiate not only the true extent of disease, but also neighboring normal tissues. It is desired that the delivery covers the true extent (i.e. clinical target volume or CTV) as a minimum, although target moves under dose delivery. The objectives of our study are to validate if the intended dose is surely delivered to the true target in gRT and to quantitatively understand the trend of dose delivery on it and neighboring normal tissues when gating window (GW), motion amplitude (MA), and CTV size changes. To fulfill the objectives, experimental and computational studies have been designed and performed. A custom-made phantom with rectangle-and pyramid-shaped targets (CTVs) on a moving platform was scanned for four-dimensional imaging. Various GWs were selected and image integration was performed to generate targets (internal target volume or ITV) for planning that included the CTVs and internal margins (IM). The planning was done conventionally for the rectangle target and IMRT optimization was done for the pyramid target. Dose evaluation was then performed on a diode array aligned perpendicularly to the gated beams through measurements and computational modeling of dose delivery under motion. This study has quantitatively demonstrated and analytically interpreted the impact of residual motion including penumbral broadening for both targets, perturbed but secured dose coverage on the CTV, and significant doses delivered in the neighboring normal tissues. Dose volume histogram analyses also demonstrated and interpreted the trend of dose coverage: for ITV, it increased as GW or MA decreased or CTV size increased; for IM, it increased as GW or MA decreased; for the neighboring normal tissue, opposite trend to that of IM was observed. This study has provided a clear understanding on the impact of the residual motion and proved that if breathing is reproducible gRT is secure despite discontinuous delivery and target motion. The procedures and computational model can be used for commissioning, routine quality assurance, and patient-specific validation of gRT. More work needs to be done for patient-specific dose reconstruction on CT images.

Nanoscale zero-valent iron (nZVI) has recently received much attention for remediation of soil an... more Nanoscale zero-valent iron (nZVI) has recently received much attention for remediation of soil and groundwater contaminated with trichloroethylene (TCE). But there have been many debates on the toxic or inhibitory effects of nZVI on the environment. The objective of this study was to investigate the effects of nZVI on the activity of Geobacter lovleyi and to determine the potent effect of combination of abiotic and biotic treatment of TCE dechlorination. TCE degradation efficiencies of Geobacter lovleyi along with nZVI were more increased than those when nZVI was solely used. The amount of total microbial protein was increased in the presence of nZVI and hydrogen evolved from nZVI was consumed as electron donor by Geobacter lovleyi. In addition, dechlorination of TCE to cis-DCE by Geobacter lovleyi along with nZVI in respiking of exogenous of TCE shows that the reactivity of Geobacter lovleyi was also maintained. These results suggest that the application of Geobacter lovleyi along ...

Progress in Medical Physics, 2013

ABSTRACT We evaluated the effect of two kinds of breathing biofeedback technique such as audio-in... more ABSTRACT We evaluated the effect of two kinds of breathing biofeedback technique such as audio-instruction and audio-visual biofeedback on breathing reproducibility and the CTV coverage during repeated treatment regimes in respiration-gated radiotherapy. In this study, the breathing data of nineteen lung cancer patients acquired from Medical College of Virginia (MCV) during five weeks were used. The dose evaluation algorithm was programmed in MATLAB. In the result, the CTV coverage was decreased as 30.0% due to the breathing irreproducibility for free-breathing. For audio-visual biofeedback, the CTV coverage was improved as 20.0% because patients can learn how control their breathing stably. And the audio-instruction was effective to preserve the breathing reproducibility.

The Journal of the …, 1998

Purpose : This study is intended to understand the sensitometric characteristics and the emulsion... more Purpose : This study is intended to understand the sensitometric characteristics and the emulsion properties of the commercially available CEA TVS film in comparison with the Kodak X-Omat V film. Materials and Methods : For this purpose, we have formulated an analytic expression of the characteristic curves for x-ray film exposed to mixed radiation of electrons, photons, and visible light. This mathematical expression was developed based on reaction-rate and target-hit theories. Unlike previous expressions, it relates optical density to emuls ion properties such as grain size and silver bromide content. We have also developed a quantity which characterizes the film response to visible light relative to that to photons and electrons. This quantity could be expressed as a function of grain area. Thus, we have developed mathematical expressions and quantities with which the emulsion properties of the films can be revealed based on the sensitometric characteristics. Demonstrating the use of this analytical study, we exposed CEA and Kodak verification films to the mixed radiation of electrons, photons, and visible light, and interpreted the experimental results accordingly. Results : We have demonstrated that: (1) the saturation density increases as the silver bromide content increases, (2) the time required to reach the threshold dose (to which the film begins to respond) when films are exposed to visible light decreases as the grain size increases, and (3) the CEA film contains more silver bromide, whereas the Kodak film contains larger grains. These findings were supported by the data provided by the manufacturers afterward. Conclusion : This study presented an analytical and experimental basis for understanding the response of X-ray film with respect to the emulsion properties.