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Search Results: 1 - 10 of 214717 matches for " Maria F. Chan "
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Editorial: The Authorship of IJMPCERO Papers  [PDF]
Maria F. Chan, Chengyu Shi
International Journal of Medical Physics,Clinical Engineering and Radiation Oncology (IJMPCERO) , 2018, DOI: 10.4236/ijmpcero.2018.74035
Abstract: International Journal of Medical Physics, Clinical Engineering and Radiation Oncology: Editorial
Is It Possible to Publish a Calibration Function for Radiochromic Film?  [PDF]
Maria F. Chan, David Lewis, Xiang Yu
International Journal of Medical Physics,Clinical Engineering and Radiation Oncology (IJMPCERO) , 2014, DOI: 10.4236/ijmpcero.2014.31005
Abstract:

Purpose: To assess the possibility of using a public calibration function for radiochromic film dosimetry in dose QA of highly conformal treatment plans. Methods: EBT3 film calibration strips (3.5 × 20 cm2 from lots A101212 and A011713) were exposed on a Varian Trilogy at a facility to a 10 × 10 cm2 open field at doses of 80, 160, 320 cGy using 6MV photons. Together with a strip of unexposed film from the same lot, the exposed films were digitized in a single scan using different Epson 10,000 XL scanners at two different facilities. The dose-response data for each color-channel from each facility were generated using the same calibration function X(D) = a + b/(D - c), where X(D) is the response at dose D and a, b and c are the coefficients. Different batches of EBT3 film were exposed to a VMAT beam. These films, plus two reference strips exposed to doses of zero and 160 cGy, were digitized on the scanners at the two facilities. Using the multi-channel dosimetry method and One-scan protocol

The Verification of iPlan Commissioning by Radiochromic EBT2 Films  [PDF]
Maria F. Chan, Qinghui Zhang, Jingdong Li, Preeti Parhar, Karen Schupak, Chandra Burman
International Journal of Medical Physics,Clinical Engineering and Radiation Oncology (IJMPCERO) , 2012, DOI: 10.4236/ijmpcero.2012.11001
Abstract: Purpose: To evaluate the measured dose distributions using radiochromic EBT2 films for small fields in iPlan (BrainLab) commissioning. Methods: Radiochromic EBT2 films were irradiated with 6 MV photons on a Varian Trilogy linac using polystyrene phantoms. The measurements included dose profiles and depth doses for field sizes of 1 × 1, 2 × 2, 3 × 3, 4 × 4, and 10 × 10 cm2 etc. The dose profile measurements were taken at the depth of 5 cm. The calibration films were irradiated at dmax(1.4 cm) for doses up to 6 Gy. Films were scanned using an Epson 10,000 XL flatbed scanner with 72 dpi resolution. Pixel values were converted to doses using the established calibration-curve. The 2D dose distributions were generated from the film data analysis. In-house software was utilized to compare the measured doses from films with the treatment planning data. In addition, selected patients’ SRS fields were also measured with the EBT2 films for comparison with iPlan. An EDGETM detector was also used to check the centralaxis doses for the SRS patients’ measurements. Results and Discussion: The measured planar dose distributions achieved more than 98% and 95% passing rates with a set of 2%/2 mm dose and DTA criteria for all square fields and all patient treatment fields (<5 × 5 cm2), respectively. Agreement with measurement data with the EDGETM detector at the central axis (±1%) was found with the plan data. This is the first report for SRS small photon-field measurement using the latest radiochromic film, EBT2. The results shown in this work indicate that the use of EBT2 film provides accurate dosimetry measure-ments for small photon beams. The measurements show excellent agreement with the iPlan TP commissioning data. Conclusions: The patient-specific EBT2 film QA for iPlan SRS patients showed good results. The EBT2 films could potentially be a useful dosimeter in verification of commissioning as well as patient-specific QA for SRS cases.
Energy Dependence of the New Gafchromic EBT3 Film:Dose Response Curves for 50 KV, 6 and 15 MV X-Ray Beams  [PDF]
Guerda Massillon-JL, Sou-Tung Chiu-Tsao, Ivan Domingo-Munoz, Maria F. Chan
International Journal of Medical Physics,Clinical Engineering and Radiation Oncology (IJMPCERO) , 2012, DOI: 10.4236/ijmpcero.2012.12008
Abstract: Purpose: To study and compare the dose response curves of the new GafChromic EBT3 film for megavoltage and kilovoltage x-ray beams, with different spatial resolutions. Methods: EBT3 films (lot#A101711-02) were exposed to each x-ray beam (6 MV, 15 MV, and 50 kV) at 7 dose values (50-3200 cGy). Each film piece was scanned three consecutive times in the center of Epson 10000XL flatbed scanner in 48-bit color at two separate spatial resolutions of 75 and 300 dpi. The data were analyzed using ImageJ and, for each scanned image, a region of interest (ROI) of 2 × 2 cm2 at the field center was selected to obtain the mean pixel value with its standard deviation in the ROI. For each energy, dose value and spatial resolution, the average net optical density (netOD) and its associated uncertainty were determined. The Student’s t-test was performed to evaluate the statistical differences between the net OD/dose values of the three energy modalities, with different color channels and spatial resolutions. Results and Discussion: The dose response curves for the three energy modalities were compared in three color channels. Weak energy dependence was found. For doses above 100 cGy, no statistical differences were observed between 6 and 15 MV beams, regardless of spatial resolution and color channel. However, statistical differences were observed between 50 kV and the megavoltage beams. The degree of energy dependence (from MV to 50 kV) was found to be a function of color channel, dose level, and spatial resolution. Conclusions: The dose response curves for GafChromic EBT3 films were found to be weakly dependent on the energy of the photon beams from 6 MV to 15 MV. For very low energy photon (e.g. 50 kV), variation of more than 11% due to the energy-dependence is observed, depending on the absorbed dose, spatial resolution and color channel used.
Visual Analysis of the Daily QA Results of Photon and Electron Beams of a Trilogy Linac over a Five-Year Period  [PDF]
Maria F. Chan, Qiongge Li, Xiaoli Tang, Xiang Li, Jingdong Li, Grace Tang, Margie A. Hunt, Joseph O. Deasy
International Journal of Medical Physics,Clinical Engineering and Radiation Oncology (IJMPCERO) , 2015, DOI: 10.4236/ijmpcero.2015.44035
Abstract: Data visualization technique was applied to analyze the daily QA results of photon and electron beams. Special attention was paid to any trend the beams might display. A Varian Trilogy Linac equipped with dual photon energies and five electron energies was commissioned in early 2010. Daily Linac QA tests including the output constancy, beam flatness and symmetry (radial and transverse directions) were performed with an ionization chamber array device (QA Beam Checker Plus, Standard Imaging). The data of five years were collected and analyzed. For each energy, the measured data were exported and processed for visual trending using an in-house Matlab program. These daily data were cross-correlated with the monthly QA and annual QA results, as well as the preventive maintenance records. Majority of the output were within 1% of variation, with a consistent positive/upward drift for all seven energies (~+0.25% per month). The baseline of daily device is reset annually right after the TG-51 calibration. This results in a sudden drop of the output. On the other hand, the large amount of data using the same baseline exhibits a sinusoidal behavior (period = 12 months; amplitude = 0.8%, 0.5% for photons, electrons, respectively) on symmetry and flatness when normalization of baselines is accounted for. The well known phenomenon of new Linac output drift was clearly displayed. This output drift was a result of the air leakage of the over-pressurized sealed monitor chambers for the specific vendor. Data visualization is a new trend in the era of big data in radiation oncology research. It allows the data to be displayed visually and therefore more intuitive. Based on the visual display from the past, the physicist might predict the trend of the Linac and take actions proactively. It also makes comparisons, alerts failures, and potentially identifies causalities.
Patient-Specific QA of Spot-Scanning Proton Beams Using Radiochromic Film  [PDF]
Maria F. Chan, Chin-Cheng Chen, Chengyu Shi, Jingdong Li, Xiaoli Tang, Xiang Li, Dennis Mah
International Journal of Medical Physics,Clinical Engineering and Radiation Oncology (IJMPCERO) , 2017, DOI: 10.4236/ijmpcero.2017.62011
Abstract: Radiochromic film for spot-scanning QA provides high spatial resolution and efficiency gains from one-shot irradiation for multiple depths. However, calibration can be a tedious procedure which may limit widespread use. Moreover, since there may be an energy dependence, which manifests as a depth dependence, this may require additional measurements for each patient. We present a one-scan protocol to simplify the procedure. A calibration using an EBT3 film, exposed by a 6-level step-wedge plan on a Proteus®PLUS proton system (IBA, Belgium), was performed at depths of 18, 20, 24 cm using Plastic Water® (CIRS, Norfolk, VA). The calibration doses ranged from 65 - 250 cGy (RBE) (relative biological effectiveness) for proton energies of 170 - 200 MeV. A clinical prostate + nodes plan was used for validation. The planar doses at selected depths were measured with EBT3 films and analyzed using one-scan protocol (one-scan digitization of QA film and at least one film exposed to a known dose). The gamma passing rates, dose-difference maps, and profiles of 2D planar doses measured with EBT3 film and IBA MatriXX-PT, versus the RayStation TPS calculations were analyzed and compared. The EBT3 film measurement results matched well with the TPS calculation data with an average passing rate of ~95% for 2%/2 mm and slightly lower passing rates were obtained from an ion chamber array detector. We were able to demonstrate that the use of a proton step-wedge provided clinically acceptable results and minimized variations between film-scanner orientation, inter-scan, and scanning conditions. Furthermore, for relative dosimetry (calibration is not done at the time of experiment), it could be derived from no more than two films exposed to known doses (one could be zero) for rescaling the master calibration curve at each depth. The sensitivity of the calibration to depth variations has been explored. One-scan protocol results appear to be comparable to that of the ion chamber array detector. The use of a proton step-wedge for calibration of EBT3 film potentially increases efficiency in patient-specific QA of proton beams.
Discrimination and stratification tests of cardiovascular disease risk assessment models against ultrasound detection of carotid plaques in type 2 diabetics  [PDF]
Lawrence W. C. Chan, Yu Sun, Iris F. F. Benzie
Health (Health) , 2013, DOI: 10.4236/health.2013.57A1001
Abstract:

Atherosclerosis is the early stage of arterial disease, and underlies development of cardiovascular disease (CVD) and stroke. Although sophisticated models for assessing CVD and stroke risk have been derived based on large-scale prospective studies, their abilities in detecting the presence or absence of atherosclerotic plaque have not been investigated. This study aimed to evaluate and compare discriminatory and risk stratifying abilities of 13 CVD risk assessment models against the ultrasound detection of carotid plaques in type 2 diabetes mellitus (T2DM) patients. Forty-nine T2DM subjects were recruited with informed consent, and major anthropomorphic and biomarker data for these models were collected. The model risk scores were evaluated against the carotid plaques detected by Doppler ultrasound. Only the FHS-Lpts-CHD-10Y model, which is a variant of the Framingham model, revealed an area under the receiver operating curve (AUROC) that was significantly different from a random scoring approach (AUROC: 0.681, p < 0.05), and was able to stratify the risk levels of carotid plaque presence (Chi-Square statistic: 5.99, p < 0.05).

Three Dimensional Expansion of Margins for Single-fraction Treatments: Stereotactic Radiosurgery Brain Cases  [PDF]
Qinghui Zhang, Maria Chan, Yulin Song, Chandra Burman
International Journal of Medical Physics,Clinical Engineering and Radiation Oncology (IJMPCERO) , 2012, DOI: 10.4236/ijmpcero.2012.12003
Abstract: Purpose: To derive a clinically-practical margin formula between clinical target volume (CTV) and planning target volume (PTV) for single-fraction stereotactic radiosurgery (SRS). Methods: In previous publications on the margin between the CTV and the PTV, a Gaussian function with zero mean was assumed for the systematic error and the machine systematic error was completely ignored. In this work we adopted a Dirac delta function for the machine systematic error for a given machine with nonzero mean systematic error. Mathematical formulas for calculating the CTV-PTV margin for single-fraction SRS treatments were proposed. Results: Margins for single fraction treatments were derived such that the CTVs received the prescribed dose in 95% of the SRS patients. The margin defined in this study was machine specific and accounted for nonzero mean systematic error. The differences between our formulas and a previously published formula were discussed. Conclusion: Clinical margin formulas were proposed for determining the margin between the CTV and the PTV in SRS treatments. Previous margin’s recipes, being derived specifically for conventional treatments, may be inappropriate for single-fraction SRS and could result in geometric miss of the target and even treatment failure for machines possessing of large systematic errors.
The melanocortin receptors and their accessory proteins
Li F. Chan
Frontiers in Endocrinology , 2013, DOI: 10.3389/fendo.2013.00009
Abstract: The five melanocortin receptors (MCRs) named MC1R–MC5R have diverse physiological roles encompassing pigmentation, steroidogenesis, energy homeostasis and feeding behavior as well as exocrine function. Since their identification almost 20 years ago much has been learnt about these receptors. As well as interacting with their endogenous ligands the melanocortin peptides, there is now a growing list of important peptides that can modulate the way these receptors signal, acting as agonists, antagonists, and inverse agonists. The discovery of melanocortin 2 receptor accessory proteins as a novel accessory factor to the MCRs provides further insight into the regulation of these important G protein-coupled receptor.
Direct medical cost of radiation therapy for cancer patients in Taiwan  [PDF]
Henry W. C. Leung, Agnes L. F. Chan
Health (Health) , 2013, DOI: 10.4236/health.2013.56131
Abstract:

Background and purpose: The rising cost of health care is of concern worldwide, in particular, for cancer care. The costs of treatment, including chemotherapeutic drugs and radiotherapy, are no exceptions. The purpose of this study is to explore the direct medical cost of radiotherapy and the annual increasing trend of expenditures in Taiwan. Methods: This study utilized data retrieving from the original claim data of the reimbursement of the Health Insurance Research Database (HIRD) derived from Taiwan’s Health Insurance (HI) program. Detailed data on the direct medical cost within the radiotherapy process for beneficences were extracted from inpatient expenditures by admissions (DD) and ambulatory care expenditures by visits (CD) database according to the reimbursed expenditure code of radiotherapy from January 1, 2000 to December 31, 2005. Prescriptions for radiotherapy were retrieved and the direct medical costs for radiotherapy were collected based on the NHI reimbursement price list of 2005. The annual increasing trend of expenditures was also explored according to the perspective of Bureau Health Insurance of Taiwan. Results: The total direct medical costs of radiotherapy for cancer patients were increasing from 2000 to 2005, which were estimated to US $7.80 million, US $8.09 million, US $7.58 million, US $10.7 million, US $12.2 million and US $15.9 million in 2000, 2001, 2002, 2003, 2004 and 2005, respectively. The increased percentage corresponded to the total healthcare expenditures claimed was increased substantially from 0.82% in 2000 to 1.22% in 2005. The total direct medical costs within the radiotherapy process were also increased gradually if identified by different types of radiotherapy and teaching hospital levels. The direct medical costs attribute to radiotherapy, compared to total health care expenditures in Taiwan, were similar to the costs of anticancer drugs for cancer patients annually. Conclusions: The direct medical costs of radiation therapy increased substantially each year. Further cost analysis on

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