International Journal of Scientific Research Updates, 2023
Purpose: The purpose of this study was to investigate the feasibility of using the Winston-Lutz (... more Purpose: The purpose of this study was to investigate the feasibility of using the Winston-Lutz (WL) interchangeability with a Machine Performance Check-enhanced couch for pretreatment quality assurance (QA) of stereotactic radiotherapy (SRS) and stereotactic body radiation therapy (SBRT). The study employed the MPC with an electronic portal imaging device (EPID) to carry out geometric checks and verify the radiation isocenter. The isocenter size was assessed using the MultiMet cube and the MPC-enhanced couch module for SRS/SBRT pretreatment QA. Methods: The isocenter size of the MPC-enhanced couch module was compared to the WL measurements of the MultiMet cube. Measurements were taken at various gantry, collimator, and couch angles over a period of one month. The data from the cube were evaluated using PIPSRO and MultiMet (MMWL), including the offset targets. Various statistical tests were performed to evaluate the agreement, normality, separability, sensitivity, and specificity be...
International journal of research in medical sciences, Jan 30, 2024
This report presents the initial clinical experience with HyperArc, a novel modality that incorpo... more This report presents the initial clinical experience with HyperArc, a novel modality that incorporates a non-coplanar, arc-based multileaf collimator (MLC) and automated treatment optimization and dose delivery. The study focuses on a patient who had previously received whole-brain radiotherapy. The effectiveness and challenges of HyperArc were assessed by evaluating various quality indices for stereotactic radiosurgery within the RTOG protocol, as well as an additional measure of toxicity in the form of the V12Gy volume. The HyperArc plan achieved quality indices of 1.13, 4.58, and 0.88 for CI, GI, and CIPaddick, respectively. The mean ICRU83 value was 0.17±0.01, and it remained consistent across all six lesions. The V12Gy value was equal to 8.76 cc. The HyperArc plan successfully met the constraints for organs-at-risk (OAR). These results suggest that HyperArc is a suitable modality for treating multiple brain metastases, as indicated by the quality indices and metrics. Additionally, V12Gy is a valuable indicator for assessing low-dose spillage.
International Journal of Research in Medical Sciences
Background: The aim of this study was to illustrate and evaluate the use of different statistical... more Background: The aim of this study was to illustrate and evaluate the use of different statistical process control (SPC) aspects to examine linear accelerator daily output variation through machine performance check (MPC) over a month. Methods: MPC daily output data were obtained over a month after AAPM TG-51 were performed. Baseline data were set, and subsequent data were conducted through SPC. The Shewhart chart was used to determine the upper and lower control limits, whereas CUSUM for subtle changes. Results: The upper and lower control limits obtained via SPC analysis of the MPC data were found to fall within AAPM Task Group 142 guidelines. MPC output variation data were within ±3% of their action limits values and were within 1% over thirty days of data. The process capability ratio and process acceptability ratio, Cp and Cpk values were ≥2 for all energies. Potential undetected deviations were captured by the CUSUM chart for photons and electrons beam energy. Conclusions: Cont...
International Journal of Scientific Research Updates
Background: The aim of this study was to evaluate the variation in the daily output of a linac Va... more Background: The aim of this study was to evaluate the variation in the daily output of a linac Varian Edge TrueBeam over a month, using a Daily QA3 (QA3) and machine performance check (MPC), after Task Group 51protocol and baseline data had been established. Methods and Materials: The daily output data were collected for all photons (6, 10 MV, and 6, 10 FFF) and electrons (6, 9, 12, and 15 MeV) energies. A Bland-Altman-Plot and intraclass correlation coefficients were used to assess agreement and reliability. Results: MPC data showed small random deviations of ≤ 2% and agreed with the QA3 measurements. The maximum mean absolute difference between the QA3 and MPC data was observed with 6 MeV (0.5633), with limits of agreement of (−0.5392–1.6658). Conclusion: These results suggest that MPC data closely track QA3 data and that the two forms are interchangeable
BACKGROUND: Several epidemiologic studies have suggested an association between Parkinson’s disea... more BACKGROUND: Several epidemiologic studies have suggested an association between Parkinson’s disease (PD) and exposure to heavy metals using subjective exposure measurements. OBJECTIVES: We investigated the association between objective chronic occupational lead exposure and the risk of PD. METHODS: We enrolled 121 PD patients and 414 age-, sex-, and race-, frequency-matched controls in a case–control study. As an indicator of chronic Pb exposure, we measured concentrations of tibial and calcaneal bone Pb stores using 109Cadmium excited K-series X-ray fluorescence. As an indicator of recent exposure, we measured blood Pb concentration. We collected occupational data on participants from 18 years of age until the age at enrollment, and an industrial hygienist determined the duration and intensity of environmental Pb exposure. We employed physiologically based pharmacokinetic modeling to combine these data, and we estimated whole-body lifetime Pb exposures for each individual. Logistic...
International Journal of Cancer Therapy and Oncology, 2017
Purpose: Traditionally, lead and Cerrobend have been employed for field shaping in radiation ther... more Purpose: Traditionally, lead and Cerrobend have been employed for field shaping in radiation therapy. Lately, another shielding material called Gamma Putty has emerged. The objective of this report is to examine its dosimetric and shielding characteristics in megavoltage photon beam. Methods: All measurements were carried out in a dual energy linac. Data were collected using a calibrated ionization chamber. Percent transmission, linear attenuation, and field size dependence were evaluated for open square fields (4 × 4 cm 2 to 10 × 10 cm 2 ) defined by collimator jaws and for different Gamma Putty thicknesses (t = 0, 0.3, 0.5, 1.0, 1.5, 2.0, and 2.5 cm) at 6 and 18 MV photon beams. The measurements were performed both in air using appropriate acrylic buildup cap and in solid water. Results: The Gamma Putty tray factor (GPTF) increased steadily with field size for both 6 and 18 MV. It was characterized by a half value thickness (HVT) of 2.513 ± 0.101 and 2.855 ± 0.024 cm for 6 and 18 ...
Background: Carbon fiber belly board is the newer immobilization device that has earned recogniti... more Background: Carbon fiber belly board is the newer immobilization device that has earned recognition in sparing small bowel during prone pelvic irradiation. It is characterized by mechanical strength, a smooth rigidity, and a low specific density. In this study, the beam attenuation for a 10x10 cm 2 field size was calculated for 6 and 18 MV photons beam. Methods: A Farmer ion chamber of 0.6 cc volume, slabs of solid water phantom, and an electrometer were used to measure the relative exit dose with or without the carbon fiber belly board at variable gantry angles. The measurements were performed at 100 cm SSD, and 100 MU were delivered. Results: The average beam attenuation amounted to 3.46±1.53% and 2.22±0.89% for 6 and 18 MV, respectively. The highest attenuation was obtained at 130 o and the lowest at 120 o gantry angle for both energies. Conclusion: Irradiating through carbon fiber immobilization devices triggered a variation of the beam attenuation at different gantry angles. As a result, there is a loss of skin-sparing effect with megavoltage photon beam. Therefore, special attention is needed in the treatment planning system when using these carbon fiber immobilization devices.
Traditionally, lead has been used for field shaping in megavoltage electron beams in radiation th... more Traditionally, lead has been used for field shaping in megavoltage electron beams in radiation therapy. In this study, we analyze the dosimetric parameters of a nontoxic, high atomic number (Z = 83), bismuth-loaded material called Gamma Putty that is malleable and can be easily molded to any desired shape. First, we placed an ionization chamber at different depths in a solid water phantom under a Gamma Putty shield of thickness (t = 0, 3, 5, 10, 15, 20, and 25 mm, respectively) and measured the ionizing radiation on the central axis (CAX) for electron beam ranging in energies from 6 to 20 MeV. Next, we investigated the relationship between the relative ionization (RI) measured at a fixed depth for several Gamma Putty shield at different cutout diameters ranging from 2 to 5 cm for various beam energies and derived an exponential fitting equation for clinical purposes. The dose profiles along the CAX show that bremsstrahlung dominates for Gamma Putty thickness >15 mm. For high-energy beams (12-20 MeV) and all Gamma Putty thicknesses up to 25 mm, RI below 5% could not be achieved due to the strong bremsstrahlung component. However, Gamma Putty is a very suitable material for reducing the transmission factor below 5% and protecting underlying normal tissues for low-energy electron beams (6-9 MeV).
Aim: The purpose of this study was to derive radiobiological parameters from the dose volume hist... more Aim: The purpose of this study was to derive radiobiological parameters from the dose volume histogram of patients that undergone prostate cancer radiotherapy via the VMAT technique. Material and Methods: A total of twenty-two cases of prostate cancer of 70.2 and 81 Gy were selected for this study. Radiobiological parameters were evaluated by the Poisson equation for the tumor and LKB model for organs at risk. Results: For prostate tumor, the average TCP was 96.28, 86.45, 68.57 for α/β of 1.2, 3.0, and 10, respectively. The average EUD was 37.98 Gy, 59.23 Gy, 21.19 Gy, 20.65 Gy, 16.32 Gy, and 21.87 Gy for bladder, rectum, right femoral head, left femoral head, small bowel, and large bowel respectively. The average NTCP was 7.6 % for the rectum and negligible for other organs at risk. Conclusion: NTCP for critical organs and TCP for prostate cancer can be determined via dose volume histogram.
American Journal of Biomedical Sciences, Jul 1, 2017
Background: Several descriptors are used to characterize the dosimetric parameters of a photon be... more Background: Several descriptors are used to characterize the dosimetric parameters of a photon beam through an attenuator. This study evaluates these descriptors analytically through various thicknesses of Gamma Putty. Specifically, we measure percent ionization depth doses as a function of depth and field size, and fit three models to the data. Materials and Methods: Measurements of percent ionization at various depths along the central axis were generated from 6 MV and 18 MV photon beams at a source-axis distance of 100 cm with an ionization in solid water phantom. We fit analytic models to the data to determine linear attenuation, beam hardening, beam quality, and electron contamination. Results: We report best-fit parameters for all the analytical models. All models yielded a root mean square (RMS) error of less than 1% with respect to the data. At depths below 5cm in the phantom, the largest attenuation coefficients (μ) were observed for the 6 MV beam, regardless of Gamma Putty thickness. Also, the smallest field sizes (4×4 and 5×5 cm 2) have the largest attenuation coefficients at these depths, for both beam energies. At a depth of 10 cm, the variation in μ was negligible for both beam energies. Conclusions: By fitting parametric models to axial ionization profiles, it is possible to characterize the dosimetric parameters of any attenuator as a function of thickness and field size, without knowing the precise spectral distribution of the beam. Parameters such as attenuation coefficients, beam hardening, and electron contamination can then be calculated accurately for any combination of field size and attenuator thickness.
Background: The aim of this study was to evaluate radiobiological model parameters and the second... more Background: The aim of this study was to evaluate radiobiological model parameters and the secondary cancer risk to patients undergoing hypofractionated or conventionally fractionated irradiation of the left breast. Materials and Methods: 17 conventional (50 Gy) and 13 hypofractionated (42.56 Gy) plans were randomly selected and both biologically equivalent dose (EQD2) and effective dose (BED) were assessed in addition to dose homogeneity index, equivalent uniform dose, normal tissue complication probability (NTCP), and tumor control probability (TCP). Secondary cancer risks were estimated through dose volume histogram (DVHs) by calculating organ equivalent doses (OED) and excess absolute risks (EAR) using linear, bell-shaped, and plateau models. Results: EQD2 and TCPs were steady throughout a spectrum of α/ βratios. TCPs for conventional treatment are 84.36 ± 7.68, 99.30 ± 0.71, and 17.87 ± 6.92 for α/β =4, α / β =2.5, and α / β =10 respectively. Likewise, the TCP values for the hypofractionated regimen are 91.04±11.43, 98.67±4.23, and 24.31±8.74 for α/β =4, α/β =2.5, α/β =10 respectively. NTCP based LKB model with the pericarditis endpoint yielded a 0% risk. Logistic regression and LKB model have similar mean lung dose and can be used interchangeably for lung pneumonitis. A combined heart-lung, cardiac failure, and logistic lung model, based on this study, discloses a higher probability of heart failure in conventional treatment and lung toxicity in hypofraction. Estimates of secondary cancer were higher for conventional plans compared to hypofraction for all models, for patients over 30 years old. Conclusions: This work reveals significant similarities and differences between the hypofractionated and conventional treatment of the left breast, via radiobiology.
JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, a... more JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact [email protected].
Journal of applied clinical medical physics / American College of Medical Physics, 2014
This study was to assess the Capri applicator for patients with endometrial cancer undergoing hig... more This study was to assess the Capri applicator for patients with endometrial cancer undergoing high-radiation dose treatments following external-beam radiation therapy. The Capri applicator is an inflatable vaginal cylinder with multiple channels. It is used to tailor the dose distribution to an asymmetric vaginal disease, and better spare organs at risk. Five patients with high-risk endometrial cancer were selected for this study. The patients were treated with a high dose of radiation using the Capri applicator: daily fraction of 7 Gy was prescribed for a total dose of 21Gy. The treatment plans included radiobiological parameters such as equivalent uniform dose (EUD), normal tissue complication probability (NTCP), and tumor control probability (TCP). Based on the dose-volume histograms (DVH), we also calculated four quality factors: conformity index (CI), dose homogeneity index (DHI), dose nonuniformity index (DNR), and overdose index (OI). The TCP values range from 82.26% to 95.92...
Journal of applied clinical medical physics / American College of Medical Physics, 2013
The aims of this study were twofold: first, to determine the impact of variance in dose-volume hi... more The aims of this study were twofold: first, to determine the impact of variance in dose-volume histograms (DVH) on patient-specific toxicity after 2 high-dose fractions in a sample of 22 men with prostate cancer; and second, to compare the effectiveness of traditional DVH analysis and principal component analysis (PCA) in predicting rectum and urethra toxicity. A series of 22 patients diagnosed with prostate adenocarcinoma was treated with 45 Gy external beam and 20 Gy dose rate brachytherapy. Principal component analysis was applied to model the shapes of the rectum and urethra dose-volume histograms. We used logistic regression to measure the correlations between the principal components and the incidence of rectal bleeding and urethra stricture. We also calculated the equivalent uniform dose (EUD) and normal tissue complication probability (NTCP) for the urethra and rectum, and tumor control probability (TCP) for the prostate using BioSuite software. We evaluated their correlatio...
Journal of applied clinical medical physics / American College of Medical Physics, 2011
The purpose is to devise a patient-specific quality assurance procedure for RapidArc radiotherapy... more The purpose is to devise a patient-specific quality assurance procedure for RapidArc radiotherapy using the MapCHECK detector array. We use our existing MapCHECK system and a Solid Water phantom with an embedded ion chamber to develop a quality assurance procedure for RapidArc treatment after commissioning. The ion chamber used to measure the absolute dose is surrounded by 6 cm layers of solid water on the anterior and posterior sides. Partial arcs derived from the treatment planning system were used with MapCHECK to determine the actual shape of the dose and correct for the angular dependence. The ion chamber measurements were within 1% of the absolute doses predicted by the Eclipse treatment system. When using a partial arc from 60° to 300° on the MapCHECK array (gamma index <1: 3%, 3 mm, 10% threshold), we obtain a 97.52% average passing rate. A combination of ion chamber phantoms, partial arcs and the MapCHECK system can be used for quality assurance of RapidArc therapies.
Veterinary therapeutics : research in applied veterinary medicine, 2004
The effect of photodynamic therapy is a function of several variables, including selective retent... more The effect of photodynamic therapy is a function of several variables, including selective retention of the drug in tumor tissue with reduced drug concentration in surrounding normal tissue. A study was designed to determine the pharmacokinetic profile and variability of porfimer sodium in dogs and cats with spontaneous tumors and to thereby determine the optimal timing of its photoactivation in these species. The results of this study indicate that there is marked variability among species in the distribution of porfimer sodium between highly proliferating tissues, which requires careful attention in the design of human and veterinary application of photodynamic therapy with porfimer sodium, as determined in rodent models.
Veterinary therapeutics : research in applied veterinary medicine, 2003
Photodynamic threshold doses in dogs with spontaneous tumors can be achieved through a mathematic... more Photodynamic threshold doses in dogs with spontaneous tumors can be achieved through a mathematical model. For this to be clinically relevant, it is important to know the treatment parameters for tissue necrosis. The threshold dose for three photosensitizers (porfimer sodium, aluminum cholorophthalocyanine [AlClPc], and tin ethyl etiopurpurin [SnET2]) commonly used in veterinary chemotherapy protocols was evaluated in 12 dogs with spontaneous tumors. To derive the photodynamic threshold dose, the tissue optical properties of each compound were determined by diffuse reflectance and thus the light fluence rate. Uptake was measured by fluorimetry using tissue solubilization techniques. The threshold values calculated were highest for AlClPc (irradiated 48 hours after administration). The radius of necrosis (4.00 to 5.48 mm) and photosensitizer uptake (3.4 to 6.91 microg/g) were elevated after injection of porfimer sodium. The threshold dose model described here is photosensitizer depen...
International Journal of Scientific Research Updates, 2023
Purpose: The purpose of this study was to investigate the feasibility of using the Winston-Lutz (... more Purpose: The purpose of this study was to investigate the feasibility of using the Winston-Lutz (WL) interchangeability with a Machine Performance Check-enhanced couch for pretreatment quality assurance (QA) of stereotactic radiotherapy (SRS) and stereotactic body radiation therapy (SBRT). The study employed the MPC with an electronic portal imaging device (EPID) to carry out geometric checks and verify the radiation isocenter. The isocenter size was assessed using the MultiMet cube and the MPC-enhanced couch module for SRS/SBRT pretreatment QA. Methods: The isocenter size of the MPC-enhanced couch module was compared to the WL measurements of the MultiMet cube. Measurements were taken at various gantry, collimator, and couch angles over a period of one month. The data from the cube were evaluated using PIPSRO and MultiMet (MMWL), including the offset targets. Various statistical tests were performed to evaluate the agreement, normality, separability, sensitivity, and specificity be...
International journal of research in medical sciences, Jan 30, 2024
This report presents the initial clinical experience with HyperArc, a novel modality that incorpo... more This report presents the initial clinical experience with HyperArc, a novel modality that incorporates a non-coplanar, arc-based multileaf collimator (MLC) and automated treatment optimization and dose delivery. The study focuses on a patient who had previously received whole-brain radiotherapy. The effectiveness and challenges of HyperArc were assessed by evaluating various quality indices for stereotactic radiosurgery within the RTOG protocol, as well as an additional measure of toxicity in the form of the V12Gy volume. The HyperArc plan achieved quality indices of 1.13, 4.58, and 0.88 for CI, GI, and CIPaddick, respectively. The mean ICRU83 value was 0.17±0.01, and it remained consistent across all six lesions. The V12Gy value was equal to 8.76 cc. The HyperArc plan successfully met the constraints for organs-at-risk (OAR). These results suggest that HyperArc is a suitable modality for treating multiple brain metastases, as indicated by the quality indices and metrics. Additionally, V12Gy is a valuable indicator for assessing low-dose spillage.
International Journal of Research in Medical Sciences
Background: The aim of this study was to illustrate and evaluate the use of different statistical... more Background: The aim of this study was to illustrate and evaluate the use of different statistical process control (SPC) aspects to examine linear accelerator daily output variation through machine performance check (MPC) over a month. Methods: MPC daily output data were obtained over a month after AAPM TG-51 were performed. Baseline data were set, and subsequent data were conducted through SPC. The Shewhart chart was used to determine the upper and lower control limits, whereas CUSUM for subtle changes. Results: The upper and lower control limits obtained via SPC analysis of the MPC data were found to fall within AAPM Task Group 142 guidelines. MPC output variation data were within ±3% of their action limits values and were within 1% over thirty days of data. The process capability ratio and process acceptability ratio, Cp and Cpk values were ≥2 for all energies. Potential undetected deviations were captured by the CUSUM chart for photons and electrons beam energy. Conclusions: Cont...
International Journal of Scientific Research Updates
Background: The aim of this study was to evaluate the variation in the daily output of a linac Va... more Background: The aim of this study was to evaluate the variation in the daily output of a linac Varian Edge TrueBeam over a month, using a Daily QA3 (QA3) and machine performance check (MPC), after Task Group 51protocol and baseline data had been established. Methods and Materials: The daily output data were collected for all photons (6, 10 MV, and 6, 10 FFF) and electrons (6, 9, 12, and 15 MeV) energies. A Bland-Altman-Plot and intraclass correlation coefficients were used to assess agreement and reliability. Results: MPC data showed small random deviations of ≤ 2% and agreed with the QA3 measurements. The maximum mean absolute difference between the QA3 and MPC data was observed with 6 MeV (0.5633), with limits of agreement of (−0.5392–1.6658). Conclusion: These results suggest that MPC data closely track QA3 data and that the two forms are interchangeable
BACKGROUND: Several epidemiologic studies have suggested an association between Parkinson’s disea... more BACKGROUND: Several epidemiologic studies have suggested an association between Parkinson’s disease (PD) and exposure to heavy metals using subjective exposure measurements. OBJECTIVES: We investigated the association between objective chronic occupational lead exposure and the risk of PD. METHODS: We enrolled 121 PD patients and 414 age-, sex-, and race-, frequency-matched controls in a case–control study. As an indicator of chronic Pb exposure, we measured concentrations of tibial and calcaneal bone Pb stores using 109Cadmium excited K-series X-ray fluorescence. As an indicator of recent exposure, we measured blood Pb concentration. We collected occupational data on participants from 18 years of age until the age at enrollment, and an industrial hygienist determined the duration and intensity of environmental Pb exposure. We employed physiologically based pharmacokinetic modeling to combine these data, and we estimated whole-body lifetime Pb exposures for each individual. Logistic...
International Journal of Cancer Therapy and Oncology, 2017
Purpose: Traditionally, lead and Cerrobend have been employed for field shaping in radiation ther... more Purpose: Traditionally, lead and Cerrobend have been employed for field shaping in radiation therapy. Lately, another shielding material called Gamma Putty has emerged. The objective of this report is to examine its dosimetric and shielding characteristics in megavoltage photon beam. Methods: All measurements were carried out in a dual energy linac. Data were collected using a calibrated ionization chamber. Percent transmission, linear attenuation, and field size dependence were evaluated for open square fields (4 × 4 cm 2 to 10 × 10 cm 2 ) defined by collimator jaws and for different Gamma Putty thicknesses (t = 0, 0.3, 0.5, 1.0, 1.5, 2.0, and 2.5 cm) at 6 and 18 MV photon beams. The measurements were performed both in air using appropriate acrylic buildup cap and in solid water. Results: The Gamma Putty tray factor (GPTF) increased steadily with field size for both 6 and 18 MV. It was characterized by a half value thickness (HVT) of 2.513 ± 0.101 and 2.855 ± 0.024 cm for 6 and 18 ...
Background: Carbon fiber belly board is the newer immobilization device that has earned recogniti... more Background: Carbon fiber belly board is the newer immobilization device that has earned recognition in sparing small bowel during prone pelvic irradiation. It is characterized by mechanical strength, a smooth rigidity, and a low specific density. In this study, the beam attenuation for a 10x10 cm 2 field size was calculated for 6 and 18 MV photons beam. Methods: A Farmer ion chamber of 0.6 cc volume, slabs of solid water phantom, and an electrometer were used to measure the relative exit dose with or without the carbon fiber belly board at variable gantry angles. The measurements were performed at 100 cm SSD, and 100 MU were delivered. Results: The average beam attenuation amounted to 3.46±1.53% and 2.22±0.89% for 6 and 18 MV, respectively. The highest attenuation was obtained at 130 o and the lowest at 120 o gantry angle for both energies. Conclusion: Irradiating through carbon fiber immobilization devices triggered a variation of the beam attenuation at different gantry angles. As a result, there is a loss of skin-sparing effect with megavoltage photon beam. Therefore, special attention is needed in the treatment planning system when using these carbon fiber immobilization devices.
Traditionally, lead has been used for field shaping in megavoltage electron beams in radiation th... more Traditionally, lead has been used for field shaping in megavoltage electron beams in radiation therapy. In this study, we analyze the dosimetric parameters of a nontoxic, high atomic number (Z = 83), bismuth-loaded material called Gamma Putty that is malleable and can be easily molded to any desired shape. First, we placed an ionization chamber at different depths in a solid water phantom under a Gamma Putty shield of thickness (t = 0, 3, 5, 10, 15, 20, and 25 mm, respectively) and measured the ionizing radiation on the central axis (CAX) for electron beam ranging in energies from 6 to 20 MeV. Next, we investigated the relationship between the relative ionization (RI) measured at a fixed depth for several Gamma Putty shield at different cutout diameters ranging from 2 to 5 cm for various beam energies and derived an exponential fitting equation for clinical purposes. The dose profiles along the CAX show that bremsstrahlung dominates for Gamma Putty thickness >15 mm. For high-energy beams (12-20 MeV) and all Gamma Putty thicknesses up to 25 mm, RI below 5% could not be achieved due to the strong bremsstrahlung component. However, Gamma Putty is a very suitable material for reducing the transmission factor below 5% and protecting underlying normal tissues for low-energy electron beams (6-9 MeV).
Aim: The purpose of this study was to derive radiobiological parameters from the dose volume hist... more Aim: The purpose of this study was to derive radiobiological parameters from the dose volume histogram of patients that undergone prostate cancer radiotherapy via the VMAT technique. Material and Methods: A total of twenty-two cases of prostate cancer of 70.2 and 81 Gy were selected for this study. Radiobiological parameters were evaluated by the Poisson equation for the tumor and LKB model for organs at risk. Results: For prostate tumor, the average TCP was 96.28, 86.45, 68.57 for α/β of 1.2, 3.0, and 10, respectively. The average EUD was 37.98 Gy, 59.23 Gy, 21.19 Gy, 20.65 Gy, 16.32 Gy, and 21.87 Gy for bladder, rectum, right femoral head, left femoral head, small bowel, and large bowel respectively. The average NTCP was 7.6 % for the rectum and negligible for other organs at risk. Conclusion: NTCP for critical organs and TCP for prostate cancer can be determined via dose volume histogram.
American Journal of Biomedical Sciences, Jul 1, 2017
Background: Several descriptors are used to characterize the dosimetric parameters of a photon be... more Background: Several descriptors are used to characterize the dosimetric parameters of a photon beam through an attenuator. This study evaluates these descriptors analytically through various thicknesses of Gamma Putty. Specifically, we measure percent ionization depth doses as a function of depth and field size, and fit three models to the data. Materials and Methods: Measurements of percent ionization at various depths along the central axis were generated from 6 MV and 18 MV photon beams at a source-axis distance of 100 cm with an ionization in solid water phantom. We fit analytic models to the data to determine linear attenuation, beam hardening, beam quality, and electron contamination. Results: We report best-fit parameters for all the analytical models. All models yielded a root mean square (RMS) error of less than 1% with respect to the data. At depths below 5cm in the phantom, the largest attenuation coefficients (μ) were observed for the 6 MV beam, regardless of Gamma Putty thickness. Also, the smallest field sizes (4×4 and 5×5 cm 2) have the largest attenuation coefficients at these depths, for both beam energies. At a depth of 10 cm, the variation in μ was negligible for both beam energies. Conclusions: By fitting parametric models to axial ionization profiles, it is possible to characterize the dosimetric parameters of any attenuator as a function of thickness and field size, without knowing the precise spectral distribution of the beam. Parameters such as attenuation coefficients, beam hardening, and electron contamination can then be calculated accurately for any combination of field size and attenuator thickness.
Background: The aim of this study was to evaluate radiobiological model parameters and the second... more Background: The aim of this study was to evaluate radiobiological model parameters and the secondary cancer risk to patients undergoing hypofractionated or conventionally fractionated irradiation of the left breast. Materials and Methods: 17 conventional (50 Gy) and 13 hypofractionated (42.56 Gy) plans were randomly selected and both biologically equivalent dose (EQD2) and effective dose (BED) were assessed in addition to dose homogeneity index, equivalent uniform dose, normal tissue complication probability (NTCP), and tumor control probability (TCP). Secondary cancer risks were estimated through dose volume histogram (DVHs) by calculating organ equivalent doses (OED) and excess absolute risks (EAR) using linear, bell-shaped, and plateau models. Results: EQD2 and TCPs were steady throughout a spectrum of α/ βratios. TCPs for conventional treatment are 84.36 ± 7.68, 99.30 ± 0.71, and 17.87 ± 6.92 for α/β =4, α / β =2.5, and α / β =10 respectively. Likewise, the TCP values for the hypofractionated regimen are 91.04±11.43, 98.67±4.23, and 24.31±8.74 for α/β =4, α/β =2.5, α/β =10 respectively. NTCP based LKB model with the pericarditis endpoint yielded a 0% risk. Logistic regression and LKB model have similar mean lung dose and can be used interchangeably for lung pneumonitis. A combined heart-lung, cardiac failure, and logistic lung model, based on this study, discloses a higher probability of heart failure in conventional treatment and lung toxicity in hypofraction. Estimates of secondary cancer were higher for conventional plans compared to hypofraction for all models, for patients over 30 years old. Conclusions: This work reveals significant similarities and differences between the hypofractionated and conventional treatment of the left breast, via radiobiology.
JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, a... more JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact [email protected].
Journal of applied clinical medical physics / American College of Medical Physics, 2014
This study was to assess the Capri applicator for patients with endometrial cancer undergoing hig... more This study was to assess the Capri applicator for patients with endometrial cancer undergoing high-radiation dose treatments following external-beam radiation therapy. The Capri applicator is an inflatable vaginal cylinder with multiple channels. It is used to tailor the dose distribution to an asymmetric vaginal disease, and better spare organs at risk. Five patients with high-risk endometrial cancer were selected for this study. The patients were treated with a high dose of radiation using the Capri applicator: daily fraction of 7 Gy was prescribed for a total dose of 21Gy. The treatment plans included radiobiological parameters such as equivalent uniform dose (EUD), normal tissue complication probability (NTCP), and tumor control probability (TCP). Based on the dose-volume histograms (DVH), we also calculated four quality factors: conformity index (CI), dose homogeneity index (DHI), dose nonuniformity index (DNR), and overdose index (OI). The TCP values range from 82.26% to 95.92...
Journal of applied clinical medical physics / American College of Medical Physics, 2013
The aims of this study were twofold: first, to determine the impact of variance in dose-volume hi... more The aims of this study were twofold: first, to determine the impact of variance in dose-volume histograms (DVH) on patient-specific toxicity after 2 high-dose fractions in a sample of 22 men with prostate cancer; and second, to compare the effectiveness of traditional DVH analysis and principal component analysis (PCA) in predicting rectum and urethra toxicity. A series of 22 patients diagnosed with prostate adenocarcinoma was treated with 45 Gy external beam and 20 Gy dose rate brachytherapy. Principal component analysis was applied to model the shapes of the rectum and urethra dose-volume histograms. We used logistic regression to measure the correlations between the principal components and the incidence of rectal bleeding and urethra stricture. We also calculated the equivalent uniform dose (EUD) and normal tissue complication probability (NTCP) for the urethra and rectum, and tumor control probability (TCP) for the prostate using BioSuite software. We evaluated their correlatio...
Journal of applied clinical medical physics / American College of Medical Physics, 2011
The purpose is to devise a patient-specific quality assurance procedure for RapidArc radiotherapy... more The purpose is to devise a patient-specific quality assurance procedure for RapidArc radiotherapy using the MapCHECK detector array. We use our existing MapCHECK system and a Solid Water phantom with an embedded ion chamber to develop a quality assurance procedure for RapidArc treatment after commissioning. The ion chamber used to measure the absolute dose is surrounded by 6 cm layers of solid water on the anterior and posterior sides. Partial arcs derived from the treatment planning system were used with MapCHECK to determine the actual shape of the dose and correct for the angular dependence. The ion chamber measurements were within 1% of the absolute doses predicted by the Eclipse treatment system. When using a partial arc from 60° to 300° on the MapCHECK array (gamma index <1: 3%, 3 mm, 10% threshold), we obtain a 97.52% average passing rate. A combination of ion chamber phantoms, partial arcs and the MapCHECK system can be used for quality assurance of RapidArc therapies.
Veterinary therapeutics : research in applied veterinary medicine, 2004
The effect of photodynamic therapy is a function of several variables, including selective retent... more The effect of photodynamic therapy is a function of several variables, including selective retention of the drug in tumor tissue with reduced drug concentration in surrounding normal tissue. A study was designed to determine the pharmacokinetic profile and variability of porfimer sodium in dogs and cats with spontaneous tumors and to thereby determine the optimal timing of its photoactivation in these species. The results of this study indicate that there is marked variability among species in the distribution of porfimer sodium between highly proliferating tissues, which requires careful attention in the design of human and veterinary application of photodynamic therapy with porfimer sodium, as determined in rodent models.
Veterinary therapeutics : research in applied veterinary medicine, 2003
Photodynamic threshold doses in dogs with spontaneous tumors can be achieved through a mathematic... more Photodynamic threshold doses in dogs with spontaneous tumors can be achieved through a mathematical model. For this to be clinically relevant, it is important to know the treatment parameters for tissue necrosis. The threshold dose for three photosensitizers (porfimer sodium, aluminum cholorophthalocyanine [AlClPc], and tin ethyl etiopurpurin [SnET2]) commonly used in veterinary chemotherapy protocols was evaluated in 12 dogs with spontaneous tumors. To derive the photodynamic threshold dose, the tissue optical properties of each compound were determined by diffuse reflectance and thus the light fluence rate. Uptake was measured by fluorimetry using tissue solubilization techniques. The threshold values calculated were highest for AlClPc (irradiated 48 hours after administration). The radius of necrosis (4.00 to 5.48 mm) and photosensitizer uptake (3.4 to 6.91 microg/g) were elevated after injection of porfimer sodium. The threshold dose model described here is photosensitizer depen...
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Papers by Aime Gloi