Hossein Lavvafi - Academia.edu (original) (raw)

Papers by Hossein Lavvafi

Advanced Welding and Deforming

Journal of Applied Clinical Medical Physics, 2020

Purpose: The COVID-19 pandemic has led to disorder in work and livelihood of a majority of the mo... more Purpose: The COVID-19 pandemic has led to disorder in work and livelihood of a majority of the modern world. In this work, we review its major impacts on procedures and workflow of clinical physics tasks, and suggest alternate pathways to avoid major disruption or discontinuity of physics tasks in the context of small, medium, and large radiation oncology clinics. We also evaluate scalability of medical physics under the stress of "social distancing". Methods: Three models of facilities characterized by the number of clinical physicists, daily patient throughput, and equipment were identified for this purpose. For identical objectives of continuity of clinical operations, with constraints such as social distancing and unavailability of staff due to system strain, however with the possibility of remote operations, the performance of these models was investigated. General clinical tasks requiring on-site personnel presence or otherwise were evaluated to determine the scalability of the three models at this point in the course of disease spread within their surroundings. Results: The clinical physics tasks within three models could be divided into two categories. The former, which requires individual presence, include safety-sensitive radiation delivery, high dose per fraction treatments, brachytherapy procedures, fulfilling state and nuclear regulatory commission's requirements, etc. The latter, which can be handled through remote means, include dose planning, physics plan review and supervision of quality assurance, general troubleshooting, etc. Conclusion: At the current level of disease in the United States, all three models have sustained major system stress in continuing reduced operation. However, the small clinic model may not perform if either the current level of infections is maintained for long or staff becomes unavailable due to health issues. With abundance, and diversity of innovative resources, medium and large clinic models can sustain further for physics-related radiotherapy services.

Advances in Nanostructured Composites, 2019

Advances in Laser Materials Processing, 2018

Abstract Micromachining using a laser is a unique fabrication process that provides innovative so... more Abstract Micromachining using a laser is a unique fabrication process that provides innovative solutions in a myriad of microengineering applications for industrial and research purposes. Laser micromachining offers a precise noncontact mode machining process that is used in the fabrication of miniature components with intricate geometry. These microcomponents are usually made of a multitude of materials with complex shape structures requiring submicron accuracy. Efficiency and accuracy of the laser micromachining process is of great importance. However, the main challenge in this process includes complicated residual stresses, recast layers, and heat affected zones (HAZs), which may cause distortion and alteration of the metallurgical microstructure, often leading to an inferior mechanical strength and lifetime of the component. This chapter reviews recent developments of laser micromachining processes that involve the integration of various micromachining processes for improving machinability. Specifically, this chapter deals with mechanical characterization and reliability testing of laser micromachined structures where the geometrical accuracy, surface properties, machining rate, and increase of process efficiency are of great concern.

Journal of Applied Clinical Medical Physics, 2018

An effective radiotherapy treatment entails maximizing radiation dose to the tumor while sparing ... more An effective radiotherapy treatment entails maximizing radiation dose to the tumor while sparing the surrounding and normal tissues. With the advent of SBRT with extreme hypo-fractionation in treating tumors including prostate where ablative dose is delivered in smaller number of fractions, rectum remains a dose-limiting organ and at the risk of rectal toxicity or secondary cancer. The same limitation of rectal toxicity exists for high-dose rate (HDR) treatments of cervical, endometrial, or prostate cancer when creating even a short distance between the anterior rectal wall and field of radiation is ideal in delivering ablative dose to the target. An effective solution to such problem is to physically displace rectum as the organ at risk. This research presents an organ retractor device that is designed to displace the rectum away from the path of radiation beam employing a Nitinol shape memory alloy that is designed for displacing the rectum upon actuation. A control system regulates the motion in a reproducible and safe manner by creating the desirable shape in moving the anterior rectal wall. The study finds the novel organ retractor device to be a promising tool that can be applied in a clinical setting for minimizing dose to the rectum during treatment of pelvic tumors, and creating the potential to deliver an ablative dose to tumor volume or to escalate the dose when needed.

Journal of Materials Science: Materials in Electronics, 2017

behaviors of soft magnetic materials. Eventually, the mechanism of mechanical alloying and effect... more behaviors of soft magnetic materials. Eventually, the mechanism of mechanical alloying and effect of diffusivity are also highlighted.

Applied Physics Letters, 2017

Carbonyl iron (CI) particles are widely used in magnetorheological (MR) fluids due to their excel... more Carbonyl iron (CI) particles are widely used in magnetorheological (MR) fluids due to their excellent magnetic properties, i.e., high saturation magnetization and low coercivity. However, pristine CI-based MR fluids have major shortcomings, which restrict their applications: abrasion of device surfaces during operation, redispersion difficulties after caking, iron oxidation, and severe sedimentation of CI particles due to higher density compared to the carrier liquid. As a remedy, the CI particles were coated with Ag shell by green-assisted method and stabilized with honey. The CI and CI-Ag particles were separately dispersed in Polyalphaolefin (PAO) oil, and the subsequent rheological effects were evaluated. Although the MR effects, e.g., yield stress and shear viscosity of CI-Ag-based MR fluids, varied slightly compared to the original one, the dispersion qualities, e.g., sedimentation stability, were remarkably improved. Published by AIP Publishing.

Materials Science and Engineering: A, 2017

Recent developments in minimally invasive surgical techniques have led to a surge in advancing al... more Recent developments in minimally invasive surgical techniques have led to a surge in advancing alternative manufacturing routes. In order to meet the functional needs of such small devices as cardiovascular stents, and guide wires, the use of new materials and delicate geometries has increased creating a new challenge for manufacturing and machining. In this work, two sets of laser parameters leading to different laser power output were employed to study the effects of systematic changes in microstructure and mechanical characteristics of AISI 316LVM biomedical grade wires. Uniaxial tension and cyclic strain-controlled fatigue with the use of flex bending machines were used in order to evaluate the mechanical properties. Surface quality, heat affected zone (HAZ), and subsequent mechanical response were also investigated.

Medical Physics, 2016

PURPOSE A major goal of an effective radiation treatment plan is to deliver the maximum dose to t... more PURPOSE A major goal of an effective radiation treatment plan is to deliver the maximum dose to the tumor while minimizing radiation exposure to the surrounding normal structures. For example, due to the radiation exposure to neighboring critical structures during prostate cancer treatment, a significant increase in cancer risk was observed for the bladder (77%) and the rectum (105%) over the following decade. Consequently, an effective treatment plan necessitates limiting the exposure to such organs which can best be achieved by physically displacing the organ at-risk. The goal of this study is to present a prototype for an organ re-positioner device designed and fabricated to physically move the rectum away from the path of radiation beam during external beam and brachytherapy treatments. This device affords patient comfort and provides a fully controlled motion to safely relocate the rectum during treatment. METHODS The NiTi shape memory alloy was designed and optimized for manufacturing a rectal re-positioner device through cooling and heating the core alloy for its shaping. This has been achieved through a prototyped custom designed electronic circuit in order to induce the reversible austenitic transformation and was tested rigorously to ensure the integrity of the actuated motion in displacement of the target anatomy. RESULTS The desirable NiTi shape-setting was configured for easy insertion and based on anatomical constraint. When the final prototype was evaluated, accuracy and precision of the maximum displacement and temperature changes revealed that the device could safely be used within the target anatomy. CONCLUSION The organ re-positioner device is a promising tool that can be implemented in clinical setting. It provides a controlled and safe displacement of the delicate organ(s) at risk. The location of the organ being treated could also be identified using conventional onboard imaging devices or MV imaging available on-board most modern clinical accelerators.

Engineering Materials, 2016

Materials behavior of the magnetorheological (MR) fluids components are important to their contro... more Materials behavior of the magnetorheological (MR) fluids components are important to their control accuracy and service life. Thus, the aim of this section is to focus on the effects of temperature on the material properties of MR fluid components and then its effect on the rheological properties of Magnetorheological fluids.

Engineering Materials, 2016

An externally applied field would result in the particles alignment in the direction of applied f... more An externally applied field would result in the particles alignment in the direction of applied field.

Engineering Materials, 2016

Engineering Materials, 2016

Potential applications of MR fluids are summarized in those devices that need quick, continuous, ... more Potential applications of MR fluids are summarized in those devices that need quick, continuous, and reversible transformation in rheological characteristics [1].

Engineering Materials, 2016

Engineering Materials, 2016

Field responsive fluids are those materials that undergo noticeable responses leading to conseque... more Field responsive fluids are those materials that undergo noticeable responses leading to consequent rheological behavior variations upon the influence of an external field. In fact, these fluids are divided into three groups in terms of their response in the presence of externally applied fields, which are briefly described as follows.

Engineering Materials, 2016

Engineering Materials, 2016

Soft magnetic nanoparticles are an important material and used widely for a variety of technologi... more Soft magnetic nanoparticles are an important material and used widely for a variety of technological applications. Magnetite(Fe3O4) in the format of soft magnetic nanoparticles have been of major interests to many researchers because of being effectively used in ferrofluids, having magnetoresistance, exhibiting strong magnet property and generating low toxicity in biological and medical applications (Can et al. in Mater Sci Eng 172(1):72–75, 2010).

Engineering Materials, 2016

To design magnetorheological devices and to understand how they work, one should first know the r... more To design magnetorheological devices and to understand how they work, one should first know the relationship between the sheer stress and sheer rate in the magnetorheological fluid [1].

RSC Advances, 2016

CoFe2O4 nanoparticles are synthesized through sol–gel and facile hydrothermal methods, and their ... more CoFe2O4 nanoparticles are synthesized through sol–gel and facile hydrothermal methods, and their magnetorheological (MR) characteristics are evaluated.

Advanced Welding and Deforming

Journal of Applied Clinical Medical Physics, 2020

Purpose: The COVID-19 pandemic has led to disorder in work and livelihood of a majority of the mo... more Purpose: The COVID-19 pandemic has led to disorder in work and livelihood of a majority of the modern world. In this work, we review its major impacts on procedures and workflow of clinical physics tasks, and suggest alternate pathways to avoid major disruption or discontinuity of physics tasks in the context of small, medium, and large radiation oncology clinics. We also evaluate scalability of medical physics under the stress of "social distancing". Methods: Three models of facilities characterized by the number of clinical physicists, daily patient throughput, and equipment were identified for this purpose. For identical objectives of continuity of clinical operations, with constraints such as social distancing and unavailability of staff due to system strain, however with the possibility of remote operations, the performance of these models was investigated. General clinical tasks requiring on-site personnel presence or otherwise were evaluated to determine the scalability of the three models at this point in the course of disease spread within their surroundings. Results: The clinical physics tasks within three models could be divided into two categories. The former, which requires individual presence, include safety-sensitive radiation delivery, high dose per fraction treatments, brachytherapy procedures, fulfilling state and nuclear regulatory commission's requirements, etc. The latter, which can be handled through remote means, include dose planning, physics plan review and supervision of quality assurance, general troubleshooting, etc. Conclusion: At the current level of disease in the United States, all three models have sustained major system stress in continuing reduced operation. However, the small clinic model may not perform if either the current level of infections is maintained for long or staff becomes unavailable due to health issues. With abundance, and diversity of innovative resources, medium and large clinic models can sustain further for physics-related radiotherapy services.

Advances in Nanostructured Composites, 2019

Advances in Laser Materials Processing, 2018

Abstract Micromachining using a laser is a unique fabrication process that provides innovative so... more Abstract Micromachining using a laser is a unique fabrication process that provides innovative solutions in a myriad of microengineering applications for industrial and research purposes. Laser micromachining offers a precise noncontact mode machining process that is used in the fabrication of miniature components with intricate geometry. These microcomponents are usually made of a multitude of materials with complex shape structures requiring submicron accuracy. Efficiency and accuracy of the laser micromachining process is of great importance. However, the main challenge in this process includes complicated residual stresses, recast layers, and heat affected zones (HAZs), which may cause distortion and alteration of the metallurgical microstructure, often leading to an inferior mechanical strength and lifetime of the component. This chapter reviews recent developments of laser micromachining processes that involve the integration of various micromachining processes for improving machinability. Specifically, this chapter deals with mechanical characterization and reliability testing of laser micromachined structures where the geometrical accuracy, surface properties, machining rate, and increase of process efficiency are of great concern.

Journal of Applied Clinical Medical Physics, 2018

An effective radiotherapy treatment entails maximizing radiation dose to the tumor while sparing ... more An effective radiotherapy treatment entails maximizing radiation dose to the tumor while sparing the surrounding and normal tissues. With the advent of SBRT with extreme hypo-fractionation in treating tumors including prostate where ablative dose is delivered in smaller number of fractions, rectum remains a dose-limiting organ and at the risk of rectal toxicity or secondary cancer. The same limitation of rectal toxicity exists for high-dose rate (HDR) treatments of cervical, endometrial, or prostate cancer when creating even a short distance between the anterior rectal wall and field of radiation is ideal in delivering ablative dose to the target. An effective solution to such problem is to physically displace rectum as the organ at risk. This research presents an organ retractor device that is designed to displace the rectum away from the path of radiation beam employing a Nitinol shape memory alloy that is designed for displacing the rectum upon actuation. A control system regulates the motion in a reproducible and safe manner by creating the desirable shape in moving the anterior rectal wall. The study finds the novel organ retractor device to be a promising tool that can be applied in a clinical setting for minimizing dose to the rectum during treatment of pelvic tumors, and creating the potential to deliver an ablative dose to tumor volume or to escalate the dose when needed.

Journal of Materials Science: Materials in Electronics, 2017

behaviors of soft magnetic materials. Eventually, the mechanism of mechanical alloying and effect... more behaviors of soft magnetic materials. Eventually, the mechanism of mechanical alloying and effect of diffusivity are also highlighted.

Applied Physics Letters, 2017

Carbonyl iron (CI) particles are widely used in magnetorheological (MR) fluids due to their excel... more Carbonyl iron (CI) particles are widely used in magnetorheological (MR) fluids due to their excellent magnetic properties, i.e., high saturation magnetization and low coercivity. However, pristine CI-based MR fluids have major shortcomings, which restrict their applications: abrasion of device surfaces during operation, redispersion difficulties after caking, iron oxidation, and severe sedimentation of CI particles due to higher density compared to the carrier liquid. As a remedy, the CI particles were coated with Ag shell by green-assisted method and stabilized with honey. The CI and CI-Ag particles were separately dispersed in Polyalphaolefin (PAO) oil, and the subsequent rheological effects were evaluated. Although the MR effects, e.g., yield stress and shear viscosity of CI-Ag-based MR fluids, varied slightly compared to the original one, the dispersion qualities, e.g., sedimentation stability, were remarkably improved. Published by AIP Publishing.

Materials Science and Engineering: A, 2017

Recent developments in minimally invasive surgical techniques have led to a surge in advancing al... more Recent developments in minimally invasive surgical techniques have led to a surge in advancing alternative manufacturing routes. In order to meet the functional needs of such small devices as cardiovascular stents, and guide wires, the use of new materials and delicate geometries has increased creating a new challenge for manufacturing and machining. In this work, two sets of laser parameters leading to different laser power output were employed to study the effects of systematic changes in microstructure and mechanical characteristics of AISI 316LVM biomedical grade wires. Uniaxial tension and cyclic strain-controlled fatigue with the use of flex bending machines were used in order to evaluate the mechanical properties. Surface quality, heat affected zone (HAZ), and subsequent mechanical response were also investigated.

Medical Physics, 2016

PURPOSE A major goal of an effective radiation treatment plan is to deliver the maximum dose to t... more PURPOSE A major goal of an effective radiation treatment plan is to deliver the maximum dose to the tumor while minimizing radiation exposure to the surrounding normal structures. For example, due to the radiation exposure to neighboring critical structures during prostate cancer treatment, a significant increase in cancer risk was observed for the bladder (77%) and the rectum (105%) over the following decade. Consequently, an effective treatment plan necessitates limiting the exposure to such organs which can best be achieved by physically displacing the organ at-risk. The goal of this study is to present a prototype for an organ re-positioner device designed and fabricated to physically move the rectum away from the path of radiation beam during external beam and brachytherapy treatments. This device affords patient comfort and provides a fully controlled motion to safely relocate the rectum during treatment. METHODS The NiTi shape memory alloy was designed and optimized for manufacturing a rectal re-positioner device through cooling and heating the core alloy for its shaping. This has been achieved through a prototyped custom designed electronic circuit in order to induce the reversible austenitic transformation and was tested rigorously to ensure the integrity of the actuated motion in displacement of the target anatomy. RESULTS The desirable NiTi shape-setting was configured for easy insertion and based on anatomical constraint. When the final prototype was evaluated, accuracy and precision of the maximum displacement and temperature changes revealed that the device could safely be used within the target anatomy. CONCLUSION The organ re-positioner device is a promising tool that can be implemented in clinical setting. It provides a controlled and safe displacement of the delicate organ(s) at risk. The location of the organ being treated could also be identified using conventional onboard imaging devices or MV imaging available on-board most modern clinical accelerators.

Engineering Materials, 2016

Materials behavior of the magnetorheological (MR) fluids components are important to their contro... more Materials behavior of the magnetorheological (MR) fluids components are important to their control accuracy and service life. Thus, the aim of this section is to focus on the effects of temperature on the material properties of MR fluid components and then its effect on the rheological properties of Magnetorheological fluids.

Engineering Materials, 2016

An externally applied field would result in the particles alignment in the direction of applied f... more An externally applied field would result in the particles alignment in the direction of applied field.

Engineering Materials, 2016

Engineering Materials, 2016

Potential applications of MR fluids are summarized in those devices that need quick, continuous, ... more Potential applications of MR fluids are summarized in those devices that need quick, continuous, and reversible transformation in rheological characteristics [1].

Engineering Materials, 2016

Engineering Materials, 2016

Field responsive fluids are those materials that undergo noticeable responses leading to conseque... more Field responsive fluids are those materials that undergo noticeable responses leading to consequent rheological behavior variations upon the influence of an external field. In fact, these fluids are divided into three groups in terms of their response in the presence of externally applied fields, which are briefly described as follows.

Engineering Materials, 2016

Engineering Materials, 2016

Soft magnetic nanoparticles are an important material and used widely for a variety of technologi... more Soft magnetic nanoparticles are an important material and used widely for a variety of technological applications. Magnetite(Fe3O4) in the format of soft magnetic nanoparticles have been of major interests to many researchers because of being effectively used in ferrofluids, having magnetoresistance, exhibiting strong magnet property and generating low toxicity in biological and medical applications (Can et al. in Mater Sci Eng 172(1):72–75, 2010).

Engineering Materials, 2016

To design magnetorheological devices and to understand how they work, one should first know the r... more To design magnetorheological devices and to understand how they work, one should first know the relationship between the sheer stress and sheer rate in the magnetorheological fluid [1].

RSC Advances, 2016

CoFe2O4 nanoparticles are synthesized through sol–gel and facile hydrothermal methods, and their ... more CoFe2O4 nanoparticles are synthesized through sol–gel and facile hydrothermal methods, and their magnetorheological (MR) characteristics are evaluated.