- Email: [email protected]
The development and implementation of the detective quantum efficiency metric in a clinical environment
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J. McFadden, M. Donoghue / Physica Medica 52 (2018) 165–182
c Dept. of Radiotherapy Physics, Galway Clinic, Ireland E-mail address: [email protected]
Modern radiation therapy treatment techniques and delivery methods introduce new challenges to existing dosimetry systems. As a result, much research has been conducted on the development of a radiation dosimetry system based on scintillating optical fibre. They offer many advantages over the currently employed dosimeters for real time dosimetry. Optical Fibre dosimeters (OFD) have small dimensions, are immune to electromagnetic fields and can be used to remotely monitor radiation in real time. For this study a novel OFD based on an inorganic scintillating material for external beam radiotherapy was developed. The dosimeter was constructed using a PMMA (polymethyl methacrylate) plastic optical fibre. The core of the PMMA was micro machined to make a 700 lm diameter and 7 mm deep cavity. The scintillating material, terbium doped gadolinium oxysulphide (Gd2O2S:Tb) was filled in the cavity and sealed with an epoxy. The scintillation material fluoresces on exposure to ionising radiation and the resultant emitted fluorescent light is detected using a multi-pixel photon counting module. Measurements to date using the novel dosimeter demonstrate very good repeatability and reproducibility with only a maximum of 0.17% and 0.68% difference from the average value, respectively. The results also show excellent linearity of the output signal with radiation doses and the dosimeter response was independent of dose rate. However, the percentage depth dose measurements showed an over response of the OFD compared to an ionization chamber. These differences are being investigated by means of Monte Carlo simulations.
stimulation the pressure stayed low and the motility showed increase in amplitude. During both tests the pylorus showed higher pressure and lack of motility waves at maximum probe distention. The pylorus seems to acts as a sphincter at low distention but when further dilated starts acting as a pump. Fully distended the pyloric motility disappears and the pressure remains high, suggesting that a stent with high radial force might show less migration. https://doi.org/10.1016/j.ejmp.2018.06.058
Poster Session P26 Personalised dosimetry for benign thyroid radioiodine therapy – An update Jennie Cooke a, Marie-Louise Healy b, Niamh Phelan b, Khaled Al Janaee b a
Medical Physics and Bioengineering, St. James’s Hospital, Dublin 8, Ireland b Dept of Endocrinology, St. James’s Hospital, Dublin 8, Ireland E-mail address: [email protected] At IAPM 2017 an overview of the dosimetry protocol for outpatient I-131 therapy which was in the process of being implemented in St. James’s Hospital was presented. A year on, 25 patients have now been treated using dosimetry, and here we present an overview of our experience and treatment outcomes for this small cohort. https://doi.org/10.1016/j.ejmp.2018.06.059
https://doi.org/10.1016/j.ejmp.2018.06.057
Poster Session P25 Exploring pyloric dynamics in stenting – Using a distensibility technique Barry McMahon a, Stephen Bligh a, Jorge Alberto Arroyo Vázquez b, Maria Bergstrom b, Per-Ola Park b a
MPCE, Tallaght Hospital, Ireland South Alvsborg Hospital, Boras, Sweden E-mail address: [email protected] b
Perforated duodenal ulcers can be treated with a stent. Stent migration is a severe complication, sometimes requiring surgery. Pyloric physiology during stent-treatment has not been studied and mechanisms for migration are unknown. To investigate the pyloric response to distention, mimicking stent-treatment, using the EndoFLIP, a non-survival study in five pigs was carried out, followed by a pilot study in one volunteer. Animals were gastroscoped during anaesthesia and the EndoFLIP was placed straddling the pylorus. Baseline distensibility readings were performed at stepwise balloon distentions to 20 ml, 30 ml, 40 ml and 50 ml, measuring pyloric Cross Sectional Area and pressure. Measurements were repeated after administration of a pro-kinetic drug and after a liquid meal. In the human study readings were performed in conscious sedation at baseline and after stimulation with metoclopramide. During baseline readings the pylorus was shown to open more with increasing distention together with higher amplitude motility waves. Reaching maximum distention-volume (50 ml), pyloric pressure increased significantly (p = 0.016) and motility waves disappeared. After pro-kinetic stimulation the pressure decreased and the motility waves increased in frequency and amplitude. After food
Poster Session P27 The development and implementation of the detective quantum efficiency metric in a clinical environment John McFadden a, Matthew Donoghue b a
University of Manchester, UK HSE, UK E-mail address: [email protected] b
Development and application of a practical DQE protocol for routine use by medical physicists during assessment of digital radiography systems. J. McFadden, M. Donoghue, E House, B. Tuohy. Measurement of the Detective Quantum Efficiency (DQE) of a DR detector provides a more quantitative assessment of the imaging performance of a system in comparison to the very subjective assessments traditionally used by medical physicists ‘‘in the field”. Although commonly used by the system manufacturers, the method has yet to be widely incorporated into quality assurance (QA) protocols in Irish hospitals. We will report in this paper on the findings from a project which aimed to adapt the IEC-62220 industrial DQE standard for a clinical environment. Results from our studies on the influence of DQE software algorithm chosen, variations in image acquisition and processing methods will be presented and explored. Development of the technique involved a compromise between the Industry standard IEC method and the practical limitations of time and equipment availability experienced by medical physicists in the field. Following adaptation of the Industry standard DQE approach, a practical methodology, which can be applied to any general radiography DR detector, allows medical physicists in the field to incorporate DQE assessment in their annual DR system assessment. A number of problems and challenges encountered during
E. Keavey et al. / Physica Medica 52 (2018) 165–182
the project will be explored and the salient findings will be presented. In conclusion, a novel adaptation of an industry standard DQE technique developed by our group is shown to be appropriate for use in a clinical environment. https://doi.org/10.1016/j.ejmp.2018.06.060
Poster Session P28 Independent assessment of MRI-induced temperature change and SAR distributions in phantoms Niall Colgan a,*, James Blackwell a, Wil Van der Putten b, Brendan Tuohy b a
Department of Physics, National University of Ireland Galway, Galway, Ireland b Medical Physics and Bioengineering, Galway University Hospital, Galway, Ireland E-mail address: [email protected] Background. During an MR procedure, most of the transmitted RF power is transformed into heat referred to as the specific energy absorption rate(SAR). EU directive(IEC60602-3-33) mandates all scanners must measure SAR and provide safeguards for tissuelimits. Accurate estimation of SAR is critical in safeguarding vulnerable patients. Modern MRI systems can easily exceed safe SAR levels and our aim is to develop a protocol to verify patient specific SAR using a MR phantom heated solely by the RF fields. Methods. Our phantom is a non-perfused material simplifying pennes-bioheat equation. The SAR at discreet points in the observation plane is determined by SARC_agar DT=Dt[Wnkg] Where C_agar is 4200 J/kg.K, DT is the change in temperature and Dt is the change in time. DT was determined via Proton Resonance Frequency Shift (PRF) thermometry. DT ¼ ð/ / 0Þ/(acB_0 TE) Where. https://doi.org/10.1016/j.ejmp.2018.06.061
Poster Session P29 Tackling the commissioning of a digital radiography AEC system Aisling McMahon, Edward Ranahan, James McCullagh Cork University Hospital, Ireland E-mail address: [email protected] AEC devices aim to maintain a consistent level of clinical image quality despite variations in patient body habitus and imaging method. The assessment of AEC performance has undergone significant revision with the advent of digital radiography and challenges still remain. Verification of manufacturers’ target detector air kerma (DAK) values with differing AEC testing protocols can be problematic, particularly when the system has been configured with integrated direct digital radiography (DDR) detectors. In addition, there is a need for comparative dose information from current DDR technology to be made available to the wider Medical Physics community. AEC testing was performed on 4 recently-installed Carestream DRX Evolution Plus digital radiographic systems as part of their commissioning tests. AEC calibration was assessed using 3 IPEMrecommended parameters; DAK, image pixel value and detector dose indicator (DDI). Testing was performed with both free and
179
scatter-free configurations and with and without antiscatter grid. A mixture of exit dose and in-bucky measurements were performed with the assistance of a field service engineer (FSE) for both free and integrated detectors. Results from the AEC testing of the four Carestream digital radiographic systems are presented for different testing conditions along with hints and tips on assessing the AEC dose levels when commissioning the systems. DAK results are compared to the manufacturers target values and to Bowden et al.’s (2011) published results on other DDR systems. These results could be used as initial AEC reference values against which others can compare their results when commissioning comparable systems. https://doi.org/10.1016/j.ejmp.2018.06.062
Poster Session P30 Breast dose audit of a symptomatic service James McCullagh, Aisling McMahon Cork University Hospital, Ireland E-mail address: [email protected] Monitoring breast dose is as important for the estimation of the radiation risk in a symptomatic service as it is in a national screening programme. The view generally held that special resources are needed to perform breast dose surveys has limited this service and others like it, from compliance with patient radiation safety legislation. In fact any medical physics department providing a support service to a breast imaging unit should be able to carry out a dose survey. This poster is a presentation of the results obtained from a dose survey of the symptomatic breast service provided in this hospital. Using a combination of commonly available software, exposure data from the examinations of 50 patients per mammography X-ray machine was compiled to perform the survey. It was found that the average breast MGD in the unit was 1.52 and 1.7 mGy for the CC and OB views, respectively. There are three digital mammography systems in the unit and the average MGD values for an OB view of compressed thickness 61 ± 5 mm on each unit was 1.59, 1.45 and 1.51 mGy. The breast dose performance of individual mammography Xray machines were commensurate with results reported in a previous survey of symptomatic services. The overall dose performance was compliant with dose reference levels established by both the national screening programme and a national dose survey of symptomatic services. This work has demonstrated the possibility of any symptomatic service utilising commonly available resources to assess breast dose performance in its own unit. https://doi.org/10.1016/j.ejmp.2018.06.063
Poster Session P31 Clinical performance of digital mammography systems in a breast screening programme – An update Elizabeth Keavey, Niall Phelan, Patricia Fitzpatrick BreastCheck, The National Screening Service, Ireland E-mail address: [email protected] The purpose of this research was to compare the clinical performance of three individual digital mammography (DM) systems
J. McFadden, M. Donoghue / Physica Medica 52 (2018) 165–182
c Dept. of Radiotherapy Physics, Galway Clinic, Ireland E-mail address: [email protected]
Modern radiation therapy treatment techniques and delivery methods introduce new challenges to existing dosimetry systems. As a result, much research has been conducted on the development of a radiation dosimetry system based on scintillating optical fibre. They offer many advantages over the currently employed dosimeters for real time dosimetry. Optical Fibre dosimeters (OFD) have small dimensions, are immune to electromagnetic fields and can be used to remotely monitor radiation in real time. For this study a novel OFD based on an inorganic scintillating material for external beam radiotherapy was developed. The dosimeter was constructed using a PMMA (polymethyl methacrylate) plastic optical fibre. The core of the PMMA was micro machined to make a 700 lm diameter and 7 mm deep cavity. The scintillating material, terbium doped gadolinium oxysulphide (Gd2O2S:Tb) was filled in the cavity and sealed with an epoxy. The scintillation material fluoresces on exposure to ionising radiation and the resultant emitted fluorescent light is detected using a multi-pixel photon counting module. Measurements to date using the novel dosimeter demonstrate very good repeatability and reproducibility with only a maximum of 0.17% and 0.68% difference from the average value, respectively. The results also show excellent linearity of the output signal with radiation doses and the dosimeter response was independent of dose rate. However, the percentage depth dose measurements showed an over response of the OFD compared to an ionization chamber. These differences are being investigated by means of Monte Carlo simulations.
stimulation the pressure stayed low and the motility showed increase in amplitude. During both tests the pylorus showed higher pressure and lack of motility waves at maximum probe distention. The pylorus seems to acts as a sphincter at low distention but when further dilated starts acting as a pump. Fully distended the pyloric motility disappears and the pressure remains high, suggesting that a stent with high radial force might show less migration. https://doi.org/10.1016/j.ejmp.2018.06.058
Poster Session P26 Personalised dosimetry for benign thyroid radioiodine therapy – An update Jennie Cooke a, Marie-Louise Healy b, Niamh Phelan b, Khaled Al Janaee b a
Medical Physics and Bioengineering, St. James’s Hospital, Dublin 8, Ireland b Dept of Endocrinology, St. James’s Hospital, Dublin 8, Ireland E-mail address: [email protected] At IAPM 2017 an overview of the dosimetry protocol for outpatient I-131 therapy which was in the process of being implemented in St. James’s Hospital was presented. A year on, 25 patients have now been treated using dosimetry, and here we present an overview of our experience and treatment outcomes for this small cohort. https://doi.org/10.1016/j.ejmp.2018.06.059
https://doi.org/10.1016/j.ejmp.2018.06.057
Poster Session P25 Exploring pyloric dynamics in stenting – Using a distensibility technique Barry McMahon a, Stephen Bligh a, Jorge Alberto Arroyo Vázquez b, Maria Bergstrom b, Per-Ola Park b a
MPCE, Tallaght Hospital, Ireland South Alvsborg Hospital, Boras, Sweden E-mail address: [email protected] b
Perforated duodenal ulcers can be treated with a stent. Stent migration is a severe complication, sometimes requiring surgery. Pyloric physiology during stent-treatment has not been studied and mechanisms for migration are unknown. To investigate the pyloric response to distention, mimicking stent-treatment, using the EndoFLIP, a non-survival study in five pigs was carried out, followed by a pilot study in one volunteer. Animals were gastroscoped during anaesthesia and the EndoFLIP was placed straddling the pylorus. Baseline distensibility readings were performed at stepwise balloon distentions to 20 ml, 30 ml, 40 ml and 50 ml, measuring pyloric Cross Sectional Area and pressure. Measurements were repeated after administration of a pro-kinetic drug and after a liquid meal. In the human study readings were performed in conscious sedation at baseline and after stimulation with metoclopramide. During baseline readings the pylorus was shown to open more with increasing distention together with higher amplitude motility waves. Reaching maximum distention-volume (50 ml), pyloric pressure increased significantly (p = 0.016) and motility waves disappeared. After pro-kinetic stimulation the pressure decreased and the motility waves increased in frequency and amplitude. After food
Poster Session P27 The development and implementation of the detective quantum efficiency metric in a clinical environment John McFadden a, Matthew Donoghue b a
University of Manchester, UK HSE, UK E-mail address: [email protected] b
Development and application of a practical DQE protocol for routine use by medical physicists during assessment of digital radiography systems. J. McFadden, M. Donoghue, E House, B. Tuohy. Measurement of the Detective Quantum Efficiency (DQE) of a DR detector provides a more quantitative assessment of the imaging performance of a system in comparison to the very subjective assessments traditionally used by medical physicists ‘‘in the field”. Although commonly used by the system manufacturers, the method has yet to be widely incorporated into quality assurance (QA) protocols in Irish hospitals. We will report in this paper on the findings from a project which aimed to adapt the IEC-62220 industrial DQE standard for a clinical environment. Results from our studies on the influence of DQE software algorithm chosen, variations in image acquisition and processing methods will be presented and explored. Development of the technique involved a compromise between the Industry standard IEC method and the practical limitations of time and equipment availability experienced by medical physicists in the field. Following adaptation of the Industry standard DQE approach, a practical methodology, which can be applied to any general radiography DR detector, allows medical physicists in the field to incorporate DQE assessment in their annual DR system assessment. A number of problems and challenges encountered during
E. Keavey et al. / Physica Medica 52 (2018) 165–182
the project will be explored and the salient findings will be presented. In conclusion, a novel adaptation of an industry standard DQE technique developed by our group is shown to be appropriate for use in a clinical environment. https://doi.org/10.1016/j.ejmp.2018.06.060
Poster Session P28 Independent assessment of MRI-induced temperature change and SAR distributions in phantoms Niall Colgan a,*, James Blackwell a, Wil Van der Putten b, Brendan Tuohy b a
Department of Physics, National University of Ireland Galway, Galway, Ireland b Medical Physics and Bioengineering, Galway University Hospital, Galway, Ireland E-mail address: [email protected] Background. During an MR procedure, most of the transmitted RF power is transformed into heat referred to as the specific energy absorption rate(SAR). EU directive(IEC60602-3-33) mandates all scanners must measure SAR and provide safeguards for tissuelimits. Accurate estimation of SAR is critical in safeguarding vulnerable patients. Modern MRI systems can easily exceed safe SAR levels and our aim is to develop a protocol to verify patient specific SAR using a MR phantom heated solely by the RF fields. Methods. Our phantom is a non-perfused material simplifying pennes-bioheat equation. The SAR at discreet points in the observation plane is determined by SARC_agar DT=Dt[Wnkg] Where C_agar is 4200 J/kg.K, DT is the change in temperature and Dt is the change in time. DT was determined via Proton Resonance Frequency Shift (PRF) thermometry. DT ¼ ð/ / 0Þ/(acB_0 TE) Where. https://doi.org/10.1016/j.ejmp.2018.06.061
Poster Session P29 Tackling the commissioning of a digital radiography AEC system Aisling McMahon, Edward Ranahan, James McCullagh Cork University Hospital, Ireland E-mail address: [email protected] AEC devices aim to maintain a consistent level of clinical image quality despite variations in patient body habitus and imaging method. The assessment of AEC performance has undergone significant revision with the advent of digital radiography and challenges still remain. Verification of manufacturers’ target detector air kerma (DAK) values with differing AEC testing protocols can be problematic, particularly when the system has been configured with integrated direct digital radiography (DDR) detectors. In addition, there is a need for comparative dose information from current DDR technology to be made available to the wider Medical Physics community. AEC testing was performed on 4 recently-installed Carestream DRX Evolution Plus digital radiographic systems as part of their commissioning tests. AEC calibration was assessed using 3 IPEMrecommended parameters; DAK, image pixel value and detector dose indicator (DDI). Testing was performed with both free and
179
scatter-free configurations and with and without antiscatter grid. A mixture of exit dose and in-bucky measurements were performed with the assistance of a field service engineer (FSE) for both free and integrated detectors. Results from the AEC testing of the four Carestream digital radiographic systems are presented for different testing conditions along with hints and tips on assessing the AEC dose levels when commissioning the systems. DAK results are compared to the manufacturers target values and to Bowden et al.’s (2011) published results on other DDR systems. These results could be used as initial AEC reference values against which others can compare their results when commissioning comparable systems. https://doi.org/10.1016/j.ejmp.2018.06.062
Poster Session P30 Breast dose audit of a symptomatic service James McCullagh, Aisling McMahon Cork University Hospital, Ireland E-mail address: [email protected] Monitoring breast dose is as important for the estimation of the radiation risk in a symptomatic service as it is in a national screening programme. The view generally held that special resources are needed to perform breast dose surveys has limited this service and others like it, from compliance with patient radiation safety legislation. In fact any medical physics department providing a support service to a breast imaging unit should be able to carry out a dose survey. This poster is a presentation of the results obtained from a dose survey of the symptomatic breast service provided in this hospital. Using a combination of commonly available software, exposure data from the examinations of 50 patients per mammography X-ray machine was compiled to perform the survey. It was found that the average breast MGD in the unit was 1.52 and 1.7 mGy for the CC and OB views, respectively. There are three digital mammography systems in the unit and the average MGD values for an OB view of compressed thickness 61 ± 5 mm on each unit was 1.59, 1.45 and 1.51 mGy. The breast dose performance of individual mammography Xray machines were commensurate with results reported in a previous survey of symptomatic services. The overall dose performance was compliant with dose reference levels established by both the national screening programme and a national dose survey of symptomatic services. This work has demonstrated the possibility of any symptomatic service utilising commonly available resources to assess breast dose performance in its own unit. https://doi.org/10.1016/j.ejmp.2018.06.063
Poster Session P31 Clinical performance of digital mammography systems in a breast screening programme – An update Elizabeth Keavey, Niall Phelan, Patricia Fitzpatrick BreastCheck, The National Screening Service, Ireland E-mail address: [email protected] The purpose of this research was to compare the clinical performance of three individual digital mammography (DM) systems