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A decade of DXA – a review of DXA QA results since protocols were published
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Abstracts/Physica Medica 32 (2016) 414–428
measurements made with a gold standard mechanical compression test with that from a novel ultrasound elastography imaging technique. Methods: Uniform samples of PVA-c were prepared to produce a range of stiffness, speed of sound and attenuation values mimicking healthy, fibrotic and fatty liver tissue. The samples were acoustically characterised using a home-built acoustic macroscope. Shear Wave Elastography (SWE) measurements were made using an Aixplorer scanner (Supersonic Imagine, France), while mechanical compression testing was carried out using a Lloyd Instruments system (Ametek, USA). Results: Samples with the following ranges were produced: Young’s modulus 2.3–24.8 kPa, speed of sound (1490–1570 m/s), and attenuation (0.26– 1.07 dB/MHz/cm) [1–2]. SWE measurements of the Young’s modulus compared well with those of mechanical compression testing (correlation coefficient: R 2 = 0.96). The penetration depth over which SWE measurements could be made decreased with increasing attenuation, to only approximately 5 cm in samples with a measured attenuation of 1.07 dB/ MHz/cm. PVA-c samples were produced which achieved similar diffusion coefficients as liver tumour (1.42 × 10−3 s/mm2). Conclusions: Good correlation was obtained between measurements of Young’s modulus made with SWE versus direct mechanical compression testing, giving confidence in the use of SWE for non-invasive in vivo tissue characterisation. References [1] Cournane S., Browne J.E., Fagan A.J. The effects of fatty deposits on the accuracy of the Fibroscan® liver transient elastography ultrasound system. Phys Med Biol 2012;57:3901–14. [2] Cournane S., Fagan A.J., Browne J.E. Review of ultrasound elastography quality control and training test phantoms. Ultrasound 2012;20:16–23. Cardiac devices in radiotherapy: What’s the problem? How do we deal with it? Caroline Lannon, Gordon Sands, Margaret Moore, Triona Brosnahan, Louise Fahy. University Hospital Galway In recent years the administration of radiotherapy to patients with cardiac devices such as pacemakers (PM) or internal cardiac defibrillators (ICD) has significantly increased. It has been shown that, if the device is in the primary radiation beam, then damage to the internal circuit may result if the device receives over a certain dose threshold: >1 Gy for ICD and >2 Gy for PM. This can be critical in some patients as the sensing and pacing functions of the devices may be compromised. A literature review and international survey was conducted in order to gather evidence to create a protocol for patients with cardiac devices undergoing radiotherapy. The survey consisted of six questions plus a section for comments. This survey was distributed to a worldwide medical physics mailing list. In total 124 responses worldwide were received. Some of the results included the following: a total of 66% had a 1–2 Gy limit on PM generators, 59% had a 1–2 Gy limit on ICD generators and 66% had no limit on the leads. In regard to energy limit 41% limited the photon energy to 10 MV or lower. A number of different radiation detectors were used for measurement such as diodes, TLDs, OSLs, Gafchromic film, and mosfets. This study showed that there is a variation in treatment protocol for patients with cardiac devices undergoing
radiotherapy. Many of the survey respondents were adhering to The Netherlands protocol and at present an institutional protocol is in the process of being adopted at University Hospital Galway using the knowledge from this study. A decade of DXA – a review of DXA QA results since protocols were published Emer Kenny, Ronan Faulkner, Louise Bowden. Department of Medical Physics & Bioengineering, St. James’s Hospital, Dublin Recommended quality assurance (QA) test methodologies for Dual Energy X-ray Absorptiometry (DXA) systems were published in the scientific literature in 2005. In almost 10 years’ experience of performing QA tests on DXA systems with various technologies including pencil and fan beam scanners, the same published protocols have remained in place. Furthermore, while suspension tolerances for DXA tests are given in RP162, DXA was not included in the IPEM 91 standard and little guidance outside of the scientific literature exists on tolerances for DXA QA results. This study reviews the results of QA tests performed on 11 different DXA scanners during 2005–2014. The study aims to identify the pass/failure frequency of tests in the current QA protocol with a view to refining the protocol and evaluating the appropriateness of the current tests. Areas where additional guidance is required are also identified and discussed. Micro-commissioning of an INTRABEAM Intraoperative Radiotherapy (IORT) X-ray source (XRS) using EBT3 Gafchromic film in conjunction with multichannel film dosimetry and Matlab analysis Tom Burrows, Ben Earner, Peter Faulkner, Neil Dancer. Royal Free London NHS Foundation Objectives: IORT is a novel approach for the treatment of breast cancer using a compact mobile kilovoltage XRS. The INTRABEAM [1] source in use in this hospital is sent for calibration on an annual basis after which it must be re-commissioned for clinical use. Currently this involves an output measurement in solid water using an ion chamber, an assessment of isotropy using thermoluminescent dosimeters and measurement of depth doses using EBT radiochromic film [2]. This is a very time consuming process. By using laser micro machined EBT3 Gafchromic film, triple channel film dosimetry and Matlab analysis it is possible to streamline the re-commissioning process into a single check. Methods: Measurements of output, isotropy and depth doses were performed for a 4.5 cm spherical applicator. Symmetry is assessed at 0.5 cm from the surface of the probe and is normalised to the Z-axis. Depth dose is assessed on the Z-axis and absolute dose is measured at the prescription point. Results: Symmetry results vary from −10 to +4%, which is in good agreement with the anisotropic distribution previously recorded. Typical absolute dose measurements are reproducible to within 4%. Measured depth doses agree to within 3% ± 2%. For current methods a tolerance of 5% and action level of 10% is in use. Conclusions: Results indicate that EBT3 is a viable option to assess percentage depth dose, probe symmetry and absolute dose. The technique is still experimental and will need further investigation but shows the potential to streamline the re-commissioning process.
Abstracts/Physica Medica 32 (2016) 414–428
measurements made with a gold standard mechanical compression test with that from a novel ultrasound elastography imaging technique. Methods: Uniform samples of PVA-c were prepared to produce a range of stiffness, speed of sound and attenuation values mimicking healthy, fibrotic and fatty liver tissue. The samples were acoustically characterised using a home-built acoustic macroscope. Shear Wave Elastography (SWE) measurements were made using an Aixplorer scanner (Supersonic Imagine, France), while mechanical compression testing was carried out using a Lloyd Instruments system (Ametek, USA). Results: Samples with the following ranges were produced: Young’s modulus 2.3–24.8 kPa, speed of sound (1490–1570 m/s), and attenuation (0.26– 1.07 dB/MHz/cm) [1–2]. SWE measurements of the Young’s modulus compared well with those of mechanical compression testing (correlation coefficient: R 2 = 0.96). The penetration depth over which SWE measurements could be made decreased with increasing attenuation, to only approximately 5 cm in samples with a measured attenuation of 1.07 dB/ MHz/cm. PVA-c samples were produced which achieved similar diffusion coefficients as liver tumour (1.42 × 10−3 s/mm2). Conclusions: Good correlation was obtained between measurements of Young’s modulus made with SWE versus direct mechanical compression testing, giving confidence in the use of SWE for non-invasive in vivo tissue characterisation. References [1] Cournane S., Browne J.E., Fagan A.J. The effects of fatty deposits on the accuracy of the Fibroscan® liver transient elastography ultrasound system. Phys Med Biol 2012;57:3901–14. [2] Cournane S., Fagan A.J., Browne J.E. Review of ultrasound elastography quality control and training test phantoms. Ultrasound 2012;20:16–23. Cardiac devices in radiotherapy: What’s the problem? How do we deal with it? Caroline Lannon, Gordon Sands, Margaret Moore, Triona Brosnahan, Louise Fahy. University Hospital Galway In recent years the administration of radiotherapy to patients with cardiac devices such as pacemakers (PM) or internal cardiac defibrillators (ICD) has significantly increased. It has been shown that, if the device is in the primary radiation beam, then damage to the internal circuit may result if the device receives over a certain dose threshold: >1 Gy for ICD and >2 Gy for PM. This can be critical in some patients as the sensing and pacing functions of the devices may be compromised. A literature review and international survey was conducted in order to gather evidence to create a protocol for patients with cardiac devices undergoing radiotherapy. The survey consisted of six questions plus a section for comments. This survey was distributed to a worldwide medical physics mailing list. In total 124 responses worldwide were received. Some of the results included the following: a total of 66% had a 1–2 Gy limit on PM generators, 59% had a 1–2 Gy limit on ICD generators and 66% had no limit on the leads. In regard to energy limit 41% limited the photon energy to 10 MV or lower. A number of different radiation detectors were used for measurement such as diodes, TLDs, OSLs, Gafchromic film, and mosfets. This study showed that there is a variation in treatment protocol for patients with cardiac devices undergoing
radiotherapy. Many of the survey respondents were adhering to The Netherlands protocol and at present an institutional protocol is in the process of being adopted at University Hospital Galway using the knowledge from this study. A decade of DXA – a review of DXA QA results since protocols were published Emer Kenny, Ronan Faulkner, Louise Bowden. Department of Medical Physics & Bioengineering, St. James’s Hospital, Dublin Recommended quality assurance (QA) test methodologies for Dual Energy X-ray Absorptiometry (DXA) systems were published in the scientific literature in 2005. In almost 10 years’ experience of performing QA tests on DXA systems with various technologies including pencil and fan beam scanners, the same published protocols have remained in place. Furthermore, while suspension tolerances for DXA tests are given in RP162, DXA was not included in the IPEM 91 standard and little guidance outside of the scientific literature exists on tolerances for DXA QA results. This study reviews the results of QA tests performed on 11 different DXA scanners during 2005–2014. The study aims to identify the pass/failure frequency of tests in the current QA protocol with a view to refining the protocol and evaluating the appropriateness of the current tests. Areas where additional guidance is required are also identified and discussed. Micro-commissioning of an INTRABEAM Intraoperative Radiotherapy (IORT) X-ray source (XRS) using EBT3 Gafchromic film in conjunction with multichannel film dosimetry and Matlab analysis Tom Burrows, Ben Earner, Peter Faulkner, Neil Dancer. Royal Free London NHS Foundation Objectives: IORT is a novel approach for the treatment of breast cancer using a compact mobile kilovoltage XRS. The INTRABEAM [1] source in use in this hospital is sent for calibration on an annual basis after which it must be re-commissioned for clinical use. Currently this involves an output measurement in solid water using an ion chamber, an assessment of isotropy using thermoluminescent dosimeters and measurement of depth doses using EBT radiochromic film [2]. This is a very time consuming process. By using laser micro machined EBT3 Gafchromic film, triple channel film dosimetry and Matlab analysis it is possible to streamline the re-commissioning process into a single check. Methods: Measurements of output, isotropy and depth doses were performed for a 4.5 cm spherical applicator. Symmetry is assessed at 0.5 cm from the surface of the probe and is normalised to the Z-axis. Depth dose is assessed on the Z-axis and absolute dose is measured at the prescription point. Results: Symmetry results vary from −10 to +4%, which is in good agreement with the anisotropic distribution previously recorded. Typical absolute dose measurements are reproducible to within 4%. Measured depth doses agree to within 3% ± 2%. For current methods a tolerance of 5% and action level of 10% is in use. Conclusions: Results indicate that EBT3 is a viable option to assess percentage depth dose, probe symmetry and absolute dose. The technique is still experimental and will need further investigation but shows the potential to streamline the re-commissioning process.