Applied Physics

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Applied Physics

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Browsing Applied Physics by Author "Azangwe, Godfrey"

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    A comparison of dosimetric properties of three solid state dosimetry systems for dosimetry audit in radiotherapy.
    (International Atomic Energy Agency (IAEA), 2014-12) Azangwe, Godfrey
    The purpose of this study is to investigate and compare characteristics of three solid state dosimetry systems in order to determine working parameters and corrections needed for remote dosimetry audits of high energy photon and electron beams. The following systems were investigated: a thermo luminescent dosimetry (TLD) system (TLD-100, PCL3 reader), an optically stimulated luminescent dosimetry (OSLD) system (nanoDots, microStar reader) and a radiophoto luminescent dosimetry (RPLD) system (GD 302M, FGD-1000 reader).
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    Detector to detector corrections: A comprehensive experimental study of detector specific correction factors for beam output measurements for small radiotherapy beams.
    (Medical Physics, 2014-07) Azangwe, Godfrey
    Purpose: The aim of the present study is to provide a comprehensive set of detector specific correction factors for beam output measurements for small beams, for a wide range of real time and passive detectors. The detector specific correction factors determined in this study may be potentially useful as a reference data set for small beam dosimetry measurements. Methods: Dose response of passive and real time detectors was investigated for small field sizes shaped with a micromultileaf collimator ranging from 0.6 × 0.6 cm2 to 4.2 × 4.2 cm2 and the measurements were extended to larger fields of up to 10 × 10 cm2. Measurements were performed at 5 cm depth, in a 6 MV photon beam. Detectors used included alanine, thermoluminescent dosimeters (TLDs), stereotactic diode, electron diode, photon diode, radiophotoluminescent dosimeters (RPLDs), radioluminescence detector based on carbon-doped aluminium oxide (Al2O3:C), organic plastic scintillators, diamond detectors, liquid filled ion chamber, and a range of small volume air filled ionization chambers (volumes ranging from 0.002 cm3 to 0.3 cm3). All detector measurements were corrected for volume averaging effect and compared with dose ratios determined from alanine to derive a detector correction factors that account for beam perturbation related to nonwater equivalence of the detector materials. Results: For the detectors used in this study, volume averaging corrections ranged from unity for the smallest detectors such as the diodes, 1.148 for the 0.14 cm3 air filled ionization chamber and were as high as 1.924 for the 0.3 cm3 ionization chamber. After applying volume averaging corrections, the detector readings were consistent among themselves and with alanine measurements for several small detectors but they differed for larger detectors, in particular for some small ionization chambers with volumes larger than 0.1 cm3.
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    EP-1308 IAEA support to national audit networks for radiotherapy dosimetry.
    (International Atomic Energy Agency (IAEA), 2013-04) Azangwe, Godfrey
    The IAEA has along-standing history providing support and assistance for radiotherapy dosimetry audits in various countries. It has supported the development of methodology and establishment of several national TLD-based QA audit networks for radiotherapy dosimetry. The main objective was to extend the availability of radiotherapy dosimetry audits to as many radiotherapy centres as possible throughout the world. The overall radiotherapy dosimetry audit approach established and developed throughout these CRPs is based on a process of increasingly complex steps and parameters being checked. The first CRP focused on the basic beam calibration audits. The basic programme was extended to audits in non-reference conditions through a second CRP.
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    IAEA section of dosimetry and medical radiation physics (DMRP).
    (2016-03) Azangwe, Godfrey
    The Dosimetry and Medical Radiation Physics (DMRP) section works on the Quality Assurance (QA) aspects of the use of radiation in medicine to ensure safety and effectiveness. Furthermore, it contributes to the increase in scientific and technical capacity in medical physics worldwide by fostering research and development in dosimetry techniques and playing a role in the education and training of medical physicists. The primary beneficiaries of these activities are hospital patients undergoing therapy and diagnosis with radiation, radiation workers who benefit from the standardization of radiation protection measurements and the general public due to improved dosimetry practice. DMRP also provides two types of service directly to Member States: dosimetry calibration and dosimetry auditing.
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    In vitro monitoring of rabbit anterior cruciate ligament damage by acoustic emission.
    (Medical Engineering Physics, 2000-06) Azangwe, Godfrey
    Anterior cruciate ligament (ACL) rupture is a major clinical problem leading to instability and degeneration of the knee joint. The problem is compounded by the limited ability of the ACL to heal when ruptured. The existing knowledge regarding the way the ACL ruptures is limited, and this investigation is an attempt to understand the nature of the ruptures using the rabbit as a model. A total of 16 rabbit tibia–ACL–femur complexes were stretched in tension to complete rupture. Four specimens were stretched to failure at a displacement rate of 0.5 mm/min and 12 specimens at 10 mm/min. Acoustic emission (AE) transducers were placed on both the tibia and the femur, and stress wave signals generated during the tensile test were recorded. Fibre fractures produced the highest amplitude signals with a relatively longer rise time. Other failure modes such as matrix failure and debonding produced lower amplitude signals with shorter rise times. We also noted that few events were recorded during the initial period of tensile loading (the elastic phase). The activity then increased significantly after maximum load was reached. The location information provided by the acoustic emission system was consistent with the final site of rupture. We have shown that AE can be used to characterise ligament damage, with fibre pull-outs and fibre fracture producing the highest signal amplitudes.
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    Quality audits of small field output factors: a multi-centre pilot study.
    (Physica Medica, 2014-12) Azangwe, Godfrey
    A new co-ordinated research project (CRP) was launched by the IAEA for the national audit networks for radiotherapy with the purpose of developing the methodology for remotely auditing IMRT related QA. The programme involves three audit steps: (1) remote verification of TPS calculation of small field output factors relevant for IMRT and audit of MLC positional performance, (2) audit of single clinical IMRT field dose delivery and (3) ‘end-to-end’ audit (imaging, planning, dose delivery) for multiple field IMRT techniques. New procedures and phantoms are being developed and examined through multi-centre pilot studies involving CRP participants.