[en] Full text: For a period of four weeks, our clinical Nucletron microSelectron high dose rate (HDR) brachytherapy system was pulled out of clinical use and relocated to a new building. During this period decommission tests, de-wiring of the treatment unit and its associated safety system (such as radiation detector, emergency off circuits and door interlocks), transportation of all equipment, re-wiring of this equipment in the new location and recommission tests were carried out. The decommission and recommission test program was designed upon consultation with the manufacturer's (Nucletron) acceptance test procedures and work carried out by others. The ACPSEM tolerances for remote afterloaders was used as a guideline. In addition to mandatory dosimetry, positional, workstation database and safety tests, two Australian Standard compliance tests were carried out. The compliance tests involved one for remote afterloaders and another for treatment room design. This testing program was designed and implemented with the aim of ensuring ongoing safe delivery of brachytherapy doses to the patient. The testing program consisted of two parts. The first involved a series of decommissioning tests that consisted of dosimetry tests such as source and check cable positional accuracy and source calibration tests. In addition to these tests an inventory of standard plans, patient records and system configuration information was catalogued. The second part involved a series of recommission tests and involved carrying out dosimetry tests on the brachytherapy system (positional accuracy and calibration tests), simulating common treatment scenarios (prostate, cervical, vaginal and bile duct) and checking standard plans; patient records and system configuration had remained unchanged. During this period, other tests were carried out. These included Nucletron acceptance and preventative maintenance tests, Australian Standards compliance testing and integrity of network transfer of brachytherapy plans tests. There were no identifiable changes to the mechanical performance of the treatment unit.Correct functional performance of the workstation database, safety interlocks and network transfer of treatment plans was demonstrated. Standard treatment simulations indicated no unusual outcomes. The Nucletron microSelectron HDR remote afterloader meets Australian Standard compliance. The treatment suite meets Australian Standards compliance except for radiation signage, which is currently being addressed. The relocation of the Nucletron MicroSelectron-HDR brachytherapy unit did not introduce any changes to the system. Compliance with the relevant Australian Standard was determined. The system was successfully released for clinical use within the planned time frame. Copyright (2004) Australasian College of Physical Scientists and Engineers in Medicine

[en] A study was made of calibrating the NACP plane parallel chamber in electron beams from linear accelerators of a different manufacture with energies, E O' from 4.4 to 19.1 MeV, and also in 4 and 6 MV photon beams as well as a cobalt⁶⁰ beam. The photon beam measurements were both IN-AIR and IN-Phantom. With the exception of the lowest energy electron beam (nominal S MeV), the ND values from measurements in the electron beams were within +1% of the average value f'rom the three different methods according to the AAPM TG 39 protocol. The preferred method of calibration of an electron chamber is of course in an electron beam at R₁₀₀ in water. This can still be done in medium energy electron beams (nominal 7 to 14 MeV) for the NACP chamber with the same degree of accuracy and precision as with AAPM TG 39 methodology. Alternatively the traditional cobalt-60 calibration beam can be replaced by a low energy (4 - 6MV) photon beam for in-phantom calibrations at 50 mm depth, giving comparable results, and with no more uncertainties than those obtained in electron beams. 9 refs., 2 tabs., 1 fig

[en] An automatic radiation damage monitoring system has been developed and tested. The system is based on two passive sensors for the measurement of integral-ionizing and non-ionizing energy losses in silicon devices. Ionizing dose is measured in terms of dose in SiO₂ and displacement damage in terms of 1 MeV(Si) equivalent neutron fluence. The system uses MOSFETs and PIN dosimetric diodes

[en] Full text: This paper reports on the investigation and comparison of performance of a Varian Portal Vision system and a Siemens Beamview Plus system using the framework outlined by ICRU Report 54. Radiation Therapy EPI (Electronic Portal Imaging) systems are one of the main applications of digital imaging technology in a radiation therapy department. Radiation Therapy EPI systems may produce images of a lesser quality than the diagnostic radiology equivalent. It is therefore important to optimise the system to obtain the best performance possible. Contrasting opinion on the performance of EPI by clinicians, radiation therapists, medical physicists and engineers often exists, even when the same system and even the same image are being evaluated. Differing opinion occurs because of differences in task end points and task assessment methods of two broad groups of individuals, the human-observer group and the technical-measurement group. Each group uses different task criteria and methodology for assessing performance. The human-observer group is primarily interested in system performance that assures a high level clinical-task performance while the technical-measurement group is concerned with system performance that assures a high level of imaging-task performance. The technical-measurement group tends to be closely associated with imaging system technology, testing, adjustment and optimisation tasks which are couched in terms imaging-task criteria. The human-observer group is usually attempting to optimise performance using clinical-task criteria. The challenge is to provide a balanced evaluation using complementary imaging-task performance and clinical-task performance assessments. Comparison of the systems is on the basis of imaging-task performance i.e. technical-measurement through physical performance assessments such as spatial resolution and noise level, and clinical-task performance i.e. human-observer measurements through the application of psychophysical analysis e.g. ROC (Receiver Operating Characteristics)

[en] Full text: The advantages of radiochromic film in radiation dosimetry are well known. They include dosimetry with high spatial resolution, response less dependent on incident beam energy than common radiotherapy films (such as the Kodak XV films), tissue equivalence and the ability to be handled and developed in room light. This study entails the design and testing of a new radiochromic densitometry system. The system consists of a single light emitting diode (LED), opaque 'diffuser' and digital camera. Customised software was developed to analyse images obtained from the digital camera. Standard characteristics of a commercially available super bright red LED (peak wavelength 625nm) was analysed in order to determine the voltage, current and intensity settings. Various methods in diffusing the single LED light source were investigated and it was determined that an opaque transmission 'diffuser' was the best alternative. While the intensity of the LED was kept constant, the digital camera exposure times were varied in order to determine a setting which would produce the best image exposure. The system was designed and built and preliminary tests were carried using the standard radiochromic film GafChromic MD-55-2. LED current vs. voltage curves were characteristically exponential for positive voltage. Studies into LED intensity versus camera exposure produced an unexpected result. At high exposures the camera saturates and if even higher exposures are used the LED intensity apparently decreases. This was thought to be due to the pixels in the charge couple device (CCD) saturating and eventually electronically 'bleeding' into adjacent pixels. Using the opaque transmission 'diffuser' enabled successful use of the single LED light producing an area of homogenous light intensity in which images of radiochromic films can be obtained. Preliminary results from radiochromic film characteristic studies show no unusual results. The single LED, diffuser and digital camera densitometer system provides a practical radiochromic film densitometer. Copyright (2004) Australasian College of Physical Scientists and Engineers in Medicine

[en] The purpose of Part 2 study of calibration methods for plane parallel ionisation chambers was to determine the feasibility of using beams for calibration of the MARKUS chamber other than the standard AAPM TG39 reference beams of ⁶⁰Co and a high energy electron beam (E₀≥ 15MeV). A previous study of the NACP chamber had demonstrated an acceptable level of accuracy with corresponding spread of -0.5% to +0.8% for its calibration in non-standard situations (medium to low energy electron and photon beams). For non-standard situations the spread in N_D^MARKUS values was found to be + 2.5%. The results suggest that user calibrations of the MARKUS chamber in non standard situations are associated with more uncertainties than is the case with the NACP chamber. (authors)

[en] Full text: The application and limitations of film, in the dosimetry of therapy beams has been reported by several authors. While the influence of beam energy, orientation and film type have been investigated, the contribution of Cerenkov radiation has received little if any attention. The conditions for the production and detection of Cerenkov radiation are well satisfied in a film medium placed in a therapy beam. The conditions include a transparent medium of refractive index 'n', particulate radiation (electrons) with sufficient velocity to cause the production of Cerenkov radiation and a sensor (the silver halide emulsion) sensitive to the spectrum of Cerenkov radiation produced. Kodak X-OmatV film was used in various configurations both in the supplied sealed film packet and placed free in a solid-water film cassette. Exposures were made using 100kV, 6MV photons and a range of electron energies. A fibre optic probe was also used to assess Cerenkov levels within a film packet. By analysing the optical density of the film in the presence and absence of Cerenkov producing materials, it has been possible to demonstrate and increase in optical densities of up to 4%. The example chart shows the increase in optical density caused by Cerenkov radiation as a function of depth. The film, in a solid-water cassette was exposed to 6MV photons. Cerenkov radiation has been shown to increase the optical density of therapy film. In high accuracy film dosimetry it may be appropriate to account for the change in optical density caused by Cerenkov radiation. Copyright (2000) Australasian College of Physical Scientists and Engineers in Medicine

[en] An energy analysis is presented for n -dodecane/air combustion in a heat recirculating Inconel microreactor under vacuum conditions. Microreactor channels are partially coated with platinum enabling operating with coupled heterogeneous and homogeneous reactions. The radiant efficiency, important for thermophotovoltaic energy conversion, was found to decrease from 57% to 52% over 5 different runs covering 377 min of operation. A similar decrease in combustion efficiency was observed with 6%-8% energy lost to incomplete combustion and 5%- 6% lost through sensible heat in the exhaust. The remaining thermal loss is from unusable radiation and conduction through inlet and outlet tubing. Changes in the Inconel microreactor geometry and emissivity properties were observed. (paper)

[en] Full text: Dosimetric artefacts in film based dosimetry have been addressed by a number of authors. We have investigated the influence on film dose results, of a number of materials that are commonly packed against the film including, solid water, paper, air and plastic. The results indicate that variations in optical density occur due to the character and relative quantity of the packing material as well as the film itself. Kodak X-omat V and GAFChromic film samples were placed in a solid water cassette with packing sheets of various materials placed in contact with the film. Photon and electron exposures were carried out with various film orientation and beam qualities. Results have been obtained for solid water, paper and air. An example of the relative change in film density as a function of depth due to four paper sheets packed adjacent to a film aligned with the central axis of a 6MV photon beam is shown. Other results indicate dose variation can be attributed to Cerenkov radiation. Packing materials in contact or in close proximity with dosimetric film, contribute to optical density variations of the order of several percent. Careful consideration of these effects is necessary when using film in high accuracy dosimetry. Copyright (2001) Australasian College of Physical Scientists and Engineers in Medicine

[en] Full text: The new generation of particle colliders provides extremely high beam densities and large beam currents. These factors increase the risk of radiation damage to the sensitive electronics and detectors that are a crucial component of the collider detector system. Monitoring systems are required to predict the survivability of the SVD. The KEK B-factory is a high luminosity asymmetric electron-positron collider being built at KEK, Japan. For the BELLE series of experiments, which are directed to the study of CP violation, the collider will accelerate positrons to an energy of 3.5 GeV with a beam current of 2.6 A, and 8 GeV electrons with a beam current of 1.1 A. Similar is a condition of experiments at SLAC BaBar. The large beam currents create unique radiation background problems in the SVD. Quadrupoles near the detector generate synchrotron radiation in the range of 5 - 15 keV, and residual gas scatters many of the electrons. The secondary showers produced by these particles will contribute to the radiation damage of the SVD. Additionally, high energy particles are created as a product of the electron-positron beam collisions. The new semiconductor radiation damage monitoring system was designed for independent measurements of Ionizing Energy Losses (IEL) and Non Ionizing Energy Losses (NEL) in mixed radiation Environment on HEP accelerators. This system is able to predict damage in CMOS readout electronics and silicon detectors. Two different version of this system was designed and installed at BELLE SVD and SLAC accelerator field for damage monitoring. Testing on pulsed nuclear reactor at Sandia National Lab in mixed gamma-neutron field and in pure Co-60 gamma field at Lokcheed Missile Corp., and on different energy electron fields at VARIAN accelerators demonstrated ability of independent measurements of EL and NIEL damage in silicon. The monitoring system was installed at BELLE SVD-I detector and supply reliable data on radiation damage during the beam testing New 8 channels system installation is in a process at SVD-2 BELLE detector. Extensive experiments in different points around SLAC and SVD BaBar detector have been carried out. Obtained results were compared with Monte Carlo simulation of SLAC Environment and were in good agreement. This research confirmed possibility of universal approach to radiation damage of electronics and SVD in mixed radiation accelerator field. Independently on components of the radiation field possible it introduces IEL radiation damage in terms of absorbed dose in SiO₂ for Co-60 radiation and NIEL damage in terms of 1MeV(Si) neutron fluence. Such system also can be ideal accident dosimetry system for new Australian reactor