Research Articles (Medical Physics)

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    Implementation of carbon fibre treatment couches in the XiO® and Monaco® treatment planning systems
    (Sciendo, 2020-12) Van Reenen, Christoffel Jacobus; Trauernicht, Christoph Jan
    Purpose: Carbon fibre treatment couches on linear accelerators provide a strong, rigid framework for patient support. Patient safety is a priority, therefore the dosimetric properties of treatment couches need to be accurately incorporated in treatment plans, to minimize differences between planned and delivered dose. This study aims to determine the attenuation effect of treatment couches for 3-D Conformal Radiotherapy (3-D CRT) and to validate the implementation thereof in the XiO and Monaco treatment planning systems (TPS). Material and methods: Attenuation measurements were performed on the ELEKTA Connexion couches of the ELEKTA Precise and Synergy-Agility linear accelerators. Measurements were made at 10° intervals in RMI-457 Solid water (30 cm x 30 cm x 30 cm) using a PTW Farmer-type ionization chamber (TW30013) positioned at the accelerator’s isocentre. The percentage attenuation was calculated as the ratio of the electrometer readings for parallelopposed fields. The Computed Tomography (CT) data sets of the set-ups were obtained on a Philips Big Bore 16-slice CT scanner and exported to the TPS. The individual couch structures were delineated and electron density (ED) values were assigned using the commissioned CT-to-ED curve. Test treatment plans were generated with 100MU per field at 10° gantry intervals. Results: The percentage attenuation was determined to be within 2% and 3% for beams perpendicular to the couch surface for XiO and Monaco, respectively. The maximum attenuation was observed for oblique fields which was significantly higher than the manufacturer specified values. TPS validation showed an agreement to 1% for XiO and Monaco. At extreme oblique angles, both planning systems overestimated this effect up to a maximum of 4%. Conclusions: Couch attenuation differs significantly with gantry angle and beam energy. As a result, the treatment couch models should be included in all treatment planning calculations.
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    Effektiewe energiewaardes van 90°- verstrooide fotone tydens urologiese en brongoskopiese stralingsondersoeke
    (1977-11) Van der Merwe, E. J.; Cilliers, F. B.
    During fluoroscopic bladder and bronchial examinations the radiation workers concerned are exposed to 90°-scattered photons. The effective energy expressed in mm Al was measured for these photons exited at tube potentials in the 60-100 kV range. An increase also depends on whether the measurements are made in the direction of the long axis or the short axis of the phantom. These findings are contrary to the recommendations stipulated in the code of practice SABS 07-1972.
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    Die frekwensie van herhaling van rontgenopnames
    (HMPG, 1980-01) Van der Merwe, E. J.
    A study of the rates of repeat radiography in two hospitals in the Cape Peninsula was undertaken. The relationship between these rates and the type of examination as well as the contributing factors was established. The total frequencies for the two hospitals varied from 10,1% to 14%. The predominant reasons for 78% of repeat radiographs were over-exposure, under-exposure and positioning.
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    Elektron- en lae energiefoton-kontaminasie van die stralingsbundel van 'n theratron 780-kobalteenheid
    (HMPG, 1980-08) Groenewald, W. A.; Van der Merwe, E. J.
    While high-energy photon radiation in radiotherapy of deeper tissues has a skin-sparing effect, contamination with electron and low-energy photon radiation can diminish and even abolish this effect. Experiments with perspex, aluminium and copper filtrates showed that a copper filter effectively diminished the skin dose owing to contaminated radiation.
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    'n Vergelykende ondersoek tussen twee kapasitorontlandings-x-straaleenhede
    (Health and Medical Publishing Group (HMPG), 1980-11) Frost, J. M.; Collins, P. D.; Van der Merwe, E. J.
    Two capacitor discharge X-ray units of different make were compared. The same radiological examinations were carried out with both units and the radiation exposure for every examination was measured on a Rando phantom with calibrated LiF-TLD Teflon discs. A large difference in radiation exposure for the same image quality was found between the two units. Factors such as the use of rare earth intensifying screens with capacitor discharge X-ray units, independent tube current settings and automatic charge replenishment are stressed.