Radiation Biophysics – Infrastructure
All research projects of the Radiation Biophysics Division rely on well-characterised beam lines and systems for the irradiation of biological and physical samples, as well as dosimetry detectors. These include:
- Horizontal 200 MeV proton therapy beam delivery system in the B-line:
A passive double scatterer and occluding ring system is used to spread and flatten the beam. A system of two opposing graphite wedges is used to adjust the range of the beam (from 3 cm up to 24 cm in water). Range modulating acrylic propellers are used to provide spread-out Bragg peaks (SOBP). The beam is collimated at several points along the beam line, including a final collimator, situated 30 cm upstream of the treatment isocentre, which allows for a maximum field of 10 cm in diameter. In addition there are multiwire and quadrant ionization chambers, with feedback systems to steering magnets in order to ensure accurate beam alignment and symmetry, and a pair of parallel-plate ionization chambers for dose monitoring.
For an incident proton beam current of 20 nA, the reference beam used for absolute dose calibrations have dose rate of 3.5 Gy/min at depth of 3 cm in water (incident beam currents of up to 100 nA can readily be tolerated).
- Quasi-mono energetic neutron beams produced in the D-line:
The neutron beams are produced by means of 7Li(p,n)7Be or 9Be(p,n)9B reactions (more information here). These beams are useful for the characterization of dosimetry detectors (neutron energies up to 200 MeV). Future developments are planned to cater for in vitro radiobiology experiments.
- Self-contained biological X-ray irradiator (X-Rad320, Precision X-ray):
This irradiator is located in the radiobiology laboratory in close proximity to the cell culture facilities. The commercial system is capable of delivering kilovotage X-ray beams with tube voltages ranging from 5 kV to 320 kV.
- Cobalt-60 source (from an older Theratron 780 teletherapy unit):
This system is typically used for in vitro radiobiology experiments and for the cross-calibration of ionization chambers and is also situated in the radiobiology laboratory. Currently, the dose rate from this source is about 0.400 Gy/min.
The p(66)/Be isocentric neutron therapy unit is no longer available, but parts of this unit may be reused in the foreseeable future to develop a horizontal neutron beam line to deliver fast, therapy quality neutron beams with higher dose rates than the quasi-mono energetic neutron beams.
Radiation biophysics experiments rely on accurate and precise dosimetry. The Division is equipped with a wide range of ionization chambers and electronic instrumentation that allows for absolute dose measurements that are traceable to a primary or secondary standards dosimetry laboratory, such as the National Metrology Institute of South Africa. Other equipment include a phantom scanning system for the measurement of dose profiles in water, radiochromic film and readers, extrapolation chambers, proportional counters of various sizes and wall materials, a silcon-based microdosimeter, and gas filling and flow systems.
Plans are in place to upgrade some of the dosimetry instrumentation and to acquire new and compact detectors, such as a micro-diamond detector, a miniature tissue-equivalent proportional counter together with a low-pressure gas flow system, bubble detectors, and fluorescence nuclear track detectors.
For more information on medical physics research and instrumentation, please contact Mr Evan de Kock.
One of the major advantages of our facility is the access to a fully equipped radiobiology laboratory within the same institute.
- Sterile cell culturing facilities.
- Microscopy infrastructure:
- Two Metafer automatic scanning and imaging platforms (Metasystems)
- Zeiss Axioscope fluorescent microscope
- Live cell imaging system (Lonza Cytosmart)
- Flow cytometry (BD Accuri C6 flow cytometer)
- Fluorescent in situ hybridization (FISH) for chromosomal aberration analysis
- Radiochemical synthesis and validation of radiolabelled compounds:
- Radiosynthesis laboratory
- Rotary evaporator
- Scintillation counter
- High-performance liquid chromatographer
- UV-VIS spectrophotometer
- Specialized equipment and radiobiology techniques. A glimpse of some of the radiobiology assays that are used for our research projects, can be found in the figure below: