Browsing by Author "Jones, Dan T L"

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    Determination of energy spectra of proton therapy beams
    (2002) Nchodu, M R; Brooks, F D; Buffler, Andy; Jones, Dan T L
    A technique has been developed for measuring the energy spectra of high-energy proton therapy beams in situ under conditions similar to those used for radiotherapy at the South African National Accelerator Centre. The method is based on proton elastic scattering, H(p,p)H, in a thin polyethylene radiator and uses two ΔE-E detector telescopes to detect coincident proton pairs. Measurements have been made to investigate the effect of standard beam modification elements on the energy spectra of proton therapy beams produced by a passive scattering system. Monte Carlo simulations of the spectra were computed with the MCNPX 2.1.5 Monte Carlo code to compare with experimental measurements.
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    Preliminary investigation of a possible dose rate effect on survival of cells irradiated with low energy protons
    (1989) Robinson, L P G; Cherry, R D; Jones, Dan T L; Bohm, L
    Apparatus has been developed for the irradiation of V79-379A Chinese hamster lung fibroblast cells with 3.6 MeV protons from the Van de Graaff accelerator at the National Accelerator Centre in Faure. The original intention of this work was to investigate and measure a possible dose rate effect on the survival of V79 cells, in the dose range from zero to 25 Gy, at dose rates of about 3 Gy/s and 300 Gy/s. The survival curves initially obtained were anomalous in that they showed abnormally high levels of survival and a tendency to remain at a constant survival level for doses above 10 Gy. Systematic attempts to correct this observed anomaly, involved the following; apparatus improvements were made, a means of measuring the beam profile was devised, the current measuring device and the dosimetry were improved and a possible dose rate effect on intracellular oxygen was investigated. After these improvements, the anomalous effect was much reduced, but not entirely eliminated. The final results showed no significant difference between the survival of cells irradiated at dose rates of about 3 Gy/s and 300 Gy/s; qualitative differences were however noticeable. After correction for the effect of a non-uniform beam profile, the survival curves were significantly different to published work. This difference suggested a possible dose rate effect between dose rates of about 0.1 Gy/s and dose rates above 3 Gy/s.
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    The use of thermoluminescent dosimeters for In-vivo dosimetry in a fast neutron therapy beam
    (2000) Bhengu, Khumbulani John; Jones, Dan T L; Langen, Katja M
    Thermoluminescent detectors (TLD-700) have been investigated for absorbed dose measurements in a p(66)/Be neutron therapy beam at the National Accelerator Centre. Chips were selected based on their reproducibility and chip individual neutron calibration factors were derived. The dose non-linearity was determined in peak 5 and peak 6 and dose non-linearity corrections were performed. The sensitivity of TLD-700 chips with depth and off-axis distance was determined. In-vivo dose measurements were performed on seven patients (9 fields). In the entrance in-vivo dose measurements, a maximal deviation of 3.2 % was detected and a systematic difference of 1.7 % was observed. On the exit side, a maximal deviation of -7.3 % was detected and a systematic difference of -5.1 % was observed. The glow curve peak 6/5 ratio was investigated and found to correlate with the qualitative variations of the average LET in the neutron beam.