The energy response of LiF, film and a chemical dosemeter to high energy photons and electrons

Microdosimetric single event spectra of Ytterbium-169 compared with commonly used brachytherapy sources and teletherapy beams

Ytterbium-169 has been developed as a possible replacement for Iridium-192 and Iodine-125. The Theory of Dual Radiation Action predicts that the initial slope of the cell survival curve and therefore the relative biological effect at low dose rate is proportional to dose average lineal energy, yd, which is the microscopic analog of the dose average linear energy transferred. The quality factor used in radiation protection has been shown to be a function of the frequency average lineal energy, yf. Single event microdosimetric spectra for 60Co, 137Cs, 192Ir, 125I and 169Yb were measured in air and at several depths in phantom with a Rossi proportional counter. These spectra show marked differences between sources. The microscopic analogs of the track average and dose average LET, (yd and yf, respectively) differ between isotopes by factors of two or even higher in comparison to megavoltage electron beams. These yd's and yf's for 169Yb are consistently higher when compared to 60Co or 137Cs but are approximately equal to those for 125I. Values of yf and yd for 192Ir are intermediate between 60Co and 169Yb. The Theory of Dual Radiation Action predicts a low dose rate RBE (assuming a 1 micron effective site diameter) compared to 60Co (in air) of: 1.00 for 137Cs, 1.29 for 192Ir, 1.60 for 169Yb and 1.77 for 125I.

An approach to an analysis of the energy response of LiF-TLD to high energy electrons

Responses of LiF-TLD to high energy electrons relative to 60Co gamma-rays were investigated experimentally and theoretically. The Burlin et al. theory, its modified version by Almond and McCray and the Holt et al. semi-empirical theory were examined in comparison with each experiment. An approximate approach to theoretical analysis of energy response of LiF-TLD was attempted and compared with some experimental results.

[Comparison of the measurement of absorbed doses by ferrous sulfate dosimetry and by ionization chambers]

A comparison has been carried out among six radiotherapy centres in Canada to determine the absorbed dose by means of ferrous sulphate dosemeters and ionization chambers. Previous to these measurements, epsilon was found to be 2196+/-7 dm3 mol-1 cm-1. The results show that: for 60Co at four centres, two are better than 1% and the other two differ by 2 to 5%; for high energy electrons at four centres, one is better than 1%, another differs by 1 to 3% and the last two differ by more than 3% (the maximum discrepancies are +7% and -6%); for high energy photons at five centres, two are equal to 1%, two others differ by 2 to 4% and the last one differs by + 12%. The chemical dosemeter with irradiation cells made of quartz appeared to be an excellent dosemeter for this type of comparison. The standard error of the means was about 0.3%.