Correction factors for two new reference beta radiation fields

Abstract

Several correction factors for two new reference beta-particle radiation fields complementing ISO 6980 have been measured and calculated for both primary beta dosimetry and the operational quantities in radiation protection. The following correction factors for primary beta dosimetry for the determination of the absorbed dose to tissue, D t, have been determined by calculations: k ba for backscatter from the collecting electrode, k pe for perturbation by the chamber’s side walls, k ih for inhomogeneity inside the collecting volume, k Sta for the stopping power ratio at different phantom depths, and k SA for the use of the Spencer-Attix theory, while the following have been measured: k br for the effect of bremsstrahlung and k abs for variations in the attenuation and scattering of beta particles between the source and the collecting volume due to variations from reference conditions and for differences of the entrance window to a tissue-equivalent thickness of 0.07 mm. Furthermore, calculations were undertaken to determine the following correction factors to assess the operational quantities H p(0.07), H p(3), H′(0.07), and H′(3): k rod(0.07) for the rod instead of the slab phantom, k cyl(3) for the cylinder instead of the slab phantom, as well as k′(0.07) and k′(3) for the ICRU sphere instead of the slab phantom, while the correction factor for oblique radiation incidence has been measured. The newly determined correction factors were determined in the same way as those for several well-established beta-particle radiation fields described in two earlier publications by the author. Furthermore, they are ready to be implemented in an updated version of the ISO 6980 series and in the software of the Beta Secondary Standard BSS 2.

Monte Carlo calculation of Spencer-Attix and Bragg-Gray stopping-power ratios of tissue-to-air for ISO reference beta sources — an EGSnrc study

“…A similar comparison for 4 mmthick PMMA flattening filter shows deviations increase to about 0.6-0.7%. However, the values published by Behrens [42], show good agreement (within 0.1%) with the Monte Carlo-calculated values for both the PMMA flattening filters. PET Filter [33].…”

“…Note that it has been previously demonstrated that Bragg-Gray values are independent of 𝑙 [31,32]. Also presented in tables 8 and 9 are published values reported in literature [6,31,42]. The Monte Carlo-calculated Bragg-Gray values at 70 μm depth with PET flattening filter and without filter compare well with the ISO-mentioned values for all the sources (within 0.2% for 90 Sr/ 90 Y source at 50 cm with PET and 147 Pm source at 20 cm with PET).…”

“…Change in the value of S t,a (𝑑) with d caused due to continuous energy loss along the path was included in the calculations. Behrens [42] calculated Bragg-Gray stopping-power ratio of tissue-to-air at desired depth d (in μm) in a tissue-equivalent slab phantom for energy-reduced radiation fields of 90 Sr/ 90 Y source using the Monte Carlo-calculated electron fluence spectra [37]. The spectral fluences at depth 𝑑 in tissue phantom were folded with the stopping power ratios of tissue and air [42].…”

“…Behrens [42] calculated Bragg-Gray stopping-power ratio of tissue-to-air at desired depth d (in μm) in a tissue-equivalent slab phantom for energy-reduced radiation fields of 90 Sr/ 90 Y source using the Monte Carlo-calculated electron fluence spectra [37]. The spectral fluences at depth 𝑑 in tissue phantom were folded with the stopping power ratios of tissue and air [42]. The Monte Carlo-calculated electron fluence spectra include attenuation of beta particles by 3 mm and 4 mm-thick PMMA flattening filters [37].…”

Monte Carlo study of the BSS2 calibration system using the PTW 23392 extrapolation chamber

“…Several computational MC codes are widely well known and used for radiation dosimetry such as, PENELOPE, GEANT4, FLUKA, EGSnrc, MCNP and others [8][9][10][11][12]. It is possible to find in literature publications reporting results on MC modelling and simulations using the varies MC codes available, of beta dosimetry systems with different types of extrapolation chambers [13][14][15][16][17][18][19][20][21][22]. However, there is no publication,…”