ICRU Muscle Research Articles

C/O Kerma coefficient ratio for 96 MeV neutrons deduced from microscopic measurements

Double-differential cross sections for neutron-induced light-ion production at 96 MeV have been measured for a variety of nuclei at The Svedberg Laboratory. Using the measured cross-section data, we deduce the Kerma coefficient from carbon and oxygen for p, d, t, He-3 and alpha particles. In order to get the total Kerma for C and O, we add GNASH calculation values where experimental data are not available and obtain a Kerma coefficient of 7.85 +/- 0.63 fGy m(2) for carbon and 7.09 +/- 0.57 fGy m(2) for oxygen. The C/O Kerma coefficient ratio then becomes 1.11 +/- 0.11. In addition we determine the Kerma ratio between ICRU muscle and A-150, again adding calculations with the GNASH code where no experimental data are available, and obtain a value of 0.98 +/- 0.05. While the Kerma coefficients for carbon and oxygen do not agree with the prediction in ICRU Report 63, the ratio values are in good agreement with existing predictions.

Differential dosimetry in a neutron-proton mixed field with low-pressure proportional counters.

For a mixed radiation field of neutrons and protons, radiation events were discriminated between photons, neutrons, and protons using a thin plastic scintillator. Distributions of lineal energy were measured with low-pressure proportional counters (LPPCs). To estimate the distribution of lineal energy for ICRU muscle, measurements were carried out using A-150-walled, graphite-walled, ZrO2-walled, and Zr-walled counters. Data were corrected for different atomic compositions between the A-150 plastic and ICRU muscle.

Calculated Fluence Spectra at Neutron Therapy Facilities

The Monte Carlo transport codes LAHET and MCNP were used to calculate energy fluence spectra at three neutron therapy facilities. The results compare very favourably with measured data. Kerma spectra and the ratio of ICRU muscle tissue kerma to A-150 kerma, along with the carbon to oxygen kerma ratio, were determined. Absorbed dose rate calculations are in reasonable agreement with measured values. Use of these codes to study modifications to existing therapy beams is briefly discussed.

High Energy Neutron and Proton Kerma Factors for Different Elements

A generalisation of the kerma concept for uncharged particles, extending it to all ionising radiations, is proposed. In accordance with the new concept, the kerma factor of ionising particles, k, is considered as a sum of the nuclear, k n , and electromagnetic, k e , components, where k e for charged particles is equal to L∞/p. The values of the nuclear component of kerma factor, k n , for neutrons and protons with energies 20-1000 MeV have been calculated for 25 elements from hydrogen to lead as well as for the ICRU muscle tissue. The cascade-exciton model of nuclear interactions was used in the calculations. The presented results of test calculations of the secondary charged particle spectra from reactions of nucleons with different nuclei demonstrate good agreement with experiment. The calculated data also agree well with the experimental values of high energy neutron kerma in light nuclei. The results obtained will remedy a shortage of information on high energy nucleon kerma and will find an application in different fields of radiation protection.

Neutron fluence and kerma spectra of a p(66)/Be(40) clinical source.

High-resolution neutron fluence spectra have been measured in the National Accelerator Centre's p(66)/Be(40) neutron therapy beam by the pulsed-beam time-of-flight method. ICRU muscle kerma spectra have been derived from the fluence spectra. Spectral changes resulting from different irradiation conditions have been quantified in terms of the average neutron energy and the fractional low-energy (< 16 MeV) contribution. The changes observed with different thicknesses of polyethylene filtration are consistent with changes in quality parameters determined in biological and microdosimetric experiments. The dosimetry parameters (KtissueA150) N and (Wgas) N calculated for the measured spectra agree with the values recommended in the neutron dosimetry protocol. The shapes of the present fluence spectra differ from previous measurements of p(> 40)/Be spectra. In particular, they differ significantly from the spectrum measured by recoil techniques in an identical neutron therapy unit at the Clatterbridge Hospital, UK. The reasons for the difference are not known.

Measurement of neutron kerma factors for carbon and A-150 plastic at neutron energies of 26.3 MeV and 37.8 MeV

Kerma factors for carbon and A-150 tissue equivalent plastic were determined in two nearly monoenergetic neutron beams. Kerma was measured with low pressure proportional counters (PCs) with walls made of graphite and A-150 plastic. The neutron fluence was measured with a proton recoil telescope. The corrections for the kerma contributions from low energy neutrons in the beams were determined by time-of-flight measurements with an NE213 scintillation detector and with the PCs. For neutron energies of (26.3+or-2.9) MeV and (37.8+or-2.5) MeV the kerma factors for carbon were (35.5+or-3.0) pGy cm2 and (42.6+or-3.9) pGy cm2, respectively, and for A-150 they were (75.6+or-5.4) pGy cm2 and (79.0=5.6) pGy cm2. At these energies the kerma factor ratio for ICRU muscle tissue to A-150 calculated on the basis of the new kerma factors, is 0.93.

Scaling relative neutron depth-dose distributions from one phantom material to another: a comparison of experimental and theoretical results

To correct percentage depth-dose data from one phantom material to another, experimental and theoretical scaling factors (SF) are compared for different neutron beam qualities. Differences of up to 10% were observed for different phantom materials relative to water. The ratio SF/ rho was plotted as a function of H concentration by mass where rho is the mass density of the phantom material. A nearly linear relationship result at all energies for the theoretical scaling factors, while, for the experimental points, important deviations appeared at high energies for materials with relatively low H and high C concentrations. It can be shown that a single linear relationship for all compounds composed of H, C and O can only be valid if the ratio of total cross sections of carbon to oxygen is equal to 3/4. Experimental scaling factors will be more accurate than calculated values because of the uncertainty in the average total cross sections. If these factors for tissue equivalent (TE) liquid relative to water are converted to those of ICRU muscle by correcting to a mass density of 1.04 g cm-3, then the scaling factors are, within experimental uncertainty, equal to one.

Progress in Lyoluminescence Dosimetry in Aberdeen

Secondary alkyl radicals have been postulated as participating in the Russell-Vassilev scheme of generation of light, in lyoluminescence (LL). Using the spin-trapping technique, the presence of these radicals has been confirmed in many LL phosphors. Low energy ß emitters incorporated in co-crystallised mannose and sucrose impart a dose to the matrix, in good agreement with the expected value when calibrated with soft X ray sources. Accuracy of a few per cent is attained using glutamine dosemeters in a series of mailed intercomparisons in the industrial radiation processing dose range, by use of a heat treatment at 114 oC for 5 hours. New LL phosphors, leucine and iso-leucine have similar hydrogen content to standard muscle and thus their neutron kerma are very close to those of ICRU muscle in the energy range from a few keV to 10 MeV. These phosphors are suitable for medical application particularly when used with sensitisers.

Progress in Lyoluminescence Dosimetry in Aberdeen

Abstract Secondary alkyl radicals have been postulated as participating in the Russell-Vassilev scheme of generation of light, in lyoluminescence (LL). Using the spin-trapping technique, the presence of these radicals has been confirmed in many LL phosphors. Low energy ß emitters incorporated in co-crystallised mannose and sucrose impart a dose to the matrix, in good agreement with the expected value when calibrated with soft X ray sources. Accuracy of a few per cent is attained using glutamine dosemeters in a series of mailed intercomparisons in the industrial radiation processing dose range, by use of a heat treatment at 114 oC for 5 hours. New LL phosphors, leucine and iso-leucine have similar hydrogen content to standard muscle and thus their neutron kerma are very close to those of ICRU muscle in the energy range from a few keV to 10 MeV. These phosphors are suitable for medical application particularly when used with sensitisers.

A Consistent Set of KERMA Values for H, C, N, and O for Neutrons of Energies from 10 to 80 MeV

A set of Kinetic Energy Released in Matter (KERMA) values for H, C, N, and O are presented based upon two sets of computer calculations. One set includes neutron energies from 20 to 80 MeV and uses the Intranuclear Cascade plus Evaporation (ICE) models. The second set includes neutron energies from 10 to 20 MeV and uses the Evaluated Nuclear Data File (ENDF/B-V) for particle species and numbers, with a modified Evaporation model for the particle energies. The 10- to 20-MeV ENDF calculations, which show good agreement with values calculated by Caswell and Coyne, were performed to allow normalization of the 20- to 80-MeV ICE calculations at 20 MeV. Values for ICRU muscle tissue and Shonka A-150 plastic are also included.

Lyoluminescence dosimetry in photon and fast neutron beams

The lyoluminescence (LL) technique using mannose, a monosaccharide, is described. Dose-response curves for 60Co gamma -rays (5 rad to 120 krad), fission neutrons, 5.3 MeV and 15 MeV neutrons (100 rad to 20 krad) have been measured. After correction for the gamma contamination of the neutron beam the LL signal per rad in ICRU muscle tissue from the neutron irradiations has been derived and the relative effectiveness of the LL signal for fast neutrons in mannose has been calculated as 0.34+or-0.03 (fission neutrons), 0.63+or-0.07 (5.3 MeV neutrons) and 0.74+or-0.05 (15 MeV neutrons). These results are compared with the data from other systems. It is concluded that mannose can be used as a transfer system in neutron dosimetry, if its variation in sensitivity with neutron energy is taken into account.

The response of thermoluminescent dosimetric lithiumborates equivalent to air, water and soft tissue and ofLiF TLD-100 to low energy x-rays

Calculations of response to mono-energetic photons show that lithiumborates containing 0, 0.1%, 0.25%, and 0.34% of Mn are equivalent to soft tissue(C5H40O18N), water, ICRU muscle, and air respectively. Results obtained withmonochromatic and broad-spectrum x-rays of effective energies between 12 and 115kev are in agreement with this finding. The monochromatic and broad-spectrumx-ray beams were also used to explore the discrepancies in response of LiF TLD-100to low energy photons. Only small discrepancies were found which were attributedeither to breadth of x-ray spectra or to additional absorbed dose due to scatteredx-rays amounting to 5% at 40 keveff.