• Energy Research

Purpose: While a commonly-used dosimeter in radiotherapy, the use of radiochromic films in particle therapy is limited due to their strong dependence on beam quality. In the case of protons, previous research has reported an underresponse of EBT3 films of up to 20% around the Bragg-peak, which has largely been associated with the linear energy transfer (LET). The main focus of this work lies on the investigation of beam quality to quantify and correct for the under-response of EBT3 films. Since exact measurements are necessary, additionally film analysis is reviewed in terms of the analytical relation between optical density (OD) and dose, the time-dependence of calibrations, and different readout methods of the scanned film image, with the aims of mitigating systematic errors and reducing statistical uncertainties. Methods: Measurements of single energy beams of 62.4, 148.2 and 252.7MeV and spread-out bragg peaks (SOBPs) were performed at the treatment and research facility MedAustron (Wiener Neustadt, Austria) in a water phantom, using EBT3 radiochromic films and an ionization chamber (Roos chamber) as validation. These experiments were accompanied by Monte-Carlo simulations using GATE v8.0, in order to infer LET and spectral information. Corrections were derived by fitting the acquired relative effectiveness (RE) of the films to the dose averaged LET, and by optimizing a weighting function over the LET spectra at points of different RE. Results: Performing the film readout using the single red channel displayed a measurement uncertainty ranging from 13% to 2.6% for doses of 0.25 to 2.5Gy, compared to higher values using the dual or triple channel readout method. Between 0.5 and 2.5Gy all examined calibration functions exhibited residuals below 2%. Calibrations with a separation of approximately half a year showed deviations in the order of 10% around 0.5Gy between each other. EBT3 films displayed an under-response of up to 30% at the Bragg peak and the modulated peak of the SOBPs at the lowest beam energies used. A functional relationship between relative effectiveness and fluence averaged LET could not be confirmed, while it was possible to describe the quenching as a function of the dose averaged LET of protons, within the confidence interval. Applying a parametrized arcustangens function of dose averaged LET to the nominal dose, agreed within 6% with the smoothed uncorrected film dose. Optimization of weights over the LET spectrum at different RE yielded a nonlinear dependence of the RE over the LET spectrum. Conclusion: For the dose range examined, single channel read out of the red channel was found to yield the most accurate results. While differences in choice of calibration function were negligible, performing the film calibration within measurement session was shown to have a large effect on accuracy. The film quenching was found to be a nonlinear function of LET, and dose averaged LET of protons, while fluence averaging was found to be conceptually limited. An online function of dose averaged LET, a parametrized arcustangens, yielded the most accurate and robust correction of the film dose under-response. The spectral correction was more susceptible to measurement and simulation inaccuracies, compared to the averaged LET approaches. Due to the high measurement uncertainties associated with steep dose gradients, the presented corrections are only valid up to approximately R80 (depth at which the dose has decreased to 80% of the maximum) and the dose fall-off, for the single energy beams and SOBPs, respectively. For more exact corrections, film dosimetry needs to be improved in terms of accuracy and precision.

"NAA-SR-6845 ; Chemistry." ; "Contract AT(11-1)-GEN-8 ; Issued: Apr 15 1962." ; Includes bibliographical references (p. 19-20). ; Mode of access: Internet.

From introduction: This report reviews the Susie program (particularly reactor dosimetry and data analysis) as well as other items that represent a smaller share of the total effort.

It is important in most radiation experiments to have both a quantitative measure of the amount of radiation involved, and a qualitative description of the radiation which uniquely defines its significant properties. The required quantitative measure is the absorbed dose, which is the amount of energy absorbed per unit mass of the irradiated material. This can be expressed in rads (1 rad = 100 ergs/gm.). The most pertinent qualitative description is that of the spatial distribution of the collisions by which the electrons (or other ionizing and exciting particles) which are responsible for the actual energy dissipation lose their energy. This concept has been termed “linear energy transfer” (LET) and is defined in terms of the energy lost per unit path length by the particle (1, p. 6). The LET is usually written as a function, L(T), of the kinetic energy, T, of the particle and is conveniently expressed in units of kev/µ where µ is 1 micron of path length. The significant information concerning the distri...

The LET-energy dissipation spectrum and mean LET of a 14 MeV monoenergetic electron beam has been calculated using a method proposed by Burch, and the importance of δ-electrons in such calculations is discussed. The mean LET of the beam is equal to the instantaneous LET of a 15 KeV electron; its variation with depth in a water phantom is negligible over the first few centimetres. The biological effectiveness of such electrons should not differ significantly from that of 60Co γ-rays. A short discussion of some calculations for high energy ion beams is also given.

In assessing the astronaut's exposure from galactic cosmic rays on space missions of long duration conversion of absorbed doses to dose equivalents is required. Since a large part of the dose contribution from heavy primaries is produced at Linear Energy Transfer (LET) values beyond the range for which radiobiological data are available, it seems preferable to analyze the LET distributions themselves and to compare them to standard x-rays rather than to assume arbitrary values for the Relative Biological Effectiveness(RBE). The local LET distributions in tissue are found to be extremely skewed, with a large maximum at the relativistic minimum LET. Lined up on the LET scale, they cover the very wide interval from 0.18 to 2790 kev/micron T as compared to an interval from 0.4 to 35 kev/micron T for standard x-rays. Applying the RBE formula of the RBE Committee of the ICRP and a saturation value of 10 leads to a grand mean RBE of 1.82 for the total absorbed dose of 13 millirads/24 hours from primaries. (Author). ; "This research was conducted under the sponsorship of the Office of Advanced Research and Technology, National Aeronautics and Space Administration."--title page. ; "Bureau of Medicine and Surgery, MF022.03-5001.37, NASA Order R-75."--title page. ; Joint report of the United States Naval Aerospace Medical Institute and the National Aeronautics and Space Administration.--cover. ; "9 December 1966." ; Includes bibliographical references (pages 13-14) ; In assessing the astronaut's exposure from galactic cosmic rays on space missions of long duration conversion of absorbed doses to dose equivalents is required. Since a large part of the dose contribution from heavy primaries is produced at Linear Energy Transfer (LET) values beyond the range for which radiobiological data are available, it seems preferable to analyze the LET distributions themselves and to compare them to standard x-rays rather than to assume arbitrary values for the Relative Biological Effectiveness(RBE). The local LET distributions in tissue are found to be extremely skewed, with a large maximum at the relativistic minimum LET. Lined up on the LET scale, they cover the very wide interval from 0.18 to 2790 kev/micron T as compared to an interval from 0.4 to 35 kev/micron T for standard x-rays. Applying the RBE formula of the RBE Committee of the ICRP and a saturation value of 10 leads to a grand mean RBE of 1.82 for the total absorbed dose of 13 millirads/24 hours from primaries. (Author). ; Mode of access: Internet.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Nuclear Science and Engineering, 2008. ; "June 2008." ; Includes bibliographical references (leaves 133-140). ; In the past fifteen years, evidence provided by many independent research groups have indicated higher numbers of cells exhibiting damage than expected based on the number of cells traversed by the radiation. This phenomenon has been coined as the "bystander effect". The purpose of this study was to characterize the ability of irradiated tumor cells to induce bystander effects in co-cultured cells. Human DU-145 prostate carcinoma cells were grown on a 1.4 [mu]m-thick mylar membrane in specially constructed cell culture dishes for irradiation with alpha particles (average energy 3.14 MeV) from a 241Am source, or in 6-well plates for irradiation with 250 kVp x-rays at 25°C. In parallel experiments, the tumor cells were incubated at 4°C for one hour prior to irradiation and irradiated on ice to test the nature of the bystander signal. Bystander cells were placed into the medium above the irradiated DU-145 and were co-incubated for a length of time. The bystander effect endpoints measured in either DU-145 tumor cells or in normal primary AGO1522 fibroblasts were micronucleus (MN) formation, [gamma]-H2AX double strand break repair foci, and survival fraction. A 1.5-2.0-fold increase in MN formation was observed in both DU-145 and AG01522 bystander cells after either alpha particle or xray irradiation of the DU-145 target cells. A 1.5-fold [gamma]-H2AX bystander increase and a survival fraction reduction to 80% were only detected in AGO1522 cells, and only after xray irradiation of target DU-145 cells. Alpha particle irradiation of the target DU-145 cells produced neither [gamma]-H2AX foci nor survival fraction bystander effect in either cell line. Lowering the temperature to 4°C during the irradiation of the DU-145 tumor cells, with either x-rays or alpha particles, eliminated both the MN formation and the decreased survival fraction bystander ...

CIES2020: As Energias Renováveis na Transição Energética: Livro de Comunicações do XVII Congresso Ibérico e XIII Congresso Ibero-americano de Energia Solar. Helder Gonçalves, Manuel Romero (Ed.). Lisboa, Portugal: LNEG, 3-5 Novembro, 2020, p. 349-356. ISBN: 978-989-675-076-3