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A S Murray - One of the best experts on this subject based on the ideXlab platform.

  • reliability of Equivalent Dose determination and age models in the osl dating of historical and modern palaeoflood sediments
    Quaternary Geochronology, 2014
    Co-Authors: Alicia Medialdea, A S Murray, Kristina Jorkov Thomsen, Gerardo Benito
    Abstract:

    Abstract The challenge of accurately estimating the deposition age of incompletely-bleached samples in luminescence dating has motivated developments in the analysis of single grain Dose distributions, and a number of statistical approaches have been proposed over the last few years. In this study, we compare the behaviour of the arithmetic average, so-called ‘robust statistics’, the Central Age Model (CAM), the Minimum Age Model (MAM) and the Internal–External Consistency Criterion (IEU) and lowest 5% method, when applied to single-grain Dose distributions from a sequence of eight recent (40–1000 years) flash-flood deposits. These sediments are expected to be incompletely bleached, but all have age control from historical records. Modifications were made to allow the use of the standard CAM and MAM models with Dose distributions containing near zero and negative Dose values. An assessment of minimum over-dispersion (OD) is based on Dose recovery tests based on gamma-irradiated samples. We then present a detailed analysis of the effect of an additional uncertainty added to the individual Dose estimates on the burial Dose estimates from the MAM and the IEU approach. The results of the various models are discussed in terms of the accuracy of the resulting age, and we conclude that, overall, the IEU approach generates the most accurate ages. We also demonstrate that accurate Doses can be obtained for those older samples for which uncertainties of ∼40 years are unimportant by applying the IEU model to small aliquot (∼30 grains) Dose distributions. From our study we conclude that these and similar young slack-water flood deposits can be accurately dated using quartz OSL, opening up the possibility of establishing time series of flood discharge in catchments for which no instrumental or historical record exists.

  • optically stimulated luminescence osl dating investigations of rock and underlying soil from three case studies
    Journal of Archaeological Science, 2007
    Co-Authors: A S Murray, A Vafiadou, Ioannis Liritzis
    Abstract:

    Abstract Three rock samples and associated underlying surface (floor) soils of geoarchaeological significance from Greece, Sweden and a modern surface stone-sample from a Danish site were investigated using OSL dating. Thin slice, sub-samples, from drilled core surfaces were prepared. A single-aliquot regenerative-Dose (SAR) protocol was used on whole rock slices to estimate the laboratory Equivalent Dose. Laboratory tests showed that the SAR protocol successfully corrected for sensitivity changes and that a known laboratory Dose could be measured accurately. The luminescence signals from quartz and feldspar stimulated by blue light and from feldspar under IR stimulation were employed in Equivalent Dose calculations. Only IR signals showed measurable fading on a laboratory timescale. Laboratory tests showed that daylight bleaching of the rock surfaces is rapid, and that the light-exposed region extended into the solid rock. The geoarchaeological ages obtained for the rocks and soils were in satisfactory agreement with independent age estimates.

  • a review of quartz optically stimulated luminescence characteristics and their relevance in single aliquot regeneration dating protocols
    Radiation Measurements, 2006
    Co-Authors: A G Wintle, A S Murray
    Abstract:

    Different single-aliquot regenerative-Dose (SAR) protocols have now been applied for some years to quartz grains for determining the Equivalent Dose, in both dating and retrospective dosimetry studies. This paper begins by laying out the basic principles of the SAR procedure on which the various SAR protocols are based. A general model is examined and three simple performance tests are laid out. Recent experimental characterisation of the optically stimulated luminescence signals from quartz grains is reviewed, giving particular regard to implications for SAR protocols. Various published SAR protocols are presented and discussed, particularly with regard to changes in experimental procedure and methods of data analysis in order to isolate the fast component of the OSL signal. It is concluded that the SAR procedure has proved to be a very powerful approach for determining the Equivalent Dose using quartz OSL signals dominated by the fast component. The presence of other components complicates the simplest protocols and further quantification of their behaviour is required.

  • Equivalent Dose estimation using a single aliquot of polymineral fine grains
    Radiation Measurements, 2001
    Co-Authors: D Banerjee, A S Murray, L Botterjensen, Andreas Lang
    Abstract:

    We have tested the suitability of a new single-aliquot regenerative-Dose protocol for estimating the Equivalent Dose (De) in polymineral fine grains extracted from colluvia from various sites in Germany. First, we report the behaviour of three OSL signals: (i) blue-stimulated, (ii) infrared-stimulated luminescence, and (iii) blue-stimulated luminescence following infrared (IR) stimulation, using a near-UV (290–380 nm) detection window in each case. For these three signals, there is a significant change in sensitivity with regeneration cycle; this change can be compensated for using the response to a fixed test Dose after each natural or regenerated measurement. The source of the three luminescence signals is then investigated using pulse-anneal and elevated-temperature experiments. Fading tests on laboratory-induced signals show that although the IR signals fade by up to 23% in 15 days at 100°C, the post-IR blue signals are stable. The preheat dependence of estimates of De obtained using fine grains is presented for the first time, for both blue- and IR-derived signals. Our results are compared with De estimates derived from multiple-aliquot additive-Dose IR luminescence data, obtained using a blue detection window, and also with expected values of De based on independent age estimates and measured Dose rates. We conclude that post-IR blue-stimulated luminescence provides reliable estimates of De, and that these are probably superior to the IRSL estimates obtained using both near-UV and blue detection windows.

  • optical dating of single sand sized grains of quartz sources of variability
    Radiation Measurements, 2000
    Co-Authors: G A T Duller, L Botterjensen, A S Murray
    Abstract:

    Optically stimulated luminescence (OSL) measurements have been made of over 3000 sand-sized grains of quartz. Analysis at this scale highlights the variability in the luminescence sensitivity and the Dose saturation characteristics of individual quartz grains. Using a new instrument capable of measuring single grains it is feasible to routinely measure the Equivalent Dose from many hundreds of grains from each sample. Analysis of such datasets requires assessment of the uncertainties on each Equivalent Dose since these may vary significantly. This paper assesses the significance of signal intensity, Dose saturation characteristics and instrument uncertainty in Equivalent Dose calculation.

David Raben - One of the best experts on this subject based on the ideXlab platform.

  • stereotactic body radiation therapy for melanoma and renal cell carcinoma impact of single fraction Equivalent Dose on local control
    Radiation Oncology, 2011
    Co-Authors: Michelle A Stinauer, Tracey E Schefter, Brian D Kavanagh, Rene Gonzalez, Thomas W Flaig, Karl D Lewis, William A Robinson, Mark Chidel, Michael Glode, David Raben
    Abstract:

    Melanoma and renal cell carcinoma (RCC) are traditionally considered less radioresponsive than other histologies. Whereas stereotactic body radiation therapy (SBRT) involves radiation Dose intensification via escalation, we hypothesize SBRT might result in similar high local control rates as previously published on metastases of varying histologies. The records of patients with metastatic melanoma (n = 17 patients, 28 lesions) or RCC (n = 13 patients, 25 lesions) treated with SBRT were reviewed. Local control (LC) was defined pathologically by negative biopsy or radiographically by lack of tumor enlargement on CT or stable/declining standardized uptake value (SUV) on PET scan. The SBRT Dose regimen was converted to the single fraction Equivalent Dose (SFED) to characterize the Dose-control relationship using a logistic tumor control probability (TCP) model. Additionally, the kinetics of decline in maximum SUV (SUVmax) were analyzed. The SBRT regimen was 40-50 Gy/5 fractions (n = 23) or 42-60 Gy/3 fractions (n = 30) delivered to lung (n = 39), liver (n = 11) and bone (n = 3) metastases. Median follow-up for patients alive at the time of analysis was 28.0 months (range, 4-68). The actuarial LC was 88% at 18 months. On univariate analysis, higher Dose per fraction (p < 0.01) and higher SFED (p = 0.06) were correlated with better LC, as was the biologic effective Dose (BED, p < 0.05). The actuarial rate of LC at 24 months was 100% for SFED ≥45 Gy v 54% for SFED <45 Gy. TCP modeling indicated that to achieve ≥90% 2 yr LC in a 3 fraction regimen, a prescription Dose of at least 48 Gy is required. In 9 patients followed with PET scans, the mean pre-SBRT SUVmax was 7.9 and declined with an estimated half-life of 3.8 months to a post-treatment plateau of approximately 3. An aggressive SBRT regimen with SFED ≥ 45 Gy is effective for controlling metastatic melanoma and RCC. The SFED metric appeared to be as robust as the BED in characterizing Dose-response, though additional studies are needed. The LC rates achieved are comparable to those obtained with SBRT for other histologies, suggesting a dominant mechanism of in vivo tumor ablation that overrides intrinsic differences in cellular radiosensitivity between histologic subtypes.

  • stereotactic body radiation therapy for melanoma and renal cell carcinoma impact of single fraction Equivalent Dose on local control
    Radiation Oncology, 2011
    Co-Authors: Michelle A Stinauer, Tracey E Schefter, Brian D Kavanagh, Thomas W Flaig, Karl D Lewis, William A Robinson, Mark Chidel, Michael Glode, Ricardo J Gonzalez, David Raben
    Abstract:

    Background: Melanoma and renal cell carcinoma (RCC) are traditionally considered less radioresponsive than other histologies. Whereas stereotactic body radiation therapy (SBRT) involves radiation Dose intensification via escalation, we hypothesize SBRT might result in similar high local control rates as previously published on metastases of varying histologies. Methods: The records of patients with metastatic melanoma (n = 17 patients, 28 lesions) or RCC (n = 13 patients, 25 lesions) treated with SBRT were reviewed. Local control (LC) was defined pathologically by negative biopsy or radiographically by lack of tumor enlargement on CT or stable/declining standardized uptake value (SUV) on PET scan. The SBRT Dose regimen was converted to the single fraction Equivalent Dose (SFED) to characterize the Dosecontrol relationship using a logistic tumor control probability (TCP) model. Additionally, the kinetics of decline in maximum SUV (SUVmax) were analyzed. Results: The SBRT regimen was 40-50 Gy/5 fractions (n = 23) or 42-60 Gy/3 fractions (n = 30) delivered to lung (n = 39), liver (n = 11) and bone (n = 3) metastases. Median follow-up for patients alive at the time of analysis was 28.0 months (range, 4-68). The actuarial LC was 88% at 18 months. On univariate analysis, higher Dose per fraction (p < 0.01) and higher SFED (p = 0.06) were correlated with better LC, as was the biologic effective Dose (BED, p < 0.05). The actuarial rate of LC at 24 months was 100% for SFED ≥45 Gy v 54% for SFED <45 Gy. TCP modeling indicated that to achieve ≥90% 2 yr LC in a 3 fraction regimen, a prescription Dose of at least 48 Gy is required. In 9 patients followed with PET scans, the mean pre-SBRT SUVmax was 7.9 and declined with an estimated half-life of 3.8 months to a post-treatment plateau of approximately 3. Conclusions: An aggressive SBRT regimen with SFED ≥ 45 Gy is effective for controlling metastatic melanoma and RCC. The SFED metric appeared to be as robust as the BED in characterizing Dose-response, though additional studies are needed. The LC rates achieved are comparable to those obtained with SBRT for other histologies, suggesting a dominant mechanism of in vivo tumor ablation that overrides intrinsic differences in cellular radiosensitivity between histologic subtypes.

Wayne D Newhauser - One of the best experts on this subject based on the ideXlab platform.

  • implementation of an analytical model for leakage neutron Equivalent Dose in a proton radiotherapy planning system
    Cancers, 2015
    Co-Authors: Kenneth Homann, Rebecca Maureen Howell, Christopher W Schneider, Jl Eley, Wayne D Newhauser, Marco Durante
    Abstract:

    Equivalent Dose from neutrons produced during proton radiotherapy increases the predicted risk of radiogenic late effects. However, out-of-field neutron Dose is not taken into account by commercial proton radiotherapy treatment planning systems. The purpose of this study was to demonstrate the feasibility of implementing an analytical model to calculate leakage neutron Equivalent Dose in a treatment planning system. Passive scattering proton treatment plans were created for a water phantom and for a patient. For both the phantom and patient, the neutron Equivalent Doses were small but non-negligible and extended far beyond the therapeutic field. The time required for neutron Equivalent Dose calculation was 1.6 times longer than that required for proton Dose calculation, with a total calculation time of less than 1 h on one processor for both treatment plans. Our results demonstrate that it is feasible to predict neutron Equivalent Dose distributions using an analytical Dose algorithm for individual patients with irregular surfaces and internal tissue heterogeneities. Eventually, personalized estimates of neutron Equivalent Dose to organs far from the treatment field may guide clinicians to create treatment plans that reduce the risk of late effects.

  • An Analytical Model of Leakage Neutron Equivalent Dose for Passively-Scattered Proton Radiotherapy and Validation with Measurements
    MDPI AG, 2015
    Co-Authors: Christopher Schneider, Wayne D Newhauser, Jad Farah
    Abstract:

    Exposure to stray neutrons increases the risk of second cancer development after proton therapy. Previously reported analytical models of this exposure were difficult to configure and had not been investigated below 100 MeV proton energy. The purposes of this study were to test an analytical model of neutron Equivalent Dose per therapeutic absorbed Dose  at 75 MeV and to improve the model by reducing the number of configuration parameters and making it continuous in proton energy from 100 to 250 MeV. To develop the analytical model, we used previously published H/D values in water from Monte Carlo simulations of a general-purpose beamline for proton energies from 100 to 250 MeV. We also configured and tested the model on in-air neutron Equivalent Doses measured for a 75 MeV ocular beamline. Predicted H/D values from the analytical model and Monte Carlo agreed well from 100 to 250 MeV (10% average difference). Predicted H/D values from the analytical model also agreed well with measurements at 75 MeV (15% average difference). The results indicate that analytical models can give fast, reliable calculations of neutron exposure after proton therapy. This ability is absent in treatment planning systems but vital to second cancer risk estimation

  • Equivalent Dose and effective Dose from stray radiation during passively scattered proton radiotherapy for prostate cancer
    Physics in Medicine and Biology, 2008
    Co-Authors: Wayne D Newhauser, Jonas D Fontenot, Phillip J Taddei, Y Zheng, Dragan Mirkovic, Thomas Jordan
    Abstract:

    Proton therapy reduces the integral therapeutic Dose required for local control in prostate patients compared to intensity-modulated radiotherapy. One proposed benefit of this reduction is an associated decrease in the incidence of radiogenic secondary cancers. However, patients are also exposed to stray radiation during the course of treatment. The purpose of this study was to quantify the stray radiation Dose received by patients during proton therapy for prostate cancer. Using a Monte Carlo model of a proton therapy nozzle and a computerized anthropomorphic phantom, we determined that the effective Dose from stray radiation per therapeutic Dose (E/D) for a typical prostate patient was approximately 5.5 mSv Gy−1. Sensitivity analysis revealed that E/D varied by ±30% over the interval of treatment parameter values used for proton therapy of the prostate. Equivalent Doses per therapeutic Dose (HT/D) in specific organs at risk were found to decrease with distance from the isocenter, with a maximum of 12 mSv Gy−1 in the organ closest to the treatment volume (bladder) and 1.9 mSv Gy−1 in the furthest (esophagus). Neutrons created in the nozzle predominated effective Dose, though neutrons created in the patient contributed substantially to the Equivalent Dose in organs near the proton field. Photons contributed less than 15% to Equivalent Doses.

Michelle A Stinauer - One of the best experts on this subject based on the ideXlab platform.

  • stereotactic body radiation therapy for melanoma and renal cell carcinoma impact of single fraction Equivalent Dose on local control
    Radiation Oncology, 2011
    Co-Authors: Michelle A Stinauer, Tracey E Schefter, Brian D Kavanagh, Rene Gonzalez, Thomas W Flaig, Karl D Lewis, William A Robinson, Mark Chidel, Michael Glode, David Raben
    Abstract:

    Melanoma and renal cell carcinoma (RCC) are traditionally considered less radioresponsive than other histologies. Whereas stereotactic body radiation therapy (SBRT) involves radiation Dose intensification via escalation, we hypothesize SBRT might result in similar high local control rates as previously published on metastases of varying histologies. The records of patients with metastatic melanoma (n = 17 patients, 28 lesions) or RCC (n = 13 patients, 25 lesions) treated with SBRT were reviewed. Local control (LC) was defined pathologically by negative biopsy or radiographically by lack of tumor enlargement on CT or stable/declining standardized uptake value (SUV) on PET scan. The SBRT Dose regimen was converted to the single fraction Equivalent Dose (SFED) to characterize the Dose-control relationship using a logistic tumor control probability (TCP) model. Additionally, the kinetics of decline in maximum SUV (SUVmax) were analyzed. The SBRT regimen was 40-50 Gy/5 fractions (n = 23) or 42-60 Gy/3 fractions (n = 30) delivered to lung (n = 39), liver (n = 11) and bone (n = 3) metastases. Median follow-up for patients alive at the time of analysis was 28.0 months (range, 4-68). The actuarial LC was 88% at 18 months. On univariate analysis, higher Dose per fraction (p < 0.01) and higher SFED (p = 0.06) were correlated with better LC, as was the biologic effective Dose (BED, p < 0.05). The actuarial rate of LC at 24 months was 100% for SFED ≥45 Gy v 54% for SFED <45 Gy. TCP modeling indicated that to achieve ≥90% 2 yr LC in a 3 fraction regimen, a prescription Dose of at least 48 Gy is required. In 9 patients followed with PET scans, the mean pre-SBRT SUVmax was 7.9 and declined with an estimated half-life of 3.8 months to a post-treatment plateau of approximately 3. An aggressive SBRT regimen with SFED ≥ 45 Gy is effective for controlling metastatic melanoma and RCC. The SFED metric appeared to be as robust as the BED in characterizing Dose-response, though additional studies are needed. The LC rates achieved are comparable to those obtained with SBRT for other histologies, suggesting a dominant mechanism of in vivo tumor ablation that overrides intrinsic differences in cellular radiosensitivity between histologic subtypes.

  • stereotactic body radiation therapy for melanoma and renal cell carcinoma impact of single fraction Equivalent Dose on local control
    Radiation Oncology, 2011
    Co-Authors: Michelle A Stinauer, Tracey E Schefter, Brian D Kavanagh, Thomas W Flaig, Karl D Lewis, William A Robinson, Mark Chidel, Michael Glode, Ricardo J Gonzalez, David Raben
    Abstract:

    Background: Melanoma and renal cell carcinoma (RCC) are traditionally considered less radioresponsive than other histologies. Whereas stereotactic body radiation therapy (SBRT) involves radiation Dose intensification via escalation, we hypothesize SBRT might result in similar high local control rates as previously published on metastases of varying histologies. Methods: The records of patients with metastatic melanoma (n = 17 patients, 28 lesions) or RCC (n = 13 patients, 25 lesions) treated with SBRT were reviewed. Local control (LC) was defined pathologically by negative biopsy or radiographically by lack of tumor enlargement on CT or stable/declining standardized uptake value (SUV) on PET scan. The SBRT Dose regimen was converted to the single fraction Equivalent Dose (SFED) to characterize the Dosecontrol relationship using a logistic tumor control probability (TCP) model. Additionally, the kinetics of decline in maximum SUV (SUVmax) were analyzed. Results: The SBRT regimen was 40-50 Gy/5 fractions (n = 23) or 42-60 Gy/3 fractions (n = 30) delivered to lung (n = 39), liver (n = 11) and bone (n = 3) metastases. Median follow-up for patients alive at the time of analysis was 28.0 months (range, 4-68). The actuarial LC was 88% at 18 months. On univariate analysis, higher Dose per fraction (p < 0.01) and higher SFED (p = 0.06) were correlated with better LC, as was the biologic effective Dose (BED, p < 0.05). The actuarial rate of LC at 24 months was 100% for SFED ≥45 Gy v 54% for SFED <45 Gy. TCP modeling indicated that to achieve ≥90% 2 yr LC in a 3 fraction regimen, a prescription Dose of at least 48 Gy is required. In 9 patients followed with PET scans, the mean pre-SBRT SUVmax was 7.9 and declined with an estimated half-life of 3.8 months to a post-treatment plateau of approximately 3. Conclusions: An aggressive SBRT regimen with SFED ≥ 45 Gy is effective for controlling metastatic melanoma and RCC. The SFED metric appeared to be as robust as the BED in characterizing Dose-response, though additional studies are needed. The LC rates achieved are comparable to those obtained with SBRT for other histologies, suggesting a dominant mechanism of in vivo tumor ablation that overrides intrinsic differences in cellular radiosensitivity between histologic subtypes.

Richard G Roberts - One of the best experts on this subject based on the ideXlab platform.

  • statistical aspects of Equivalent Dose and error calculation and display in osl dating an overview and some recommendations
    Quaternary Geochronology, 2012
    Co-Authors: R F Galbraith, Richard G Roberts
    Abstract:

    All Quaternary dating methods involve the measurement of one or more variables to estimate the age of a sample. Each measured quantity has an associated error and uncertainty, and may also be subject to natural variation. We review the statistical estimation of such uncertainties and variation for comparing and interpreting age estimates, with specific reference to the estimation of Equivalent Dose (De) values in the optically stimulated luminescence (OSL) dating of sediments. We discuss statistical aspects of OSL signal and background estimation, the determination of De values for multi-grain aliquots and individual mineral grains from the same and different samples, and the extent of variation commonly observed among such estimates. Examples are drawn from geological and archaeological contexts. We discuss the strengths and weaknesses of various graphical methods of displaying multiple, independent estimates of De, along with statistical tests and models to compare and appropriately combine them. Many of our recommendations are applicable also to the clear presentation of data obtained using other Quaternary dating methods. We encourage the use of models and methods that are based on well established statistical principles and, ideally, are validated by appropriate numerical simulations; and we discourage the adoption of ad hoc methods developed using a particular set of measurement conditions and tested on a limited number of samples, as these may not be applicable more generally. We emphasise that the choice of statistical models should not be made solely on statistical grounds (or arbitrary rules) but should take into account the broader scientific context of each sample and any additional pertinent information.

  • measurement of the Equivalent Dose in quartz using a regenerative Dose single aliquot protocol
    Radiation Measurements, 1998
    Co-Authors: A S Murray, Richard G Roberts
    Abstract:

    Abstract The principles behind a regenerative-Dose single-aliquot protocol are outlined. It is shown for three laboratory-bleached Australian sedimentary quartz samples that the relative change in sensitivity of the optically stimulated luminescence (OSL) during a repeated measurement cycle (consisting of a Dose followed by a 10 s preheat at a given temperature and then a 100 s exposure to blue/green light at 125°C) is very similar to that of the 110°C thermoluminescence (TL) peak measured during the preheat cycle. The absolute change in the TL sensitivity with preheat temperature is different for samples containing a natural or a regenerative Dose. Furthermore, the absolute change in sensitivity in both the OSL and TL signals is non-linear with regeneration cycle, but the relative change in the OSL signal compared to the following 110°C TL measurement is well approximated by a straight line. Both signals are thought to use the same luminescence centres, and so some common behaviour is not unexpected. A new regenerative-Dose protocol is presented which makes use of this linear relationship to correct for sensitivity changes with regeneration cycle, and requires only one aliquot for the estimation of the Equivalent Dose (D e ). The protocol has been applied to quartz from nine Australian sites. To illustrate the value of the regenerative-Dose single-aliquot approach, the apparent values of D e for 13 samples, containing Doses of between 0.01 and 100 Gy, have been measured at various preheat temperatures of between 160 and 300°C, using a single aliquot for each D e measurement. Excellent agreement is found between these single-aliquot estimates of D e and those obtained from additive-Dose multiple-aliquot and single-aliquot protocols, over the entire Dose range.