Tissue Dose Rate Research Articles

Two-dimensional oxygen-diffusion modelling for FLASH proton therapy with pencil beam scanning—Impact of diffusive tissue properties, dose, dose rate and scan patterns

Objective. Oxygen depletion is generally believed to play an important role in the FLASH effect—a differential reduction of the radiosensitivity of healthy tissues, relative to that of the tumour under ultra-high dose-rate (UHDR) irradiation conditions. In proton therapy (PT) with pencil-beam scanning (PBS), the deposition of dose, and, hence, the degree of (radiolytic) oxygen depletion varies both spatially and temporally. Therefore, the resulting oxygen concentration and the healthy-tissue sparing effect through radiation-induced hypoxia varies both spatially and temporally as well. Approach. We propose and numerically solve a physical oxygen diffusion model to study these effects and their dependence on tissue parameters and the scan pattern in pencil-beam delivery. Since current clinical FLASH PT (FLASH-PT) is based on 250 MeV shoot-through (transmission) beams, for which dose and dose rate (DR) hardly vary with depth compared to the variation transverse to the beam axis, we focus on the two-dimensional case. We numerically integrate the model to obtain the oxygen concentration in each voxel as a function of time and extract voxel-based and spatially and temporarily integrated metrics for oxygen (FLASH) enhanced dose. Furthermore, we evaluate the impact on oxygen enhancement of standard pencil-beam delivery patterns and patterns that were optimised on dose-rate. Our model can contribute to the identification of tissue properties and pencil-beam delivery parameters that are critical for FLASH-PT and it may be used for the optimisation of FLASH-PT treatment plans and their delivery. Main results. (i) the diffusive properties of oxygen are critical for the steady state concentration and therefore the FLASH effect, even more so in two dimensions when compared to one dimension. (ii) The FLASH effect through oxygen depletion depends primarily on dose and less on other parameters. (iii) At a fixed fraction dose there is a slight dependence on DR. (iv) Scan patterns optimised on DR slightly increase the oxygen induced FLASH effect. Significance. To our best knowledge, this is the first study assessing the impact of scan-pattern optimization (SPO) in FLASH-PT with PBS on a biological FLASH model. While the observed impact of SPO is relatively small, a larger effect is expected for larger target volumes. A better understanding of the FLASH effect and the role of oxygen (depletion) therein is essential for the further development of FLASH-PT with PBS, and SPO.

RETRACTED: Surface dose rate variations in planar and curved geometries of 106Ru/106Rh plaque sources for ocular tumors

Investigation of surface dose rate variation with respect to the source configuration of 106Ru/106Rh eye plaque. To explore an alternate way to determine activity of brachytherapy plaques.The surface dose rates of 106Ru/106Rh plaque developed indigenously were measured by extrapolation chamber. To rule out possibility of any error in the activity distribution and quantity, same source was used in two different configurations namely planar and curved. EBT3 Gafchromic film was used for determination of uniformity in activity. Monte Carlo-based Codes EGSnrc and FLUKA were used to calculate dose rate in tissue, percentage depth dose and for determination of activity. Parameters and correction factors were estimated using simulations.The measured reference absorbed dose rates for planar and curved 106Ru/106Rh eye plaques are found to be 589 ± 29 mGy/h and 560 ± 28 mGy/h, respectively. The difference in the reference absorbed dose rate of curved eye plaque is about ~5% as compared to planar configuration. The FLUKA-calculated dose values are almost independent of cavity length of the extrapolation chamber for both eye plaques. The FLUKA-based dose rates per μCi 106Ru/106Rh are about 17.28 ± 0.08 mGy/h and 16.48 ± 0.06 mGy/h, respectively for planar and curved eye plaques which match well with the measurements. The calculated activities for planar and curved eye plaques are 34.08 μCi and 33.98 μCi, respectively.Surface dose rates for a prototype 106Ru/106Rh eye plaque with different configurations were estimated using simulations and measured experimentally. An alternate way to determine activity of beta-gamma brachytherapy plaque has been proposed.

Modelling the absorbed dose rate of the beta standard BSS2 147Pm source

The dosimetric measurements of 147Pm beta radiation beams have limitations due to their low energy, low dose rate, great dispersion and attenuation in air or tissue. In this work, the Monte Carlo model was developed for a 147Pm absorbed dose rate determination. This model consists of an extrapolation chamber and a 147Pm beta radiation source. Moreover, the absorbed dose rate was determined by experimental measurements and the MCNP Monte Carlo code was used. The relative number of particles that crossed the radioactive source window and the particles that crossed the extrapolation chamber entrance window were determined. The source fluence spectrum was also determined. The results of the simulation and the experimental calculations are in agreement with the absorbed dose rate from the PTB calibration certificate. The results obtained are considered acceptable, and they agree within the uncertainties. The difference between the experimental result and that from the Monte Carlo model, compared to that from the calibration certificate, was only 0.8% in both cases.

Variance reduction technique in a beta radiation beam using an extrapolation chamber

This paper aims to show how the variance reduction technique “Geometry splitting/Russian roulette” improves the statistical error and reduces uncertainties in the determination of the absorbed dose rate in tissue using an extrapolation chamber for beta radiation. The results show that the use of this technique can increase the number of events in the chamber cavity leading to a closer approximation of simulation result with the physical problem. There was a good agreement among the experimental measurements, the certificate of manufacture and the simulation results of the absorbed dose rate values and uncertainties. The absorbed dose rate variation coefficient using the variance reduction technique “Geometry splitting/Russian roulette” was 2.85%.

Datation par les méthodes ESR/U-Th combinées de sites du Pléistocène supérieur : méthodologie et application en contexte karstique

Combined ESR/U-Th methods were principally used to date fossil teeth from Lower and Middle Pleistocene deposits. For samples of such ages, methodological issues are focusing on the determination of the equivalent dose and the modelling of uranium uptake. For Upper Pleistocene sites located in karstic settings, the application of ESR/U-Th is usually constrained by the measurement of a low equivalent dose, which is correlated to a low uranium content in the dental tissues. The use of Inductively Coupled Plasma-Mass Spectrometry (ICP-MS) for the measurement of U-content and isotopic ratios (234U/238U and 230Th/234U) is necessary to determine the dental tissue dose rates. Ages thus primarily depend on the gamma dose rate, and sometimes even on the cosmic dose rate as well, which can make up to 40% of the annual dose in very low dose rate contexts. In that case, in situ measurements, using dosimeters and/or field gamma-ray spectrometer, and 3D modelling of the cosmic dose received by the sample are essential for an accurate estimation of the annual dose and the age calculation. The application of ESR/U-Th requires both field and laboratory measurements, and should not be undertaken without a good knowledge of the sample origin and its geological context. Moreover, the time range of applicability of ESR/U-Th (between around 2 Ma and 30 ka) and Radiocarbon (which reaches its limits around 45–50ka) overlap for about 15–20ka. This allows the comparison of results obtained by these two methods for the same context in order to obtain a more precise chronological framework for Upper Pleistocene sites.

APMP supplementary comparison report of absorbed dose rate in tissue for beta radiation (BIPM KCDB: APMP.RI(I)-S2)

The supplementary comparison of absorbed dose rate in tissue for beta radiation (APMP.RI(I)-S2) was performed with five national metrology institutes in 2013 and 2014. Two commercial thin window ionization chambers were used as transfer instruments and circulated among the participants. Two of the NMIs measured the calibration coefficients of the chambers in reference fields produced from Pm-147, Kr-85 and Sr-90/Y-90, while the other three measured those only in Sr-90/Y-90 beta-particle field. The degree of equivalence for the participants was determined and this comparison verifies the calibration capabilities of the participating laboratories. In addition, most of the results of this comparison are consistent with another international comparison (EUROMET.RI(I)-S2) reported before this work.Main textTo reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/.The final report has been peer-reviewed and approved for publication by the CCRI, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

SU‐F‐T‐669: Commissioning of An Electronic Brachytherapy System for Targeted Mouse Irradiation

Purpose:The aim of this study was to commission the Xoft Axxent™ electronic brachytherapy (eBT) source and 10 mm diameter surface applicator with NIST traceability for targeted irradiations of mouse anal carcinomas.Methods:The Xoft Axxent™ electronic brachytherapy (eBT) and 10 mm diameter surface applicator was chosen by the collaborating physician as a radiation delivery mechanism for mouse anal carcinomas. The target dose was 2 Gy at a depth of 3 mm in tissue to be delivered in a single fraction. To implement an accurate and reliable irradiation plan, the system was commissioned by first determining the eBT source output and corresponding dose rate at a depth of 3 mm in tissue. This was determined through parallel‐plate ion chamber measurements and published conversion factors. Well‐type ionization chamber measurements were used to determine a transfer coefficient, which correlates the measured dose rate at 3 mm to the NIST‐traceable quantity, air‐kerma rate at 50 cm in air, for eBT sources. By correlating these two quantities, daily monitoring in the well chamber becomes an accurate and efficient quality assurance technique. Once the dose‐rate was determined, a treatment recipe was developed and confirmed with chamber measurements to deliver the requested dose. Radiochromic film was used to verify the dose distribution across the field.Results:Dose rates at 3 mm depth in tissue were determined for two different Xoft Axxent™ sources and correlated with NIST‐traceable well‐type ionization chamber measurements. Unique transfer coefficients were determined for each source and the treatment recipe was validated by measurements. Film profiles showed a uniform dose distribution across the field.Conclusion:A Xoft Axxent™ eBT system was successfully commissioned for use in the irradiation of mouse rectal tumors. Dose rates in tissue were determined as well as other pertinent parameters to ensure accurate delivery of dose to the target region.

Effects of Charged Particles on Human Tumor Cells.

The use of charged particle therapy in cancer treatment is growing rapidly, in large part because the exquisite dose localization of charged particles allows for higher radiation doses to be given to tumor tissue while normal tissues are exposed to lower doses and decreased volumes of normal tissues are irradiated. In addition, charged particles heavier than protons have substantial potential clinical advantages because of their additional biological effects, including greater cell killing effectiveness, decreased radiation resistance of hypoxic cells in tumors, and reduced cell cycle dependence of radiation response. These biological advantages depend on many factors, such as endpoint, cell or tissue type, dose, dose rate or fractionation, charged particle type and energy, and oxygen concentration. This review summarizes the unique biological advantages of charged particle therapy and highlights recent research and areas of particular research needs, such as quantification of relative biological effectiveness (RBE) for various tumor types and radiation qualities, role of genetic background of tumor cells in determining response to charged particles, sensitivity of cancer stem-like cells to charged particles, role of charged particles in tumors with hypoxic fractions, and importance of fractionation, including use of hypofractionation, with charged particles.

Absorbed Dose Rates in Tissue from Prompt Gamma Emissions from Near-thermal Neutron Absorption

Prompt gamma emission data from the International Atomic Energy Agency's Prompt Gamma-ray Neutron Activation Analysis database are analyzed to determine the absorbed dose rates in tissue to be expected when natural elements are exposed in a near-thermal neutron environment.

Monte Carlo simulation applied to the characterization of an extrapolation chamber for beta radiation dosimetry

Abstract An extrapolation chamber is a parallel-plate ionization chamber with an adjustable air-cavity volume through the variation of the distance between the collecting electrode and the entrance foil. The measured ionization currents can be obtained for different chamber depths, and extrapolated towards zero chamber depth. In this work, results of Monte Carlo simulations using MCNP5 and MCNPX codes are reported for 90 Sr/ 90 Y and 85 Kr beta radiation spectra incident on a 23392 model PTW extrapolation chamber. The results for transmission factor, absorbed dose rate in tissue as well as the chamber response as a function of the chamber depth are in good agreement with experimental data.

Children Absorb Higher Doses of Radio Frequency Electromagnetic Radiation From Mobile Phones Than Adults

The greater vulnerability of children to the effects of environmental hazards has raised concerns about their exposure to and the resultant absorption of mobile phone radiation. Foster and Chou (2014) reviewed published studies that used computer models of radio-frequency electromagnetic fields to estimate and compare the tissue dose rate in the heads of children and adults using mobile phones. Their review confuses exposure with absorption, and the study results conclude erroneously that children are not more exposed than adults. We show that their review was not executed systematically. There are discrepancies between text summaries and the graphed ratios of child: adult peak special specific absorption rate, in line with the author's hypothesis that children have the same or lower tissue dose than adults. Even the underlying precept of their review is flawed, as the results of deterministic models are treated as random variables. In fact, model results are entirely determined by the underlying assumptions and the structure of the model. Models are included in their unsystematic review that do not consider differences in dielectric constants among different tissues, or across ages, while other models that consider such differences are not included. In this paper, we discuss the differences between exposure and tissue absorption and re-examine the results presented by Foster and Chou. Based upon our review, we suggest an alternative interpretation of the published literature. In an Appendix, we discuss modeling of tissue dose in the context of governmental safety certification processes.

Biophysical modelling of the effects of inhaled radon progeny on the bronchial epithelium for the estimation of the relationships applied in the two-stage clonal expansion model of carcinogenesis

There is a considerable debate between research groups applying the two-stage clonal expansion model for lung cancer risk estimation, whether radon exposure affects initiation and transformation or promotion. The aim of the present study is to quantify the effects of radon progeny on these stages with biophysical models. For this purpose, numerical models of mutation induction and clonal growth were applied in order to estimate how initiation, transformation and promotion rates depend on tissue dose rate. It was found that rates of initiation and transformation increase monotonically with dose rate, whereas effective promotion rate decreases with time but increases sublinearly with dose rate. Despite the uncertainty of results due to the lack of experimental data, present study suggests that effects of radon exposure on both mutational events and clonal growth are significant and should be considered in mechanistic models of carcinogenesis applied for analysing epidemiological data.

Development and Dosimetry of a Small Animal Lung Irradiation Platform

Advances in large scale screening of medical countermeasures for radiation-induced normal tissue toxicity are currently hampered by animal irradiation paradigms that are both inefficient and highly variable among institutions. Here, a novel high-throughput small animal irradiation platform is introduced for use in orthovoltage small animal irradiators. Radiochromic film and metal oxide semiconductor field effect transistor detectors were used to examine several parameters, including 2D field uniformity, dose rate consistency, and shielding transmission. The authors posit that this setup will improve efficiency of drug screens by allowing for simultaneous targeted irradiation of multiple animals to improve efficiency within a single institution. Additionally, they suggest that measurement of the described parameters in all centers conducting countermeasure studies will improve the translatability of findings among institutions. The use of tissue equivalent phantoms in performing dosimetry measurements for small animal irradiation experiments was also investigated. Though these phantoms are commonly used in dosimetry, the authors recorded a significant difference in both the entrance and target tissue dose rates between euthanized rats and mice with implanted detectors and the corresponding phantom measurement. This suggests that measurements using these phantoms may not provide accurate dosimetry for in vivo experiments. Based on these measurements, the authors propose that this small animal irradiation platform can increase the capacity of animal studies by allowing for more efficient animal irradiation. They also suggest that researchers fully characterize the parameters of whatever radiation setup is in use in order to facilitate better comparison among institutions.

Direct comparison of extrapolation chamber measurements of the absorbed dose rate for beta radiation between PTB (Germany) and VNIIM (Russia)

An intercomparison of the absorbed dose rate in tissue, , at radiation protection levels for beta dosimetry was performed between two national metrology institutes, the D I Mendeleyev Institute for Metrology (VNIIM) in St Petersburg (Russia) and the Physikalisch-Technische Bundesanstalt (PTB) in Braunschweig (Germany), from 2009 to 2010. For this comparison, radiation sources of both institutes were calibrated using the primary standard measuring devices (extrapolation chambers) of both institutes, i.e. no transfer instrument was used as both primary standards were directly compared. The values of the absorbed dose rates in tissue agree within 1.2% for two different 90Sr/90Y sources, within 1.0% for one 85Kr source and within 1.5% and 4.2% for two different 147Pm sources. All these deviations are within 1 to 2 times the corresponding standard deviations.

Brain tumour and infiltrations dosimetry of boron neutron capture therapy combined with 252Cf brachytherapy

This article presents a dosimetric investigation of boron neutron capture therapy (BNCT) combined with (252)Cf brachytherapy for brain tumour control. The study was conducted through computational simulation in MCNP5 code, using a precise and discrete voxel model of a human head, in which a hypothetical brain tumour was incorporated. A boron concentration ratio of 1:5 for healthy-tissue: tumour was considered. Absorbed and biologically weighted dose rates and neutron fluency in the voxel model were evaluated. The absorbed dose rate results were exported to SISCODES software, which generates the isodose surfaces on the brain. Analyses were performed to clarify the relevance of boron concentrations in occult infiltrations far from the target tumour, with boron concentration ratios of 1:1 up to 1:50 for healthy-tissue:infiltrations and healthy-tissue:tumour. The average biologically weighted dose rates at tumour area exceed up to 40 times the surrounding healthy tissue dose rates. In addition, the biologically weighted dose rates from boron have the main contribution at the infiltrations, especially far from primary tumour. In conclusion, BNCT combined with (252)Cf brachytherapy is an alternative technique for brain tumour treatment because it intensifies dose deposition at the tumour and at infiltrations, sparing healthy brain tissue.

RADIATION DOSES TO MEMBERS OF THE U.S. POPULATION FROM UBIQUITOUS RADIONUCLIDES IN THE BODY: PART 2, METHODS AND DOSE CALCULATIONS

This paper is Part 2 of a three-part series investigating effective dose rates to residents of the United States from intakes of ubiquitous radionuclides, including radionuclides occurring naturally, radionuclides whose concentrations are technologically enhanced, and anthropogenic radionuclides. This series of papers explicitly excludes intakes from inhaling (222)Rn, (220)Rn, and their short-lived decay products; it also excludes intakes of radionuclides in occupational and medical settings. In this work, it is assumed that instantaneous dose rates in target organs are proportional to steady-state radionuclide concentrations in source regions. Part 1 reviewed, summarized, characterized, and grouped all published and some unpublished data for U.S. residents on ubiquitous radionuclide concentrations in tissues and organs. Assumptions about equilibrium with long-lived parents are made for the 28 other radionuclides in these series lacking data. This paper describes the methods developed to group the collected data into source regions described in the Radiation Dose Assessment Resource (RADAR) dosimetric methodology. Methods for converting the various units of data published over 50 y into a standard form are developed and described. Often, meaningful values of uncertainty of measurements were not published, so that variability in data sets is confounded with measurement uncertainty. A description of the methods developed to estimate variability is included in this paper. The data described in Part 1 are grouped by gender and age to match the RADAR dosimetric phantoms. Within these phantoms, concentration values are grouped into source tissue regions by radionuclide, and they are imputed for source regions lacking tissue data. Radionuclide concentrations are then imputed for the source regions of other phantoms with missing concentration values, and the uncertainties of the imputed values are increased. The concentrations of hollow organs' contents are calculated, and activities are apportioned to the bone source regions using assumptions about each radionuclide's bone-seeking behavior. The data sets are then ready to be used to estimate equivalent dose rates to target tissues from these source regions. The target tissues are then mapped to lists of tissues with International Commission on Radiation Protection (ICRP) tissue weighting factors, or they are mapped to surrogate tissue regions when there is no direct match. Effective dose rates, using ICRP tissue weighting factors recommended in 1977, 1990, and 2007, can be calculated from the tissue and organ equivalent dose rates. These effective dose rates are reported in Part 3 of this series.

SU-FF-T-333: Orthovoltage Dosimetry: Percent Depth Dose Multiplicity From Two Energies

Purpose: To produce a multiplicity of depth dose curves on a two‐kVp orthovoltage system by appropriate combination of the 75 kVp and 225 kVp x‐ray beams. Method and Materials: Using tabulated percent depth dose (PDD) curves at 75 and 225 kVp for five rectangular applicators (4×6, 6×8, 8×10, 10×15, and 15×20 cm2) for our Philips RT‐250 unit, we calculated the mixed‐beam PDDs for each applicator using w 75 ⋅ PDD 75 + w 225 ⋅ PDD 225 , where w denotes the beam component weight, the subscript indicates the component kVp, and w 75 +w 225 =1 . By specifying a dose D0 at the surface and an isodose level at a particular depth, we calculated the required beam weights; incorporating the tissue dose rates then allows us to calculate the beam‐on times for the 75 and 225 kVp beams, respectively. All single‐ and mixed‐energy PDDs were verified in 20×20 cm2 blocks of solid water (Gammex RMI, Middleton, WI) using a field standard electrometer and ion chamber set. The ion chamber fit snugly at the centre of a 2.0 cm thick block. The depth doses were measured at solid water depths of 1.0 to 15.0 cm keeping the source‐to‐surface distance constant at 50.0 cm, and using 10.0 cm of backscatter material. The PDD values were calculated by scaling the measurements relative to the tabulated or theoretical values at a depth of 1.0 cm. Results: The ion chamber measurements at 75 and 225 kVp were within 2 percentage points of the tabulated values for all rectangular applicators. Similarly, the mixed‐energy PDD curves for f 75={0.25, 0.5, 1.0} were also within 2 percentage points of the theoretical expectations. Conclusion: A firm theoretical formalism to create PDDs combining the 75 kVp and 225 kVp beams was formulated and verified experimentally using ion chamber measurements. Our mixed‐energy methodology allows one to synthesize a multiplicity of PDDs between any two orthovoltage energies.

International comparison EUROMET.RI(I)-S2 of extrapolation chamber measurements of the absorbed dose rate in tissue for beta radiation (EUROMET project No 739): Final report

For quality assurance in the realization and transfer by the national standard laboratories of the unit of the absorbed dose rate at 0.07 mm tissue depth for beta radiation, comparison measurements among the primary standard facilities are needed. Although some bilateral comparisons have taken place for this quantity, the CCRI decided in May 2003 that a EUROMET supplementary comparison would be appropriate if inclusive of primary standards laboratories of other regional metrology organizations. The operation and results of such a comparison are reported here. A flat ionization chamber and measurement system was used as the transfer instrument. A comparison was made of the calibration coefficients of this transfer instrument in various beta-particle laboratory reference fields (Pm-147, Kr-85, Tl-204 and Sr-90/Y-90) measured by each of the eight participants from France, Italy, Finland, Germany, Russian Federation, USA, Canada and Japan. The PTB was the pilot laboratory and the comparison ran from January 2004 until April 2007 under EUROMET project No 739 and EUROMET.RI(I)-S2. The results for most of the participants are consistent with the stated uncertainties although an extreme deviation is apparent for Pm-147 beta radiation for one participant.Main text. To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/.The final report has been peer-reviewed and approved for publication by EUROMET, according to the provisions of the CIPM Mutual Recognition Arrangement (MRA).

Miniature X-ray Source—Development of a Prototype

The development of a miniature X-ray source prototype is presented. The source consists of two tungsten electrodes which are vacuum brazed onto an alumina (Al2O3) tube. Field emission current from the cathode results in X-ray production in the anode. Simulations indicate that operation of the source at 20 kV and 15 μA would be feasible for post dilation treatment of coronary arteries in respect of tissue dose rate and heat dissipation. The X-ray source offers comparable treatment times to radioactive sources but minimizes the dose administered to non-target tissue. By variation of electrode spacing and acceleration voltage the radiation range in tissue can be tailored for different medical applications. The first prototypes work well in vacuum but exhibit short lifetimes at atmospheric pressure.

Extrapolation chamber response in low-energy x radiation standard beams

Measurements of absorbed dose rates in air and tissue produced by low-energy x radiation are often difficult to obtain with accuracy. The recommended instruments for these applications are extrapolation chambers. The performance of an extrapolation chamber, developed at IPEN, was studied in low energy x radiation standard beams in relation to its response linearity, extrapolation curves and energy dependence. The results obtained indicate that the developed chamber is suitable for x radiation measurements.