Low-energy Photon Radiation Research Articles

Quantifying the impact of lead doping on plastic scintillator response to radiation.

Through the addition of high-Z dopants, the sensitivity of plastic scintillators to low-energy radiation can be increased. This study quantifies this change in sensitivity as a function of dopant concentration. Measurements were conducted using four different lead-doped scintillators (0%, 1%, 1.5%, and 5% Pb) in high-energy electrons (6 to 15MeV) and low-energy photon (100 to 300kVp) radiation fields. High-energy and low-energy irradiations were done using a clinical linear accelerator and an orthovoltage unit, respectively. Light emitted by the scintillator was quantified using a photosensor module. The experimental setup was replicated in Geant4.10.3 Monte Carlo and scintillator parameters (Quenching parameter: kB and the light yield: L0 ) were varied until agreement between measured and simulated results was reached. Monoenergetic electrons were used to simulate the high-energy electron beam while a spectrum generated using SpekCalc® software was used in the low-energy simulations. Light produced by the scintillator was quantified using a flux scorer sensitive only to photons in the visible wavelength range. In order to compare measured and simulated results, the light produced by the scintillator was normalized to the absorbed dose-to-water at the point of measurement. At high lead dopant concentrations, the scintillator's sensitivity to the 100kVp beam increased by 474% relative to the 15MeV electron beam; the scintillator's kB parameter increased from 0.126 to 0.27mm/MeV. A model quantifying the change in kB and L0 as a function of Zeff was derived; presenting a modified Birks' Law for metal-doped plastic scintillators. The impact of high-Z doping on plastic scintillator response was quantified; this can allow for the controlled induction of energy dependence in plastic scintillator detectors.

Radiation Therapy–Induced Dysfunction in Cardiovascular Implantable Electronic Devices

PurposeThe prevalence of patients with cardiovascular implantable electronic devices (CIEDs) who receive radiation treatment for cancer is increasing. External beam radiation therapy (RT) can affect the electronic components. This study aimed to evaluate the incidence and predictors of new onset CIED dysfunction in patients treated with RT. Methods and materialsWe retrospectively analyzed data from 230 patients with CIEDs who received radiation treatment at the Radiation Oncology Center of CHU de Québec - Université Laval between February 2007 and November 2013. The reviewed data included baseline characteristics, CIEDs, and RT treatment specifications. Patients with CIEDs were analyzed before, during, and at the end of radiation treatment. High- and low-energy photon or electron beam radiation from linear accelerators, orthovoltage machines, and high-dose rate brachytherapy delivery were used. Abnormal events could be one of the following: total or partial deprogramming of the CIED parameters, onset of new symptoms, or new arrhythmia. ResultsThis study is based on one of the largest cohorts. A total of 18 events in 16 patients (7.8%) were recorded. Of the 18 events, 16 had at least part of the radiation treatment delivered with photo neutrons producing high-energy RT (neutron producing RT). Only 2 abnormal events occurred during non-neutron producing RT. Both the prescription dose and the dose estimated at the location of the pacemaker were correlated with the probability of an abnormal event (P = .0006 and P = .003, respectively). Among the 16 patients, clinical symptoms were noted in only 1 patient (6.3%). ConclusionsCIED malfunctions are relatively uncommon and do not seem to be life threatening. We recommend limiting the dose at the CIED and avoid neutron-producing RT to reduce the risk of CIED malfunction.

Subleading soft theorem for arbitrary number of external soft photons and gravitons

We obtain the subleading soft theorem for a generic theory of quantum gravity, for arbitrary number of soft photons and gravitons and for arbitrary number of finite energy particles with arbitrary mass and spin when all the soft particles are soft in the same rate. This result is valid at tree level for spacetime dimensions equal to four and five and to all loop orders in spacetime dimensions greater than five. We verify that in classical limit, low energy photon and graviton radiation decouple from each other.

Simulation of 75Se Encapsulated Sources for Their Potential Use in Brachytherapy

The physical characteristics of the 75Se radionuclide make it a promising gamma radiator for use as a brachytherapy sealed source. This radionuclide combines relatively low-energy photon radiation emitted during decay with a sufficiently long half-life (approximately 120 days) and the possibility of obtaining high specific activity. All this makes this radionuclide attractive for automated injection brachytherapy. The aim of this work was to study the dosimetric characteristics of 75Se for its potential use in high and medium dose rate brachytherapy. According to the TG-43 formalism, the radial dose function g(r) and the anisotropy function F(r, θ) are calculated. 75Se as a radionuclide for sealed source brachytherapy has many advantages over widely used isotopes and can serve as an alternative to iridium sources.

A new fully integrated X-ray irradiator system for dosimetric research

A fully housed X-ray irradiator was developed for use within lexsyg or Magnettech desktop equipment. The importance of hardening of the low energy photon radiation is discussed, its performance and feasibility is empirically shown and sustained by basic numerical simulations. Results of the latter for various materials are given for different X-ray source settings in order to provide estimates on the required setup for the irradiation of different geometries and materials. A Si-photodiode provides real-time monitoring of the X-ray-irradiator designed for use in dosimetric dating and other dosimetric application where irradiation of small samples or dosemeters is required.

Simulation of irradiation of thin layers of biological matter by low-energy photon radiation

Passage of 1–400 keV photons through thin layers (0.001–1.0 mm) of biological matter was simulated. Monte Carlo simulation was performed using the GEANT4.9 software package. The energy dependences of the absorbed dose and number of ionizing events and the number of ionizing events per unit absorbed dose were obtained. It was shown that the dependences in many respects are determined by the thickness of layers. Assuming that equal numbers of ionizing events in the layer cause equal biological effects, energy dependences of relative biological effectiveness of photons in the energy range studied have been estimated.

SU-E-T-120: Minimum Absorbed Dose Limit for Gafchromic EBT2 Film Response after Exposure to Low-Energy Photons.

To investigate the accuracy of the absorbed dose measured with Gafchromic EBT2 film in low-energy photon radiation fieldsMethods: Six EBT2 film (lot # F06110901) pieces (1cm2 ) per dose were exposed to x-rays of 50 kV, 80 kV, 120 kV and 60Co gamma rays from a Leksell Gamma Knife at dose values from 50 mGy to 100 Gy. The x-ray beams were calibrated following the AAPMTG-61 protocol using ionization chambers calibrated at NIST or Wisconsin University depending on the beam quality, while the 60Co gamma was calibrated in water using MD-V2-55 film. Each film piece was scanned once using a HP Scanjet 7650 document flatbed scanner in transmission mode, 48-bit color at 300 dpi spatial-resolution. The data analysis was made through the ImageJ. The measured light intensity for the red channel with its associate standard deviation was used to evaluate the netOD and its standard combined uncertainty. The absorbed dose as a function of the netOD was fitted using the logistic model and the relative combined uncertainties were evaluated for each energy photon beam. EBT2 film response curve depends on the low-energy photons and the degree of energy-dependence is a function of absorbed dose. The absorbed dose relative combined uncertainty as a function of the absorbed dose indicates that the minimum absorbed dose limit is also energy dependent. Lower is the energy photon; more accurate is the measurement at low dose value. This can be explain by the fact that comparing to high energy photons, low energy photons can produce locally enough ionization density to create more color centre in the same film area. Minimum absorbed dose limit of Gafchromic EBT2 films were found to be energy dependent. The response curve depends on the low-energy photons and the degree of energy-dependence is a function of absorbed dose This work is partially supported by DGAPA-UNAM grant IN102610 and Conacyt Mexico grant 127409.

Release criteria for patients having undergone radionuclide therapy and criteria for their crossing the state border of the Russian Federation

By means of a conservative dosimetry model, the values of operational radiological criteria for patients released from hospital--residual activity in a body and dose rate near the patient's body--are substantiated based on the effective dose limit of 5 mSv for persons helping the patient or living with him and 1 mSv for other adults and children. Two sets of operative criteria for radionuclides (125)I, (131)I, (153)Sm and (188)Re used in Russia for radionuclide therapy were derived. Release criteria for (125)I well differ from such values in other countries because in this work absorption of (125)I low-energy photon radiation in the patient was taken into account. When a patient having undergone radionuclide therapy crosses the frontier of Russia, high-sensitivity devices for radiation control at the custom can detect the patient. A simplified radiological assessment of the patient was suggested aimed at provision of radiation safety for patient companions in transport.

A robust method for determining the absorbed dose to water in a phantom for low-energy photon radiation

The application of more and more low-energy photon radiation in brachytherapy—either in the form of low-dose-rate radioactive seeds such as Pd-103 or I-125 or in the form of miniature x-ray tubes—has induced greater interest in determining the absorbed dose to water in water in this energy range. As it seems to be hardly feasible to measure the absorbed dose with calorimetric methods in this low energy range, ionometric methods are the preferred choice. However, the determination of the absorbed dose to water in water by ionometric methods is difficult in this energy range. With decreasing energy, the relative uncertainty of the photon cross sections increases and as the mass energy transfer coefficients show a steep gradient, the spectra of the radiation field must be known precisely. In this work two ionometric methods to determine the absorbed dose to water are evaluated with respect to their sensitivity to the uncertainties of the spectra and of the atomic database. The first is the measurement of the air kerma free in air and the application of an MC-based conversion factor to the absorbed dose to water. The second is the determination of the absorbed dose to water by means of an extrapolation chamber as an integral part of a phantom. In the complementing MC-calculations, two assortments of spectra each of which is based on a separate unfolding procedure were used as well as two kinds of databases: the standard PEGS and the recently implemented NIST database of EGSnrc. Experimental results were obtained by using a parallel-plate graphite extrapolation chamber and a free-air chamber. In the case when the water kerma in a phantom is determined from the measurements of air kerma free in air, differences in the order of 10% were found, according to which the database or the kind of spectrum is used. In contrast to this, for the second method, the differences found were about 0.5%.

High-resolution 3D dose distribution measured for two low-energy x-ray brachytherapy seeds: 125I and 103Pd

Abstract In this work, we have investigated the 3D absorbed dose distribution around 125 I and 103 Pd low-energy photon brachytherapy seeds using a high-spatial-resolution gel scanning system to address the current difficulty in measuring absorbed dose at close distances to these sources as a consequence of high dose rate gradient. A new version of BANG-gel coupled with a small format laser CT scanner has been used. Measurements were performed with 100 μm resolution in all dimensions. In particular, radial dose function and absorbed dose rate in the plane parallel to the sources longitudinal-axis were derived at radial distances smaller than or equal to 1 cm. In addition, the energy dependence was evaluated, finding that, within measurement uncertainties, the gel response is independent of the energy for energy photon values between 20 keV and 1250 keV. We have observed that at distances larger than 1.4 mm from the source, the delivered dose is similar to predictions from published Monte Carlo calculations (MC) for the 125 I seed. For distances between 1 mm and 3 mm, differences in magnitude and shape are significant for the 103 Pd seed, where an enhancement is observed. In the enhancement region, a difference of up to 70% in the radial dose function was obtained. Such observation suggests a contribution from other radionuclides emitting beta-particles or electrons, and not considered by MC. To understand the effect, spectrometry measurements were performed. A small contribution of 102 Rh/ 102 m Rh radionuclide relative to 103 Pd was observed and its importance on the absorbed dose measured at close distances to the seed is time dependent and consequently, avoids reproducible measurements. Finally, the results obtained in this work underscore the importance of using high-spatial-resolution and water-equivalent detectors for measuring absorbed dose in low-energy photon radiation fields.

1090 PUBLICATION Low energy photon radiation boost combined with surgery and external beam radiotherapy (EBRT) in early oral cancer. preliminary results on treatment tolerance

1090 PUBLICATION Low energy photon radiation boost combined with surgery and external beam radiotherapy (EBRT) in early oral cancer. preliminary results on treatment tolerance

The outlook for the application of electronic dosemeters as legal dosimetry.

This study analyses new trends of a set of 12 electronic personal dosemeters in order to gain an overview of their main advantages and limitations. Physical characteristics and radiological, mechanical and environmental performance were tested according to IEC-61526 Standard requirements. The study highlights the different behaviour of the selected dosemeters. In particular, it is demonstrated that three of the tested devices fulfilled most of the established requirements, whereas another three of them presented important faults. The parameters that need more development are, in general, the response at low energy photon and beta radiation, and the dose rate alarm features. In some cases, mechanical problems as well as interference in the response due to external electromagnetic fields were also found. However, the results of the study foresee a promising future for the application of the newest personal electronic dosemeters as legal personal dosemeters and show the need for internationally agreed technical requirements within the European countries.

A Prototype Ionisation Chamber as a Secondary Standard for the Measurement of Personal Dose Equivalent, Hp(10), on a Slab Phantom

The construction and technical characteristics of a secondary standard chamber for measuring the conventionally true value of the personal dose equivalent, H p (10), on a slab phantom are presented. The chamber was optimised to get a nearly constant response with respect to H p (10) for photon energies from about 10 keV to 1400keV and for angles of incidence, α, from 0° to 75°, Thus, once calibrated at the facility of the calibration laboratory, the H p (10) chamber can be used at other facilities without any need to consider the spectral differences of radiation fields of the same nominal radiation quality but generated by two different facilities. This is a great advantage over the procedure recommended in ISO/FDIS 4037-3, according to which these differences have to be considered for low energy photon radiation and may lead to differences of the conversion coefficients from air kerma, K a , to H p (10) of up to several tens of per cent.

Perspectives of Personnel External Dosimetry at Stanford Linear Accelerator Centre

The need for providing personnel external monitoring for exposure to low energy photon (<150 keV) and beta radiation at the Stanford Linear Accelerator Center (SLAC) has been studied. At SLAC, a high energy electron accelerator facility, the major sources of low energy photons and betas (electrons and positrons) are from the induced activities in accelerator parts and components. Shower theory and measurements show that these induced activities are generally distributed deep inside the materials. Therefore, the low energy photons and betas will be significantly absorbed within the materials. Calculations based on the characteristics of the radionuclides produced by photonuclear reactions in several common materials have indicated that the beta doses on the material surface are small fractions of the photon doses. Field measurements at SLAC were made using Kodak type 2 films, Panasonic UD810 TLDs and a Victoreen 450 survey meter to determine the doses from low energy photons and betas, and then compared them with the doses from high energy photons. The X rays from the klystrons and the synchrotron radiation are also discussed. The results verify that the doses are small enough that, from the technical point of view, no personnel monitoring is needed for low energy photons and betas.

Accident Dosimetry of Weakly Penetrating Radiation Utilising Carbon Loaded LiF Pellets in a Mylar Phantom

A dosemeter for measuring depth dose profiles in skin from weakly penetrating radiation, utilising carbon loaded LiF pellets embedded in a Mylar phantom has been developed. The purpose of the dosemeter is to assess skin doses at various depths in order to evaluate the stochastic and deterministic effects of large skin exposures. The dosimetric thickness of the pellets is approximately 9 mg.cm 2 , and their response to low energy photon radiation and to beta radiation have been measured. For photons, the sensitivity of the pellets drops dramatically below 8 keV, due to internal self shielding. The response to low energy betas from 147 Pm was found to be 0.38 of the corresponding 90 Sr/ 90 Y response. Information from the measured depth-dose profile can be used to correct for the self shielding under response. Measured depth-dose profiles for different soft X ray spectra, illustrating different self shielding under response factors, are presented. Measured depth dose profiles from 90 Sr/ 90 Y and 204 Tl beta sources are also shown, and compared with published beta depth-dose profiles calculated by Monte Carlo methods

Review of Personal Monitoring Techniques for the Measurement of Absorbed Dose from External Beta and Low Energy Photon Radiation

The techniques available at present for personal monitoring of doses from external beta and low energy photon radiation are reviewed. The performance of currently used dosimetry systems is compared with that recommended internationally, and developments for improving the actual performance are outlined. The subjects dealt with comprise: the quantity to be measured, the required accuracy of measurement, calibration procedures, and dosemeter design including the main parameters influencing the energy and angular response of the dosemeter, such as detector thickness, filter thickness, dosemeter materials and detector/filter geometry. Improvements in the energy and angular response of dosemeters for the measurement of doses from beta and low energy photon radiation can be achieved essentially through two different approaches: either by using thin detectors or multi-element dosemeters. Their relative merits are discussed.

Estimation of quality and intensity of low energy photon radiation using a single sample of CaF 2:Tm

This paper reports measurements of the TL response of 150° and 240°C peaks in CaF 2:Tm as a function of photon energy and the time between irradiation and readout. The 240°C peak height and the 240°C to 150° peak height ratio were used to determine the quality and intensity of low energy photons using a single sample of CaF 2:Tm. The higher photon energy dependence of 240°C peak in CaF 2:Tm and peak 7 in LiF TLD-100 are due to the 2-hit nature of their TL traps.

Measured Attenuation Coefficients at Low Photon Energies (9.88-59.32 keV) for 44 Materials and Tissues

Measurements have been made of narrow-beam linear attenuation coefficients for six important human tissues using low-energy photon radiation in the range 9.88 to 59.32 keV and, at 9.88 and 17.44 keV, for 38 materials employed in experimental radiation physics. The study was performed to assess and improve the accuracy of dosimetric measurements in which such substitute materials are used to simulate body tissues and air. The results obtained are compared with attenuation coefficients calculated for published elemental compositions using photon interaction data and a polynomial fitting routine. In general, good agreement was obtained between measured and calculated data for the basic and substitute materials. However, inhomogeneities in certain human tissues produced large discrepancies.

LARYNGEAL MALIGNANCY FOLLOWING IODINE-125 THERAPY FOR THYROTOXICOSIS

A 52-year-old woman presented with a laryngeal sarcoma eight years after receiving two doses, each of 30 mCi, of iodine-125 for thyrotoxicosis. That extrathyroidal tissue receives a higher radiation dose of low-energy photon radiation from iodine-125 than from an equivalent microcurie dose of iodine-131 and that the tumour was of a type which rarely arises spontaneously in the larynx suggest a possible link between the development of the tumour and iodine-125 therapy.