Alanine response to low energy synchrotron x-ray radiation.

Objective. The radiation response of alanine is very well characterized in the MV photon energy range where it can be used to determine the dose delivered with an accuracy better than 1%, making it suitable as a secondary standard detector in cancer radiation therapy. This is not the case in the very low energy keV x-ray range where the alanine response is affected by large uncertainties and is strongly dependent on the x-ray beam energy. This motivated the study undertaken here.Approach. Alanine pellets with a nominal thickness of 0.5 mm and diameter of 5 mm were irradiated with monoenergetic x-rays at the Diamond Light Source synchrotron, to quantify their response in the 8-20 keV range relative to60Co radiation. The absorbed dose to graphite was measured with a small portable graphite calorimeter, and the DOSRZnrc code in the EGSnrc Monte Carlo package was used to calculate conversion factors between the measured dose to graphite and the absorbed dose to water delivered to the alanine pellets. GafChromic EBT3 films were used to measure the beam profile for modelling in the MC simulations.Main results. The relative responses measured in this energy range were found to range from 0.616 to 0.643, with a combined relative expanded uncertainty of 3.4%-3.5% (k= 2), where the majority of the uncertainty originated from the uncertainty in the alanine readout, due to the small size of the pellets used.Significance. The measured values were in good agreement with previously published data in the overlapping region of x-ray energies, while this work extended the dataset to lower energies. By measuring the response to monoenergetic x-rays, the response to a more complex broad-spectrum x-ray source can be inferred if the spectrum is known, meaning that this work supports the establishment of alanine as a secondary standard dosimeter for low-energy x-ray sources.

Verification of the pure alanine in PMMA tube dosimeter applicability for dosimetry of radiotherapy photon beams: a feasibility study.

Alanine dosimeters in the form of pure alanine powder in PMMA plastic tubes were investigated for dosimetry in a clinical application. Electron paramagnetic resonance (EPR) spectroscopy was used to measure absorbed radiation doses by detection of signals from radicals generated in irradiated alanine. The measurements were performed for low-dose ranges typical for single-fraction doses often used in external photon beam radiotherapy. First, the dosimeters were irradiated in a solid water phantom to establish calibration curves in the dose range from 0.3 to 3 Gy for 6 and 18 MV X-ray beams from a clinical linear accelerator. Next, the dosimeters were placed at various locations in an anthropomorphic pelvic phantom to measure the dose delivery of a conventional four-field box technique treatment plan to the pelvis. Finally, the doses measured with alanine dosimeters were compared against the doses calculated with a commercial treatment planning system (TPS). The results showed that the alanine dosimeters have a highly sensitive dose response with good linearity and no energy dependence in the dose range and photon beams used in this work. Also, a fairly good agreement was found between the in-phantom dose measurements with alanine dosimeters and the TPS dose calculations. The mean value of the ratios of measured to calculated dose values was found to be near unity. The measured points in the in-field region passed dose-difference acceptance criterion of 3% and those in the penumbral region passed distance-to-agreement acceptance criterion of 3 mm. These findings suggest that the pure alanine powder in PMMA tube dosimeter is a suitable option for dosimetry of radiotherapy photon beams.

Relative response of the alanine dosimeter to medium energy x-rays.

The response of the alanine dosimeter to kilovoltage x-rays with respect to the dose to water was measured, relative to the response to Co-60 radiation.Two series of x-ray qualities were investigated, one ranging from 30 kV to 100 kV tube voltage (TW series), the other one ranging from 70 kV to 280 kV (TH series). Due to the use of the water calorimeter as a primary standard, the uncertainty of the delivered dose is significantly lower than for other published data. The alanine response was measured as described in a previous publication (Anton et al 2013 Phys. Med. Biol. 58 3259-82). The uncertainty component due to the alanine measurement and analysis is ⩽0.4%, the major part of the combined uncertainty of the relative response originates from the uncertainty of the delivered dose. The relative uncertainties of the relative response vary from ⩽2% for the TW series to ⩽1.1% for the TH series.Different from the behaviour of the alanine dosimeter for megavoltage x-rays or electrons, the relative response drops significantly from unity for Co-60 radiation to less than 64% for the TW quality with a tube voltage of 30 kV. In order to reproduce this behaviour through Monte Carlo simulations, not only the ratio of the absorbed dose to alanine to the absorbed dose to water has to be known, but also the intrinsic efficiency, i.e. the dependence of the number of free radicals generated per unit of absorbed dose on the photon energy. This quantity is not yet accessible for the TW series.For a possible use of the alanine dosimeter for kilovoltage x-rays, for example in electronic brachytherapy, users should rely on the measured data for the relative response which have become available with this publication.

The alanine detector in BNCT dosimetry: dose response in thermal and epithermal neutron fields.

PURPOSE: The response of alanine solid state dosimeters to ionizing radiation strongly depends on particle type and energy. Due to nuclear interactions, neutron fields usually also consist of secondary particles such as photons and protons of diverse energies. Various experiments have been carried out in three different neutron beams to explore the alanine dose response behavior and to validate model predictions. Additionally, application in medical neutron fields for boron neutron capture therapy is discussed. METHODS: Alanine detectors have been irradiated in the thermal neutron field of the research reactor TRIGA Mainz, Germany, in five experimental conditions, generating different secondary particle spectra. Further irradiations have been made in the epithermal neutron beams at the research reactors FiR 1 in Helsinki, Finland, and Tsing Hua open pool reactor in HsinChu, Taiwan ROC. Readout has been performed with electron spin resonance spectrometry with reference to an absorbed dose standard in a (60)Co gamma ray beam. Absorbed doses and dose components have been calculated using the Monte Carlo codes fluka and mcnp. The relative effectiveness (RE), linking absorbed dose and detector response, has been calculated using the Hansen & Olsen alanine response model. RESULTS: The measured dose response of the alanine detector in the different experiments has been evaluated and compared to model predictions. Therefore, a relative effectiveness has been calculated for each dose component, accounting for its dependence on particle type and energy. Agreement within 5% between model and measurement has been achieved for most irradiated detectors. Significant differences have been observed in response behavior between thermal and epithermal neutron fields, especially regarding dose composition and depth dose curves. The calculated dose components could be verified with the experimental results in the different primary and secondary particle fields. CONCLUSIONS: The alanine detector can be used without difficulty in neutron fields. The response has been understood with the model used which includes the relative effectiveness. Results and the corresponding discussion lead to the conclusion that application in neutron fields for medical purpose is limited by its sensitivity but that it is a useful tool as supplement to other detectors and verification of neutron source descriptions.

Response of the alanine/ESR dosimeter to radiation from an Ir-192 HDR brachytherapy source.

The response of the alanine dosimeter to radiation from an Ir-192 source with respect to the absorbed dose to water, relative to Co-60 radiation, was determined experimentally as well as by Monte Carlo simulations. The experimental and Monte Carlo results for the response agree well within the limits of uncertainty. The relative response decreases with an increasing distance between the measurement volume and the source from approximately 98% at a 1 cm distance to 96% at 5 cm. The present data are more accurate, but agree well with data published by Schaeken et al (2011 Phys. Med. Biol. 56 6625-34). The decrease of the relative response with an increasing distance that had already been observed by these authors is confirmed. In the appendix, the properties of the alanine dosimeter with respect to volume and sensitivity corrections are investigated. The inhomogeneous distribution of the detection probability that was taken into account for the analysis was determined experimentally.

Extended use of alanine irradiated in experimental reactor for combined gamma- and neutron-dose assessment by ESR spectroscopy and thermal neutron fluence assessment by measurement of (14)C by LSC.

Gamma- and neutron doses in an experimental reactor were measured using alanine/electron spin resonance (ESR) spectrometry. The absorbed dose in alanine was decomposed into contributions caused by gamma and neutron radiation using neutron kerma factors. To overcome a low sensitivity of the alanine/ESR response to thermal neutrons, a novel method has been proposed for the assessment of a thermal neutron flux using the (14)N(n,p) (14)C reaction on nitrogen present in alanine and subsequent measurement of (14)C by liquid scintillation counting (LSC).

Synthesis and characterization of gold/alanine nanocomposites with potential properties for medical application as radiation sensors.

Radiation dose assessment is essential for several medical treatments and diagnostic procedures. In this context, nanotechnology has been used in the development of improved radiation sensors, with higher sensitivity as well as smaller sizes and energy dependence. This paper deals with the synthesis and characterization of gold/alanine nanocomposites with varying mass percentage of gold, for application as radiation sensors. Alanine is an excellent stabilizing agent for gold nanoparticles because the size of the nanoparticles does not augment with increasing mass percentage of gold, as evidenced by UV-vis spectroscopy, dynamic light scattering, and transmission electron microscopy. X-ray diffraction patterns suggest that the alanine crystalline orientation undergoes alterations upon the addition of gold nanoparticles. Fourier transform infrared spectroscopy indicates that there is interaction between the gold nanoparticles and the amine group of the alanine molecules, which may be the reason for the enhanced stability of the nanocomposite. The application of the nanocomposites as radiation detectors was evaluated by the electron spin resonance technique. The sensitivity is improved almost 3 times in the case of the nanocomposite containing 3% (w/w) gold, so it can be easily tuned by changing the amount of gold nanoparticles in the nanocomposites, without the size of the nanoparticles influencing the radiation absorption. In conclusion, the featured properties, such as homogeneity, nanoparticle size stability, and enhanced sensitivity, make these nanocomposites potential candidates for the construction of small-sized radiation sensors with tunable sensitivity for application in several medical procedures.

The gamma ray response of alanine film dosimeters at low temperatures.

The response of alanine film EPR dosimeters was studied for low temperature gamma irradiation conditions (77-293 K) in the dose interval from 6.3 to 80 kGy. It was found that the response of the dosimeter decreases with decreased irradiation temperature and saturates at lower doses for lower irradiation temperatures. The analysis of the EPR signal suggests that the radical species formed at low temperature are the same as those used for dosimetry at room temperature, but with different concentrations. Their concentrations evolve as the temperature of the sample increases until the usual EPR signal used at room temperature is obtained.

Structure and behaviour of the free radicals generated in gamma irradiated amino acid and iminodiacetic acid derivatives.

An EPR study has been carried out to investigate the structure and behaviour of the free radical formed γ-irradiated l-alaninamide hydrochloride, dl-glutamic acid monohydrate and N-(2-carboxyethyl) iminodiacetic acid powders at room temperature. The observed paramagnetic species have been attributed to the CH(3)CHCONH(2), HOOCCH(2)CH(2)CHCOOH and HOOCCH(2)CH(2)NCHCH(2)(COOH)(2) radicals, respectively. Some spectroscopic properties and suggestions concerning possible structure of the radicals were also discussed in this study.

Uncertainty attributed to signal averaging in a single averaged alanine EPR spectrum for low-dose applications.

During the past 50 y alanine has been considered a reference dosimetry system using electron paramagnetic resonance (EPR), especially for the high doses associated with radiation processing. Extension of alanine/EPR system applications to the lower doses associated with radiation therapy and/or radiation protection is limited by the ability to extract the dosimetric signal with minimum associated noise. The signal-averaging technique is one of the common numerical methods used for enhancing the signal-to-noise ratio, through which the accumulated repetitive scans causes the reduction of noise due to its random behaviour and the signal growth due to its persistence. However, the use of signal averaging is usually associated with some uncertainty, which is not usually considered. In this work, there is a clarification of the importance of the evaluation of uncertainty associated to the single averaged alanine spectrum.

ENDOR study on the dynamic properties of the first stable paramagnetic center in gamma-irradiated L-alanine crystals.

Dynamic properties of the first stable l-alanine radical, SAR1, induced by gamma-irradiation of l-alanine crystals, have been investigated by the electron nuclear double resonance technique (ENDOR). The study focuses on the dynamic properties of the alpha-proton hyperfine splitting in the temperature range from 180 to 320 K. In this region the motion of the NH(3)(+) and CH(3) groups exhibits slow and fast motional dynamics in comparison to the nuclear and electron Larmor frequencies, respectively. Evidence for different conformations of the SAR1 center is presented on the basis of thermodynamic properties of the alpha-hyperfine splitting. The activation processes causing the broadening of the ENDOR lines are studied. At room temperature the motional dynamics of the SAR1 center are modulated by the dynamics of the charged, neighboring NH(3)(+) group.

Gamma/neutron dose evaluation using Fricke gel and alanine gel dosimeters to be applied in boron neutron capture therapy.

Gel dosimetry has been studied mainly for medical applications. The radiation induced ferric ions concentration can be measured by different techniques to be related with the absorbed dose. Aiming to assess gamma/thermal neutrons dose from research reactors, Fricke gel and alanine gel solutions produced at IPEN using 300 bloom gelatin were mixed with Na(2)B(4)O(7) salt, and the mixtures were irradiated at the beam hole #3 of the IEA-R1 research reactor, (BH#3) adapted to BNCT studies, and the dose-response was evaluated using spectrophotometry technique.

Sensitivity comparison of two L-alanine doped blends to different photon energies.

Blends of L-alanine (85% weight proportion) with KI (10%) and with PbI2 (10%), these last two compounds acting as dopants, and with PVA (5%) acting as binder, were prepared in water at 80 degrees C. A blend of pure L-alanine (95%) with PVA (5%) was also prepared. The three blends were irradiated with photon beams of different energies (120 kV, Co, and 10 MV) to a unique dose of 30 Gy to compare their sensitivities for those three energies. EPR spectra of the three irradiated blends were recorded in a K-Band spectrometer (24 GHz) taking aliquots of about 4 mg for each blend. The energy sensitivity of a blend was defined as the peak-to-peak amplitude of its EPR spectrum central line. For the Co energy (1.25 MeV) the blends presented practically the same sensitivity, indicating that the presence of the dopants does not affect the sensitivity of L-alanine. For 10 MV x-rays, there was an increment (around 10%-20%) in sensitivity for the two L-alanine doped blends compared with the pure L-alanine blend (not doped). In the case of 120 kV x-rays, the blends ala+KI and ala+PbI showed increments of 10 and 20 times more sensitivity than the pure L-alanine blend. It is concluded that the dopants KI and PbI2 produce a great enhancement of the L-alanine sensitivity to low-energy photons. For the same dopant's content (10%) in the blend, PbI2 showed a better performance. Increasing the PbI2 proportion (30%) in the blend allows the detection of radiation dose as low as 10 mGy for 120 kV x-rays. These results encourage the authors to try to enhance the sensitivity of L-alanine even more by increasing the dopant's content in the blend and diminishing the lower limit detection. Application of these L-alanine doped blends in the dosimetry in diagnostic radiology could be possible.

Response of alanine and barium dithionate EPR dosimeters.

The response of alanine and barium dithionate EPR dosimeters to proton irradiation with energies ranging from 6.6-25 MeV has been investigated. EPR dosimeters were calibrated using calibrated gamma sources. Alanine dosimeters show a value 29% higher than those obtained by a Markus chamber at the same energy, and barium dithionate shows a value 22% smaller. The response of the EPR dosimeters to irradiation at a mean dose of about 40 Gy depends on the proton energy. Using experimental data, the yield of the radicals in the tracks for the alanine pellets was calculated. The yield of the radicals was determined to be proportional to the linear energy transfer (LET) on the straight-line length of the proton track, and the proportional coefficient for alanine is equal to 0.109 eV-1. In the area of the Bragg peak, the probability of recombination of the ionized electrons with cations is increased. As a result, approximately 4.6 MeV of proton energy is used for ionization that results in electron-cation recombination instead of formation of radicals, and maximum LET does not coincide with the maximum concentration of the radicals.

Influencia de la radiación gamma como método de esterilización sobre el polímero poli VPAVG (Valina-Prolina-Alanina-Valina- Glicina) / Influence of gamma radiation as a sterilization method on polymer poli VPAVG (Valine- Proline- Alanine-Valine-Glicine)

El polímero poli (VPAVG) pertenece a la familia de materiales bioelásticos derivados de la elastina y ha demostrado poseer cualidades óptimas para la formación de sistemas de cesión controlada, así como una biocompatibilidad aceptable en determinados tejidos. Las formulaciones preparadas a partir del biomaterial deben ser estériles, si se pretende administrar por una vía que implique ruptura de barreras biológicas. Por lo anterior, resulta esencial conocer el comportamiento del polímero y sus formulaciones frente al proceso de esterilización empleado. El objetivo de este trabajo fue, por tanto, evaluar la influencia de la radiación gamma como método de esterilización sobre las ca - racterísticas físicas del poli (VPAVG) y de las partículas for - madas con éste. En cuanto al polímero, no se apreciaron diferencias en su apariencia física antes y después de la esterilización. Sin embargo, las partículas obtenidas a partir del poli (VPAVG) y posteriormente esterilizadas experimentaban cambios en su morfología. En cuanto al tamaño de las partículas, se determinó que las obtenidas con polímero esterilizado presentaban cierta tendencia a formar agregados de menor tamaño que los encontrados con el polímero sin esterilizar. Se concluyó que el biomaterial ensayado y las formulaciones eran susceptibles a las radiaciones gamma como método de esterilización final, proponiéndose recurrir a otro tratamiento que garantice su esterilidad final.

The poli polymer (VPAVG) belongs to the family of bioelastic materials derived from elastin, and it has showed the best qualities for the creation of systems of controlled cession, as well as an acceptable biocompatibility in certain tissues. If any preparation made from this biomaterial has to be administered in any way that implies the rupture of biological barriers, the preparation must be sterile. By this means, it is essential to know the behaviour of this polymer and its formulations, facing the sterilization process being used. The objective of this research was learn the influence of gamma radiation as a sterilization method over the physical characteristics of poli (VPAVG) and the particles formed by it. As the polymer, we did not observe any differences in physical appearance before and after sterilization. Particles formed by the polymer (VPAVG) and sterilized after, experimented changes in their morphology. As the size of the particles, we observed that those obtained with the sterilized polymer showed a tendency to form smaller aggregates than those found with the non-sterilized polymer. We concluded that the essayed biomaterial and its formulations were susceptible to gamma radiations as final sterilization method, proposing to use another treatment to guarantee the final sterile condition.

Response of the alanine/ESR dosimetry system to MV X-rays relative to (60)Co radiation.

The measurand relevant in dosimetry for radiation therapy is the absorbed dose to water, D(W). The Physikalisch-Technische Bundesanstalt (PTB) has established a secondary standard for D(W) for high-energy photon and electron radiation based on electron spin resonance (ESR) of the amino acid alanine. Since the calibration is usually performed using (60)Co radiation while a huge part of the external radiation therapy is done with high-energy x-rays from linear accelerators, determination of the response is an important issue. The results presented in this paper are the most accurate ones available today with uncertainties assigned to the relative response for 8 MV and 16 MV of the order of 0.3%. The experimental results are compared to Monte Carlo simulations using the EGSnrc software package. In the appendix, it is demonstrated how mean values from repetitive irradiations and their uncertainties are obtained in a consistent way using Bayesian statistics, even in the presence of at first sight inconsistent data. It is important to note that the formulae derived to obtain the final results follow from first principles, without recurring to ad hoc solutions or simple recipes and are valid for all kinds of repetitive measurements.

The Effect of gadolinium on the ESR response of alanine and ammonium tartrate exposed to thermal neutrons.

Many efforts have been made to develop neutron capture therapy (NCT) for cancer treatment. Among the challenges in using NCT is the characterization of the features of the mixed radiation field and of its components. In this study, we examined the enhancement of the ESR response of pellets of alanine and ammonium tartrate with gadolinium oxide exposed to a thermal neutron beam. In particular, the ESR response of these dosimeters as a function of the gadolinium content inside the dosimeter was analyzed. We found that the addition of gadolinium improves the sensitivity of both alanine and ammonium tartrate. However, the use of gadolinium reduces or abolishes tissue equivalence because of its high atomic number (Z(Gd) = 64). Therefore, it is necessary to find the optimum compromise between the sensitivity to thermal neutrons and the reduction of tissue equivalence. Our analysis showed that a low concentration of gadolinium oxide (of the order of 5% of the total mass of the dosimeter) can enhance the thermal neutron sensitivity more than 13 times with an insignificant reduction of tissue equivalence.

EPR spectra of gamma-irradiated DL-alpha-alanine supported on molecular sieves.

The aim of the work was to collect information concerning boundary effects which are suspected in alpha-alanine dosimeters consisted of powdered microcrystalline alpha-alanine and binders. In our experiments the conventional binders were replaced by molecular sieves (MS). MS are inorganic porous materials (host structures) with well organized and uniform intra-crystalline pore systems of nano-scale size. The guest molecules can be either physically adsorbed on very large inner MS surface, or chemically bound to the active sites. They can be also encapsulated inside the intracrystalline cavities. The EPR spectra of gamma irradiated DL-alpha-alanine supported on NaY, CeY, SOD, mordenite, ZSM-5 and ALPO(4)-5 were very similar to that one observed for irradiated microcrystalline DL-alpha-alanine. In the case of alanine supported on HY an initial EPR spectrum was different and only after some weeks it made resemble to the well known quintet observed in microcrystalline samples. In sodalites synthesized in the presence of DL-alpha-alanine EPR signal appeared in non-irradiated sample was very low and structureless. The irradiated sample showed a distinct spectrum which was quite different from that one observed for crystalline DL-alpha-alanine.

Sucrose radical-production cross-section regarding heavy-ion irradiation.

We investigated the sucrose radical-production cross-section induced by heavy-ion irradiation. L-alanine was also used in order to compare radical yield and cross-section. The stable free radicals after irradiation were analyzed by electron paramagnetic resonance (EPR). The radical yield obtained by the irradiated samples had a logarithmic correlation with the LET (linear energy transfer). Quantitative EPR analyses showed that radical productions for sucrose and L-alanine vary both by different particle irradiation and the LET under the same absorbed dose. Furthermore, the cross-sections of radical productions for samples were calculated. Both cross-sections for C ions irradiation under LET 30 keV/microm at 50 Gy dose were approximately 3.0x10(-9) microm(2), taking account of the molecular areas of the samples. The values of the cross-sections imply that multiple ionizing particles involve producing stable radicals.

The effect of dose on light-sensitivity of radicals in alanine EPR dosimeters.

In this work we present a study of light-induced effects on free radicals and their transformations in gamma-irradiated pure L-alanine and in commercially available alanine detectors: rods, pellets and films. Samples irradiated to doses from 2 Gy to 4000 kGy were exposed to light from a fluorescent lamp and to ordinary daylight. The observed changes in EPR spectra of the samples were analyzed with regard to their intensity and shape. The shape analysis was based on numerical decomposition of the measured spectra into model spectra reflecting contributions of R1, R2 and R3 radical populations in the samples. The illumination of alanine dosimeters resulted in significant decrease of the central EPR line and was accompanied by distinct variations in the shape of EPR spectra. The rate of light-induced decay in spectra amplitude was found to be dependent on dose of ionizing radiation--the sensitivity to light was decreasing with increase in dose in all detectors in the 2-5x10(5) Gy dose range. The exposure of gamma-irradiated (to 300 Gy) alanine to normal, diffused daylight resulted in decay of the signal amplitude at rate about 0.5% per week. It was shown that decay in the R1 component was responsible for the observed reduction of the spectra amplitude. The observed increase in R2 contributions in samples exposed to light confirmed a hypothesis of R-->R2 radical transformations promoted by visible light. The reported effects indicate a necessity of protection of irradiated dosimeters from their prolonged exposure to light.