In Quest of the Alanine R3 Radical: Multivariate EPR Spectral Analyses of X-Irradiated Alanine in the Solid State.

The amino acid l-α-alanine is the most commonly used material for solid-state electron paramagnetic resonance (EPR) dosimetry, due to the formation of highly stable radicals upon irradiation, with yields proportional to the radiation dose. Two major alanine radical components designated R1 and R2 have previously been uniquely characterized from EPR and electron-nuclear double resonance (ENDOR) studies as well as from quantum chemical calculations. There is also convincing experimental evidence of a third minor radical component R3, and a tentative radical structure has been suggested, even though no well-defined spectral signature has been observed experimentally.

Validation of dose painting of lung tumours using alanine/EPR dosimetry.

Biologic image guided radiotherapy (RT) with escalated doses to tumour sub volumes challenges today's RT dose planning and delivery systems. In this phantom study, we verify the capability of a clinical dose planning and delivery system to deliver an 18F-FDG-PET based dose painted treatment plan to a lung tumour. Furthermore, we estimate the uncertainties of the dose painted treatment compared to conventional RT plans.

Lithium Formate for EPR Dosimetry (2): Secondary Radicals in X-Irradiated Crystals.

The secondary radiation-induced radicals in lithium formate monohydrate were studied using electron paramagnetic resonance (EPR), electron nuclear double resonance (ENDOR) and ENDOR-induced EPR (EIE) techniques complemented with periodic density functional theory (DFT) calculations. Single crystals of lithium formate monohydrate were X irradiated at 77 K and at room temperature. The main radicals present after irradiation at 77 K are the CO(2)(•-) radical (R1), the recently identified protonated electron-gain product, HCOOH(•-) (R2) (Krivokapić et al.

Direct radiation effects to the amino acid side chain: EMR and periodic DFT of X-irradiated L-asparagine at 6 K.

Radical formation in single crystals of L-asparagine monohydrate following X-irradiation at 6 K has been investigated at 6 K and at elevated temperatures using various electron magnetic resonance (EMR) techniques such as electron paramagnetic resonance (EPR), electron nuclear double resonance (ENDOR), and ENDOR-induced EPR (EIE) spectroscopy. Molecular structures of the three free radicals stable at 6 K were assessed by detailed analysis of the experimental data and density functional theory (DFT) calculations in a periodic approach. Radical LI is assumed to result from one-electron reduction at the amide functional group in the asparagine side chain followed by protonation at the amide carbonyl oxygen by proton transfer from a neighboring molecule across a hydrogen bond.

Lithium formate for EPR dosimetry: radiation-induced radical trapping at low temperatures.

Radiation-induced primary radicals in lithium formate. A material used in EPR dosimetry have been studied using electron paramagnetic resonance (EPR), electron nuclear double resonance (ENDOR) and ENDOR-Induced EPR (EIE) techniques. In this study, single crystals were X irradiated at 6-8 K and radical formation at these and higher temperatures were investigated.

EPR dosimetry intercomparison using smart phone touch screen glass.

This paper presents the results of an interlaboratory comparison of retrospective dosimetry using the electron paramagnetic resonance method. The test material used in this exercise was glass coming from the touch screens of smart phones that might be used as fortuitous dosimeters in a large-scale radiological incident. There were 13 participants to whom samples were dispatched, and 11 laboratories reported results.

Solved? The reductive radiation chemistry of alanine.

The structural changes throughout the entire reductive radiation-induced pathway of l-α-alanine are solved on an atomistic level with the aid of periodic DFT and nudged elastic band (NEB) simulations. This yields unprecedented information on the conformational changes taking place, including the protonation state of the carboxyl group in the "unstable" and "stable" alanine radicals and the internal transformation converting these two radical variants at temperatures above 220 K. The structures of all stable radicals were verified by calculating EPR properties and comparing those with experimental data.

The risk of radiation-induced breast cancers due to biennial mammographic screening in women aged 50-69 years is minimal.

Background: The main aim of mammographic screening is to reduce the mortality from breast cancer. However, use of ionizing radiation is considered a potential harm due to the possible risk of inducing cancer in healthy women.

Purpose: To estimate the potential number of radiation-induced breast cancers, radiation-induced breast cancer deaths, and lives saved due to implementation of organized mammographic screening as performed in Norway.

Structural specificity of alkoxy radical formation in crystalline carbohydrates.

A DFT study of radiation induced alkoxy radical formation in crystalline α-l-rhamnose has been performed to better understand the processes leading to selective radical formation in carbohydrates upon exposure to ionizing radiation at low temperatures. The apparent specificity of radiation damage to carbohydrates is of great interest for understanding radiation damage processes in the ribose backbone of the DNA molecule. Alkoxy radicals are formed by deprotonation from hydroxyl groups in oxidized sugar molecules.

Radiation products at 77 K in trehalose single crystals: EMR and DFT analysis.

The radicals obtained in trehalose dihydrate single crystals after 77 K X-irradiation have been investigated at the same temperature using X-band electron paramagnetic resonance (EPR), electron nuclear double resonance (ENDOR), and ENDOR-induced EPR (EIE) techniques. Five proton hyperfine coupling tensors were unambiguously determined from the ENDOR measurements and assigned to three carbon-centered radical species (T1, T1*, and T2) based on the EIE spectra. EPR angular variations revealed the presence of four additional alkoxy radical species (T3 to T6) and allowed determination of their g tensors.

The energy dependence of lithium formate and alanine EPR dosimeters for medium energy x rays.

Purpose: To perform a systematic investigation of the energy dependence of alanine and lilthium formate EPR dosimeters for medium energy x rays.

Methods: Lithium formate and alanine EPR dosimeters were exposed to eight different x-ray beam qualities, with nominal potentials ranging from 50 to 200 kV. Following ionometry based on standards of absorbed dose to water, the dosimeters were given two different doses of approximately 3 and 6 Gy for each radiation quality, with three dosimeters for each dose.

Interphantom and interscanner variations for Hounsfield units--establishment of reference values for HU in a commercial QA phantom.

In computer tomography (CT) diagnostics, the measured Hounsfield units (HU) are used to characterize tissue and are in that respect compared to nominal HU values found in the radiological literature. Quality assurance (QA) phantoms are commercially available with a variety of tissue substitutes and materials to test the HU values in CT. It is however recognized from CT physics that the HU for a given material is energy dependent and may vary substantially between scanners.

Radical formation in lithium formate EPR dosimeters after irradiation with protons and nitrogen ions.

Radical formation in polycrystalline lithium formate monohydrate after irradiation with gamma rays, protons and nitrogen ions at room temperature was studied by continuous-wave electron paramagnetic resonance (EPR) spectroscopy. The linear energy transfer (LET) of the various radiation beams was 0.2, 0.

On the identity of the radiation-induced stable alanine radical.

Using periodic DFT calculations, it is concluded that the stable radiation-induced alanine radical most probably is the result of reductive deamination and protonation of the detached amino group, yielding an NH(4)(+) ammonium ion and a negatively charged radical.

Radicals in 5-methylcytosine induced by ionizing radiation. Electron magnetic resonance for structural and mechanistic analyses.

Single crystals of 5-methylcytosine hemihydrate and 5-methylcytosine hydrochloride were X-irradiated and studied at 10 K and at higher temperatures using X- and K-band EPR, ENDOR and EIE spectroscopy. In the hemihydrate crystals, four radicals were identified at 10 K, one of them being the recently reported N1-deprotonated one-electron oxidation product (Krivokapić et al., J.

Dosimetry of stereotactic radiosurgery using lithium formate EPR dosimeters.

Small lithium formate EPR (electron paramagnetic resonance) dosimeters (diameter 3 mm, height 2 mm) were produced and employed for 2D dosimetry of stereotactic radiosurgery (SRS). An anthropomorphic head phantom with an in-house made insert holding 45 lithium formate dosimeters was used. A spherical target was outlined centrally in planning CT images of the head and an SRS dose plan with three arcs was made using the iPlan planning system.

Primary oxidation products of 5-methylcytosine: methyl dynamics and environmental influences.

The primary oxidation product in X-irradiated single crystals of 5-methylcytosine hemihydrate and 5-methylcytosine hydrochloride has been studied at 10 K, using electron paramagnetic resonance (EPR), electron-nuclear double resonance (ENDOR), and ENDOR-induced EPR (EIE) spectroscopies. The radical is characterized by large couplings to the methyl protons and appears to be deprotonated at N1 in both crystal systems. In the hydrochloride crystal the methyl group is completely frozen at 10 K, whereas in the hemihydrate crystal it undergoes tunneling rotation.

The energy dependence of lithium formate EPR dosimeters for clinical electron beams.

The objective of this study was to investigate the potential of using polycrystalline lithium formate for EPR (electron paramagnetic resonance) dosimetry of clinical electron beams, with the main focus on the dose-to-water energy response. Lithium formate dosimeters were irradiated using (60)Co gamma-rays and 6-20 MeV electrons in a PMMA phantom to doses in the range of 3-9 Gy. A plane-parallel ion chamber was used for water-based absolute dosimetry.

EPR dosimetry of radiotherapy photon beams in inhomogeneous media using alanine films.

In the current work, EPR (electron paramagnetic resonance) dosimetry using alanine films (134 microm thick) was utilized for dose measurements in inhomogeneous phantoms irradiated with radiotherapy photon beams. The main phantom material was PMMA, while either Styrofoam or aluminium was introduced as an inhomogeneity. The phantoms were irradiated to a maximum dose of about 30 Gy with 6 or 15 MV photons.

Single crystals of L-O-serine phosphate X-irradiated at low temperatures: EPR, ENDOR, EIE, and DFT studies.

Single crystals of the phosphorylated amino acid L-O-serine phosphate were X-irradiated and studied at 10 K and at 77 K using EPR, ENDOR, and EIE techniques. Two radicals, R1(10 K) and R1(77 K), were detected and characterized as two different geometrical conformations of the protonated reduction product >CH-C(OH)(2). R1(10 K) is only observed after irradiation at 10 K, and upon heating to 40 K, R1(10 K) transforms rapidly and irreversibly into R1(77 K).

Electron transfer in amino acid.nucleic acid base complexes: EPR, ENDOR, and DFT study of X-irradiated N-formylglycine.cytosine complex crystals.

Single crystals of the 1:1 complex of the nucleic acid base cytosine and the dipeptide N-formylglycine (C.NFG) have been irradiated at 10 and 273 K to doses of about 70 kGy and studied at temperatures between 10 and 293 K using 24 GHz (K-band) and 9.5 GHz (X-band) electron paramagnetic resonance (EPR), electron nuclear double resonance (ENDOR), and ENDOR-induced EPR (EIE) spectroscopy.

LET effects following neutron irradiation of lithium formate EPR dosimeters.

Lithium formate electron paramagnetic resonance (EPR) dosimeters were irradiated using 60Co gamma-rays or fast neutrons to doses ranging from 5 to 20 Gy and investigated by EPR spectroscopy. Using a polynomial fitting procedure in order to accurately analyze peak-to-peak line widths of first derivative EPR spectra, dosimeters irradiated with neutrons had on average 4.4+/-0.

Electron paramagnetic resonance (EPR) dosimetry using lithium formate in radiotherapy: comparison with thermoluminescence (TL) dosimetry using lithium fluoride rods.

Solid-state radiation dosimetry by electron paramagnetic resonance (EPR) spectroscopy and thermoluminescence (TL) was utilized for the determination of absorbed doses in the range of 0.5-2.5 Gy.

The solid-state radiation chemistry of simple amino acids, revisited.

The solid-state radiation-induced free radical formation in simple amino acids like alpha-glycine (gly) and L-alpha-alanine (ala) has been the subject of investigations by EPR spectroscopy since the late 1950s. The EPR spectra from crystals of gly and ala generally are very complex due to the simultaneous trapping of several free radicals regardless of irradiation and observation temperatures. Untangling these complex spectra is necessary for understanding the mechanisms for the solid-state radiation chemistry of amino acids.

Estimation of X-ray beam quality by electron paramagnetic resonance (EPR) spectroscopy.

A novel dosimetry-based technique using EPR spectroscopy to determine X-ray beam quality is proposed. The radiation-sensitive material is made of a mixture of two polycrystalline substances with different X-ray absorption properties. The composite samples, consisting of polycrystalline lithium formate monohydrate and calcium formate, were prepared as pellets, X-irradiated, and analyzed with EPR spectroscopy.