Effect of inaccurate small field output factors on brain SRS plans

External beam radiotherapy often includes the use of field sizes 3 × 3 cm2 or less, which can be defined as small fields. Dosimetry is a difficult, yet important part of the radiotherapy process. The dosimetry of small fields has additional challenges, which can lead to treatment inconsistencies if not done properly. Most important is the use of an appropriate detector, as well as the application of the necessary corrections. The International Atomic Energy Agency and the American Association of Physicists in Medicine provide the International Code of Practice (CoP) TRS-483 for the dosimetry of small static fields used in external MV photon beams. It gives guidelines on how to apply small-field correction factors for small field dosimetry. The purpose of this study was to evaluate the impact of inaccurate small-field output factors on clinical brain stereotactic radiosurgery plans with and without applying the small-field correction factors as suggested in the CoP. Small-field correction factors for a Varian TrueBeam linear accelerator were applied to uncorrected relative dose factors. Uncorrected and corrected clinical plans were created with two different beam configurations, 6 MV with a flattening filter (6 WFF) and 6 MV without a flattening filter (6 FFF). For the corrected plans, the planning target volume mean dose was 1.6 ± 0.9% lower with p < 0.001 for 6 WFF and 1.8 ± 1.5% lower with p < 0.001 for 6 FFF. For brainstem, a major organ at risk, the corrected plans had a dose that was 1.6 ± 0.9% lower with p = 0.03 for 6 WFF and 1.8 ± 1.5% lower with p = 0.10 for 6 FFF. This represents a systematic error that should and can be corrected.

The magnetic field dependent displacement effect and its correction in reference and relative dosimetry

Objective This study investigates the perturbation correction factors of air-filled ionization chambers regarding their depth and magnetic field dependence. Focus has been placed on the displacement or gradient correction factor Pgr. Besides, the shift of the effective point of measurement Peff that can be applied to account for the gradient effect has been compared between the cases with and without magnetic field. Approach The perturbation correction factors have been simulated by stepwise modifications of the models of three ionization chambers (Farmer 30013, Semiflex 3D 31021 and PinPoint 3D 31022, all from PTW Freiburg). A 10 cm x 10 cm 6 MV photon beam perpendicular to the chamber’s axis was used. A 1.5 T magnetic field was aligned parallel to the chamber’s axis. The correction factors were determined between 0.4 and 20 cm depth. The shift of Peff from the chamber's reference point Pref, ∆z, was determined by minimizing the variation of the ratio between dose-to-water Dw(zref+∆z) and the dose-to-air Dair(zref) along the depth. Main Results The perturbation correction factors with and without magnetic field are depth dependent in the build-up region but can be considered as constant beyond the depth of dose maximum. Additionally, the correction factors are modified by the magnetic field. Pgr at the reference depth is found to be larger in 1.5 T magnetic field than in the magnetic field free case, where an increase of up to 1% is obserbed for the largest chamber (Farmer 30013). The magnitude of ∆z for all chambers decreases by 40% in a 1.5 T magnetic field with the sign of ∆z remains negative. Significance In reference dosimetry, the change of Pgr in a magnetic field can be corrected by applying the magnetic field correction factor kB Qmsr when the chamber is positioned with its Pref at the depth of measurement. However, due to the depth dependence of the perturbation factors, it is more convenient to apply the ∆z-shift during chamber positioning in relative dosimetry.

Об экспериментальном определении параметров интенсивности 4f-4f-переходов по спектрам излучения соединений европия (III)

Eu3+ complexes and specially β-diketonate compounds are well known and studied in several areas due to their luminescence properties, such as sensors and lightning devices. A unique feature of the Eu3+ ion is the experimental determination of the 4f-4f intensity parameters Ωλ directly from the emission spectrum. The equations for determining Ωλ from the emission spectra are different for the detection of emitted power compared to modern equipment that detects photons per second. It is shown that the differences between Ωλ determined by misusing the equations are sizable for Ω4 (ca. 15.5%) for several Eu3+β-diketonate complexes and leads to differences of ca. 5% in the intrinsic quantum yields Q_Ln^Ln. Due to the unique features of trivalent lanthanide ions, such as the shielding of 4f-electrons, which lead to small covalency and crystal field effects, a linear correlation was observed between Ωλ obtained using the emitted power and photon counting equations. We stress that care should be exercised with the type of detection should be taken and provide the correction factors for the intensity parameters. In addition, we suggest that the integrated intensity (proportional to the areas of the emission band) and the centroid (or barycenter) of the transition for obtaining Ωλ should be determined in the properly Jacobian-transformed spectrum in wavenumbers (or energy). Due to the small widths of the emission bands of typical 4f-4f transitions, the areas and centroids of the bands do not depend on the transformation within the experimental uncertainties. These assessments are relevant because they validate previously determined Ωλ without the proper spectral transformation.

Simultaneous Determination of Four Ingredients in Plantago Depressa by Single Marker

Objective. To establish a quantitative analysis of multicomponents by single marker (QAMS) method for the simultaneous determination of 4 active components such as protocatechuic acid, catechin, quercetin, and luteolin in Plantago depressa. Method. 4 active components in Plantago depressa were studied. Quercetin was used as an internal reference to establish the relative correction factors among protocatechuic acid, catechin, and luteolin and calculate the contents of each component; the results were compared with those measured by the external standard method. Results. 4 components showed a good linear relationship in their respective concentration ranges (r > 0.9995). The relative correction factors (fs/k) of protocatechuic acid, catechin, and luteolin were 1.1992, 0.8613, and 1.6069, respectively. The method had good durability. The contents of protocatechuic acid, catechin, and luteolin calculated by QAMS were not significantly different from those measured by the external standard method. Conclusion. QAMS can be used to determine the content of 4 components in Plantago depressa at the same time, and the method is simple, accurate, and can be used for quality control.

Look−up tables resolved by complex refractive index to correct particle sizes measured by common research−grade optical particle counters

Optical particle counters (OPC) are widely used to measure the aerosol particle number size distribution at atmospheric ambient conditions and over a large size range. Their measurement principle is based on the dependence of light scattering on particle size. However, this dependence is not monotonic at all sizes and light scattering also depends on the particle composition (i.e., the complex refractive index, CRI) and morphology. Therefore, the conversion of the measured scattered intensity to the desired particle size depends on the microphysical properties of the sampled aerosol population and might not be unique at all sizes. While these complexities have been addressed before, corrections are typically applied ad-hoc and are not standardised. This paper addresses this issue by providing a consistent and extended database of pre−computed correction factors for a wide range of complex refractive index values representing the composition variability of atmospheric aerosols. These correction factors are calculated for five different commercial OPCs (USHAS, PCASP, FSSP, GRIMM and its airborne version Sky− GRIMM, CDP) by assuming Mie theory for homogeneous spherical particles, and by varying the real part of the CRI between 1.33 and 1.75 in steps of 0.01 and the imaginary part between 0.0 and 0.4 in steps of 0.001. Correction factors for mineral dust are provided at the CRI of 1.53 – 0.003i and account for the asphericity of these particles. The datasets described in this paper are distributed at open-access repository: https://doi.org/10.25326/234 (license CC BY, Formenti et al., 2021) maintained by the French national center for Atmospheric data and services AERIS to data users/geophysicists who number size distribution measurements from OPC for their research on atmospheric aerosols. Application and caveats of the CRI-corrections factors are presented and discussed. The dataset presented in this paper is not only useful for correcting the size distribution from an OPC when the particle refractive index is known, but even when only assumptions can be made. Furthermore, this dataset can be useful in calculating uncertainties or sensitivities of aerosol volume/mass/extinction from OPCs given no or limited knowledge of refractive index.

Combining δ13C and δ15N from bone and dentine in marine mammal palaeoecological research: insights from toothed whales

Rationale Stable carbon (δ13C) and nitrogen (δ15N) isotope compositions of bone and dentine collagen extracted from subfossil specimens of extinct and extant mammalian species have been widely used to study the paleoecology of past populations. Due to possible systematic differences in stable isotope values between bone and dentine, dentine values can be transformed into bone-collagen equivalent using a correction factor. This approach has been applied to terrestrial species, but correction factors specifically for marine mammals are lacking. Here, we provide correction factors to transform dentine δ13C and δ15N values into bone-collagen equivalent for two toothed whale sister species: narwhal and beluga. Methods We sampled bone and tooth dentine from the skulls of 11 narwhals and 26 belugas. In narwhals, dentine was sampled from tusk and embedded tooth; in beluga, dentine was sampled from tooth. δ13C and δ15N were measured using an elemental analyzer coupled to a continuous flow isotope ratio mass spectrometer. Intraindividual bone and dentine isotopic compositions were used to calculate correction factors for each species, and to translate dentine isotopic values into bone-collagen equivalent. Results Our analysis revealed differences in δ13C and δ15N between bone and dentine. In narwhals, we found (i) lower average δ13C in bone compared with dentine from tusk and embedded tooth; (ii) no difference in dentine δ13C between tusk and embedded tooth; (iii) lower average δ15N in bone compared with dentine, with the highest values found in embedded tooth. For belugas, we also detected lower δ13C and δ15N in bone compared with tooth dentine. Conclusions Based on our analysis, we provide bone/dentine correction factors for narwhals (both at species and population level), and for belugas. The correction factors, when applied to dentine δ13C and δ15N values, enable the combined analysis of stable isotope data from bone and dentine.