The cellular track structure theory (TST), introduced by Katz in 1968, applies the concept of action cross section as the probability of targets in the radiation detector being activated to elicit ...the observed endpoint (e.g. cell killing). The ion beam radiation field is specified by the charge Z, speed β (or energy), fluence and linear energy transfer (LET) of the ion, rather than by its total absorbed dose or dose-averaged LET. The detector is represented by radiosensitive elements of size a0 and radiosensitivity D0, its gamma-ray response being represented by c-hit or multi-target expressions rather than by the linear-quadratic formula. Key to TST is the Dδ(r) formula describing the radial distribution of delta-ray dose (RDD) around the ion path. This formula, when folded with the dose response of the detector and radially integrated, yields the 'point target' action cross section value, σPT. The averaged value of the cross section, σ, is obtained by radially integrating the a0-averaged RDD. In the 'track width' regime which may occur at the distal end of the ion's path, the value of σ may considerably exceed its geometrical value, Formula: see text. Several scaling principles are applied in TST, resulting in its simple analytic formulation. Multi-target detectors, such as cells, are represented in TST by m, D0, σ0 (the 'saturation value' of the cross section which replaces a0) and κ (a 'detector saturation index'), as the fourth model parameter. With increasing LET of the ion, the two-component formulation of TST allows for successive transition from shouldered survival curves at low LET values to exponential ones at radiobiological effectiveness (RBE) maximum, followed by 'thindown' at the end of the ion track. For a given cell line, having best-fitted the four model parameters (m, D0, σ0 and κ) to an available data set of measured survival curves, TST is able to quantitatively predict cell survival and RBE for this cell line after any other ion irradiation.
An algorithm was developed of a treatment planning system (TPS) kernel for carbon radiotherapy in which Katz's Track Structure Theory of cellular survival (TST) is applied as its radiobiology ...component. The physical beam model is based on available tabularised data, prepared by Monte Carlo simulations of a set of pristine carbon beams of different input energies. An optimisation tool developed for this purpose is used to find the composition of pristine carbon beams of input energies and fluences which delivers a pre-selected depth-dose distribution profile over the spread-out Bragg peak (SOBP) region. Using an extrapolation algorithm, energy-fluence spectra of the primary carbon ions and of all their secondary fragments are obtained over regular steps of beam depths. To obtain survival vs. depth distributions, the TST calculation is applied to the energy-fluence spectra of the mixed field of primary ions and of their secondary products at the given beam depths. Katz's TST offers a unique analytical and quantitative prediction of cell survival in such mixed ion fields. By optimising the pristine beam composition to a published depth-dose profile over the SOBP region of a carbon beam and using TST model parameters representing the survival of CHO (Chinese Hamster Ovary) cells in vitro, it was possible to satisfactorily reproduce a published data set of CHO cell survival vs. depth measurements after carbon ion irradiation. The authors also show by a TST calculation that 'biological dose' is neither linear nor additive.
The authors describe a numerical algorithm to optimise the entrance spectra of a composition of pristine carbon ion beams which delivers a pre-assumed dose-depth profile over a given depth range ...within the spread-out Bragg peak. The physical beam transport model is based on tabularised data generated using the SHIELD-HIT10A Monte-Carlo code. Depth-dose profile optimisation is achieved by minimising the deviation from the pre-assumed profile evaluated on a regular grid of points over a given depth range. This multi-dimensional minimisation problem is solved using the L-BFGS-B algorithm, with parallel processing support. Another multi-dimensional interpolation algorithm is used to calculate at given beam depths the cumulative energy-fluence spectra for primary and secondary ions in the optimised beam composition. Knowledge of such energy-fluence spectra for each ion is required by the mixed-field calculation of Katz's cellular Track Structure Theory (TST) that predicts the resulting depth-survival profile. The optimisation algorithm and the TST mixed-field calculation are essential tools in the development of a one-dimensional kernel of a carbon ion therapy planning system. All codes used in the work are generally accessible within the libamtrack open source platform.
In a study of amorphous track models, in the local effect model (LEM), the Kellerer algorithm was used, which folds radial dose distributions from different ion tracks. In representative set of 10 ...experimental cell survival curves of normal human skin fibroblast cells irradiated with carbon ions, the method that applies the Kellerer algorithm was found to be more accurate and 10(4) times faster than the usual Monte Carlo summation method based on a regular grid.
Abstract
Charged lepton system symmetry under combined charge, parity, and time-reversal transformation (CPT) remains scarcely tested. Despite stringent quantum-electrodynamic limits, discrepancies ...in predictions for the electron–positron bound state (positronium atom) motivate further investigation, including fundamental symmetry tests. While CPT noninvariance effects could be manifested in non-vanishing angular correlations between final-state photons and spin of annihilating positronium, measurements were previously limited by knowledge of the latter. Here, we demonstrate tomographic reconstruction techniques applied to three-photon annihilations of ortho-positronium atoms to estimate their spin polarisation without magnetic field or polarised positronium source. We use a plastic-scintillator-based positron-emission-tomography scanner to record ortho-positronium (o-Ps) annihilations with single-event estimation of o-Ps spin and determine the complete spectrum of an angular correlation operator sensitive to CPT-violating effects. We find no violation at the precision level of 10
−4
, with an over threefold improvement on the previous measurement.
A novel approach to tomographic data processing has been developed and evaluated using the Jagiellonian positron emission tomography scanner as an example. We propose a system in which there is no ...need for powerful, local to the scanner processing facility, capable to reconstruct images on the fly. Instead, we introduce a field programmable gate array system-on-chip platform connected directly to data streams coming from the scanner, which can perform event building, filtering, coincidence search, and region-of-response reconstruction by the programmable logic and visualization by the integrated processors. The platform significantly reduces data volume converting raw data to a list-mode representation, while generating visualization on the fly.
Building upon our recent study G. S. Bali et al., Eur. Phys. J. C 78, 217 (2018), we investigate the feasibility of calculating the pion distribution amplitude from suitably chosen Euclidean ...correlation functions at large momentum. We demonstrate in this work the advantage of analyzing several correlation functions simultaneously and extracting the pion distribution amplitude from a global fit. This approach also allows us to study higher-twist corrections, which are a major source of systematic error. Our result for the higher-twist parameter δ2π is in good agreement with estimates from QCD sum rules. Another novel element is the use of all-to-all propagators, calculated using stochastic estimators, which enables an additional volume average of the correlation functions, thereby reducing statistical errors.
J-PET is a detector optimized for registration of photons from the electron–positron annihilation via plastic scintillators where photons interact predominantly via Compton scattering. Registration ...of both primary and scattered photons enables to determinate the linear polarization of the primary photon on the event by event basis with a certain probability. Here we present quantitative results on the feasibility of such polarization measurements of photons from the decay of positronium with the J-PET and explore the physical limitations for the resolution of the polarization determination of 511 keV photons via Compton scattering. For scattering angles of about 82
∘
(where the best contrast for polarization measurement is theoretically predicted) we find that the single event resolution for the determination of the polarization is about 40
∘
(predominantly due to properties of the Compton effect). However, for samples larger than ten thousand events the J-PET is capable of determining relative average polarization of these photons with the precision of about few degrees. The obtained results open new perspectives for studies of various physics phenomena such as quantum entanglement and tests of discrete symmetries in decays of positronium and extend the energy range of polarization measurements by five orders of magnitude beyond the optical wavelength regime.
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