•MC calculation of dose average LET and RBE evaluation.•Cross Sections for the production of secondary particles in proton therapy.•Calculation of fluence of secondary particles at different depth in ...water for the implementation in a TPS of next generation.
In proton therapy, secondary fragments are created in nuclear interactions of the beam with the target nuclei. The secondary fragments have low kinetic energies and high atomic numbers as compared to primary protons. Fragments have a high LET and deposit all their energy close to the generation point. For their characteristics, secondary fragments can alter the dose distribution and lead to an increase of RBE for the same delivered physical dose. Moreover, the radiobiological impact of target fragmentation is significant mostly in the region before the Bragg peak, where generally healthy tissues are present, and immediately after Bragg peak. Considering the high biological impact of those particles, especially in the case of healthy tissues or organs at risk, the inclusion of target fragmentation processes in the dose calculation of a treatment planning system can be relevant to improve the treatment accuracy and for this reason it is one of the major tasks of the MoVe IT project.
In this study, Monte Carlo simulations were employed to fully characterize the mixed radiation field generated by target fragmentation in proton therapy. The dose averaged LET has been evaluated in case of a Spread Out Bragg Peak (SOBP). Starting from LET distribution, RBE has been evaluated with two different phenomenological models. In order to characterize the mixed radiation field, the production cross section has been evaluated by means of the FLUKA code. The future development of present work is to generate a MC database of fragments fluence to be included in TPS.
•Averaged LET values reported for RBE studies may strongly depend on the details of how the averaging was done. Typically, these are not specified.•Some LET-RBE models are derived from data using ...inconsistent types of averaged LET, introducing a source of error to the RBE(LET) relationship.•We recommend that the averaged LET is recorded more carefully and provide details on how to do so.
Linear Energy Transfer (LET) is widely used to express the radiation quality of ion beams, when characterizing the biological effectiveness. However, averaged LET may be defined in multiple ways, and the chosen definition may impact the resulting reported value. We review averaged LET definitions found in the literature, and quantify which impact using these various definitions have for different reference setups. We recorded the averaged LET definitions used in 354 publications quantifying the relative biological effectiveness (RBE) of hadronic beams, and investigated how these various definitions impact the reported averaged LET using a Monte Carlo particle transport code. We find that the kind of averaged LET being applied is, generally, poorly defined. Some definitions of averaged LET may influence the reported averaged LET values up to an order of magnitude. For publications involving protons, most applied dose averaged LET when reporting RBE. The absence of what target medium is used and what secondary particles are included further contributes to an ill-defined averaged LET. We also found evidence of inconsistent usage of averaged LET definitions when deriving LET-based RBE models. To conclude, due to commonly ill-defined averaged LET and to the inherent problems of LET-based RBE models, averaged LET may only be used as a coarse indicator of radiation quality. We propose a more rigorous way of reporting LET values, and suggest that ideally the entire particle fluence spectra should be recorded and provided for future RBE studies, from which any type of averaged LET (or other quantities) may be inferred.
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.
Precise knowledge of the beam optics at the LHC is crucial to fulfill the physics goals of the TOTEM experiment, where the kinematics of the scattered protons is reconstructed with near-beam ...telescopes-so-called Roman pots (RP). Before being detected, the protons' trajectories are influenced by the magnetic fields of the accelerator lattice. Thus precise understanding of the proton transport is of key importance for the experiment. A novel method of optics evaluation is proposed which exploits kinematical distributions of elastically scattered protons observed in the RPs. Theoretical predictions, as well as Monte Carlo studies, show that the residual uncertainty of the optics estimation method is smaller than .
We present an open-source code library for amorphous track modelling which is suppose to faciliate the application and numerical comparability as well as serve as a frame-work for the implementation ...of new models. We show an example of using the library indicating the choice of submodels has a significant impact on the modelling outcome.
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.
Several models of Radial Dose Distribution predict that in the track core of the heavy ion, at the radial distances closer than 1 nm the local dose can exceed 100 kGy, but this prediction has never ...been experimentally verified. Within this work MCP-N (LiF:Mg,Cu,P) thermoluminescence (TL) detectors, which show high temperature TL glow peak structure between 350 °C and 500 °C after exposure to doses of gamma-rays as high as 1 MGy, were irradiated with Am-241 α-particles with fluences 10
7–10
11 particles/cm
2. For fluences 9 × 10
9 cm
−2 in MCP-N TL glow curves high temperature peaks were observed which confirmed that a fraction of energy of α-particles was transferred with the local doses exceeding 50 kGy. Calculation of dose (fluence) dependent microdosimetric distributions confirmed that at these fluences and target diameters of 80 nm high dose regions do not result from overlapping of tracks. It was estimated that approximately 20% of entire energy of 5.5 MeV α-particle penetrating LiF was deposited with local doses exceeding 50 kGy.
PDF
