Photon Fluence Research Articles

Photon spectra in NPL standard monoenergetic neutron fields.

A High Purity Germanium (HPGe) detector has been used to measure the photon spectra in the majority of monoenergetic neutron fields produced at NPL (0.144, 0.250, 0.565, 2.0, 5.0 and 16.5MeV). The HPGe was characterised and then modelled to produce a response matrix. The measured pulse height spectra were then unfolded to produce photon fluence spectra. The new spectra were used to improve the photon to neutron dose equivalent ratios from some earlier work at NPL with Geiger-Muller tubes and electronic personal dosemeters.

Interstellar Carbonaceous Dust Erosion Induced by X-Ray Irradiation of Water Ice in Star-forming Regions

The chemical inventory of protoplanetary midplanes is the basis for forming planetesimals. Among them, solid-state reactions based on CO/CO2 toward molecular complexity on interstellar dust grains have been studied in theoretical and laboratory work. The physicochemical interactions between ice, constituted mainly of H2O, and dust surfaces are limited to a few experimental studies focusing on vacuum ultraviolet and cosmic-ray processing. In this work, the erosion of C dust grains induced by X-ray irradiation of H2O ice was systematically investigated for the first time. The work aims to provide a better understanding of the reaction mechanism using selectively isotope-labeled oxygen/carbon species in kinetic analysis. Ultrahigh vacuum experiments were performed to study the interstellar ice analog on submicron, thick C dust at ∼13 K. H2O or O2 ice was deposited on the presynthesized amorphous C dust and exposed to soft X-ray photons (250–1250 eV). Fourier-transform infrared spectroscopy was used to monitor in situ the newly formed species as a function of the incident photon fluence. Field emission scanning electron microscopy was used to monitor the morphological changes of (non-)eroded carbon samples. The X-ray processing of the ice/dust interface leads to the formation of CO2, which further dissociates and forms CO. Carbonyl groups are formed by oxygen addition to grain surfaces and are confirmed as intermediate species in the formation process. The yields of CO and CO2 were found to be dependent on the thickness of the carbon layer. The astronomical relevance of the experimental findings is discussed.

Vertex Position Optimization for LATTICE Therapy

LATTICE radiation therapy (RT) aims to deliver 3D heterogenous dose of high peak-to-valley dose ratio (PVDR) to the tumor target, with peak dose at lattice vertices inside the target and valley dose for the rest of the target. In current clinical practice the lattice vertex positions are constant during treatment planning. This work proposes a new LATTICE plan optimization method that can optimize lattice vertex positions as plan variables, which is the first lattice vertex position optimization study to the best of our knowledge. The new LATTICE treatment planning method optimizes lattice vertex positions as well as other plan variables (e.g., photon fluences or proton spot weights), with optimization objectives for target PVDR and organs-at-risk (OAR) sparing. To satisfy mathematical differentiability, the lattice vertices are approximated in sigmoid functions. For geometric feasibility, proper geometry constraints are enforced onto the lattice vertex positions. The lattice vertex position optimization problem is solved by iterative convex relaxation method, where lattice vertex positions and photon/proton plan variables are jointly updated via the Quasi-Newton method. Both photon and proton LATTICE RT were considered, and the optimal lattice vertex positions in terms of plan objectives were found by solving all possible combinations on given discrete positions via heuristic searching based on standard IMRT/IMPT, which served as the ground truth for validating the new LATTICE method ("NEW"). That is, the plan with the smallest optimization objective ("BEST"), the plan with the median optimization objective ("MID"), and the plan with the largest optimization objective ("WORST") were selected as the reference plans to be compared with NEW. The table was for an abdomen case with the large bowel as the OAR, where the parameters are total optimization objective f, the mean valley dose of target Dvalley, the mean peak dose of target Dpeak, PVDR = Dpeak/Dvalley, and the mean dose of large bowel Dbowel. The unit of doses is Gy. The results in the table show that the new method indeed provided the optimal lattice vertex positions with the smallest optimization objective, the largest target PVDR, and the best OAR sparing. A new LATTICE treatment planning method is proposed and validated that can optimize lattice vertex positions as well as other photon or proton plan variables for improving target PVDR and OAR sparing.

A discrete ordinates Boltzmann solver for application to inverse planning of photons and protons

The aim of this work is to develop a discrete ordinates Boltzmann solver that can be used for calculation of absorbed dose from both photons and protons within an inverse planning optimiser, so as to perform accurate dose calculation throughout the whole of the inverse planning process. With photons, five transport sweeps were performed to obtain scattered photon fluence, and unscattered electron fluence was then obtained and used as a fixed source for solution of the electron transport equations. With protons, continuous slowing down was treated as a fixed source, and five transport sweeps were used to calculate scattered fluence. The total electron or proton fluence was multiplied by the stopping power ratio for the transport medium to obtain absorbed dose. The method was evaluated in homogeneous media and in a lung case where the planning target volume was surrounded by low-density lung material. Photon arc, proton passive scattering and proton arc treatments were considered. The results were compared to a clinically validated convolution dose calculation for photons, and with an analytical method for protons. In water-equivalent media, the discrete ordinates method agrees with the alternative algorithms to within 2%. Convergence is found to be sufficiently complete for water-, lung- and bone-equivalent materials after five iterations. The dose calculated by the relatively simple angular quadrature is seen to be very close to that calculated by a more comprehensive quadrature. For inhomogeneous lung plans, the method shows more heterogeneity of dose to the planning target volume than the comparative methods. The discrete ordinates Boltzmann solver provides a general framework for dose calculation with both photons and protons. The method is suitable for incorporation into an inverse planning optimiser, so that accurate dose calculation in a heterogeneous medium can be obtained throughout inverse planning, with the result that the final dose distribution is as predicted by the optimiser.

Accumulated dose implications from systematic dose-rate transients in gated treatments with Viewray MRIdian accelerators

The combination of magnetic resonance (MR) imaging and linear accelerators (linacs) into MR-Linacs enables continuous MR imaging and advanced gated treatments of patients. Previously, a dose-rate transient (∼8% reduced dose rate during the initial 0.5 s of each beam) was identified for a Viewray MRIdian MR-Linac (Klavsen et al 2022 Radiation Measurement 106759). Here, the dose-rate transient is studied in more detail at four linacs of the same type at different hospitals. The implications of dose-rate transients were examined for gated treatments. The dose-rate transients were investigated using dose-per pulse measurements with organic plastic scintillators in three experiments: (i) A gated treatment with the scintillator placed in a moving target in a dynamic phantom, (ii) a gated treatment with the same dynamic conditions but with the scintillator placed in a stationary target, and (iii) measurements in a water-equivalent material to examine beam quality deviations at a dose-per-pulse basis. Gated treatments (i) compared with non-gated treatments with a static target in the same setup showed a broadening of accumulated dose profiles due to motion (dose smearing). The linac with the largest dose-rate transient had a reduced accumulated dose of up to (3.1 ± 0.65) % in the center of the PTV due to the combined dose smearing and dose-rate transient effect. Dose-rate transients were found to vary between different machines. Two MR-Linacs showed initial dose-rate transients that could not be identified from conventional linearity tests. The source of the transients includes an initial change in photon fluence rate and an initial change in x-ray beam quality. For gated treatments, this caused a reduction of more than 1% dose delivered at the central part of the beam for the studied, cyclic-motion treatment plan. Quality assurance of this effect should be considered when gated treatment with the Viewray MRIdian is implemented clinically.

Search for Ultra-high-energy Photons from Gravitational Wave Sources with the Pierre Auger Observatory

A search for time-directional coincidences of ultra-high-energy (UHE) photons above 10 EeV with gravitational wave (GW) events from the LIGO/Virgo runs O1 to O3 is conducted with the Pierre Auger Observatory. Due to the distinctive properties of photon interactions and to the background expected from hadronic showers, a subset of the most interesting GW events is selected based on their localization quality and distance. Time periods of 1000 s around and 1 day after the GW events are analyzed. No coincidences are observed. Upper limits on the UHE photon fluence from a GW event are derived that are typically at ∼7 MeV cm−2 (time period 1000 s) and ∼35 MeV cm−2 (time period 1 day). Due to the proximity of the binary neutron star merger GW170817, the energy of the source transferred into UHE photons above 40 EeV is constrained to be less than 20% of its total GW energy. These are the first limits on UHE photons from GW sources.

Lattice position optimization for LATTICE therapy.

LATTICE radiation therapy delivers 3D heterogenous dose of high peak-to-valley dose ratio (PVDR) to the tumor target, with peak dose at lattice vertices inside the target and valley dose for the rest of the target. Although the lattice vertex positions can impact PVDR inside the target and sparing of organs-at-risk (OAR), they are fixed as constants and not optimized during treatment planning in current clinical practice. This work proposes a new LATTICE plan optimization method that can optimize lattice vertex positions during LATTICE treatment planning, which is the first lattice position optimization study to the best of our knowledge. The new LATTICE treatment planning method optimizes lattice vertex positions as well as other plan variables (e.g., photon fluences or proton spot weights), with optimization objectives for target PVDR and OAR sparing. To satisfy mathematical differentiability, the lattice vertices are approximated in sigmoid functions. For geometric feasibility, proper geometry constraints are enforced onto lattice vertex positions. The lattice position optimization problem is solved by iterative convex relaxation (ICR) method and alternating direction method of multipliers (ADMM), and lattice vertex positions and photon/proton plan variables are jointly updated via the Quasi-Newton method. Both photon and proton LATTICE RT were considered, and the optimal lattice vertex positions in terms of plan objectives were found by solving all possible combinations on given discrete positions via exhaustive searching based on standard IMRT/IMPT, which served as the ground truth for validating the new LATTICE method. The results show that the new method indeed provided the optimal lattice vertex positions with the smallest optimization objective, the largest target PVDR, and the best OAR sparing. A new LATTICE treatment planning method is proposed and validated that can optimize lattice vertex positions as well as other photon or proton plan variables for improving target PVDR and OAR sparing.

Fetal atomic bomb survivor dosimetry using the J45 series of pregnant female phantoms with realistic survivor exposure scenarios: comparisons to dose estimates in the DS02 system.

A significant source of information on radiation-induced biological effects following in-utero irradiation stems from studies of atomic bomb survivors who were pregnant at the time of exposure in Hiroshima, and to a lesser extent, from survivors in Nagasaki. Dose estimates to the developing fetus for these survivors have been assigned in prior dosimetry systems of the Radiation Effects Research Foundation as the dose to the uterine wall within the non-pregnant adult stylized phantom, originally designed for the dosimetry system DS86 and then carried forward in DS02. In a prior study, a new J45 (Japanese 1945) series of high-resolution phantoms of the adult pregnant female at 8weeks, 15weeks, 25weeks, and 38-weeks post-conception was presented. Fetal and maternal organ doses were estimated by computationally exposing the pregnant female phantom series to DS02 free-in-air cumulative photon and neutron fluences at three distances from the hypocenter at both Hiroshima and Nagasaki under idealized frontal (AP) and isotropic (ISO) particle incidence. In this present study, this work was extended using realistic angular fluences (480 directions) from the DS02 system for seven radiation source terms, nine different radiation dose components, and five shielding conditions. In addition, to explore the effects of fetal position within the womb, four new phantoms were created and the same irradiation scenarios were performed. General findings are that the current DS02 fetal dose surrogate overestimates values of fetal organ dose seen in the J45 phantoms towards the cranial end of the fetus, especially in the later stages of pregnancy. For example, for in-open exposures at 1000m in Hiroshima, the ratio of J45 fetal brain dose to DS02 uterine wall dose is 0.90, 0.82, and 0.70 at 15weeks, 25weeks, and 38-weeks, respectively, for total gamma exposures, and are 0.64, 0.44, and 0.37 at these same gestational ages for total neutron exposures. For organs in the abdominal and pelvic regions of the fetus, dose gradients across gestational age flatten and later reverse, so that DS02 fetal dosimetry begins to underestimate values of fetal organ dose as seen in the J45 phantoms. For example, for the same exposure scenario, the ratios of J45 fetal kidney dose to DS02 uterine wall dose are about 1.09 from 15 to 38weeks for total gamma dose, and are 1.30, 1.56, and 1.75 at 15weeks, 25weeks, and 38weeks, respectively, for the total neutron dose. Results using the new fetal positioning phantoms show this trend reversing for a head-up, breach fetal position. This work supports previous findings that the J45 pregnant female phantom series offers significant opportunities for gestational age-dependent assessment of fetal organ dose without the need to invoke the uterine wall as a fetal organ surrogate.

Kinetic modeling of charge transfer following photon bleaching post-irradiation of spatially correlated trapping and luminescent centers in LiF:Mg,Ti

Illumination of LiF:Mg,Ti by photons of energy 3.65 eV and levels of fluence from 1.2 1018 ph cm−2 to 3.6 1018 ph cm−2 results in a decrease of the thermoluminescence (TL) dose response supralinearity of peak 5 in the glow curve of LiF:Mg,Ti. No further effect on the dose response is observed at higher photon fluences up to 1.4 × 1019 ph cm−2. The threshold of dose response non-linearity usually reported at a dose of 1 Gy, is increased to 30 Gy. A kinetic model is described herein in the framework of conduction band/valence band solid state theory incorporating spatially correlated trapping centers (TCs) and luminescent centers (LCs). The model successfully simulates the bleaching action of the 3.65 eV photons on the increased region of TL dose response linearity as resulting from the depletion of the occupied trapping centers and to a lesser degree by charge transfer via the conduction band between the various configurations of the TC/LC system associated with composite peak 5.

Bremsstrahlung production from 10–30 MeV electrons incident on thick targets: Monte Carlo simulation with penelope

Purpose: To study the effect of the user-defined electron/positron simulation parameters C1 and C2 of the Monte Carlo code penelope on the results from simulations of bremsstrahlung photons generated by high energy electrons incident on thick targets. Methods:The version 2018 of the code system penelope, with four different sets of simulation parameters, is used to calculate the photon fluences produced by electron beams with initial energies ranging between 10 and 30MeV impinging on thick elemental targets of Be, Al and Pb. Using the calculated fluences, the integrated photon yields and the mean energies of the detected photons are also evaluated. The Monte Carlo results are compared to the available experimental data, the comparison being quantified by means of χ2 statistics. Results:Although acceptable agreement of simulation results with experimental data is found for all the simulations performed, a significant improvement in this agreement is observed when the parameter values C1=C2=0.01 or 0.001 are used, that is, when the simulations are more detailed. In the case of the mean energy of the detected photons, similar results are obtained in all the simulations. The results obtained with this version of the code improve those found with older versions in case of the Pb target. Conclusions:Regarding the emission of bremsstrahlung photons by MeV electrons, simulations with C1=C2=0.01 produce results that approximate the experimental data equally well as more detailed simulations with C1=C2=0.001, with a reduction of the simulation time between 81% and 89%, depending on the initial energy of the electrons.

Fraction optimization for hybrid proton-photon treatment planning.

Hybrid proton-photon radiotherapy (RT) can provide better plan quality than proton or photon only RT, in terms of robustness of target coverage and sparing of organs-at-risk (OAR). This work develops a hybrid treatment planning method that can optimize the number of proton and photon fractions as well as proton and photon plan variables, so that the hybrid plans can be clinically delivered day-to-day using either proton or photon machine. In the new hybrid treatment planning method, the total dose distribution (sum of proton dose and photon dose) is optimized for robust target coverage and optimal OAR sparing, by jointly optimizing proton spots and photon fluences, while the target dose uniformity is also enforced individually on both proton dose and photon dose, so that the hybrid plans can be separately and robustly delivered on proton or photon machine. To ensure the target dose uniformity for proton and photon plans, the number of proton and photon fractions is explicitly modeled and optimized, so that the target dose for proton and photon dose components is constrained to be a constant fraction of the total prescription dose while the plan quality based on total dose is optimized. The feasibility of hybrid planning using the proposed method is validated with representative clinical cases including abdomen, lung, head-and-neck (HN), and brain. For all cases, hybrid plans provided better overall plan quality and OAR sparing than proton-only or photon-only plans, better target dose uniformity and robustness than proton-only plans, quantified by treatment planning objectives and dosimetric parameters. Moreover, for HN and brain cases, hybrid plans also had better target coverage than photon-only plans. We have developed a new hybrid treatment planning method that optimizes number of proton and photon fractions as well as proton spots and photon fluences, for generating hybrid plans that can be separately and robustly delivered on proton or photon machines. Preliminary results have demonstrated that hybrid plans generated by the new method have better plan quality than proton-only or photon-only plans.

Investigation of variance reduction techniques on photon fluence and dose calculation efficiency for Elekta Agility head using EGSnrc MC code

The aim of this study is to investigate the effects of these Variance reduction techniques on photon fluence and dose calculation efficiency. Different VRTs available in the BEAMnrc code were used to investigate the simulation efficiency for a 6 MV photon beam from an Elekta Agility head. The optimum combination of directional bremsstrahlung splitting (DBS) and bremsstrahlung cross-section enhancement (BCSE) techniques was investigated for photon fluence and dose calculation efficiency. Further combinations with other VRTs were performed. As a result, the combination of DBS and BCSE was most efficient combination for both efficiencies. Furthermore, the combination of DBS and BCSE with photon splitting VRT in DOSXYZnrc further maximized the efficiency. The setting for combining different VRTs that maximize the photon fluence efficiency at the surface of the phantom can be different to those that maximize the dose efficiency inside the phantom. Different VRT combinations, as presented in this study, can improve the simulation efficiency.

Evolution of the ionic polarization in multiple sequential ionization: General equations and an illustrative example

Modern free-electron lasers generate a highly intense polarized radiation which initiates a sequence of ionization and decay events. Their probability depends on the polarization of each involved state as a function of time. Its complete account is limited by the fact that a state can be formed in various ways. Here we present an equivalent of rate equations for population that completely accounts for polarization of radiation formulated in terms of statistical tensors. To illustrate our approach we theoretically consider the sequential photoionization of krypton by an intense extreme ultraviolet femtosecond pulse for photon energies below the $3d$-shell excitation threshold. The calculations of the ion yields, photoelectron spectra, and ionic polarization for various photon fluences are presented and the role of the polarization is discussed.

Neutron shielding assessment of a 16O hadron therapy room by means of Monte Carlo simulations with the PHITS code

Hadron radiation therapy is of great interest worldwide. Heavy-ion beams provide ideal therapeutic conditions for deep-seated local tumours. At the Heidelberg Ion Beam Therapy Center (HIT, Germany), protons and carbon ions are already integrated into the clinical routine, while 16O ions are still used for research only. To ensure the protection of the technical staff and members of the public, it is required to estimate the neutron dose distribution for optimal working conditions and at different locations. The Particle and Heavy Ion Transport Code System (PHITS) is used in this work to evaluate the dose rate distribution of secondary neutrons in a treatment room at HIT where 16O ions are used: an equivalent target in soft tissue is considered in the shielding assessment to simulate the interaction of the beam with patients. The angular dependence of neutron fluences and energy spectra around the considered phantom were calculated. Alongside the spatial distribution of the neutron and photon fluence, a map of the effective dose rate was estimated using the ICRP fluence-to-effective dose conversion coefficients, exploiting the PHITS code’s built-in capabilities. The capability of the actual shielding design of the studied HIT treatment room was approved.

Multi-messenger studies with the Pierre Auger Observatory

The combination of data from observatories measuring ultra-high energy cosmic rays, photons, neutrinos and gravitational waves has provided new insights into the most extreme phenomena in the Universe. Sharing information within a broad community is the foundation of the multi-messenger approach. The Pierre Auger Observatory, the world’s largest cosmic ray detector, provides sensitivity to photons and neutrinos above 1017eV, thus contributing significantly to this joint effort. The latest results from diffuse and targeted searches will be reviewed here, along with results from follow-up analyses and future perspectives. In particular, preliminary limits on photon fluence from a selection of gravitational wave sources detected by LIGO/Virgo and results of the search for ultra-high energy neutrinos from binary black hole mergers will be presented.

Impact of the anode tilt on photon emission spectrum and temperature rise in an x-ray tube

In radiology, the photon fluence and the energy spectrum generated from an x-ray tube may depend on the anode tilt angle. In this contribution, a Monte Carlo investigation is performed to quantify this effect by modeling an x-ray tube based on published data Bujila R. et al (2020 Physica. Med. 75 44–54). The GATE simulation code is used for this purpose. The calculations have moreover confirmed this dependence; the tilt of the anode could be used to increase the photon fluence. The thermal analysis has shown that the hot spot size is dependent as well on the anode tilt angle. The thermal focus temperature (ΔT) decreases when the anode tilt angle increases. Finally, by moving the acquisition angle from 293°–337° to 248°–292° and changing the anode tilt angle from 8° to 28°, the photon fluence can be increased by 55%.

Photophysical Study of Electron and Hole Trapping in TiO2 and TiO2/Au Nanoparticles through a Selective Electron Injection

The photophysics surrounding the electron and hole trapping in TiO2 do not have a scientific consensus. Herein, we studied the steady-state photoluminescence and time-resolved spectroscopy features from TiO2 and TiO2/Au nanoparticles (NPs). In TiO2/Au NPs, time-resolved photoluminescence indicates that the electrons from bandgap excitation decay slower (∼30 ps) than in TiO2 (<24 ps). We conclude this as a result of the band bending passivation effect on the surface electron traps. Meanwhile, electron trapping is proved as the dominant surface depopulation process because of the easy-fill characteristics of surface hole traps even under low excitation density, which also interprets the slow surface hole trapping (∼2 ns) in TiO2. Through plasmon-assisted electron injection, we distinguished the electron and hole behaviors at varied photon fluences and then obtained the intrinsic bulk trapping of electrons and holes in the ∼50 and ∼400 ps time range, respectively.

Analysis and Data-Based Modeling of the Photochemical Reaction Dynamics of the Induced Singlet Oxygen in Light Therapies.

The macroscopic singlet oxygen (MSO) model for quantifying the light-induced singlet oxygen ( 1O2) always contain a set of nonlinear dynamic equations and therefore are generally difficult to be applied. This work was devoted to analyze and simplify this dynamic model. Firstly, the nonlinearity of the MSO model was analyzed with control theory. The conditions, under which it can be simplified to a linear one, were derived. Secondly, in the case of ample triplet oxygen concentration, a closed-form exact solution of the 1O2 model was further derived, in a nonlinear algebraic form with only four parameters that can be easily fitted to experimental data. Finally, in vitro experiments of anti-fungal light therapies were conducted, where the fungi, Candida albicans, were irradiated respectively by the 385, 405, 415, and 450 nm wavelength light. The singlet oxygen concentration levels in the fungi were measured, and then used to fit the developed models. The parameters of the closed-form exact solution were estimated from both the simulated and the measured experimental data. Based on this model, a functional relationship between the photon energy, fluence rate and singlet oxygen concentration was also established. The fitting accuracy of this model to the data was satisfactory, which therefore demonstrates the effectiveness of the proposed modeling techniques. The results from simulating the closed-form model indicate that the photon energy within the range of either 2.7 ∼ 2.8 eV or 3.0 ∼ 3. 2 eV (388 ∼ 413 nm or 443 ∼ 459 nm in wavelength) is more effective in generating singlet oxygen in the fungi studied in this work. It is the first attempt of applying control theory to analyze the photochemical reaction dynamics of light therapies in terms of their nonlinearity. The proposed modeling techniques also offer opportunities for determining the light dosages in treating fungal infection diseases, especially those on the surface tissues of human body.

Hybrid Proton-Photon Treatment Planning with Fraction Optimization

<h3>Purpose/Objective(s)</h3> Hybrid proton-photon radiotherapy (RT) can provide better plan quality than proton or photon only RT, in terms of robustness of target coverage and sparing of organs-at-risk (OAR). This work develops a hybrid treatment planning method that can optimize the number of proton and photon fractions as well as proton and photon plan variables, so that the hybrid plans can be clinically delivered day-to-day using either proton or photon machine. <h3>Materials/Methods</h3> In the new hybrid treatment planning method, the total dose distribution (sum of proton dose and photon dose) is optimized for robust target coverage and optimal OAR sparing, by jointly optimizing proton spots and photon fluences, while the target dose uniformity is also enforced individually on both proton dose and photon dose, so that the hybrid plans can be separately and robustly delivered on proton or photon machine. To ensure the target dose uniformity for proton and photon plans, the number of proton and photon fractions is explicitly modeled and optimized, so that the target dose for proton and photon dose components is constrained to be a constant fraction of the total prescription dose while the plan quality based on total dose is optimized. The feasibility of the generation of clinically deliverable hybrid plans using the proposed method is validated with representative clinical cases including abdomen, lung, head-and-neck (HN), and brain. <h3>Results</h3> For all cases, hybrid plans provided better overall plan quality and OAR sparing than proton-only or photon-only plans, better target dose uniformity and robustness than proton-only plans, quantified by treatment planning objectives and dosimetric parameters. Moreover, for HN and brain cases, hybrid plans also had better target coverage than photon-only plans. <h3>Conclusion</h3> We have developed a new hybrid treatment planning method that optimizes number of proton and photon fractions as well as proton spots and photon fluences, for generating clinically deliverable hybrid plans that can be separately and robustly delivered on proton or photon machines. Preliminary results have demonstrated that hybrid plans generated via the new method have better plan quality than proton-only or photon-only plans.

Practical X-ray beam spectrometry with cadmium telluride detector in 10–300 kVp range at Czech Metrology Institute. Part I. Instrumentation

The paper describes instrumentation used at Czech Metrology Institute for measurement of photon fluence spectra directly in X-ray beams. Detector with a cadmium telluride (CdTe) sensor was characterized by means of energy resolution and precise energy calibration. The hole trapping effect in CdTe causing full-energy peak deformations in measured spectra was adopted consisting of analytical models of incomplete charge collection and carrier trapping based on Hecht equation. The detector collimator provided by the manufacturer was modified with additional tungsten shielding that effectively absorbs the majority of photons scattered in the collimator body resulting in significant improvement of the consistency of measured and Monte Carlo simulated detector response. The purpose-made alignment platform increased the accuracy of orientation of the collimator axis improving the measurement in high photon fluence rate beams using collimation disks with very small apertures (down to 100 μm in diameter). The adopted instrumentation and methods for X-ray beam spectrometry enabled to fulfil the requirements of the new ISO 4037:2019-ed.2.0 standard for reference metrology laboratories. Software-focused part dealing with Monte Carlo simulations and procedures for photon fluence spectra unfolding is summarized in [1].