High-energy Beam Research Articles

Longitudinal MR imaging after unilateral MR-guided focused ultrasound thalamotomy: clinical and radiological correlation.

Magnetic-resonance-guided focused ultrasound (MRgFUS) thalamotomy uses multiple converging high-energy ultrasonic beams to produce thermal lesions in the thalamus. Early postoperative MR imaging demonstrates the location and extent of the lesion, but there is no consensus on the utility or frequency of postoperative imaging. We aimed to evaluate the evolution of MRgFUS lesions and describe the incidence, predictors, and clinical effects of lesion persistence in a large patient cohort. A total of 215 unilateral MRgFUS thalamotomy procedures for essential tremor (ET) by a single surgeon were retrospectively analyzed. All patients had MR imaging 1 day postoperatively; 106 had imaging at 3 months and 32 had imaging at 1 year. Thin cut (2 mm) axial and coronal T2-weighted MRIs at these timepoints were analyzed visually on a binary scale for lesion presence and when visible, lesion volumes were measured. SWI and DWI sequences were also analyzed when available. Clinical outcomes including tremor scores and side effects were recorded at these same time points. We analyzed if patient characteristics (age, skull density ratio), preoperative tremor score, and sonication parameters influenced lesion evolution and if imaging characteristics correlated with clinical outcomes. Visible lesions were present in all patients 1 day post- MRgFUS and measured 307.4 ± 128.7 mm3. At 3 months, residual lesions (excluding patients where lesions were not visible) were 83.6% smaller and detectable in only 54.7% of patients (n = 58). At 1 year, residual lesions were detected in 50.0% of patients (n = 16) and were 90.7% smaller than 24 h and 46.5% smaller than 3 months. Lesions were more frequently visible on SWI (100%, n = 17), DWI (n = 38, 97.4%) and ADC (n = 36, 92.3%). At 3 months, fewer treatment sonications, higher maximum power, and greater distance between individual sonications led to larger lesion volumes. Volume at 24 h did not predict if a lesion was visible later. Lesion visibility at 3 months predicted sensory side effects but was not correlated with tremor outcomes. Overall, lesions are visible on T2-weighted MRI in about half of patients at both 3 months and 1 year post-MRgFUS thalamotomy. Certain sonication parameters significantly predicted persistent volume, but residual lesions did not correlate with tremor outcomes.

Weakly nonlinear ray tracing approximations for focused ultrasound propagation

Focused ultrasound is used in a therapeutic treatment (HIFU) and uses ultrasound waves to non-invasively destroy malignant cells inside the human body. The technique works by sending a high-energy beam of ultrasound into the tissue using a focused transducer. Numerically modeling HIFU presents a problem due to nonlinear effects leading to the formation of harmonics of the source frequency. Each harmonic requires a finer grid to resolve, rapidly increasing computational complexity. This work will focus on the derivation and benefits of two ray tracing methods using weakly nonlinear ray theory formed by different asymptotic expansions of the governing acoustic equations. The first has the ray equations identical to those from linear ray theory while the amplitude equation is a nonlinear transformation of the Burgers’ equation. In the second method the Eikonal and transport equations are coupled which results in ray trajectories which depend on the amplitude.

Tumor Regression with 5-Aminolevulinic Acid (5-ALA)-Mediated Radiodynamic Therapy (RDT) Using Different Megavoltage Energies

5-aminolevulinic acid (5-ALA) accumulates in target tumor cells, where it is metabolized to a photosensitizer - protoporphyrin IX (PpIX). Cherenkov light induced by high-energy photon beams effectively activates the PpIX due to the Soret band. The activated photosensitizers lead to cellular toxicities to kill malignant tumor cells by converting surrounding tissue oxygens into singlet oxygens. Radiodynamic therapy (RDT) utilizes cellular damage caused by both radiation dose and activated photosensitizer. The emission of Cherenkov light was observed higher with higher energy irradiation in phantom and ex-vivo tissues. Therefore, using an in-vivo mouse model, this study aimed to investigate the efficacy and energy dependency of RDT combined with 5-ALA and different ranges of megavoltage photon irradiation. In order to investigate individual and synergistic effects of 5-ALA administration and radiation treatment, the tumors (n = 344) were randomized into eight groups: control (untreated), 5-ALA only, 6-, 15-, and 45-MV conventional radiation treatment (RT) only, 6-, 15-, and 45-MV RDT. 4 Gy in a single fraction was delivered to the tumors using three different energy photons for RT only and RDT groups. 5-ALA was systemically injected into 5-ALA only and RDT groups at 100 mg/kg by tail-vein 4 hours before irradiation for endogenous PpIX accumulation in the tumor. Tumor growth was measured using a 1.5 T MR scanner on the day of treatment (prior to the treatment), 3, 7, and 14 days post-treatment. Two-way repeated ANOVA with Bonferroni correction was used to compare each treatment group to determine the statistically significant difference in tumor growth. A total of 45 MV RDT resulted in the most significant decrease in tumor growth by 58.8 ± 3.4 %, 58.0 ± 3.0 %, and 55.0 ± 3.0 % compared to 5-ALA, 45 MV RT, and control group on 7 days post-treatment (P<0.001), respectively. Moreover, a synergistic effect of 45 MV RDT causes a 47.1-54.1 % additional decrease in tumor growth toward the effective treatment outcome. Compared to the different energies, 45 MV RDT resulted in a 52.2 ± 3.1 % and 19.7 ± 7.2 % decrease in tumor growth compared to 6 MV RDT and 15 MV RDT on 7 days post-treatment, respectively (P<0.001), whereas the conventional RT was not. Radiodynamic therapy using 5-ALA administration and 45MV photon beam irradiation resulted in the most significant tumor growth control. A photon energy dependency was observed in radiodynamic therapy. 45MV photon beams showed greater in activating PpIX, improving the synergistic effects of radiation dose and activated photosensitizer than the other energies. The preliminary results provide a foundation for new innovative treatment strategies that have the potential to improve cancer treatment.

TiC morphology and corrosion resistance of CrMnFeCoNi+x(TiC) coatings prepared by laser cladding

The corrosion resistance of CrMnFeCoNi coatings with varying TiC contents and the evolution of TiC within these coatings were comprehensively investigated. These CrMnFeCoNi coatings, with different TiC concentrations, were fabricated using laser cladding technology. The behavior of TiC evolution in CrMnFeCoNi coatings was observed to follow a distinct pattern. At a TiC loading of 2 wt%, TiC exhibited a dispersed distribution. Interestingly, in coatings loaded with 4 wt% TiC, TiC was observed in various shapes, including elongated, square, petaled, and circular forms owing to the melting of TiC particles under the influence of a high-energy laser beam. The convection action of the molten pool combined several unmelted, partially melted, and precipitated TiC particles, resulting in diverse shapes. Furthermore, increasing the TiC content to 10 wt% led to the aggregation and fusion of TiC into clusters. Additionally, the electrochemical corrosion resistance behavior of CrMnFeCoNi coatings with varying TiC content displayed a significant correlation with the TiC concentration. As the TiC content increased, the galvanic corrosion resistance also increased. At lower TiC content levels, a higher number of electrochemical cells formed between the CrMnFeCoNi matrix and the dispersed TiC, leading to an elevated corrosion rate. In contrast, as the TiC content increased, the dispersed TiC phase fused together, reducing the likelihood of electrochemical cell formation. Notably, the electrochemical corrosion resistance of the CrMnFeCoNi coating containing 10 wt% TiC resembled that of the TiC-free coating.

High-energy quasi-monoenergetic proton beam from micro-tube targets driven by Laguerre–Gaussian lasers

High-energy proton beams with low energy spread and angular divergence are highly valuable in various applications, such as proton therapy, ultrafast science, and nuclear physics. Laser-driven ion sources are being explored as a more compact and cost-effective alternative to conventional accelerators. However, producing high-quality proton beams using lasers has been a significant challenge. In this study, we propose a novel approach to achieve high-energy quasi-monoenergetic proton beams by utilizing a Laguerre–Gaussian (LG) laser to irradiate a solid hollow tube target. Our three-dimensional particle-in-cell simulations demonstrate that the LG laser efficiently pulls out and accelerates electrons. As these electrons exit the rear side of the tube, a charge-separation electric field for proton acceleration is self-established. Meanwhile, a considerable part of the electrons are confined to the laser axis by the ponderomotive force of the LG laser, generating a longitudinal bunching field and transverse focusing field. As a result, protons are accelerated and focused in these fields, producing a high- quality proton beam with high energy (247 MeV) and low energy spread (∼2%) using an LG laser with an intensity of W cm−2 and a tube target with an electron density of 40nc . In comparison to a standard Gaussian laser, the LG laser exhibits superior performance in terms of proton cut-off energy, energy spread, and angular divergence.

Thermodynamic analysis and heat transfer optimization of the CRAFT NNBI calorimeter

ABSTRACT In the process of neutral beam injection (NBI), the high-energy neutral beams, which are up to 31 MW/m2 and last for 3600 s in some cases, impinge on the calorimeter, which is a high-heat-flux component. Therefore, it is necessary to study the heat transfer performance of the calorimeter to ensure the testing and commissioning of NBI systems. First, the uniformity of the water mass flow distribution in each branch pipe of the calorimeter under five different flow configurations was studied. The results show that when two adjacent branches form a group of circuits, the uniformity of the mass flow distribution and the heat transfer capacity are better. Second, the influence of bending the middle of the pipe into several different buffer support structures on the deformation of the branch pipe was studied. Third, the heat transfer performance was compared between the optimized structure and the original circular pipe. Under the same water mass flow conditions, the maximum deformation of the optimized structure is reduced to 2.79 mm, and the maximum temperature is reduced by 30.31%, indicating effective improvement in the heat transfer performance and a reduction in deformation. Therefore, the optimized calorimeter can adapt to the future operational environment under a higher heat flux and long pulse. Finally, several groups of branch pipes were assessed to verify the feasibility of the design. This research can also provide theoretical and engineering support for the future design of calorimeters and other components under long-pulse and high-heat-flux operation.

Investigating the hard X-ray production via proton spallation on different materials to detect elements.

Various atomic and nuclear methods use hard (high-energy) X-rays to detect elements. The current study aims to investigate the hard X-ray production rate via high-energy proton beam irradiation of various materials. For which, appropriate conditions for producing X-rays were established. The MCNPX code, based on the Monte Carlo method, was used for simulation. Protons with energies up to 1650 MeV were irradiated on various materials such as carbon, lithium, lead, nickel, salt, and soil, where the resulting X-ray spectra were extracted. The production of X-rays in lead was observed to increase 16 times, with the gain reaching 0.18 as the proton energy increases from 100 MeV to 1650 MeV. Comparatively, salt is a good candidate among the lightweight elements to produce X-rays at a low proton energy of 30 MeV with a production gain of 0.03. Therefore, it is suggested to irradiate the NaCl target with 30 MeV proton to produce X-rays in the 0-2 MeV range.

Beamline and vacuum system design of HEBT for the A-FNS accelerator

The Advanced Fusion Neutron Source (A-FNS) project is progressing at the QST Rokkasho institute, Japan. The A-FNS will conduct fusion neutron irradiation tests of materials for a fusion demonstration reactor (DEMO reactor). For these tests a high intensity deuteron beam accelerator is used to produce a high neutron flux with the neutron energies around 14 MeV. The accelerator system accelerates a deuteron beam to a beam energy of 40 MeV, guides the beam towards a liquid lithium target and shapes the uniform beam at the Li target using a magnet system.Two of the main considerations for the A-FNS high energy beam transport (HEBT) design are protection of the Superconducting Radio-Frequency linear accelerator (SRF) and vacuum system design for the interface of the HEBT and the target system. For the A-FNS, back streaming of Li vapor from the windowless free surface of the Li target is a concern. In addition, widely different vacuum pressure must be maintained between the accelerator system and the target system. This paper shows the detailed design of the A-FNS HEBT section regarding these considerations.

Continuous photon energy modulation in IMRT of pancreatic cancer

Purpose: To develop a novel IMRT optimization method based on the principle of photon energy synthesis that simultaneously optimizes fluence map and beamlet energy. The method was validated on pancreatic cancers to demonstrate the benefits of the additional degree of freedom of photon energy in IMRT.Methods: Previous work has demonstrated that the effect of a photon beam of known energy can be achieved by the combination of two existing energy photons in the proper ratio. It further implied that any energy photon can be synthesized. Based on this, we propose the concept of continuous beamlet energy modulation in IMRT, or IMRT-BEM. The IMRT-BEM was modeled as the simultaneous optimization of two fluence maps, one for the low energy beam and one for the high energy beam, and it was implemented in an in-house inverse planning system. The IMRT-BEM was applied on 10 pancreatic cancer cases, where the IMRT-BEM plan was compared with single-energy IMRT plans of 6 MV (IMRT-6MV) and 15 MV photons (IMRT-15MV).Results: The IMRT-BEM plan provides a noticeable reduction to the volume irradiated at the high dose level (PTV105%) for PTV, at least 24.7% (6.4 ± 6.8 vs. 31.1 ± 18.7 (p = 0.005) and 43.8 ± 19.8 (p = 0.005) for IMRT-BEM, IMRT-6MV, and IMRT-15MV respectively). For target dose coverage, there were statistically significant improvements between the IMRT-BEM plans and the other two plans in terms of CI and HI. Compared to the IMRT-6MV plan, there were significant reductions in the Dmean of the spinal cord, liver, bowel, duodenum, and stomach. The irradiation volumes of the medium dose (V20Gy, and V40Gy) for the duodenum and bowel were reduced significantly. There were no significant differences between the IMRT-BEM and IMRT-15MV plans except for the Dmean of the spinal cord and the duodenum, the V20Gy, and V40Gy for the duodenum, and the V20Gy of the stomach.Conclusion: IMRT-BEM has certain dosimetric advantages for PTV and improves OAR sparing in pancreatic cancer, and can be effectively used in radiation treatment planning, providing another degree of freedom for planners to improve treatment plan quality.

Optimization of Deuteron Irradiation of 176Yb for Producing 177Lu of High Specific Activity Exceeding 3000 GBq/mg.

The irradiation of 176Yb with deuterons offers a promising pathway for the production of the theranostic radionuclide 177Lu. To optimize this process, calculations integrating deuteron transport, isotope production, and decay have been performed. In pure 176Yb, the undesired production of 174g+mLu occurs at higher deuteron energies, corresponding to a distribution slightly shallower than that of 177Lu. Hence, 174g+mLu can be effectively filtered out by employing either a low-energy deuteron beam or stacked foils. The utilization of stacked foils enables the production of 177Lu using a high-energy linear accelerator. Another unwanted isotope, 176mLu, is produced roughly at the same depth as 177Lu, but its concentration can be significantly reduced by selecting an appropriate post-irradiation processing time, owing to its relatively short half-life. The modeling approach extended to the mapping of yields as a function of irradiation time and post-irradiation processing time. An optimized processing time window was identified. The study demonstrates that a high-energy deuteron beam can be employed to produce 177Lu with high specific activity exceeding 3000 GBq/mg. The effect of different purity levels (ranging from 98% to 100%) was also discussed. The impurity levels have a slight impact. The modeling demonstrates the feasibility of obtaining 177Lu with a specific activity > 3000 GBq/mg and radionuclidic purity > 99.5% when using a commercially available 176Yb target of 99.6% purity.

Comparing sputter rates, depth resolution, and ion yields for different gas cluster ion beams (GCIB): A practical guide to choosing the best GCIB for every application

Molecular gas species for gas cluster ion beams (GCIBs), such as carbon dioxide and water, were examined with a range of beam energies and cluster sizes to compare with the “universal relation” of the sputter yield, Y, per cluster atom against incident beam energy, E, per cluster atom of Arn cluster beam using Irganox 1010. In this work, we compare Arn, (CO2)n, and (H2O)n gas clusters to the universal equations for Arn clusters. To discuss molecular gas species for GCIBs, energy per nucleon (E/N) needs to replace energy per atom. We monitored sputter rate, depth resolution, and secondary ion yield as a function of the beam parameters: gas species, beam energy, and cluster size. (H2O)n GCIB shows reduced sputter rates and improved depth resolution with high sensitivity compared to Arn and (CO2)n GCIBs. These initial results indicate the potential to achieve high-depth resolution with high sensitivity and suggest that (H2O)n cluster ion beam has the potential to play a significant role in surface analysis techniques with organic materials. Results also show that no single set of conditions will provide the “best gas cluster ion beam” for all applications. However, it is possible to choose a set of conditions that will be more or less optimal depending on the experimental goals, such as maximizing the sputter rate, depth resolution, and molecular ion yield. In this work, we recommend the following three guidelines for GCIB users to set their own conditions: (1) to maximize the sputter rate, select a smaller cluster (higher E/N), but be aware that this will increase fragmentation and reduce molecular ion yield; (2) to maximize the depth resolution, select a larger cluster (lower E/N), and use (H2O)n GCIB, if possible; and (3) to maximize the molecular ion signal, use the highest beam energy available, and select a cluster with 0.15–0.25 eV/nucleon for Ar and (CO2)n GCIBs or around 0.1 eV/nucleon if using (H2O)n GCIB. These results are valid for XPS, SIMS, and any technique that utilizes GCIBs.

Early stages of X-ray induced molecular unit modifications in poly(lactic acid)

Exposure of polymers to ionizing radiation and high-energy particle beams is involved in many processes – from food sterilization to radiotherapy protocols. The resulting effects, at the final stages, determine the functional, structural, and morphological alteration of the material. However, the processes responsible for cumulative chain scission, crosslinking, and reactions with the environment are often difficult to disentangle as a sequence of elementary events. Here we report a spectroscopic study – by attenuated-total reflection Fourier transform infrared spectroscopy and powder x-ray diffraction measurements, together with differential scanning calorimetry and thermogravimetric analyses – that sheds light on the very initial stages of the mechanisms involved in radiation-induced modifications of poly(lactic acid) (PLA). The results, collected on samples from biobased processes and exposed to low x-ray doses in the range of 100–103Gy after different thermal treatments, show spectroscopic evidence of the emergence of molecular unit perturbations – mainly related to methyl and carbonyl groups with the formation of C=C double bonds – with a clear-cut dependence on the polymer conformation. Understanding the mechanisms involved and the role of crystallinity provides information potentially useful for the development of PLA with a suitable radiation hardness for applications in radiotherapy.

Towards Understanding Incomplete Fusion Reactions at Low Beam Energies: Modified Sum Rule Model

We investigated the enhanced production of nuclei formed via incomplete fusion (ICF) reactions near and above the Coulomb barrier energies (5–8 MeV/A). The cross-sections of the evaporation residues formed in the reactions—11B+124Sn, 10B+124Sn and 11B+122Sn—were measured using off-line gamma-ray spectrometry. The sum rule model (SRM) by Wilczyński et al. predicted the cross-section values too low compared to our experimental results. In earlier studies, the same model has been very successful in explaining ICF reactions at high beam energies (&gt;10 MeV/A). We, therefore, modified the SRM, specifically incorporating the energy dependence in the definition of critical angular momentum ℓcr. The resulting modified SRM gave an improved theoretical estimate for the reactions we studied.

High-precision calculation and experiments on the thermal blooming of high-energy lasers.

Thermal blooming (TB) is one of the important factors affecting the quality of high-energy laser beams. Reasonable simulation of thermal blooming is important to the application of a high-energy laser. However, reported investigations on TB simulation are mainly based on one method, such as the perturbation method or the phase screen method, which often leads to obvious errors in some conditions. In the paper, the reasonable ranges of optical generalized distortion parameters for both methods are determined based on the reported experimental data, which solves the problem of accurate TB simulations for the first time. In addition, the dynamic effect of thermal blooming is also calculated. Finally, the formula method is presented to extract the phase of thermal blooming distortion. We then use LC-SLM (Liquid crystal spatial light modulator) to emulate thermal blooming effect in the lab. The experimental results are more consistent with the numerical simulation results than conventional phase extraction methods. Our work provides a quantitatively and programmable way to accurately simulate TB with LC-SLM in the lab.

Production of 99Mo in inverse kinematics heavy ion reactions

Following the successful production of the radioimmunotheranostic nuclide 67Cu through the reaction of a 70Zn beam on a hydrogen gas target, our interest turned to the 99Mo/99mTc generator system. We produced 99Mo in inverse kinematics, with a100Mo beam at 12.0 MeV/nucleon impinging on a 4He gas target. The gas target was kept at liquid nitrogen temperature and pressures of 0.134(3), 0.280(6) and 1.33(3) atm. The produced isotopes and the beam were collected on a thick Al catcher foil. The 99Mo radioisotope can be produced in a one nucleon transfer occurring in peripheral reactions. Two competing factors determine the yield in such reactions, one is the cross-section which favors high mass targets, the other is the effective range which favors low-mass targets. Thus, at low 4He densities, higher beam energy at the exit of the gas target, most of the 99Mo production is generated in the Al foil, while at higher densities, most is generated in the gas target. The activity obtained at the end of the bombardment (given in Becquerel per particle nano-Amps per hour of irradiation), including the 4He gas and Al catcher contribution, were determined as 4.8(14), 2.5(7) and 3.8(11) kBq/(pnAh) for ρgas = 0.83, 0.18 and 0.09 mg/cm3, respectively. These results are competitive to other accelerator production methods; however, the method reported has the additional advantages of needing significantly less amount of expensive enriched isotope and offers an easier and cleaner collection/separation method.

Mechanical design of the gamma blockers for the high-energy beam transport region of the European Spallation Source

Abstract The European Spallation Source (ESS) is a collaboration of 13 European countries to build the world’s most powerful neutron source for research. The project, situated in the south of Sweden, is approaching the end of the construction phase, and the first scientific results are planned for 2023. This paper gives an overview of mechanical design of the gamma blockers (GBs) in the accelerator to target (A2T) and dump line (DmpL) sections. The presence of GBs in the beam line should limit the gamma radiation emitted from the activated tungsten target and beam dump to allow the safe access of the staff to the machine. The presented design allows for efficient operation and the same shutting time independently of the vacuum status.

Hi'CT: a pixel sensor-based device for ion tomography

Carbon ions, commonly referred to as particle therapy, have become increasingly popular in the last decade. Accurately predicting the range of ions in tissues is important for the precise delivery of doses in heavy-ion radiotherapy. Range uncertainty is currently the largest contributor to dose uncertainty in normal tissues, leading to the use of safety margins in treatment planning. One potential method is the direct relative stopping measurement (RSP) with ions. Heavy-ion CT (Hi′CT), a compact segmented full digital tomography detector using monolithic active pixel sensors, was designed and evaluated using a 430 MeV/u high-energy carbon ion pencil beam in Geant4. The precise position of the individual carbon ion track can be recorded and reconstructed using a 30 μm × 30 μm small pixel pitch size. Two types of customized image reconstruction algorithms were developed, and their performances were evaluated using three different modules of CATPHAN 600-series phantoms. The RSP measurement accuracy of the tracking algorithm for different types of materials in the CTP404 module was less than 1%. In terms of spatial resolution, the tracking algorithm could achieve a 20% modulation transfer function normalization value of CTP528 imaging results at 5 lp/cm, which is significantly better than that of the fast imaging algorithm (3 lp/cm). The density resolution obtained using the tracking algorithm of the customized CTP515 was approximately 10.5%. In conclusion, a compact digital Hi'CT system was designed, and its nominal performance was evaluated in a simulation. The RSP resolution and image quality provide potential feasibility for scanning most parts of an adult body or pediatric patient, particularly for head and neck tumor treatment.

Superconducting undulator activities at the European X-ray Free-Electron Laser Facility

For more than 5 years, superconducting undulators (SCUs) have been successfully delivering X-rays in storage rings. The European X-Ray Free-Electron Laser Facility (XFEL) plans to demonstrate the operation of SCUs in X-ray free-electron lasers (FELs). For the same geometry, SCUs can reach a higher peak field on the axis with respect to all other available technologies, offering a larger photon energy tunability range. The application of short-period SCUs in a high electron beam energy FEL &amp;gt; 11 GeV will enable lasing at very hard X-rays &amp;gt; 40 keV. The large tunability range of SCUs will allow covering the complete photon energy range of the soft X-ray experiments at the European XFEL without changing electron beam energy, as currently needed with the installed permanent magnet undulators. For a possible continuous-wave (CW) upgrade under discussion at the European XFEL with a lower electron beam energy of approximately 7–8 GeV, SCUs can provide the same photon energy range as available at present with the permanent magnet undulators and electron energies. This paper will describe the potential of SCUs for X-ray FELs. In particular, it will focus on the different activities ongoing at the European XFEL and in collaboration with DESY to allow the implementation of SCUs in the European XFEL in the upcoming years.

Mathematic modeling of the dose in water for calculating collimator scatter factor of flattening filter and flattening filter free megavoltage photon beams

This study presents an empirical method to model the percent depth dose (PDD) curves of flattening filter (FF) and FF-free (FFF) high-energy photon beams using a home-generated buildup function and tail function (buildup-tail function) in radiation therapy. The modeling parameters n and &amp;mu; of the buildup-tail function were used to characterize the collimator scatter factor (Sc). The buildup function was a quadratic function in the form of d/ &amp;radic;(d2 + n) with main parameters of d (depth in water) and n, while the tail function was in the form of e&amp;minus;&amp;mu;d and was composed of an exponential function with d and &amp;mu;. PDD was the product of buildup-tail function and characterized by the buildup-tail function by adjusting the parameters n and &amp;mu;. The Sc of 6 and 10 MV in FF and FFF beams can be expressed simply by the modeling parameters n and &amp;mu;. The main parameter n increases when photon energy increases. Its physical meaning expresses the beam hardening of photon energy in PDD. The parameter &amp;mu; can be treated as an attenuation coefficient in the tail function, decreasing when photon energy increases. The values of n and &amp;mu; obtained from the fitted buildup-tail function were applied into an analytical formula of Sc,FF = nE(S)0.63 &amp;mu; E, Sc,FFF = nE(S)4.45 &amp;mu; E to get the Sc of 6 and 10 MV in FF and FFF photon beams, with nE, &amp;mu; E, S denoting n and &amp;mu; at photon energy E of field size S. The calculated Sc was compared with the measured data and showed agreement, finding that the field difference was size within &amp;plusmn;1%. This model can be used to parameterize the Sc for some clinical requirements. The modeling parameters n and &amp;mu; can be used to predict the Sc in either FF or FFF beams for the treatment monitor unit in double-check dose calculation. The technique developed in this study can also be used for systematic or random errors in the quality assurance program, thus improving the clinical dose computation accuracy for patient treatment.

Studies of OSL properties of alkali- and rare earth-doped BeO based novel dosimeters for applications in external beam radiotherapy

This study aims to assess the feasibility of a novel Beryllium Oxide (BeO) based ceramics to be used as optically stimulated luminescence (OSL) dosimeters for monitoring of high-energy beams used in radiotherapy. The BeO ceramic dosimeters doped with alkali and rare earth metals (BeO:Na5%,Ce0.005%,Tb0.05%, BeO:Na5%,Ce0.01%,Er0.01%, and BeO:Na5%,Ce0.01%,Dy0.01%) were fabricated in pellet forms, and their luminescence responses were measured at the virtual water phantom interfaces for various field sizes of a 6 MV flattening filter-free photon beam of Varian LINAC. The OSL dosimeter's performance has been confirmed their practical usefulness as in vivo dosimeters in radiotherapy clinics. The provided dose estimates were validated using varying X-ray energies and doses, typically employed for actual medical radiotherapy systems. Our results indicated that the studied dosimeters rendered an almost linear response in the dose range of 0.05 Gy–20 Gy delivered from the 6 MV X-ray beam. Fading of the stored OSL was found to be less than 5% after a short storage period. The dependencies of OSL responses concerning beam energy, dose rate, irradiation angle, depth, and field size are all found to be supportive of the successful utilization of the BeO OSLDs in clinical environments.