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Due to numerous characteristics (chemical stability, optical transparency, etc.), tissue equivalency, and other factors, lithium borates are an appropriate material for radiation dosimetry. This work explores the optical stimulated luminescence (OSL) dosimetry of lithium triborate (LiB3O5) doped with Ag. Here, we have used thermally-assisted OSL (TA-OSL), where OSL is recorded following thermal stimulation of the sample, to assess the presence of primary dosimetric and deep defects. The optimized elevated temperature for LiB3O5:Ag was found to be 100°C corresponding to maximum TA-OSL intensity due to depletion of its filled traps (indicating deep defects). X-ray diffraction (XRD), transmission electron microscopy (TEM), energy dispersive x-ray spectroscopy (EDS), and ultraviolet–visible (UV-Vis) spectrophotometry were all used to characterized the structural and chemical properties of the sample. Along with other OSL characteristics like fading and repeatability, response of the obtained nanophosphor under CW-OSL with x-ray photons and electrons of a range of energies including cobalt-60 in radiotherapy has also been examined. [ABSTRACT FROM AUTHOR]

Optically Stimulated Luminescence (OSL) based dosimeters are garnering attention in the field of radiation dosimetry due to a number of benefits like portable equipment, easy and efficient excitation and read out process, re-readability of the dose etc.. Though varieties of fluoroperovskites have been studied as OSL materials, no research on LiMgF 3 (Lithium Magnesium Fluoride) as an OSL material has yet been conducted. In the current work, LiF–MgF 2 system with a low effective atomic number was synthesized using the high temperature solid state reaction approach and its OSL dosimetry properties were investigated. The prepared sample was thoroughly characterized by employing a variety of techniques, such as X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), and UV–Vis (ultraviolet–visible) spectrophotometry. The structure of the sample was found to be polycrystalline with size in the micrometre range. OSL properties of LMF have been investigated for different doses of gamma and beta along with related OSL kinetic parameters. It exhibits good dose linearity under blue stimulation for gamma (100 mGy - 700 Gy) and beta (30 mGy - 5Gy) radiation. We have also investigated the reusability (3%), reproducibility (2–3%), and fading (45% in 40 days) of the phosphor. To check the viability of the sample in radiation dosimetry under medical treatment in radiotherapy, various dosimetric properties were studied in Linear Accelerator (LINAC) x-rays in MV energy range and Cobalt-60 gamma radiation. These studies include the response of the phosphor to various energies (called energy dependence), field size effect, the effect of the dose rate of the radiation beam, and relative depth dose response. The overall response of the phosphor (comparable with ion chamber in RT experiments) makes the material a potential candidate to be used as an OSL phosphor in medical radiation dosimetry. [ABSTRACT FROM AUTHOR]

Purpose: We apply Failure Mode and Effects Analysis (FMEA) to investigate and alleviate linear accelerator (linac) downtime issues due to various mechanical and electrical interlocks. Methods: A working group filled out questionnaires to identify different linac failure modes and assign severity, occurrence, and detectability scores to six frequent interlocks. The three scores were multiplied to obtain an overall risk probability number (RPN) for each interlock. The consistency of scores assigned by the therapists was evaluated using Cronbach's Alpha. Results: A total of 61 failure modes were identified. Six recurring interlocks were analyzed over a study period of three months, by five therapists. A fault tree was generated for a generic interlock and for the complex hardware (HFWA) interlock. The Cronbach's Alpha statistics show generally poor agreement among the scores assigned by therapists. Conclusions: On the basis of these findings, the clinic proposed novel solutions for mitigating the risk of linac failures, thus reducing linac downtime and improving patient satisfaction. [ABSTRACT FROM AUTHOR]

Digital X-ray imaging systems for megaelectronvolt (MeV)-range photon beams are based on a combination of a scintillator screen and either a camera or an amorphous silicon array. To limit dose rate on electronics and enhance imaging device lifetime, the scintillator screen can be mirror-coupled to the camera. Performances of such devices are a compromise between exposure time and spatial resolution. These technical characteristics are especially scintillator-dependent. In this article, we present, in the first part, a performance evaluation of six different scintillators with a 9-MeV Bremsstrahlung X-ray source. The tested scintillators are composed of one microstructured CsI:Tl scintillator, two phosphor [Gd2O2S (GOS)] screens, and three transparent scintillators. These scintillators present a wide range of density, thickness, and conversion efficiency. The scintillator’s performance assessment is based on the combination of light output and spatial resolution. The results are helpful to guide design and engineering of high-energy imaging devices adapted to specific requirements. In the second part, imaging performance comparison is done between our current GOS screen detector and a new CsI screen detector. [ABSTRACT FROM AUTHOR]

The Electronic Portal Image Device (EPID) is commonly used to evaluate the difference between the mechanical and radiation centers of a linear accelerator; however, the gantry and EPID are limited in some non-coplanar angles due to collisions with the treatment couch. This study aimed to compare the results of mathematical calculations and actual measurements to evaluate the feasibility of assessing the differences in the mechanical and radiation field isocenters. A 20 mm Stereotactic Circular Collimator was mounted on the head of the linear accelerator (LINAC), and an Elekta 8 mm ball-bearing (BB) was placed on the couch, following the Winston-Lutz (WL) measurement method. Measurements were taken with varying gantry and couch positions, and Image J software was used to analyze the images. Two regions with a difference of more than 0.1 mm were identified. The first region was between T270 and T330, with gantry angles ranging from G120 to G160. The second region was between T280 and T340, with gantry angles ranging from G290 to G330, and the two regions showed a symmetric diagonal relationship in terms of the gantry angles. The paired sample t -test showed no significant difference between the actual measurements and the calculated results (p -value = 0.11). The study concluded that mathematical calculations can complement the limitations imposed by equipment collisions, providing valuable insights for treatment planning. • Using EPID for radiation center point measurements. • EPID is easier to operate than a film system. • Identify non-coplanar collision restrictions. • Using mathematical formulas for compensating collision restrictions. [ABSTRACT FROM AUTHOR]

Background: Communicating hydrocephalus (cHCP) after radiosurgery (RS) for vestibular schwannomas (VS) has been reported. Many hypothetical mechanisms for this pathology have been proposed without consensus. The aim of this study is to determine if the platform used to treat the disease, Gamma Knife (GK) versus linear accelerator (LINAC)-based RS, makes a difference in outcome. Methods: We conducted a meta-analysis of databases PubMed and Cochrane to identify all articles for the period January 2000–August 2018 with the following inclusion criteria: (1) VS treated with single fraction SRS (2) > 10 patients (3) original reports only (4) hydrocephalus reported as complication (5) human study. Results: A total of 7039 and 988 VS patients reported in 35 and 10 papers were treated with GK or LINAC RS, respectively. Demographic baseline characteristics not reported in aggregate did not differ between the two groups. The incidence of cHCP was 3% [95% CI 2–4] and 2% [95% CI 1–3] for GK and LINAC RS patients, respectively. Surgical CSF diversion was performed in 88% and 68% of patients evaluated for cHPC in the GK and LINAC group, respectively. Follow-up range was 30–150 and 29–92 months for GK and LINAC, respectively. Conclusions: The incidence of cHCP following RS for VS is very low in both GK and LINAC treated patients, albeit not identical. The higher reported surgical intervention rate for VS patients treated with GK RS might be multi-factorial, including longer follow-up in the GK group. [ABSTRACT FROM AUTHOR]

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Purpose: The increased use of image‐guided radiation therapy (IGRT) has led to increased use of kV on board imaging (OBI) devices. At present, directly measured OBI beam quality data have only been reported in terms of half‐value layers (HVL). However, the HVL metric alone does not give the full OBI energy spectra as needed for accurate beam modeling. Although direct kV spectrometer devices exist they typically suffer from detector pile‐up when used with OBI sources. We therefore present, for the first time, a novel laser‐guided collimation system that allows direct measurement of the full energy spectrum for clinical OBI systems. Methods: Several clinically relevant spectra (80, 100, and 125 kVp), with and without the half bow‐tie filter, were measured using a thermoelectric cooled cadmium telluride (CdTe) detector paired with a multichannel analyzer. To prevent detector saturation, the photon flux at the detector was reduced by use of an in‐house designed laser‐guided collimation system. After applying energy bin corrections, direct spectroscopic measurements were compared to Monte Carlo (MC) simulated spectra in order to verify accuracy of collected data. Both percent depth dose (PDD) curves and digitally reconstructed radiographs (DRR) were compared using the measured vs MC spectra. Results: Measured and MC spectra agree with RMSD between 1.96% and 3.29%. PDD curves generated from the measured and MC spectra were found to match except for in the small buildup region, with an overall match for the six beams ranging between 0.3% and 2.7% RMSD. DRRs matched well with a maximum difference in contrast of 1.1% and RMSD of 0.46% contrast for various materials in DRRs. Conclusions: The use of a laser‐guided collimation system provided a method for quickly obtaining highly accurate kV spectrum data from OBI sources. For kV dose or DRR calculation, it was found that both spectra produced similar results. [ABSTRACT FROM AUTHOR]

This paper presents the synthesis of a coaxial cavity for high-power X-band coaxial magnetron. In the proposed design, cavity parameters corresponding to optimum quality factor are determined. The quality factor of the coaxial cavity for the TE011 mode is obtained analytically and verified by CST and HFSS simulations. The maximum value of the quality factor achieved is 17 150 for the TE011 mode at an operating frequency of 9.32 GHz, considering the cavity walls to be made of copper. Resonant frequencies of various competing modes (such as TE121, TE221, and so on) of the operating TE011 mode are also determined and shown using a mode diagram. The dominant interfering mode, TE121, is suppressed considerably using an auxiliary cavity filled with lossy dielectric material. The quality factor of the unwanted TE121 mode is reduced by 75.49%, while keeping quality factor of the desired TE011 mode unaffected. A significant reduction in the quality factors of other unwanted modes is also observed. [ABSTRACT FROM AUTHOR]

The effect of a linear accelerator’s (LINAC’s) microstructure (i.e., train of narrow pulses) on devices and the associated transient photocurrent models are investigated. The data indicate that the photocurrent response of Si-based RF bipolar junction transistors and RF p-i-n diodes is considerably higher when taking into account the microstructure effects. Similarly, the response of diamond, SiO2, and GaAs photoconductive detectors (standard radiation diagnostics) is higher when taking into account the microstructure. This has obvious hardness assurance implications when assessing the transient response of devices because the measured photocurrent and dose rate levels could be underestimated if microstructure effects are not captured. Indeed, the rate the energy is deposited in a material during the microstructure peaks is much higher than the filtered rate which is traditionally measured. In addition, photocurrent models developed with filtered LINAC data may be inherently inaccurate if a device is able to respond to the microstructure. [ABSTRACT FROM PUBLISHER]

AimTo perform a retrospective analysis of survival, local–regional control and the effect of prognostic factors in 61 non-small cell lung cancer patients who were treated with postoperative radiotherapy (PORT) by a linear accelerator (LINAC).Material and methodsA total of 50–66 Gy PORT with a fractional dose of 1·8–2 Gy was administered to 24 patients (24·5%) for surgical margin positivity, 33 patients (54%) for mediastinal lymph node involvement and 13 patients (21·5%) for both mediastinal lymph node involvement and positive surgical margins.ResultsMedian follow-up was 17 months, and the median survival and median distant metastasis-free survival were 25 and 19 months, respectively. Local-regional progression was observed in 10 patients (16·4%). Treatment modality (2D/3D) (p=0·021), tumour size >4 cm (p=0·004), surgical margin positivity (p=0·001), and left lung localisation of the tumour (p≤0·05) were the prognostic factors in terms of survival.ConclusionsA survey of the literature shows that, without PORT, local recurrence or progression rates increase while overall survival rates decrease. In this study, only patients with PORT are studied and the results show that the local progression and overall survival rates are comparable with literature of LINAC-based PORT. In the case of overall survival, 3D treatment shows better results than 2D treatment modality. [ABSTRACT FROM PUBLISHER]

Purpose: While microsurgical resection plays a central role in the management of ACMs, extensive surgery may be associated with substantial morbidity particularly for tumors in intimate association with critical structures. In this study, we evaluated the use of HFSRT in the management of ACM.Materials and Methods: A total of 22 patients with ACM were treated using HFSRT. Frameless image guided volumetric modulated arc therapy (VMAT) was performed with a 6 MV linear accelerator (LINAC). The total dose was 25 Gy delivered in five fractions over five consecutive treatment days. Local control (LC) and progression free survival (PFS) rates were calculated using the Kaplan-Meier method. Common Terminology Criteria for Adverse Events, version 4.0 was used in toxicity grading.Results: Out of the total 22 patients, outcomes of 19 patients with at least 36 months of periodic follow-up were assessed. Median patient age was 40 years old (range 24-77 years old). Median follow-up time was 53 months (range 36-63 months). LC and PFS rates were 100 and 89.4 % at 1 and 3 years, respectively. Only two patients (10.5 %) experienced clinical deterioration during the follow-up period.Conclusion: LINAC-based HFSRT offers high rates of LC and PFS for patients with ACMs. [ABSTRACT FROM AUTHOR]

Background Glomus tumors are benign slow-growing hypervascular neoplasms. The role of radiosurgery for the treatment of these tumors has increased. The purpose of this study was to show our experience with glomus tumors and to analyze different prognostic factors. Methods Data from 39 adult patients were retrospectively analyzed. All of them underwent head frame stereotactic radiosurgery with linear accelerator (LINAC). Tumor and symptomatic control were calculated using the Kaplan-Meier method. Bivariate statistical analyses were performed to examine different prognostic factors. Results The median follow-up was 71 months. The radiological local and symptomatic control was achieved in 37 patients (94.8%) and 29 patients (74.3%), respectively. Toxicity was detected in 4 patients (10%). In the bivariate analysis, dose coverage and maximum dose were associated with tumor control with an odds ratio (OR) of 5.29 ( p = .041) and 2.67 ( p = .056), respectively. Conclusion Stereotactic radiosurgery is a safe and efficient treatment for glomus tumors that is associated with high probability of radiological and symptomatic control and low incidence of morbidity. © 2015 Wiley Periodicals, Inc. Head Neck 38: E798-E804, 2016 [ABSTRACT FROM AUTHOR]

Prime dosimetric properties, including dose–response, linearity with dose, energy response, fading and threshold doses were investigated for three different dimension Ge-doped flat fibers. The results of measurement were also compared with two of the more commonly used standard TLD media, TLD-100 (LiF:Mg,Ti−7.5% 6 LiF) and TLD−700 ( 7 LiF:Mg,Ti−99.9% 7 LiF) chips. The flat cross-section samples (60×180) µm 2 , (100×350) µm 2 and (200×750) µm 2 were fabricated using the Modified Chemical Vapor Deposition (MCVD) process and pulled from the same “preform.” In the study, all flat fiber samples provided good linear dose–response for the photon and electron beams generated using a medical linear accelerator (LINAC), for doses in the range 0.5–8 Gy. Among the samples, the smallest dimension flat fiber provided the best response, with a sensitivity of some 61% and 54%, respectively of that of the TLD-100 and TLD-700 chips. The energy responses of the samples were studied for various photon (6 MV, 10 MV) and electron (6 MeV, 9 MeV) beam energies. TL fading of around 20% was observed over a period of thirty (30) days. These favorable TL characteristics point towards promising development of Ge-doped flat fibers for use in radiotherapy dosimetry. [ABSTRACT FROM AUTHOR]

Although benign histologically, craniopharyngiomas may display clinically malignant behavior with a strong propensity for recurrence. Contemporary therapeutic approaches for craniopharyngiomas include stereotactic irradiation in the form of Stereotactic Radiosurgery (SRS) or Fractionated Stereotactic Radiation Therapy (FSRT) as part of multimodality treatment particularly when complete surgical removal is not feasible. In this study, we evaluate the use of Linear Accelerator (LINAC)-based SRS in the multidisciplinary management of patients with craniopharyngiomas. Between July 1998 and July 2013, 20 patients (11 male, 9 female) with residual or recurrent craniopharyngio¬mas were treated using LINAC-based SRS at Department of Radiation Oncology, Gulhane Military Medical Academy. Median age was 37 (9-69) years. Median tumor volume was 1.1 (0.9-6.9) cc. Median dose was 13 Gy (range: 10-16 Gy) prescribed to the 80%-95% isodose line encompassing the target volume. Median follow-up time was 47 (7-93) months. Overall local control rate was 88% at 1 year, 79% at 3 years and 66% at 5 years. Three and 5-year progression free survival rates were 95% and 91% whereras 3 and 5-year overall survival rates were 94% and 88%, respectively. Our study supports the usage of LINAC-based SRS as a safe and effective management strategy for patients with recurrent or residual craniopharyngiomas. [ABSTRACT FROM AUTHOR]

Abstract: Monte Carlo method is often used in radiation therapy as utilized in all the branches of science. For this purpose, various preset codes are used for the dose calculations in radiotherapy. In this study, a new Monte Carlo Simulation Program (MCSP) was developed for the dose distributions of a clinical linear accelerator (LINAC) in water phantom. MCSP was carried out by taking into account the interactions of photons with matter in MATLAB (The Mathworks, Inc.). In the study, 6MeV (6MV photon mode) energies of photons are examined. In order to validate the performance and accuracy of the simulation, the experimental measurements and MCSP calculations were compared for both percentage depth dose curves and beam profiles. The Monte Carlo results show good agreement with experimental results. [ABSTRACT FROM AUTHOR]

The effects of high dose rate electron beam exposures on the electrical conductivity of fused silica and sapphire films are investigated via modern experimental techniques. Transient measurements have been obtained for dose rates ranging from 3×10^5 rad(Si)/s to 1×10^10 rad(Si)/s and for pulse widths ranging from 50 ns to 500 ns. The data indicate that the radiation-induced conductivity (RIC) has a varying power-law relationship with dose rate (i.e., the power-law relationship for low dose rates is different than for high dose rates) and that the RIC coefficient (kc) increases at lower dose rates, peaks, and then decreases at higher dose rates. It is also shown that the RIC response of each film increases several orders of magnitude during a high-intensity ionizing radiation exposure and is linearly dependent on applied bias. Two-dimensional (2-D) numerical simulations are used to qualitatively capture the observed RIC response and provide insight into the physics of the induced current transients. [ABSTRACT FROM PUBLISHER]

Highlights: [•] EU FP7 CDT/FASTEF project related to the multi-purpose irradiation facility MYRRHA. [•] MYRRHA-FASTEF cores design for both critical and sub-critical operational modes. [•] Detailed neutronic analyses by deterministic and Monte Carlo methods. [•] Accurate TH studies at the fuel assembly and pin sub-channel level. [•] Investigation of the potential for the transmutation of minor actinides. [Copyright &y& Elsevier]

External beam radiation therapy attempts to deliver a high dose of ionizing radiation to destroy cancerous tissue, while sparing healthy tissues and organs at risk (OAR). Recent advances in intensity modulated radiotherapy treatment call for a greater understanding of uncertainties in the treatment process and more rigorous protocols leading to greater precision in treatment delivery. The degree to which this can be achieved depends largely on the cancer site. The treatment of organs comprises soft tissue (e.g. in the abdomen) and those subject to rhythmic movements (e.g. lungs) causing inter and intra-fraction motion artifacts that are particularly problematic. Various methods have been developed to tackle the problems caused by organ motion during radiotherapy treatment, e.g. Real-time position management respiratory gating (Varian) and synchronized moving aperture radiation therapy, developed by researchers at Harvard Medical School. The majority of the work focuses on tracking the position of the pathologic region, with the intra-fraction shape variation of the region being largely ignored. This paper proposes a novel method that addresses both the position and shape variation caused by the intra-fraction movement. We believe this approach is able to reduce the clinical target volume margin, hence, sparing yet more of the surrounding healthy tissues from radiation exposure and limiting irradiation of OAR. [ABSTRACT FROM AUTHOR]