TLD Dosimeters Research Articles

A calibration method for a wireless real-time CMOS pixel medical dosimeter

This study introduces and validates a novel calibration function for wireless wearable dosimeters, crucial for real-time dosimetry in interventional radiology. Focusing on enhancing accuracy and safety, it compares data from threshold-based wireless dosimeters with a full-data-read detector. The research involves a central detector and four lateral wireless dosimeters, each equipped with an identically-typed CMOS Image Sensor (CIS), subjected to various photon dose rates and doses from a certified beam. Two key calibration functions were developed: one that correlates the pixel count over a threshold with the dose rate, and the other that links the cumulative pixel value above the threshold to the total absorbed dose. These functions are essential in converting raw CIS data into precise dosimetric information.The study findings reveal that the single-pixel sensitivity of wireless prototypes is approximately 8.5 ± 0.8 ADC/nGy. Following the application of calibration functions, the responses of these prototypes align consistently with the TLD dosimeter measurements. In particular, for three of the prototypes, this calibration ensures that the measurement uncertainty remains within 6% for the dose rate and within 8% for the dose.This research confirms the effectiveness and feasibility of pixel-based wireless dosimeters in interventional radiology, highlighting the importance of integrating offline data processing for enhanced measurement precision.

Evaluating Radiation Exposure to Oral Tissues in C-Arm Fluoroscopy A Dose Analysis

This study investigates the radiation dose to oral mucosal tissues during C-arm fluoroscopy imaging using an Alderson Rando phantom and thermoluminescent dosimeters (TLD-100) for precise measurements. The aim is to assess the potential risks for patients and healthcare personnel exposed to ionising radiation during these procedures. The Alderson Rando phantom, a human-equivalent model, was utilized to simulate radiation exposure in a controlled environment. TLD-100 dosimeters were strategically positioned in the 6th section of the phantom and exposed to radiation at intervals of 0.5, 1, 2, 4, and 8 minutes. The experiments were carried out at Hisar Hospital Intercontinental and the dosimeter readings were then evaluated at Çekmece Nuclear Research Centre. The study demonstrated that the mean radiation doses affecting the internal tissue of the oral mucosa were 0.912 mSv (0.5 minutes), 1.604 mSv (1 minute), 2.719 mSv (2 minutes), 6.763 mSv (4 minutes), and 13.811 mSv (8 minutes). The mean radiation doses affecting the lip skin tissue were 1.423 mSv (0.5 minutes), 2.435 mSv (1 minute), 5.2 mSv (2 minutes), 10.195 mSv (4 minutes), and 17.404 mSv (8 minutes). Results indicate a direct relationship between radiation dose and exposure time, with increasing doses observed at longer exposure times. This research aims to improve patient safety during C-arm scope imaging procedures by determining precise radiation dosage levels for oral mucosal tissues and addressing the lack of published reference values in the literature.

Thermoluminescence dosimetry (TLD) in a 3 T magnetic resonance imaging (MRI) environment: implications for personnel exposure monitoring.

Thermoluminescent dosimeters (TLDs) serve as compact and user-friendly tools for various applications, including personal radiation dosimetry and radiation therapy. This study explores the potential of utilizing TLD-100 personal dosimetry, conventionally applied in PET/CT (positron emission tomography/computed tomography) settings, in the PET/MRI (magnetic resonance imaging) environment. The integration of MRI into conventional radiotherapy and PET systems necessitates ionizing radiation dosimetry in the presence of static magnetic fields. In this study, TLD-100 dosimeters were exposed on the surface of a water-filled cylindrical phantom containing PET-radioisotope and positioned on the patient table of a 3 T PET/MRI, where the magnetic field strength is around 0.2 T, aiming to replicate real-world scenarios experienced by personnel in PET/MRI environments. Results indicate that the modified MR-safe TLD-100 personal dosimeters exhibit no significant impact from the static magnetic field of the 3 T PET/MRI, supporting their suitability for personal dosimetry in PET/MRI settings. This study addresses a notable gap in existing literature on the effect of MRI static magnetic field on TLDs.

Thermal neutron dose measurements using TLD-100 detectors in the IPEN/MB-01 reactor core

Considerable experimental effort has been aimed at uncovering a reliable way to perform a dosimetric assessment in mixed radiation fields. In fields composed by gammas and neutrons, TLD dosimeters are usually applied to execute such measurements, although there is no consensus on the most favorable strategy to employ them. In this context, TLD-100 measurements within two different core configurations of the IPEN/MB-01 research reactor and Monte Carlo simulations have been used to investigate the behavior of those detectors in multiple mixed radiation fields, deriving a methodology to evaluate the dose deposition in the dosimeter by different gamma and neutron energy spectra and intensities. A surprising outcome is the linear neutron dose response shown by TLD-100 even irradiated by so distinct irradiation fields.

Effects of UVC irradiation on polystyrene for healthcare packaging: Study by FTIR and Raman spectroscopy with thermoluminescence

The interaction between ultraviolet C radiation (UVC) and polystyrene (PS) materials has been investigated, particularly in post-packaging irradiation processes for healthcare applications. Effective UVC penetration through PS materials, regardless of their thickness (0.16 and 0.40 mm) has been observed. However, the penetration effectiveness could be affected by the thickness of the PS material. Achieving optimal post-packaging UVC treatment requires a thorough evaluation of chemical composition and material thickness, especially in pharmaceutical and medical packaging industries.Preliminary results reveal minimal degradation in UVC-irradiated PS packaging samples, as supported by FTIR and Raman spectroscopy characterization. Minor variations could be attributed to intrinsic PS materials properties and/or their respective background, rather than the influence of UVC radiation. Consequently, PS materials exhibit resilience under the experimental conditions following UVC irradiation treatment. Furthermore, a comprehensive analysis of thermoluminescence (TL) emissions evaluates several commercial dosimeter materials for UVC radiation detection. The TLD-100 and TLD-200 dosimeters show potential as UVC detectors, displaying distinct responses linked to the non-ionizing component of UVC radiation at 310 °C and in the range of 150–250 °C, respectively. However, the TLD-400 and GR-200 dosimeters are not suitable for UVC detection due to their spread TL emissions considering intensity and curve shape.This UVC-TL analysis consistently detects radiation in the proposed commercial dosimeter materials one-hour post-exposure, providing assurance that healthcare materials have been irradiated. Such analysis enhances reliability during extended UVC exposures, offering valuable insights for industries employing UVC-irradiated materials, particularly in healthcare applications.

Investigation of Dosage Distributions of Polyvinyl Siloxane Dental Impression Shields for Head and Neck Radiotherapy with Thermoluminances Dosimeters

Objective: This study aimed to assess the effects of denture materials on dose distribution on a head and neck radiotherapy-appropriate model and calculate the thickness of a stent by polyvinyl siloxane dental impression material for shielding scattered radiation from dental restorations.
 Methods: In the first step of the study, 5mm diameter and 5mm height of cylindrical dental material of titanium, zirconia lithium disilicate were irradiated with 6-Megavoltage photons from a clinical linear accelerator. In the second step, dental materials at the center of polyvinyl siloxane thicknesses of 5, 10, and 20mm were irradiated with 2 Gray and 10 Gray fractional doses. Measurements were made using three thermoluminescent dosimeters positioned laterally. The percentage backscattered dose and percentage dose decrease values were calculated to interpret the results. 
 Results: According to the result, dosages scattered from dental materials increased for samples irradiated with 2Gy; a decreased dose was reported for samples irradiated with a 10Gy. 5mm PVS samples provided higher dose attenuation than others. Regardless of dental material, it is seen that the attenuation intensities calculated from TLD-100 dosimeters ranged from 22.7 to 38,62 for 2Gy, and 10.01 to 38,87 for 10Gy.
 Conclusion: Dental material alters the scattered radiation. In irradiated head and neck cancer patients, a 5mm thick guard is sufficient to prevent radiation diffused from dental materials in clinical usage.

Editorial

According to Taheri's theory, T-Consciousness is one of the three primary elements of the universe, apart from matter and energy. In this perspective, material particles are described as hardware, which, equipped with software programs that transfer specific information indices, can exhibit specific behaviors and characteristics. When the subject of study, which in these investigations are TLD discs, is affected by T-Consciousness Fields, their behavior changes relative to the control. These results provide evidence of variability in information indices as proposed by Taheri. For experimental and laboratory examination of new evidence of T-Consciousness Field Theory, after choosing the topic specific to the reaction between radiation and sensitive TLD dosimeter, and investigating the composite effects of T-Consciousness Fields 1, 2, and 3 on this reaction, several main objectives are pursued: The first objective is to obtain empirical and laboratory evidence of the distinction and difference between T-Consciousness Fields and energy, especially different types of radiation. The second is to study the effect of T-Consciousness Fields on the material and energetic components of the system under investigation. Using a sensitive system to record changes, we can examine the effect of T-Consciousness Fields on radiation as a significant component of the universe since its inception. Third, some studies that are impossible or challenging in other systems due to their complexity, and the presence of numerous uncontrollable variables, or lengthy observation periods should be considered and included in this study. For instance, investigating long-term changes while maintaining identical conditions between the sample and control, analyzing the memory of T-Consciousness Field effects, studying the effect of initial population differences in the type and intensity of response to T-Consciousness Fields (similar to biological studies with cellular and animal models where results analysis is complex), or examining the effect of different TCF Users in measurable empirical results.

A machine learning approach for correcting glow curve anomalies in CaSO4:Dy-based TLD dosimeters used in personnel monitoring

The study presents a novel approach to analysing the thermoluminescence (TL) glow curves (GCs) of CaSO4:Dy-based personnel monitoring dosimeters using machine learning (ML). This study demonstrates the qualitative and quantitative impact of different types of anomalies on the TL signal and trains ML algorithms to estimate correction factors (CFs) to account for these anomalies. The results show a good degree of agreement between the predicted and actual CFs, with a coefficient of determination greater than 0.95, a root mean square error less than 0.025, and a mean absolute error less than 0.015. The use of ML algorithms leads to a significant two-fold reduction in the coefficient of variation of TL counts from anomalous GCs. This study proposes a promising approach to address anomalies caused by dosimeter, reader, and handling-related factors. Furthermore, it accounts for non-radiation-induced TL at low dose levels towards improving the dosimetric accuracy in personnel monitoring.

A Radiation Levels Measurement at Workplace of Cyclotron-PET/CT Facilities (in Karachi) using TLD Dosimeters

Cyclotron is the most widely used proton particle accelerator for production of short lived radionuclides particularly F-18 for diagnostic purpose in oncology imaging. Currently, only Fluorine [F-18] is being produced in Pakistan. F-18 is tagged with glucose analogue and converted into [18F] FDG (Fluorodeoxyglucose) by synthesis process. [18F] FDG emits positron and, via annihilation process, produces two gamma photons of 511keV energy, which is of great concern for occupational safety. Therefore, a study was carried out to assess the dose incurred by radiation workers working in controlled and supervised areas of cyclotron facility.
 In this study, the ten (10) calibrated Thermoluminescene dosimeters (TLD-100) were annealed and placed in different locations of four Cyclotron-PET/CT facilities for determination of dose in work area. In the selected cyclotron facilities, one out of four was unshielded cyclotron and other three were self-shielded. Ten (10) TLDs were placed in preselected controlled and supervised areas of facilities for the duration of 30 days. After four weeks of exposure, TLDs were removed and assessed on TLD reader for dose evaluation.
 The evaluated results of radiation levels from TLDs are in good agreement with the criteria for classification of areas as defined in Regulations on Radiation Protection (PAK/904). The measured doses of work area are well below the defined regulatory dose limits for controlled area (>6mSv/yr) as well as supervised area (>1mSv/yr) except in case of unshielded cyclotron vault. It is concluded that the facilities have implemented the requirement 27 of PNRA Regulations on Radiation Protection (PAK/904) and also have established strong radiation safety measures for minimization of occupational exposure.

Determination of Radiation Exposure of Individuals in the Population by Patients after Radioiodine Therapy - Comparison of two Measurement Systems.

In 147 patients after RIT and their relatives, the dosage was measured over 14 days with different measuring systems. Finger ring dosimeters (FRD) were worn during the whole day, furthermore the dose was determined by non-official OSL and TLD dosimeters during the sleep phase. 88 data sets were used for the final analysis. With the FRD, dose values between 0.1-50 mSv were determined for the patients. As expected, the finger ring dose of the relatives was significantly lower, averaging 0.75 mSv compared to 10 mSv for the patient. For the TLD and OSL used in the sleep phase, the measured values were in the same range. The reproducibility of the measurement results was significantly better for the OSL than for the TLD. Despite method-related measurement uncertainties, it can be concluded that the exposure dose of patients' relatives after radioiodine therapy is low and that the legal requirements are met. Moreover, the now official OSL dosimeters represent a more accurate and for the chosen measurement task better suited measurement system than the TLD. · The exposure dose of patients' relatives after radioiodine therapy is low.. · The requirements of radiation protection legislation after discharge from the nuclear medicine therapy ward are complied with. · OSL dosimeters are a accurate and for the measurement task suited system. · Hartmann H, Andreeff M, Claußnitzer J et al. Determination of Radiation Exposure of Individuals in the Population by Patients after Radioiodine Therapy - Comparison of two Measurement Systems. Fortschr Röntgenstr 2023; 195: 605 - 612.

Comparative study of Lutetium-177 and Phosphorus-32 in radioactive bone cement for the treatment of vertebral body metastasis.

Vertebroplasty is a minimally invasive outpatient procedure to stabilize compression fractures in the spine. This procedure involves injecting bone cement into the vertebrae that have been cracked or broken, typically due to osteoporosis. The cement hardens inside the bones, providing stability to the fractures and supporting the spine. Additionally, radioactive bone cement and brachytherapy sources have been utilized to suppress tumor growth in the vertebral body. We present a novel brachytherapy technique for treating vertebral body metastases using a liquid form of radioactive sources, Phosphorus-32 and Lutetium-177, separately mixed with bone cement and injected into vertebral body bone prostheses. We also investigated the dose distribution of the radioactive bone cement by theoretically calculating it using GEANT4 Monte Carlo and measuring it using TLD dosimeters for Phosphorus-32 and Lutetium-177 loaded in vertebral bodies. CT-scanned images of each vertebral body (L2 and L3) were imported into GEANT4 for simulation purposes. Two simulations were performed to evaluate the possibility of using PLA prostheses in ex vivo measurements, using bone and PLA material as a bone substitute for brachytherapy of Lutetium-177 and Phosphorus-32. The simulations calculated the dose distribution, dose rates, and deposited dose to the spinal cord and aorta. Next, 3D-printed bone prostheses were drilled and separately filled with bone cement, including PMMA-P32 and PMMA-Lu177, in liquid form using the Vertebroplasty technique. The dose to regions of interest was measured using Thermoluminescence dosimeters. When comparing the simulated and measured results of dose rates, it was observed that P32 delivers higher doses to normal organs such as the spinal cord and aorta. At the same time, Lu177 has better sparing in these regions of interest. Therefore, while P32 and Lu177 are suitable for radioactive bone cement treatment, Lu177 delivers relatively lower doses to vital organs such as the spinal cord and aorta. Additionally, Lu177 has characteristics such as a shorter range and lower energies of beta particles in tissue and the presence of gamma rays that make it a better choice for the same treatments. It also provides the possibility of SPECT imaging.

Determination of the Absorbed Dose in Water for Small Photon Beams Using Micro-TLDs of LiF:Mg,Ti (Pilot Audit Proposal)

Background: Small-field dosimetry remains an open challenge globally. Thus, it is crucial to consider adequate reference codes of practice for the performance of dosimetry. Furthermore, as part of good clinical practice, the implementation of new codes of practice implies the development of a dosimetry audit program. In this work, a pilot dosimetric audit protocol is established for measuring the absolute dose in water for small fields using micro-TLDs LiF:Mg,Ti dosimeters. Methods: The dosimeters were irradiated with a 6 MV X-ray beam in a linear accelerator. The TLDs were calibrated between 0.5 and 3 Gy for different field sizes. For audit, the TLDs were irradiated at 2 Gy for different circular field sizes. The proposed protocol consists of five TLD dosimeters forming a cross with a marked radiochromic film to identify the position of the central dosimeter during irradiation. Only the dosimeter measurement in the center of the field is used. Results: It was found that the percentage difference between the measured dose and the prescribed dose (2 Gy) for irradiation in circular fields is less than 3%. Conclusions: A pilot dosimetric audit was carried out using the proposed protocol over a linear accelerator using small circular collimator photon beams.

Comparing the effect of electron beam, beta and ultraviolet C exposure on the luminescence emission of commercial dosimeters

This paper reports on the luminescence characterization of TLD-100 (LiF: Ti, Mg), TLD-200 (CaF2: Dy), TLD-400 (CaF2: Mn) and GR-200 (LiF: Mg, Cu, P) dosimeters exposed to electro beam, beta and ultraviolet C radiation -UVC-. All of them show high sensitivity to radiation regardless of whether it is ionizing or partially ionizing radiation based on their luminescence properties (cathodoluminescence -CL- or thermoluminescence -TL-). CL emission differs significantly among them in shape and intensity due to their chemical compositions. LiF samples display three maxima at: (i) 300–450 nm linked to intrinsic and structural defects, (ii) a green waveband probably due to F3+ centres or the presence of hydroxyl groups and (iii) the red-infrared emission band associated with F2 centres. However, CL spectra from the CaF2 dosimeters display meaningful differences due to the dopant. TLD-200 is characterized by an emission with four sharp individual peaks in the green-IR spectral region (due to the Dy3+), whilst TLD-400 exhibits a broad maximum peaked at ̴500 nm (linked to the Mn2+). On the other hand, the variation in the TL glow curves allows to discriminate the TLDs exposed to beta and UVC radiation since they give rise to different chemical-physical processes and that have been studied from the estimation of the kinetic parameters by means of the Computerised Glow Curve Deconvolution (CGCD) method.

Cardiologist’s exposure to radiation in cath lab measured with InstadoseTM dosimeter

Introduction: complex fluoroscopy-guided interventional procedures in cardiology are known to result in higher radiation doses for patients and staff. Purpose: to estimate the equivalent dose received in different regions of the cardiologist’s body in catheterism (CATH) and percutaneous coronary intervention (PCI) procedures, as well as to evaluate the effectiveness of monitoring the doses in the catheritization laboratory (cath lab) using a direct ion storage dosimeter. Materials and methods: the InstadoseTM and the thermoluminescent dosimeters (TLD-100) were fixed simultaneously in the following regions of the cardiologist’s body: near the eyes (left and right), the trunk region (over the lead apron) and the left ankle. Occupational doses were recorded during 86 procedures (60% CATH). Results: catheterization procedures showed third quartile dose values near to the left eye region equal to 0.10 mSv (TLD-100) and 0.12 (InstadoseTM) and for intervention 0.15 mSv (TLD-100 and InstadoseTM). The doses measured in the trunk region, over the lead apron, were about 13% higher for catheterization procedures and 20% higher for intervention procedures compared to left eye region measurements. The Wilcoxon–Mann–Whitney test was applied for unpaired data for all body regions, comparing the data obtained between the TLD-100 and InstadoseTM dosimeters. For CATH and PCI, the responses of the TLD-100 and InstadoseTM dosimeters are considered equal for all analysed regions (p > 0.05) with the exception of the right eye region. Conclusion: the InstadoseTM passive dosimeter can be useful as a complementary assessment in the monitoring of a cardiologist’s personal occupational doses in the cath lab.

Monitoring the Environmental Radiation Levels for Some Regions in Iraq

The absorbed dose rates in air have been monitored in 23 different urban areas in Iraq using TLD dosimeter for the period 1992-1994 and in 2011-2012, with no significant differences observed. The risk of cancer incidence (morbidity) and mortality to the individuals related to external exposure to ambient gamma radiation is evaluated in this study using the linear, no-threshold (LNT) dose-response model. The risk estimations include delayed radiation effects (cancer morbidity, mortality and hereditary genetic damages). The mean effective dose equivalent to the individuals of 0.48 mSv/y is found to be less than the recommended dose limit to the public established by the International Atomic Energy Agency of 1 mSv/y. However, the findings of this study report that about 0.24% of the respective population are expected to be diagnosed with radiation-induced cancer over there lifetime. The lifetime fatal cancer probability (mortality) is estimated to be occurs at a rate of 0.18%. The risk of developing fatal stomach cancer is found to be occurs at a largest extent in comparison with other exposed body organs and tissues. Other consequences of radiation injury such as genetic effects transmitted to succeeding generations are expected to occur at a rate of 0.03% in the offspring of the respective population as a result of changes transmitted via the genetic mechanisms due to irradiation of gonads

Preparation and study of the main dosimetric properties by TL of sintered lithium silicate pellets

This work presents the structural characteristics and the dosimetric properties under ionizing radiation of the lithium silicate (LSO) (LSO) phosphor. The structure of the synthesized material was determined by X-ray diffraction (XRD) method and Rietveld refinement method. The dosimetric properties of LSOLSO in the form of pellets were studied by thermoluminescence (TL) under the effect of different doses of γ-irradiation. The phosphor exhibited a TL emission curve with four TL peaks centered at 100, 182, 250 and 290 °C, with a light emission band centered at 385 nm. The TL dose-dependent γ-radiation dose response of the TL peak at 182 °C was linear in the low-dose region, from the order of mGy to 50 Gy. In addition, the phosphor exhibits lower fading, good reproducibility, and sensitivity of the order of commercial TLD-100 dosimeters.

Dose metrology: TLD/OSL dose accuracy and energy response performance

An essential step in evaluating and comparing the performance of two passive radiation dosimeter types, thermosluminescent (TLD) and optically stimulated luminescence (OSL), used by workers in environments with ionizing radiation for individual radiological monitoring and control of external exposure at various times (cumulative dose for 1 month), is to compare the measured dose accuracy, energy response, and coefficient of variation.In fact this performance study consists in determining the accuracy of both R(10) and R(0.07) which are considered as the ratios of the measured dose (Hp(10) or Hp(0.07)) to the delivered dose (Hp(10) or Hp(0.07)) for each photon energy. The validity of the results of this test is based on the acceptance limits of the ICRP and the international standard IEC-62387. The relative energy response used is normalized to the 137Cs 662 keV energy to find which energy response is closest to the ideal case, and the coefficient of variation that allows to determine the statistical fluctuation of the Hp(10) and Hp(0.07) doses.The results of the accuracy test for the OSL and TLD dosimeters are acceptable because they fall within the ICRP limits. For the energy response, the OSL performs better than the TLD for Hp(10) and Hp(0.07), and for the coefficient of variation, the OSL satisfies the requirements of ISO 62387 for both Hp(10) and Hp(0.07), while the TLD satisfies these requirements only for the measurement of Hp (0.07).

Does Electron Spectrum Affect TLD-100 Dose Response in 6 MV Photon Beam Irradiation?

In this study, the electron spectrum effect on the TLD-100 dosimeter response to a 6 MV photon beam in different media like water, aluminum, polystyrene, iron, copper, and lead using Monte Carlo and Burlin cavity theory was evaluated. To calculate and compare the dose to medium to dose to cavity correction factors (f), the electronic equilibrium spectrum produced by the 6 MV photon beam and its maximum electron energy in different media were used. The electronic equilibrium spectra were obtained using Beamdp Monte Carlo Simulation. Using two different methods, the cavity theory was applied to obtain the response of the TLD-100 to 6 MV photon beam in the media considered. In the first method, the average mass collision stopping power ratios and the average mass effective attenuation coefficients were calculated using the electron spectrum of 6 MV. In the second method, these parameters were calculated based on the maximum energy value of 6 MV. The maximum difference between the f values obtained using the two methods was about 10 % for lead, while it was less than 2.5 % for other media. Consequently, the differences between f factors calculated using these two methods were insignificant except for lead.

Determination of energy correction coefficient for neutron albedo dosimeter. Three approaches

To accurately determine dose, albedo TLD dosimeters require application of a neutron energy correction factor (NECF). In this paper, the results from three different methods were used to determine NECFs. In the first method, NECF values were calculated as a ratio of the known “conventional true” dose and the neutron dose reported by albedo dosimeter(s) irradiated on a phantom. The results from this direct method were utilized for verification of two other methods. The second method used a specially designed device called the Neutron Area Monitor (NAM) model 5. The third method of NECF determination was based on the response of a BF3 tube under different levels of moderation. The results of this work showed that the Navy-developed Neutron Area Monitor (NAM) model 5 measures NECF values correctly when irradiated with 252Cf (bare and D2O-moderated). This was an important result, because it validated the use of the NAM-5 in nuclear power and marine propulsion reactors, as their neutron energy spectrum is approximated by the field of a Cadmium-coated 30 cm diameter steel sphere of D2O moderated 252Cf. In the case of a broad neutron energy spectrum the 6Li response to the small amount of slow neutrons outweighs its response to the fast neutrons overwhelmingly responsible for the neutron dose rate. Based on the obtained results we can conclude that NAM-5 provides correct NECF determination if the fraction of slow neutrons in the neutron dose rate is more than 20%. A satisfactory correlation between the NECF determined by NAM-5 and the multi-moderated BF3 tube method was observed, but the multi-moderated BF3 tube values were ∼30% lower than those obtained by the NAM-5 at the same locations for broader neutron energy spectrum locations.

Out-of-field mean photon energy and dose from 6 MV and 6 MV FFF beams measured with TLD-300 and TLD-100 dosimeters.

To measure the out-of-field mean photon energy and dose imparted by the secondary radiation field generated by 6 MV and 6 MV FFF beams using TLD-300 and TLD-100 dosimeters and to use the technique to quantify the contributions from the different sources that generate out-of-field radiation. The mean photon energy and the dose were measured using the TLD-300 glow curve properties and the TLD-100 response, respectively. The TLD-300 glow curve shape was energy-calibrated with gamma rays from 99m Tc, 18 F, 137 Cs, and 60 Co sources, and its energy dependence was quantified by a parameter obtained from the curve deconvolution. The TLD-100 signal was calibrated in absorbed dose-to-water inside the primary field. Dosimeters were placed on the linac head, and on the surface and at 4.5cm depth in PMMA at 1-15cm lateral distances from a 10 × 10 cm2 field edge at the isocenter plane. Three configurations of dosimeters around the linac were defined to identify and quantify the contributions from the different sources of out-of-field radiation. Typical energies of head leakage were about 500keV for both beams. The mean energy of collimator-scattered radiation was equal to or larger than 1250keV and, for phantom-scattered radiation, mean photon energies were 400keV for the 6 MV and 300keV for the 6 MV FFF beam. Relative uncertainties to determine mean photon energy were better than 15% for energies below 700keV, and 40% above 1000keV. The technique lost its sensitivity to the incident photon energy above 1250keV. On the phantom surface and at 1-15cm from the field edge, 80%-90% of out-of-field dose came from scattering in the secondary collimator. At 4.5cm deep in the phantom and 1-5cm from the field edge, 50%-60% of the out-of-field dose originated in the phantom. At the points of measurement, the head leakage imparted less than 0.1% of the dose at the isocenter. The 6 MV FFF beam imparted 8-36% less out-of-field dose than the 6 MV beam. These energy results are consistent with general Monte Carlo simulation predictions and show excellent agreement with simulations for a similar linac. The measured out-of-field doses showed good agreement with independent evaluations. The out-of-field mean photon energy and dose imparted by the secondary radiation field were quantified by the applied TLD-300/TLD-100 method. The main sources of out-of-field dose were identified and quantified using three configurations of dosimeters around the linac. This technique could be of value to validate Monte Carlo simulations where the linac head design, configuration, or material composition are unavailable.