Thermoluminescent Dosimeter Measurements Research Articles

The Effects of Abnormal Exposure on Individual Dose Monitoring with TLD Dosimeter

Abstract Objectives: To analyze the effects of normal x-ray inspection, machine washing, and machine drying on thermoluminescent dosimeter (TLD) measurements during external individual monitoring and to provide suggestions for determining individual monitoring measurements under the mentioned abnormal situations. In this study, we focused on three abnormal situations: x-ray inspection, machine washing, and machine drying, which are common in external individual dose monitoring. We measured and compared the doses from TLD with and without 11, 23, 35, and 50 security checks. We used different radiation sources to expose the TLDs before or after machine washing with or without hot drying. The three radiation sources are natural background radiation, 137Cs γ rays, and 320 kVp x-rays. We measured 20 TLDs for each situation. The average doses for the TLDs with 11, 23, 35, 50 security checks are 27.7 μGy, 59.7 μGy, 84.1 μGy, and 121.0 μGy, respectively. We measured an average dose of 2.5 μGy per exposure. The doses showed no significant difference between different times of washing with different radiation sources, natural background radiation, 137Cs, or x-ray exposures. There was also no significant difference between the dose coming from the controlled group, drying at 60 °C and 90 °C for 1 h after exposure to 137Cs γ rays and 320 kVp x-rays. The common machine drying under the temperature of 90 °C did not affect TLD measured doses.

A novel silicon PIN photodiode device for radiation exposure monitoring in dental CBCT

This paper presents a versatile and cost-effective system for the monitoring of X-ray exposure during dental cone beam computed tomography procedures based on silicon PIN photodiode detectors. The system, developed and implemented at the University of Pisa's School of Engineering, underwent characterization under a range of operational conditions focusing on full field-of-view 3D protocols used in adult patient examinations. This study was facilitated by the Azienda Ospedaliero Universitaria Pisana, which provided access to a Planmeca ProMax 3D Classic scanner for the research. During the investigation, photodiodes were placed both on the surface and inside an Alderson RANDO phantom head to assess the dose delivered to regions near radiation-sensitive areas such as the salivary glands, thyroid, eye lens, and laryngopharynx. The evaluation process spanned a spectrum of tube voltages, ranging from 60 to 90 kVp, and tube currents, extending up to 16 mA, to ensure a broad and thorough analysis. Furthermore, to reinforce the effectiveness of the silicon photodiodes' measurement capabilities, calibrated GR-200 A-type thermoluminescent dosimeters were positioned within the phantom head inserts to serve as a reference point. Complementing this setup, PCXMC Rotation 2.0 simulations were conducted to further the efficacy of the monitoring system, particularly tailored to the specific dental CBCT protocols being investigated. In conclusion, while the research revealed a generally consistent correlation across PCXMC simulations, photodiode readings, and thermoluminescent dosimeter measurements, it is important to note that a direct comparison was not exactly possible due to limitations in the size and positioning of the systems. Variations up to 20–35% were observed, primarily due to the different positioning of the dosimeters and the unique physical and operational traits of the different measurement methods employed. Nevertheless, the development of an affordable, easily deployable, and scalable dosimetry monitoring system may provide a substantial contribution to enhancing patient safety in dental radiology and aid in the optimization of diagnostic X-ray protocols.

Dose rate conversion coefficients for ocular contamination in nuclear medicine: A Monte Carlo simulation with experimental validation.

Since 2011, the International Commission on Radiological Protection (ICRP) has recommended an annual eye lens dose limit of 20 mSv for radiation workers, averaged over 5 years, with no year exceeding 50 mSv. However, limited research has been conducted on dose rate conversion coefficients (DCCs) for direct contamination of the eye. This study aimed to accurately determine DCCs for the eye lens and cornea for ocular contamination with radionuclides used in nuclear medicine. DCCs for 37 radionuclides used in nuclear medicine were determined using two different methods. Method 1 involved conducting Monte Carlo (MC) simulations of an ICRU cylinder to determine the absorbed dose at a depth of 3mm resulting from a point source. The accuracy of this simulation approach was validated by experimental thermoluminescent dosimeter (TLD) measurements for 18F, 68Ga, 99mTc, and 177Lu. In method 2, average DCCs were calculated for the eye lens (complete and radiosensitive parts) and the cornea for both a point source and thin surface contamination centered on the cornea using MC simulations on the adult mesh-type reference computational phantom of the eye from the ICRP (MRCP). DCCs determined from TLD measurements showed excellent agreement (deviations: +1.4%, +4.7%, -3.1%, and -2.5% for 18F, 68Ga, 99mTc, and 177Lu, respectively) compared to MC simulations of the experimental set-up. For the 37 radionuclides, DCCs of the complete eye-lens for a point source ranged from 2.53×10-7 to 4.15×10-2 mGy MBq-1 s-1 for the adult MRCPs, being substantially smaller compared to DCCs determined via MC simulations of a ICRU cylinder. In general, point source and surface contamination showed comparable DCCs for the eye lens. Radionuclides emitting low-energy beta radiation or conversion electrons (e.g., 177Lu, 99mTc) showed low DCCs as the radiation does not penetrate to the depth of the eye lens, while radionuclides emitting high-energy beta radiation (e.g., 90Y) showed high DCCs. Overall, DCCs for the radiosensitive part of the eye lens were larger (up to a factor of 3) compared to the complete eye lens. DCCs for the cornea were larger than for the eye lens with a factor that strongly depended on the emitted radiation type. Especially alpha emitters (e.g., 211At, 223Ra) showed high DCCs for the cornea because of the short range of alpha radiation, leading to local maxima in the cornea and not reaching the eye lens. DCCs at a depth of 3mm in an ICRU cylinder and adult MRCP DCCs for both the complete and sensitive parts of the eye lens and cornea were determined for 37 radionuclides having applications in nuclear medicine. These DCCs are highly useful in radiation safety assessments and radiation dose calculations in ocular contamination incidents.

TLD measurement to investigate the bolus effect on skin dose in total body irradiation with helical tomotherapy

The aim of this study is to investigate the skin dose of total body irradiation (TBI) with Helical Tomotherapy and the need to use a bolus to achieve an adequate skin dose. To simulate the RANDO phantom geometrically, arms and legs created from rice were added to the RANDO phantom and it was immobilized in a vacuum bed. Computed tomography (CT) images of the lower and upper parts of the phantom with a slice thickness of 3 mm were acquired with and without bolus. Fifteen thermoluminescent dosimeters (TLDs) were placed on the skin line of the RANDO phantom. Treatment plans were prepared, and the phantom was irradiated both with and without bolus by the Helical Tomotherapy technique. Results of the measurements and treatment planning system (TPS) doses were compared by the non-parametric Wilcoxon signed-rank test. All procedures were repeated three times and results were evaluated. At the end of the study, it was proven that even when no bolus is used, the skin receives an adequate dose in TBI with Helical Tomotherapy while achieving homogeneous dose distribution and saving critical organs at the same time.

Evaluation of organ and effective doses using anthropomorphic phantom: A comparison between experimental measurement and a commercial dose calculator

IntroductionThe aim of this study was to experimentally measure organ doses for computed tomography (CT) procedures using thermoluminescence dosimeters (TLDs) on a RANDO anthropomorphic phantom and verify the measured doses using CT-Expo software. MethodsThe phantom was irradiated using clinical CT scan protocols routinely used for specific procedures in the radiology department. Fifty TLD chips were used in this study. The scanning parameters (kVp, mA, s) used to scan the phantom were used as input parameters for CT-Expo dose estimations. ResultsThe TLD measured organ doses varied between 3.97 mGy for the esophagus and 56.22 mGy for the brain. High doses were recorded in the brain (37.80–56.22 mGy) and the eye lens (29.94–36.16 mGy). Comparing the organ dose measurements between TLD and CT-Expo, the maximum organ dose difference was obtained for the eye lens. A comparison between the two methods for the other organs were all less than 32 %. The effective doses from the TLD measurements for the head, chest, and abdominopelvic CT examinations were 2.78, 6.67, and 17 mSv, respectively and CT-Expo were 2.20, 10.30, and 16.70 mSv, respectively. ConclusionThe experimental and computational results are comparable, and the reliability of the TLD measurements and CT-Expo dose calculator has been proven. Implications for studyA reason for the difference in dose measurements between the two methods has been attributed to the dissimilarity in the organ position in the Rando anthropomorphic phantom and the standard mathematical phantom used by CT-Expo. The experimental and computational results have been found to be comparable.

Comparison of absorbed doses and organ doses measured with thermoluminescent dosimeters and Gafchromic film for cone beam computed tomography examination of the posterior mandibular region in a head phantom

We aimed to map the correlation between thermoluminescent dosimeters (TLDs) and Gafchromic film for measuring absorbed doses and to compare minimum, maximum, and mean absorbed doses over larger regions of interest and at various craniofacial organs and tissues during cone beam computed tomography (CBCT) exposure of the mandibular third molar region. We positioned TLDs at 75 measurement points in a head phantom. Gafchromic film was cut to the same shape as the 5 levels of the phantom and was placed on top of the TLDs. Both dosimetry methods thus included the surface of each level simultaneously. CBCT scans were made using a 5×5 cm field of view and a rotation angle of 200°. Measurements included absorbed dose distributions, doses at all 75 points, and minimum, maximum, and mean doses within organs and tissues. The correlation of point-dose measurements at all TLD sites with doses measured on film was strong (R2=0.9687), with greatest correlation at lower doses (<2 mGy). Large deviations between TLD and film measurements of minimum and maximum doses and absorbed doses to the organs occurred at all 5 levels. TLD positioning failed to cover several organ sites; for these, only absorbed dose measurements from the film were available. TLDs were unable to sample dose distributions and gradients accurately. The characteristics of Gafchromic LD-V1 film make it a favorable alternative in dental CBCT dosimetry.

Creation of waterproof, TLD probes for dose measurements to validate image-based radiopharmaceutical therapy dosimetry workflow

Voxel-level dosimetry based on nuclear medicine images offers patient-specific personalization of radiopharmaceutical therapy (RPT) treatments. Clinical evidence is emerging demonstrating improvements in treatment precision in patients when voxel-level dosimetry is used compared to MIRD. Voxel-level dosimetry requires absolute quantification of activity concentrations in the patient, but images from SPECT/CT scanners are not quantitative and require calibration using nuclear medicine phantoms. While phantom studies can validate a scanner’s ability to recover activity concentrations, these studies provide only a surrogate for the true metric of interest: absorbed doses. Measurements using thermoluminescent dosimeters (TLDs) are a versatile and accurate method of measuring absorbed dose. In this work, a TLD probe was manufactured that can fit into currently available nuclear medicine phantoms for the measurement of absorbed dose of RPT agents. Next, 748 MBq of I-131 was administered to a 16 ml hollow source sphere placed in a 6.4 L Jaszczak phantom in addition to six TLD probes, each holding 4 TLD-100 1 × 1 × 1 mm TLD-100 (LiF:Mg,Ti) microcubes. The phantom then underwent a SPECT/CT scan in accordance with a standard SPECT/CT imaging protocol for I-131. The SPECT/CT images were then input into a Monte Carlo based RPT dosimetry platform named RAPID and a three dimensional dose distribution in the phantom was estimated. Additionally, a GEANT4 benchmarking scenario (denoted ‘idealized’) was created using a stylized representation of the phantom. There was good agreement for all six probes, the differences between measurement and RAPID ranged between −5.5% and 0.9%. The difference between the measured and the idealized GEANT4 scenario was calculated and ranged from −4.3% and −20.5%. This work demonstrates good agreement between TLD measurements and RAPID. In addition, it introduces a novel TLD probe that can be easily introduced into clinical nuclear medicine workflows to provide QA of image-based dosimetry for RPT treatments.

Effects of high ambient temperature on the accuracy of thermoluminescent dosimeters for environmental monitoring

Thermoluminescence dosimeters (TLDs) are widely used for both personal and environmental dosimetry. TLDs should have high accuracy under different conditions. The TL signal can drop over time because of fading (loss of signal due to thermally induced recombination of trapped charriers), thus leading to underestimation of the irradiation dose. The Saudi climate is extremely hot for most of the year, which could significantly affect TLD measurements. Therefore, the effect of ambient temperature, storage time and irradiation dose were investigated both in laboratory controlled-temperature conditions and field experiments, for two commercial dosimeters: Harshaw (TLD-100H™) and RADCARD (MCP-N™), which are used for environmental monitoring. The irradiated TLDs were exposed to a range of ambient temperatures (25 °C–65 °C) then stored for 30, 60, and 90 days. A signal fading due to increasing ambient temperature and storage time was generally observed. MCP-N shows good stability and is less responsive to increasing ambient temperature compared to TLD-100H. TLD-100H is less affected by storage time compared to MCP-N. Irradiation doses play a role in TL signal fading, and TLDs irradiated with 5 mSv have a higher rate of loss compared to those irradiated with 2 mSv in all TLD types. The obtained results permitted to conclude that all TLD types used in this study suffer from TL signal fading, and its degree varies between TLD types.

Evaluation of Surface Dose for Intensity Modulated Radiotherapy of Head and Neck Cancer Using Thermoluminescent Dosimeters

Accurate estimation of the surface dose in radiotherapy of patients with head and neck cancer is very important in terms of treatment. The aim of this study is to evaluate the surface dose for intensity-modulated radiotherapy (IMRT) of head and neck cancer using thermoluminescent dosimeters (TLDs). In addition, it is aimed to examine the surface dose estimates of the treatment planning system (TPS) for different grid sizes. Before the computed tomography (CT) images were taken for 15 head and neck cancer patients, 5 different points determined in the neck region were marked in a way that would not cause artifacts. IMRT plans are created for 1.5 and 2.5 mm grid sizes. Surface doses were obtained for TPS calculations and TLD measurements at 5 different points in the neck region. Surface doses obtained from TLD measurements and TPS calculations with different grid sizes were compared. All patients received 3-stage adaptive radiotherapy (ART) and the surface dose comparison was repeated for each plan. According to plan 0, the height of TLD measurements for the 1.5 and 2.5 mm grid size were 4.06% and 7.87%, respectively. In Plan 1, the difference between TPS and TLD doses was 4.00% and 8.15% for grid size 1.5mm and 2.5mm, respectively (p=0.00 and p=0.00). For dose measurements from Plan 2, the difference between TPS and TLD doses was 4.07% and 9.96% for grid size 1.5mm and 2.5mm, respectively (p=0.00 and p=0.00). Surface doses obtained in TLD measurements for all treatment plans were higher than in TPS dose calculations. Accurate estimation of the surface dose in head and neck cancer radiotherapy is very important for treatment. Surface doses calculated with TPS are usually lower than the prescribed dose. Therefore, during the evaluation of radiotherapy plans, it should be considered that TPS underestimates the surface dose. This ratio can be determined by dosimetric measurements. Thermoluminescent dosimeters are suitable equipment for this process.

Effective dose for kidney-ureter-bladder plain radiography, intravenous urography, and abdominal computed tomography scan: A phantom study

Abdominal colic pain or hematuria is suspected to be caused by urinary tract stones. Commonly used X-ray examinations include kidney-ureter-bladder plain radiography (KUB), intravenous urography (IVU), and abdominal computed tomography (CT). In this study, a high-sensitivity thermoluminescent dosimeter (TLD) was embedded in a Rando phantom to directly measure organ dose and evaluate effective dose. During each experiment, 139 TLD measurement points that cover almost all organs (as recommended by the ICRP 103 report) were examined. Red bone-marrow and remainder tissues have a high tissue weighting factor (0.12), and they are widely distributed. In the phantom, 34 TLDs and 31 TLDs were embedded in the red bone-marrow and remainder tissues to improve the accuracy and representativeness of organ doses. The detailed organ dose distributions for KUB, IVU, and abdominal CT are presented. The effective doses for KUB and IVU were 0.22 and 1.51 mSv, respectively, and those for two abdominal CTs were 8.21 and 9.27 mSv. This experiment presents a conversion factor of 0.0177 mSv·mGy−1 cm−1 for the abdominal CT examination, which differs from most of the conversion factors obtained through the Monte Carlo simulation method.

Evaluation of dose distribution of an intraoperative radiotherapy device using thermoluminescent dosimeters and radiographic films.

BackgroundTo investigate dose distribution of the 5cm spherical applicator of the INTRABEAM™ intraoperative radiation therapy (IORT) device via thermoluminescence dosimeters (TLDs) and Radiographic films. Independent dose distribution assessment of IORT devices is considered important. Several methods are described for this purpose, including TLDs and films. However, Radiographic films are not routinely used.Materials and methodsTwenty TLDs were used for depth dose measuring and evaluating the isotropy in water. Additionally, the isotropy was assessed separately via Radiographic films in air by drawing isodose curves.ResultsTLD measurements showed a steep dose decline which the relative average dose of 0.94 at the applicator surface reduced to 0.32, 0.13, and 0.07 at 1, 2, and 3 cm depths in water, respectively. Some remarkable isodose curves prepared using Radiographic films showed forward anisotropy of the 5 cm applicator.ConclusionA very steep dose decline and approximately isotropic dose distribution of the 5 cm applicator were observed via TLD measurements. Radiographic films showed acceptable potential for drawing dose distribution maps. However, they should be applied in more various radiation setups to be implemented more confidently.

Comparison of organ and effective dose estimations from different Monte Carlo simulation-based software methods in infant CT and comparison with direct phantom measurements.

PurposeComputational dosimetry software is routinely used to evaluate the organ and effective doses from computed tomography (CT) examinations. Studies have shown a significant variation in dose estimates between software in adult cohorts, and few studies have evaluated software for pediatric dose estimates. This study aims to compare the primary organ and effective doses estimated by four commercially available CT dosimetry software to thermoluminescent dosimeter (TLD) measurements in a 1‐year‐old phantom.MethodsOne hundred fifteen calibrated LiF (Mg, Cu, P)‐TLD 100‐H chips were embedded within an anthropomorphic phantom representing a 1‐year‐old child at positions that matched the approximate location of organs within an infant. The phantom was scanned under three protocols, each with whole‐body coverage. The mean absorbed doses from 25 radiosensitive organs and skeletal tissues were determined from the TLD readings. Effective doses for each of the protocols were subsequently calculated using ICRP 103 formalism. Dose estimates by the four Monte Carlo–based dose calculation systems were determined and compared to the directly measured doses.ResultsMost organ doses determined by computation dosimetry software aligned to phantom measurements within 20%. Additionally, comparisons between effective doses are calculated using computational and direct measurement methods aligned within 20% across the three protocols. Significant variances were found in bone surface dose estimations among dosimetry methods, likely caused by differences in bone tissue modeling.ConclusionAll four‐dosimetry software evaluated in this study provide adequate primary organ and effective dose estimations. Users should be aware, however, of the possible estimated uncertainty associated with each of the programs.

The Effect of Mouse Size on Dose from an X-Rad320 Irradiator.

Irradiation protocols for murine experiments often use standardized dose rate estimates for calculating dose delivered, regardless of physical variations between mouse subjects. This work sought to determine the significance of mouse size on absorbed dose. Five mouse-like phantoms of various sizes based on the mouse whole-body (MOBY) model were 3D printed. The phantoms were placed in an X-Rad320 biological irradiator and a standard irradiation protocol was used to deliver dose. Dose was measured using thermoluminescent dosimeter (TLD) microcubes inside each phantom, and the relative readings were used to calculate output factors (OFs), normalized to the phantom of median volume. Additionally, the OF for each mouse was simulated in Monte Carlo N-Particle (MCNP) code. For both the TLD measurements and MCNP simulations, the OF for each mouse was determined by both experiments and calculations to be unity within the relative standard uncertainties (k = 1). This work supports comparing results across various studies using the X-Rad320 irradiator without need for corrections based on mouse size.

Patient-specific dose assessment using CBCT images and Monte Carlo calculations

Today, the use of Cone-Beam Computed Tomography (CBCT) is increasing rapidly in medical diagnosis, therefore evaluation of patient's dose is a very important issue in radiation protection of patients. This study aimed to evaluate the patient-specific dose using CBCT images. Since CBCT images only showed a part of the head and while, the total anatomical specification of the head should be defined for dose assessment, therefore the whole parts of the head were generated using the data of the Extended Cardiac-Torso (XCAT) reference phantoms and pseudo-images were created. Tissue densities were calculated by the voxel values of pseudo-images and were used as the input file of Gate8.2 Monte Carlo (MC) code. Also, the GIANO CBCT unit was simulated and the absorbed dose was calculated by the code. For verification of this method, Rando phantom with embedded thermoluminescence dosimeters (TLD) with different protocols was used. The results of MC calculations and TLD measurements were compared and statistical analysis was performed using IBM SPSS Statistics. The calculated effective dose values determined by CBCT images for three different Temporomandibular joint, Single-Arch, and Both-Arch protocols were found to be 87 ± 3 μSv, 64 ± 1 μSv, and 66 ± 2 μSv, and the results of thermoluminescence dosimetry were 86 ± 2 μSv, 57 ± 1 μSv, and 63 ± 3 μSv, respectively. There were no significant differences (P-Value>0.05) between the results of MC calculations using CBCT images and the results of TLD dosimeters. In this study, a method for patient-specific dose assessment using CBCT images was introduced. It was shown that the dose of patients with its specification can be evaluated by CBCT images with acceptable accuracy.

Investigation of Eye Lens Dose Estimate based on AAPM Report 293 in Head Computed Tomography.

Background: Estimation of eye lens dose is important in head computed tomography (CT) examination since the eye lens is a sensitive organ to ionizing radiation.Objective: The purpose of this study is to compare estimations of eye lens dose in head CT examinations using local size-specific dose estimate (SSDE) based on size-conversion factors of the American Association of Physicists in Medicine (AAPM) Report No. 293 with those based on size-conversion factors of the AAPM Report No. 220.Material and Methods: This experimental study is conducted on a group of patients who had undergone nasopharyngeal CT examination. Due to the longitudinal (z-axis) dose fluctuation, the average global SSDE and average local SSDE (i.e. particular slices where the eyes are located) were investigated. All estimates were compared to the measurement results using thermo-luminescent dosimeters (TLDs). The estimated and measured doses were implemented for 14 patients undergoing nasopharyngeal CT examination.Results: It was found that the percentage differences of the volume CT dose index (CTDIvol), average global SSDE based on AAPM No. 220 (SSDEo,g), average local SSDE based on AAPM No. 220 (SSDEo,l), average global SSDE based on AAPM No. 293 (SSDEn,g) and average local SSDE based on AAPM No. 293 (SSDEn,l) against the measured TLD doses were 22.5, 21.7, 15.0, 9.3, and 2.1%, respectively. All comparisons between dose estimates and TLD measurements gave p-values less than 0.001, except for SSDEn,l (p-value = 0.566). Conclusion: SSDE based on AAPM Report No. 293 can be used to accurately estimate eye lens radiation doses by performing the calculations on a number of specific slices containing the eyes.

Skin dose measurement and estimating the dosimetric effect of applicator misplacement in gynecological brachytherapy: A patient and phantom study.

To evaluate skin dose differences between TPS (treatment planning system) calculations and TLD (thermo-luminescent dosimeters) measurements along with the dosimetric effect of applicator misplacement for patients diagnosed with gynecological (GYN) cancers undergoing brachytherapy. The skin doses were measured using TLDs attached in different locations on patients' skin in pelvic regions (anterior, left, and right) for 20 patients, as well as on a phantom. In addition, the applicator surface dose was calculated with TLDs attached to the applicator. The measured doses were compared with TPS calculations to find TPS accuracy. For the phantom, different applicator shifts were applied to find the effect of applicator misplacement on the surface dose. The mean absolute dose differences between the TPS and TLDs results for anterior, left, and right points were 3.14±1.03, 6.25±1.88, and 6.20±1.97 %, respectively. The mean difference on the applicator surface was obtained 1.92±0.46 %. Applicator misplacements of 0.5, 2, and 4 cm (average of three locations) resulted in 9, 36, and 61%, dose errors respectively. The surface/skin differences between the calculations and measurements are higher in the left and right regions, which relate to the higher uncertainty of TPS dose calculation in these regions. Furthermore, applicator misplacements can result in high skin dose variations, therefore it can be an appropriate quality assurance method for future research.

Assessment of the uterine dose in digital mammography and digital breast tomosynthesis

IntroductionDigital Mammography (DM-2D) and more recently Digital Breast Tomosynthesis (DBT), are two of the most effective imaging modalities for breast cancer detection, often used in screening programmes. It may happen that exams using these two imaging modalities are inadvertently performed to pregnant women. The objective of this study is to assess the dose in the uterus due to DM-2D and DBT exams, according to two main irradiation scenarios: in the 1st scenario the exposure parameters were pre-selected directly by the imaging system, while in the 2nd scenario, the maximum exposure parameters were chosen. MethodsThe mammography equipment used was a Siemens Mammomat Inspiration. A physical anthropomorphic phantom, PMMA plates (simulating a breast thickness of 6 cm) and thermoluminescent dosimeters (TLDs) were used to measure entrance air kerma values on the phantom's breast and abdomen in order to successively estimate the mean glandular dose (MGD) and the dose in the uterus. For the two irradiation scenarios chosen, two-breast imaging modalities were selected: 1) DBT in Cranio-Caudal (CC) view (with 28 kV and 160 mAs as exposure parameters), 2) DBT and DM in Medio Lateral-Oblique (MLO) and CC views (with 34 kV and 250 mAs as exposure parameters). ResultsIn the 1st scenario, the TLD measurements did not detect significant dose values in the abdomen whereas the MGD estimated using the D.R. Dance model was in close agreement with data available in the literature. In the 2nd scenario, there was no significant difference in MGD estimation between the different views, whereas the air kerma values in the abdomen (in DBT mode, CC and MLO) were 0.049 mGy and 0.004 mGy respectively. In CC DM-2D mode the abdomen air kerma value was 0.026 mGy, with no significant detected value in MLO view. ConclusionsFor the dose in the uterus, the obtained values seem to indicate that DM-2D and DBT examinations inadvertently performed during pregnancy do not pose a significant radiological risk, even considering the case of overexposure in both breasts. Implications for practiceThe accurate knowledge of the doses in DM-2D and DBT will contribute to raise the awareness among medical practitioners involved in breast imaging empowering them to provide accurate information about dose levels in the uterus, improving their radiation risk communication skills and consequently helping to reduce the anxiety of pregnant women undergoing this type of examinations.

Chest X-rays of newborns in a medical facility: variation between the entrance skin dose measurements using the indirect and direct methods for clinical dose audit

This study aims to determine the mean and 75th percentile entrance skin dose (ESDcal) from anteroposterior (AP) chest X-rays using machine parameters (indirect method). Also, a comparison was made between the ESDcaland already determined thermoluminescent dosimeter (TLD) measurements (ESDTLD) from a previous study from the same patients' data. In addition, the results were compared to similar articles, where the direct and indirect methods were used in estimating ESD to newborns. The study determined the digital radiography (DR) X-ray machine output using a calibrated XR Multidetector (silicon photodiode). X-ray machine milliampere-seconds (mAs), peak kilovoltage (kVp), focus to detector distance (FDD) and focus to skin distance (FSD) were used from a previous study. The mean kVp and mAs were 56.63 (52-60) and 5.7 (5-6.3) and the patient thickness was 9.5 (8-11.5) cm. The mean ESDs of the newborn between 0 and 28days were 0.67 ± 0.09mGy, and the 75th percentile was 0.75mGy. The effective dose (E) for the 40 patients was 0.19mSv and the estimated prenatal cancer risk ranged from (5-24.7) 10-6 Sv-1. The variation between the indirect and the direct methods for assessing ESD was 39.6 (33.7-45.1)%. The 75th percentile ESD was the highest compared to the American College of Radiology-American Association of Physicists in Medicine-Society for Pediatric Radiology (ACR-AAPM-SPR), European Commission (EC) and United Kingdom (UK) reports. Comparison of both methods for assessing ESD was within 40% as compared to other studies. Based on the above results, the indirect method can be implemented for clinical dose audit.

Gel and thermoluminescence dosimetry for dose verifications of a real anatomy simulated prostate conformal radiation treatment in the presence of metallic femoral prosthesis.

This study aims to verify the dose delivery of prostate radiotherapy treatments in an adult pelvic phantom with two metallic hip and femur prosthesis using a four‐field box technique. The prostate planned target volume (PTV) tridimensional (3D) dose distribution was evaluated using gel dosimetry, and thermoluminescent dosimeters (TLD) were used for point‐dose measurements outside it. Both results were compared to the treatment planning system (TPS) dose calculation without using heterogeneity corrections to evaluate the influence of the metal in the dose distribution. MAGIC‐f gel dosimeter (Methacrylic and Ascorbic acid in Gelatin Initiated by Copper with Formaldehyde) associated with magnetic resonance imaging was used. TLD were positioned at several points at the bone metal interface and the sacrum region. The comparison of the gel measured and the TPS calculated dose distributions were done using gamma analysis (3%/3 mm), and a pass rate of 93% was achieved. The TLD dose values at the bone‐metal interface showed variations from the planned dose. However, at the sacrum region, where the beams did not intercept the prosthesis, there was a good agreement between TPS planning and TLD measurements. Our results show how the combination of 3D dosimetry and measurements at specific points in the phantom allowed a comprehensive view of the dose distribution and identified that care must also be paid to regions outside the PTV.

Dose distrubution evaluation of different dental implants on a real human dry-skull model for head and neck cancer radiotherapy

ObjectivesIn this study, the effect of different dental implant materials on dose distribution in head and neck cancer radiotherapy planning was investigated in a real human dry-skull taken from cadaver. MethodsThe effect of Root-shaped Yttrium (Y) stabilized tetragonal Zr polycrystalline (Y-TZP), Titanium (Ti), Alumina (Al2O3) and polyether ether ketone (PEEK) dental implants on dose distribution was investigated by three different methods; Monte Carlo (MC) simulation, Eclipse Treatment Planning System's (TPS) Pencil Beam Convolution (PBC) algorithm and Thermoluminescence Dosimeter (TLD). The 6 MV photon beam simulation was performed for the Varian 2300 C/D linear accelerator using the EGSnrc based BEAMnrc MC Code. To perform MC simulation on skull phantom, phantom CT images with extended CT scale were imported to BEAMnrc/EGSnrc MC code via CTCREATE code. ResultsAccording to the dose distribution measurement in dry skull, the calculated dose differences between PBC and MC algorithms were in the range of 0.6–4.5% whereas the dose difference between MC and TLD were in the range of 1,1–14.6% range depending on implant material. The PBC calculated dose increase difference range confirmed with TLD measurements was between 1.7% and 19.8%. The PBC algorithm could not fully determine the dose due to backscattering caused by dental implants. This is probably due to the limitations and shortcomings of the PBC algorithm. ConclusionThe maximum dose increase was observed for the Y-TZP dental implant material, which has the highest physical density. No significant dose increase was observed for the PEEK implant probably due to the low physical density of implants close to the physical density of water.