Phantom Dosimeters Research Articles

Is digital mammography reducing radiation doses to women?

This study aims to investigate the impact of national quality programs in mammography and technological advances in digital mammography units on the radiation doses delivered to women in Brazil. Radiation dose assessments in mammography units were conducted through a mail-based dosimetric system. For each unit of facilities that applied to one of the two national quality programs, a postal dosimetric system is dispatched, comprising an optically stimulated luminescent dosimeter (OSL) attached to the surface of a 4.0 cm thick polymethyl methacrylate (PMMA) phantom, simulating a compressed breast with 4.5 cm thickness. Testing instructions to expose the dosimetric phantom for assessing the mean glandular dose (MGD) are provided. Between 2012 and 2023, the programs evaluated the MGD in 1,687 mammography units of computed radiography (CR) and direct digital radiography (DR) technologies from 1,399 facilities located in all Brazilian regions. A total of 1,660 (70.5%) evaluations were carried out on CR technology mammography units and 696 (29.5%) on DR units, totaling 2,356 MGD evaluations. The overall average MGD was 1.60 ± 0.80 mGy, with 1.68 ± 0.83 mGy for CR technology and 1.42 ± 0.68 mGy for DR technology. A comparison of average MGD between the periods 2012 - 2018 and from 2019 onwards shows a dose reduction of 8.6% for CR systems and of 26.0% for DR systems (p = 0.000). As CR systems use analog mammography units, which did not undergo technological advances between the two periods, the reduction in doses observed is due to the actions of national quality certification programs and by using image plates for dual-sided reading or needle-based image plates. The reduction observed in DR systems is due to both national quality programs and technological advances in mammography units, especially the use of radiation beams generated by X-ray tubes with tungsten targets.

Quality assurance of magnetic resonance imaging for a polymer gel dosimeter using a 3D-printed phantom

PurposeQuality assurance (QA) of magnetic resonance imaging (MRI) for gel dosimetry using an in-house phantom was established to ensure consistent dosimetric performance. MethodsA normoxic N-vinylpyrrolidone-based gel dosimeter sensitized with an inorganic salt was used. Each individual gel dosimeter, in addition to a specially designed image QA phantom, was imaged at three institutions with different MRI systems. ResultsBoth the gel dosimeter and QA phantom had linear dose–response curves at all institutions, with correlation coefficients = 1.00 and ≥ 0.99, respectively. Minor inter-institutional variations in the sensitivity (gel dosimeter, 0.096 ± 0.010 s−1Gy−1; QA phantom, 0.140 ± 0.003 s−1Gy−1) and offset value (gel dosimeter, 2.188 ± 0.222 s−1; QA phantom, 3.318 ± 0.081 s−1) were found. Dose uncertainties for the gel dosimeter ranged from 3.2% to 3.5% at 10 Gy and 1.7%–2.1% at 20 Gy, and these were comparable with the corresponding QA phantom uncertainties. Dose resolutions were 0.8–1.2 Gy for the gel dosimeter and 0.6–1.4 Gy for the QA phantom. Uniformity factors were ≥98% at all institutions. Spatial linearity had a geometric distortion ≤1.0%, Gamma passing rates of 95%–100% met recommended QA guidelines; strong correlations between the QA phantom and gel dosimeter were also obtained for each of these measures. ConclusionOur study demonstrates the viability of applying MRI acquisition parameters validated using a QA phantom to polymer gel dosimetry across diverse MRI systems. This approach enables robust QA measures, focusing on effective management of uniformity and dose uncertainty.

Pilot scale validation campaign of gel dosimetry for pre-treatment quality assurance in stereotactic radiotherapy

PurposeComplex stereotactic radiotherapy treatment plans require prior verification. A gel dosimetry system was developed and tested to serve as a high-resolution 3D dosimeter for Quality Assurance (QA) purposes. Materials and MethodsA modified version of a polyacrylamide polymer gel dosimeter based on chemical response inhibition was employed. Different sample geometries (cuvettes and phantoms) were manufactured for calibration and QA acquisitions. Irradiations were performed with a Varian Trilogy linac, and analyses of irradiated gel dosimeters were performed via MRI with a 1.5 T Philips Achieva at 1 mm3 or 2 mm3 isotropic spatial resolution. To assess reliability of polymer gel data, 54 stereotactic clinical treatment plans were delivered both on dosimetric gel phantoms and on the Delta4 dosimeter. Results from the two devices were evaluated through a global gamma index over a range of acceptance criteria and compared with each other. ResultsA quantitative and tunable control of dosimetric gel response sensitivity was achieved through chemical inhibition. An optimized MRI analysis protocol allowed to acquire high resolution phantom dose data in timeframes of ≈ 1 h. Conversion of gel dosimeter data into absorbed dose was achieved through internal calibration. Polymer gel dosimeters (2 mm3 resolution) and Delta4 presented an agreement within 4.8 % and 2.7 % at the 3 %/1 mm and 2 %/2 mm gamma criteria, respectively. ConclusionsGel dosimeters appear as promising tools for high resolution 3D QA. Added complexity of the gel dosimetry protocol may be justifiable in case of small target volumes and steep dose gradients.

Radiation exposure in cone beam CT measured using a MOSFET and RPLGD dosimeter and Monte Carlo simulation in phantom.

Due to the wide application of the cone beam computed tomography (CBCT) in clinical practice, it is important to assess radiation dose of CBCT more accurately and efficiently in different clinical applications. This study aims to calculate effective and absorbed doses in CBCT measured in an anthropomorphic phantom using computer-based Monte Carlo (PCXMC) software, and to conduct comparative evaluations of MOSFET (metal- oxide- semiconductor field-effect transistor) and radiophotoluminescence glass dosimeters (RPLGD). Effective and absorbed organ doses are compared with those obtained using MOSFET and RPLGD dosimetry in an anthropomorphic phantom given the same exposure settings. Effective and absorbed organ doses from CBCT during scout and main projections are calculated using PCXMC and PCXMCRotation software, respectively. The mean effective dose from CBCT calculated using PCXMC software is 233.8μSv, while the doses calculated using dosimetry (MOSFET and RPLGD) are 266.67μSv and 268.78μSv, respectively. The X-ray source variation is 0.79%. The prescription limits based on the Friedman test for MOSFET and RPLGD pre-points (i.e., in an analytical analysis of diagnostic names in CBCT) are not statistically significant. The calculated correlation coefficient between MOSFET- and RPLGD-derived absorbed dose values with respect to a field of view CBCT parameter of 17×13.5 mm is r = 0.8623. The study demonstrates that the PCXMC software may be used as an alternative to MOSFET and RPLGD dosimetry for effective and absorbed organ dose estimation in CBCT conducted with a large FOV in an anthropomorphic phantom.

Technical note: Feasibility of gating for dynamic trajectory radiotherapy - Mechanical accuracy and dosimetric performance.

Dynamic trajectory radiotherapy (DTRT) extends state-of-the-art volumetric modulated arc therapy (VMAT) by dynamic table and collimator rotations during beam-on. The effects of intrafraction motion during DTRT delivery are unknown, especially regarding the possible interplay between patient and machine motion with additional dynamic axes. To experimentally assess the technical feasibility and quantify the mechanical and dosimetric accuracy of respiratory gating during DTRT delivery. A DTRT and VMAT plan are created for a clinically motivated lung cancer case and delivered to a dosimetric motion phantom (MP) placed on the table of a TrueBeam system using Developer Mode. The MP reproduces four different 3D motion traces. Gating is triggered using an external marker block, placed on the MP. Mechanical accuracy and delivery time of the VMAT and DTRT deliveries with and without gating are extracted from the logfiles. Dosimetric performance is assessed by means of gamma evaluation (3% global/2 mm, 10% threshold). The DTRT and VMAT plans are successfully delivered with and without gating for all motion traces. Mechanical accuracy is similar for all experiments with deviations<0.14° (gantry angle),<0.15° (table angle),<0.09° (collimator angle) and<0.08 mm (MLC leaf positions). For DTRT (VMAT), delivery times are 1.6-2.3 (1.6- 2.5) times longer with than without gating for all motion traces except one, where DTRT (VMAT) delivery is 5.0 (3.6) times longer due to a substantial uncorrected baseline drift affecting only DTRT delivery. Gamma passing rates with (without) gating for DTRT/VMAT were ≥96.7%/98.5% (≤88.3%/84.8%). For one VMAT arc without gating it was 99.6%. Gating is successfully applied during DTRT delivery on a TrueBeam system for the first time. Mechanical accuracy is similar for VMAT and DTRT deliveries with and without gating. Gating substantially improved dosimetric performance for DTRT and VMAT.

Effectiveness of protective thyroid shield in chest X-ray imaging

Chest X-ray imaging is the most common X-ray imaging method for diagnosing coronavirus disease. The thyroid gland is one of the most radiation-sensitive organs of the body, particularly in infants and children. Therefore, it must be protected during chest X-ray imaging. Yet, because it has benefits and drawbacks, using a thyroid shield as protection during chest X-ray imaging is still up for debate.Therefore, this study aims to clarify the need for using a protective thyroid shield during chest X-ray imaging. This study was performed using different dosimeters (silica beads as a thermoluminescent dosimeter and an optically stimulated luminance dosimeter) embedded in an adult male ATOM dosimetric phantom. The phantom was irradiated using a portable X-ray machine with and without thyroid shielding. The dosimeter readings indicated that a thyroid shield reduced the radiation dose to the thyroid gland by 69% ± 18% without degrading the obtained radiograph. The use of a protective thyroid shield during chest X-ray imaging is recommended because its benefits outweigh the risks.

A phamtom study: In vivo rectal dosimetry of high dose rate brachytherapy in cervical cancer

The purpose of this study was to perform in-vivo dosimetry using a diode rectal dosimeter in phantom and compare the dose delivered to the rectum between the dose measured by the diode dosimeter and the dose calculated by the treatment planning system in cervical cancer. The PTW T9112 diode detector calibrations were performed to find the correction factor. Then the calibrated diode detector was used to measure the radiation dose received in the rectum area in the in-house pelvic phantom. An Iridium-192 source was loaded into the phantom with 7 Gy, the measurements were 3 times per treatment plan, with 15 total plans studied. The average cumulative charge (nC) of each plan was converted to the absorbed dose (mGy) for comparison with the treatment planning system. Finally, to test the hypothesis that an absorbed dose from the detector and the treatment planning system were not significantly different, dependent t–test statistical analysis was applied with p-value <0.05. For distance and direction correction factors, we found that the factors were approximately 1 at 5 cm and 180°. The percentage differences of radiation dose between the diode dosimeter and the treatment planning system were between −3.3 and 4.1%. Statistical analysis revealed that the doses from the detector and the treatment planning system were not statistically significant different. The comparison showed that the percent difference between diode dosimeter and treatment planning system was acceptable to perform the in vivo dosimetry in brachytherapy. Therefore, the diode detector may be a suitable candidate for a treatment verification system in cervical cancer brachytherapy to prevent the dose delivery errors that directly affect the prognosis and may cause complications for the patient.

АНАТОМО-МОРФОЛОГИЧЕСКИЙ БАЗИС ДЛЯ ДОЗИМЕТРИЧЕСКОГО МОДЕЛИРОВАНИЯ ТРАБЕКУЛЯРНОЙ КОСТИ ЧЕЛОВЕКА С ИСПОЛЬЗОВАНИЕМ СТОХАСТИЧЕСКОГО ПАРАМЕТРИЧЕСКОГО ПОДХОДА

Purpose: To create an anatomical and morphological basis for a Stochastic Parametric Skeletal Dosimetric model (SPSDmodel) for a human of different age, which includes an assessment of the parameters of the trabecular bone microstructure in the hematopoietic regions of the human skeleton. The model is necessary to estimate the doses to red bone marrow from osteotropic radionuclides (89,90Sr). The model is being created as a part of the dosimetric support for epidemiological studies of the South Ural cohorts, the members of which lived in territories radioactively contaminated in the 1950s. Materials and methods: Estimation of model parameters is based on the collection and analysis of published data. The selection of publications was made using Internet search engines: Google, PubMed, Academia, e-library, etc. Original articles in peerreviewed publications were selected, atlases, manuals, monographs and dissertations were considered. Information was collected only on healthy individuals. The collected data reffered to the following parameters of the trabecular bone: trabecular thickness, intertrabecular space, the proportion of bone in the total tissue volume. The parameters were assessed using histomorphometry and micro-CT. To make a decision about bone modeling, the data on a hematopoietic activity in it, obtained by MRI and PET, were considered. Result: Based on the results of the analysis of published information, primary data files were generated containing bibliographic data on the source of information, data on the subjects of the study and the measurement results of trabecular bone parameters. On this basis, average population estimates of the parameters were obtained and their variability (standard deviation, coefficients of variation) was estimated. Data on the duration of hematopoiesis in various parts of the skeleton and data on age-related changes in the microstructure were analyzed. The paper presents a description of a full set of parameters of the SPSD model of trabecular bones for newborns, children aged 1, 5 and 10 years, as well as for adolescents aged 15 years and adults. Conclusion: The obtained numerical values are used as input data (parameters) for generating dosimetric phantoms in voxel form. Our results will make it possible in the future to calculate conversion factors that relate the specific activity of radionuclides in the source tissue (bone trabeculae) to the dose rate in the detector tissue (red bone marrow), as well as the uncertainty of their estimates.

Dosimetric phantom consistency of TMR-10 protocol in homogeneous and inhomogeneous regions in Gamma Knife radiosurgery planning

Dosimetric phantom consistency of TMR-10 protocol in homogeneous and inhomogeneous regions in Gamma Knife radiosurgery planning

Development of radiation dosimetric phantoms made from SPC/NaOH/IA-PAE/Rhizophora spp. particleboards

Development of radiation dosimetric phantoms made from SPC/NaOH/IA-PAE/Rhizophora spp. particleboards

Development of radiation dosimetric phantoms made from SPC/NaOH/IA-PAE/Rhizophora spp. particleboards

Development of radiation dosimetric phantoms made from SPC/NaOH/IA-PAE/Rhizophora spp. particleboards

Compliance Assessment of the Epithelial or Absorbed Power Density Below 10 GHz Using SAR Measurement Systems.

The introduction of new dosimetric quantities, in particular, epithelial or absorbed power density for frequencies above 6 GHz, in exposure guidelines and safety standards requires the development of new experimental assessment procedures for compliance testing. In this study, we propose to approximate the peak spatial-average absorbed power density (psSab ) using the same measured data and algorithms that are used for determining the peak spatial-average specific absorption rate psSAR, which is currently limited to frequencies up to 10 GHz. The uncertainty component for the transformation of psSAR to psSab was evaluated as less than 0.55 dB (13.5%) for any source as close as from the tissue simulating media. The approach is easy to implement and allows determining compliance with the basic restrictions of the latest safety guidelines. In the next project, we will expand dosimetric probes, phantoms, and procedures for frequencies above 10 GHz. © 2021 Bioelectromagnetics Society.

Research on obtaining pseudo CT images based on stacked generative adversarial network.

To investigate the feasibility of using a stacked generative adversarial network (sGAN) to synthesize pseudo computed tomography (CT) images based on ultrasound (US) images. The pre-radiotherapy US and CT images of 75 patients with cervical cancer were selected for the training set of pseudo-image synthesis. In the first stage, labeled US images were used as the first conditional GAN input to obtain low-resolution pseudo CT images, and in the second stage, a super-resolution reconstruction GAN was used. The pseudo CT image obtained in the first stage was used as an input, following which a high-resolution pseudo CT image with clear texture and accurate grayscale information was obtained. Five cross validation tests were performed to verify our model. The mean absolute error (MAE) was used to compare each pseudo CT with the same patient's real CT image. Also, another 10 cases of patients with cervical cancer, before radiotherapy, were selected for testing, and the pseudo CT image obtained using the neural style transfer (NSF) and CycleGAN methods were compared with that obtained using the sGAN method proposed in this study. Finally, the dosimetric accuracy of pseudo CT images was verified by phantom experiments. The MAE metric values between the pseudo CT obtained based on sGAN, and the real CT in five-fold cross validation are 66.82±1.59 HU, 66.36±1.85 HU, 67.26±2.37 HU, 66.34±1.75 HU, and 67.22±1.30 HU, respectively. The results of the metrics, namely, normalized mutual information (NMI), structural similarity index (SSIM), and peak signal-to-noise ratio (PSNR), between the pseudo CT images obtained using the sGAN method and the ground truth CT (CTgt) images were compared with those of the other two methods via the paired t-test, and the differences were statistically significant. The dice similarity coefficient (DSC) measurement results showed that the pseudo CT images obtained using the sGAN method were more similar to the CTgt images of organs at risk. The dosimetric phantom experiments also showed that the dose distribution between the pseudo CT images synthesized by the new method was similar to that of the CTgt images. Compared with NSF and CycleGAN methods, the sGAN method can obtain more accurate pseudo CT images, thereby providing a new method for image guidance in radiotherapy for cervical cancer.

Treatment planning system and beam data validation for the ZAP-X: A novel self-shielded stereotactic radiosurgery system.

To evaluate the treatment planning system (TPS) performance of the ZAP-X stereotactic radiosurgery (SRS) system through nondosimetric, dosimetric, and end-to-end (E2E) tests. A comprehensive set of TPS commissioning and validation tests was developed using published guidelines. Nondosimetric validation tests included information transfer, computed tomography-magnetic resonance (CT-MR) image registration, structure/contouring, geometry, dose tools, and CT density. Dosimetric validation included comparisons between TPS and water tank/Solid Water measurements for various geometries and beam arrangements and end-to-end (E2E) tests. Patient-specific quality assurance was performed with an ion chamber in the Lucy phantom and with Gafchromic EBT3 film in the CyberKnife head phantom. RadCalc was used for independent verification of monitor units. Additional E2E tests were performed using the RPC Gamma Knife thermoluminescent dosimeter (TLD) phantom, MD Anderson SRS head phantom, and PseudoPatient gel phantom for independent absolute dose verification. CT-MR image registrations with known translational and rotational offsets were within tolerance (<0.5×maximum voxel dimension). Slice thickness and distance accuracy were within 0.1mm, and volume accuracy was within 0 to 0.11cm3 . Treatment planning system volume measurement uncertainty was within 0.1 to 0.4cm3 . Ion chamber point-dose measurements for a single beam in a water phantom agreed to TPS-calculated values within ±4% for collimator diameters 10 to 25mm, and ±6% for 7.5mm, for all measured depths (7, 50, 100, 150, and 200mm). In homogeneous Solid Water, point-dose measurements agreed to within ±4% for cones sizes 7.5 to 25mm. With 1-cm high/low density inserts, measurements were within ±4.2% for cone sizes 10 to 25mm. Film-based E2E using 4/5-mm cones resulted in a gamma passing rate (%GP) of 99.8% (2%/1.5mm). Point-dose measurements in a Lucy phantom with an ion chamber using 36 beams distributed along three noncoplanar arcs agreed to within ±4% for cone sizes 10 to 25mm. The RPC Gamma Knife TLD phantom yielded passing results with a measured-to-expected TLD dose ratio of 1.02. The MD Anderson SRS head phantom yielded passing results, with 4% TLD agreement and %GP of 95%/93% (5%/3mm) for coronal/sagittal film planes. The RTsafe gel phantom gave %GP of >95% (5%/2mm) for all four targets. For our first 58 patients, film-based patient-specific quality assurance has resulted in an average %GP of 98.7% (range, 94-100%) at 2%/2mm. Core ZAP-X features were found to be functional. On the basis of our results, point-dose and planar measurements were in agreement with TPS calculations using multiple phantoms and setup geometries, validating the ZAP-X TPS beam model for clinical use.

Development of all-in-one phantom dosimeter to measure multidimensional dose distribution for 60Co radiotherapy unit

In this study, we used square-type organic scintillating fibers and polymethyl methacrylate phantoms to develop an all-in-one phantom dosimeter measure the multidimensional dose distributions for a 60Co radiotherapy source. Multidimensional dose distributions, which include the transverse, depth, and surface dose distributions, can be obtained by measuring scintillating light simultaneously in real time. An additional phantom for quality assurance before radiotherapy is not required because square-type organic scintillating fibers are directly inserted into the polymethyl methacrylate phantom. Multidimensional dose distributions can also be measured simultaneously by changing the arrangement of one-dimensional phantom dosimeters, which are very thin and can be stacked, similar to books placed on a shelf. Therefore, the proposed dosimeter can be applied as an all-in-one phantom dosimeter with a variable structure that can respond to changes in various radiotherapy treatment environments. Through experiments, the multidimensional dose distributions for the 60Co radiotherapy unit were measured to evaluate the performance of the proposed all-in-one phantom dosimeter. The results were compared and evaluated using external beam therapy films and Monte Carlo simulations. Based on the results of this study, significant time is expected to be saved during dose measurements for quality assurance in radiotherapy, as simultaneous measurements can yield multidimensional data on the transverse, depth and surface dose distributions in real time.

Monte Carlo Simulation of the Gamma-Ray Transmissions for the newly Designed Shielding Blocks used in Radiotherapy

Radiotherapy is one of the most important treatment methods of cancer, which is the worldwide disease nowa-days. It is essential to protect the critical organs and healthy tissue inside the radiated area during the radiotherapy. For this reason, Cerrobend block (lipowitz alloy), which is made specifically for each patient, are commonly used in the hospitals. In the clinical application, the acceptable level of the gamma-ray transmission for Cerrobend blocks must be less than 5%. In this research, GEANT4 based GATE simulation program modelled to compare between gamma-ray transmissions of the standard Cerrobend block and newly designed Cerrobend blocks formed by adding the various number of the pure lead marbles. Experimental measurements were carried out with Alcyon II model Co-60 teletherapy machine for various field sizes by using Farmer type 0,6 cc ion chamber, PTW Unidos Dosimeter and solid phantom in Dr. Abdurrahman Yurtaslan Ankara Oncology Training and Research Hospital in 2010. The gamma-ray transmission of the newly designed Cerrobend block was found less than the standard block, therefore the protection of the critical organs for the patient could be better. The dose acquired by GEANT4 based GATE simulation program is consistent in experimentally measured radiation dose. Furthermore, the values of the linear attenuation coefficient theoretically obtained from XCOM software agree with the values acquired by experiment and simulation

The influence of model iterative reconstruction on the image quality in standard and low-dose computer tomography of the chest. Experimental study

Background. One of the ways to reduce the radiation dose in CT is to the image reconstruction algorithms. The latest offer from CT scanner manufacturers is Model Iterative Reconstruction (MIR). Aims: to compare the quality of visualization of the structures of the chest organs and to prove the effectiveness of the low-dose protocol with iterative model reconstruction. Methods. A calibration phantom with a spatial resolution module and an anthropomorphic phantom of the upper body of an adult with nodules in the lungs were scanned using two CT scanners of different manufacturers. Two protocols were applied: the standard dose protocol (SDCT) with the algorithms of hybrid iterative reconstruction (HIR) of images and MIR and a low-dose protocol (LDCT) with the MIRalgorithm. The quality of the obtained images was evaluated by the following parameters: noise (SD), the contrast-to-noise ratio (CNR), spatial resolution and visualization of pulmonary nodules. The radiation dose was calculated according to the scanner data, the data of individual dosimeters placed on the anthropomorphic phantom, and using a dosimetric phantom. Results. The average SD was 11.5; 24.4 and 21.6; CNR 85.47; 40.6 and 45.6; spatial resolution 2 mm; 2 mm and 3 mm for SDCT with MIR, SDCT with HIR and LDCT with MIR respectively. Visualization of the pulmonary lesions remained excellent in all cases. The radiation dose in case of SDCT was 2.7, and in case of LDCT 0.67 mSv. The dose reduction was confirmed by the dosimeter data. Similar results were obtained by repeating the experiment with a second scanner. Conclusions. The model iterative reconstruction application will allow reducing the irradiatin dose during CT scanning of the chest organs without deterioration of the visualization quality.

A Novel Ultrasonic Gel Phantom Dosimetry for Evaluation of the Dose Response

Ultrasonic imaging is able to detect structural changes due to chemical reactions occurring due to ionizing irradiation. The purpose of this study to create a gel phantom dosimeter (developed MAGIC gel), which has ultrasonic properties equivalent to human tissue for readout with ultrasonic imaging. The speed of sound and the attenuation coefficient were determined as a function of the absorbed dose in the range of 0–50 Gy by using this dosimeter. A gel phantom was prepared by adding MAGIC polymer gel proprietary combinations in ultrasonic soft tissue-mimicking gel. Then, the ultrasonic parameters (response) of the samples, including the propagation speed of sound (SOS) and the attenuation coefficient (BUA) were measured in the absorbed dose range of 0-50 Gy in steps 2 Gy. The dose response curve is plotted and a sigmoid function is fitted. Ultrasonic images were recorded to assess the quality of the novel gel phantom. At 24 h postirradiation, the gel samples were imaged by using a magnetic resonance (MR) scanner. The mean values of the transverse relaxation rates (R2) were taken. The sensitivities of the speed of sound and the attenuation coefficient parameters and the R2 parameter were determined for the soft tissue-mimicking ultrasonic gel phantom. The concentrations of gel phantom, including 14% gelatin, 0.25% graphite, and 2% formaldehyde, with a maximum variation in the speed of sound (21.9 ± 2.3, 20.5 ± 2.1, and 24.3 ± 3.3 m/s) and attenuation coefficient (49.6 ± 9.1, 29.5 ± 5.5, and 47.9 ± 15.4 dB/MHz·m) were selected, respectively. The sensitivities of the speed of sound and the attenuation coefficient parameters and the R2 parameter were determined for the soft tissue-mimicking ultrasonic gel phantom as 1.01 m/s, 2.9 dB/MHz-m, and 0.48 s−1 per Gy and for the MAGIC-f polymer gel as 0.79 m/s, 1.9 dB/MHz-m, and 0.26 s−1 per Gy (R = 0.98), respectively. A significant correlation was found between the MAGIC-f polymer gel and the ultrasonic soft tissue-mimicking gel phantom with the R2 parameter (R = 0.9). Thus, the ultrasonic tissue-mimicking gel phantom can be concluded to be suitable for read-out using ultrasound waves as a free radical polymerization sensor. The cost effectiveness due to the utility of edible gelatin and the formation of breast soft tissue-mimicking ultrasonic images due to the presence of graphite scattering particles are distinctive features of the gel phantom introduced in this study.

Experience in Clinical Operation of New Rotating Gamma System (RGS) for Cranial Stereotactic Radiosurgery

The objective of this study is to develop a quality assurance program to implement for the new Rotating Gamma System (RGS) in stereotactic surgery. Our experience supports the reliability of the operation of the hardware and software pertaining to RGS to deliver precise treatment to patients. This rotating gamma system with thirty Cobalt-60 sources with an initial total activity of 7465.5 Ci is in operation as the second unit in the USA. The source body and collimator body are synchronously rotating during the treatment procedure with a precise alignment. The radiation exposure is controlled by ON/OFF switches, which are automatically regulated by the computerized control system along with the precision table movement. Machine parameters such as output constancy, radiation isocentricity, alignment of collimator and source bodies, the accuracy of table positioning coordinate system, operation of the ON/OFF switches are independently verified as a part of pre-treatment quality assurance procedure using Ion chambers and Gaf-chromic film. Consistency of the Full Width at Half Maximum (FWHM), Penumbra 80-20% (P80-20%) are monitored periodically. Point dose to an acrylic phantom is calculated in Infini Superplan 4.2.118, and the dose is compared to the measured value. Periodic end-to-end testing is performed to verify the geometrical positioning of the shots and evaluating the MRI fiducials. End-to-End tests and other complicated patient plans are monitored using MAX-HD Head SRS dosimetric Phantom analysis. The interlock tests are performed before the commencement of the treatment as a part of a quality assurance procedure. Mechanical and radiation geometrical iso-center for all collimators (Diameter: 18mm, 14mm, 8mm, and 4mm) with all gamma angles (70, 90, and 100) are less than 0.16mm. Error in output factors(OF) and alignment of collimator and source body ratio(ACSR) is within 0.511±0.393% and 1.527±1.168% on average, respectively. FWHM and P80-20% for each collimator are within an acceptable range in comparison to the acceptance and commissioning data. The verification of the delivered point dose is found to be less than 4.7%. Patient treatment on this unit started on April 22, 2019 and up to date, 125 patients have been treated successfully. Fifty or more cases with multiple metastasis have been treated, and patients with a single metastasis, Trigeminal neuralgia, Meningioma, schwannoma, Acoustic Neuroma have completed treatment. The downtime of the system is minimal. With sub-millimeter accuracy, this new rotating gamma system is accurate, reliable, and shows safe delivery of the radiation dose for cranial stereotactic radiosurgery. A periodic Quality assurance procedure is important to assure the proper monitoring of this dynamic system.

Bulk-density controlled thermoluminescence dosimeters based on Al2O3:Cr ceramics as anthropomorphic phantom dosimeters for photon therapy

In radiation therapy, the dose distribution is determined using a homogeneous phantom. However, given that the human body includes not only soft tissue but also air and bone, it is desirable to be able to verify the dose distribution in a human body. In the context of developing an anthropomorphic phantom dosimeter for photon therapy, there is therefore a need to improve the tissue equivalencies of Al2O3:Cr thermoluminescence dosimeters (TLDs) with a relatively high effective atomic number (11.14). For this purpose, the use of Al2O3:Cr TLDs with bulk-density control was examined by Monte Carlo simulations. Furthermore, the TL properties of several manufactured bulk-density controlled TLDs were investigated. In photon therapy, it was found that the equivalence of the bulk-density controlled TLDs relative to human body was effectively matched, while maintaining the TL characteristics of the base Al2O3:Cr TLDs.