In-house Phantoms Research Articles

Evaluation of direct point dose estimation based on the distribution of the size-specific dose estimate.

The aim of this study was to evaluate the point doses using a distribution of the size-specific dose estimate (SSDE) from axial CT images of in-house phantoms having diameters from 8 to 40cm. In-house phantoms made of polyester-resin (PESR) mixed with methyl ethyl ketone peroxide (MEKP) were used. The phantoms were built with different diameter sizes of 8, 16, 24, 32, and 40cm. The phantoms were scanned by Siemens a SOMATOM Perspective-128 slice CT scanner with constant input parameters. The point doses were interpolated from the central SSDE (SSDEc) and the peripheral SSDE (SSDEp). The SSDEc and SSDEp were calculated from the SSDE with h- and k-factors. The point doses were compared to the direct measurements using the nanoDot™ optically-stimulated luminescence dosimeter (OSLD) in dedicated holes on the phantoms. It was found that the point dose decreases as the phantom diameter increased. The doses obtained using two approaches differed by 11% on average. The highest difference was 40% and the lowest difference was < 1%. It was found that dose based on the SSDE concept tended to be higher compared to the measured dose by OSLD. Point dose estimation using the concept of SSDE distribution can be considered an alternative for accurate and simple estimation. This approach still requires improvements to increase its accuracy and its application to estimate the organ dose needs further investigation.

Evaluation of Changes in Dose Estimation on Abdomen CT Scan with Automatic Tube Current Modulation Using In-House Phantom

This study evaluates the effect of the Automatic Tube Current Modulation (ATCM) technique on pitch and effective diameter variation in estimating dose values and noise levels for abdominal examination on Philips Ingenuity CT scan machine using in-house Phantoms. The in-house phantoms are oval in shape with three effective diameter sizes, namely 23.2 cm, 28.3 cm, and 33.3 cm to represent abdominal region. The three size Phantoms were scanned using an Ingenuity 128 Philips CT scan with the abdominal protocol exposure parameters of 120 kVp tube voltage, Dose Right Index (DRI) variations of 10,11,12,13, and 14, and pitch variations of 0.6; 0.8; 1.0; 1.2; and 1.49. The changes in mAs, CTDIvol, and noise to the Philips reference value were then verified (i.e. an addition of one DRI value increases mAs by 12 %). For evaluation, a metric to express the change in DRI is defined as ΔDRI. The study demonstrates that noise level is influenced by object size; size information of the object could be useful to predict the change of tube current and pitch due to ATCM with respect to selected DRI. The DRI value is proportional to the tube current, thus selecting the DRI at a certain pitch will directly determine tube current. The ΔDRI in general, according to Philips specifications, is verified to be approximately 10 % to 13 %, except for DRI 10 to 11 which is relatively high on average 15 % to 17 %. Increasing DRI increases the CTDIvol. The CTDI/mAs constantly ranges of 0.06 to 0.07. The value could serve as a characteristic parameter for quality assurance. The ATCM specifications of the Ingenuity 128 CT Scanner is according to Philips regulations.

Evaluation of in-house phantoms for mammography accreditation with various 3D printer filaments

One of the routine activities in the mammography modality is image quality testing using the American College of Radiology (ACR) accreditation phantom, approved by the Mammography Quality Standards Act (MQSA). ACR has approved the CIRS Model 015 for use in the Mammography Accreditation Program. However, because the price of this phantom can be reasonably high, not all hospitals have it. This study aims to fabricate the ACR CIRS model 015 phantom with various 3D printer filaments and compare it with the ACR phantom standard. Phantom was designed by depicting small structures similar to those found clinically to test the capabilities of quantitatively evaluated mammographic imaging systems. The designed in-house phantom consists of fibers, microcalcifications or specks, and masses to simulate tumors. Polylactic Acid (PLA) and Polyvinyl Alcohol (PVA) were used to fabricate in-house phantoms. Meanwhile, the fibers and specks were filled with nylon fiber and Al2CO3. The phantom was designed using the CATIA 3D design based on the CIRS phantom mammography accreditation model 015. The diameter of the specks was printed with the 3D printer in various sizes of 1, 0.9, 0.8, 0.7, and 0.6 mm, respectively. The fabricated phantom was irradiated three times to maintain accuracy using mammography type Siemens Mammomat Inspiration with serial number control 11238. The assessment was conducted with manual irradiation mode at a voltage of 28 kV, 100 mAs, target/filter W/Rh, and a compression rate of 50 N. The all-fabricated phantoms met the ACR standard phantom for fiber, and mass detection with the best result was achieved for the second material with six fibers, four specks, and five masses. The fabricated phantom can potentially be used for image quality control for mammography systems in determining the early detection of breast cancer.

Evaluation of radiation dose accuracy calculated using IndoseCT software with direct measurement on polyester-resin phantoms

The current study aims to compare the radiation doses (size-specific dose estimate, SSDE) calculated using IndoseCT software and dose measurements obtained with a pencil ionization chamber on in-house phantoms of different sizes. In-house phantoms with different diameters (i.e. 8, 16, 24, and 32 cm) were constructed using polyester-resin (PESR) as the main ingredient and methyl ethyl ketone peroxide (MEKP) as a catalyst. Axial images of the phantoms were used to calculate the SSDE using IndoseCT software. In addition, doses were direcly measured using a pencil ionization chamber. The scan parameters were 120 kVp tube voltage, 100 mA tube current, and 1 s tube rotation. Measurements were carried out at each hole within the in-house phantoms. The SSDE calculated using IndoseCT was comparable to the dose measured using a pencil ionization chamber. The percentage differences of the doses from IndoseCT and a pencil ionization chamber were 9.83, 3.11, 2.10, and 0.47% for phantom diameters of 8, 16, 24, and 32 cm, respectively. The size-specific dose calculated using IndoseCT is accurate. The percentage difference between the doses calculated using IndoseCT and measured doses using a pencil ionzation chamber on in-house phantoms of diameters 8–32 cm were within ±10%.

Evaluating impact of medium variation on dose calculated through planning system in a low cost in-house phantom

Purpose: In radiotherapy, accuracy in dose estimation of dose calculation methods is critical. The influence of deformity on radiation dose calculations derived by planning system is evaluated in present study. The goal of study was to create a low-cost inhomogeneous phantom for measuring absorbed dose using an Ionisation chamber and Gafchromic film, which was validated using treatment planning system (TPS) dose outcome. Methods:and Materials: The central axis dose calculations were computed using Pencil Beam Convolution algorithm (PBC), Collapsed Cone Convolution (CCC) and Monte Carlo (MC) algorithm in the Monaco treatment planning system using an In-house phantom (20 × 20 × 20cm3) made up of acrylic sheet containing water and inhomogeneous material wooden powder equivalent to lung. Phantom was scanned in Computed Tomography (CT) scanner and image set was sent to the planning workstation. The depth dose evaluations were performed using ionization chamber and Gafchromic film with same beam settings and monitor units in every setup. Following that, the calculated doses obtained from TPS and measured depth doses were compared. Results: The results was reported for photon energies 6MV, 10MV, 15MV, 6FFF and 10FFF at varying field sizes of 4 × 4 cm2, 5 × 5 cm2, 10 × 10 cm2, and 15 × 15 cm2. MC maximum dose variation predicted was 2.06% in 15MV of measured chamber dose and −2.06% of measured gafchromic film dose in 6MVFFF. CCC maximum dose variation predicted was 2.68% of measured chamber dose in 6MV and 3.31% of measured gafchromic film dose in 6MV whereas PB maximum dose variation predicted was −5.94% in 15MV of measured chamber dose and −11.6% of measured gafchromic film dose in 6MVFFF. Conclusion: Low-cost in-house phantoms can be utilised to assess point and planar doses during patient-specific quality assurance in centres that don’t have accessibility to phantoms due to the high cost of commercially available tools.

Development of in-house phantoms from polyester resin and methyl ethyl ketone peroxide materials with various diameters:Investigation their CT numbers for various tube voltages and field of views

Development phantoms with various sizes reflecting the variation among patients to investigate the accuracy size-specific dose estimate (SSDE)is essential. The aim of this work was to develop in-house phantoms from polyester resin (PR) and methyl ethyl ketone peroxide (MEKP) for various diameters and investigate the CT numbers of the phantoms with various tube voltages and reconstructed field of views (FOV). In-house phantoms with diameters of 8, 16, 24, and 32 cm were developed. The phantoms were made from the PR and MEKP materials. The composition of MEKP was 0.3 wt% and PR was 99.7%. The phantoms were scanned with a Siemens SOMATOM Emotion 6 CT scanner with various tube voltage (i.e. 80, 110, and 130 kVp), and various field of views (FOVs) (i.e. 35, 40, 45, 50 cm). CT numbersof the phantoms for various diameters, tube voltages and FOVs were investigated. It was found that the CT number was in range of 86 HU to 147 HU. The CT number increased with the increases of diameter and tube voltage. However, the CT number was independent with the FOV. The in-house phantom based on PR andMEKP with various diameters from 8 cm to 32 cm have been successfully developed. The CT numbers of the phantoms depend on diameter and tube voltage,but do not depend with the FOV.

Dosimetric Effect of Biozorb Markers for Accelerated Partial Breast Irradiation in Proton Therapy.

PurposeTo investigate dosimetric implications of biodegradable Biozorb (BZ) markers for proton accelerated partial breast irradiation (APBI) plans.Materials and MethodsSix different BZs were placed within in-house breast phantoms to acquire computed tomography (CT) images. A contour correction method with proper mass density overriding for BZ titanium clip and surrounding tissue was applied to minimize inaccuracies found in the CT images in the RayStation planning system. Each breast phantom was irradiated by a monoenergetic proton beam (103.23 MeV and 8×8 cm2) using a pencil-beam scanning proton therapy system. For a range perturbation study, doses were measured at 5 depths below the breast phantoms by using an ionization chamber and compared to the RayStation calculations with 3 scenarios for the clip density: the density correction method (S1: 1.6 g/cm3), raw CT (S2), and titanium density (S3: 4.54 g/cm3). For the local dose perturbation study, the radiographic EDR2 film was placed at 0 and 2 cm below the phantoms and compared to the RayStation calculations. Clinical effects of the perturbations were retrospectively examined with 10 APBI plans for the 3 scenarios (approved by our institutional review board).ResultsIn the range perturbation study, the S1 simulation showed a good agreement with the chamber measurements, while excess pullbacks of 1∼2 mm were found in the S2 and S3 simulations. The film study showed local dose shadowing and perturbation by the clips that RayStation could not predict. In the plan study, no significant differences in the plan quality were found among the 3 scenarios. However, substantial range pullbacks were observed for S3.ConclusionThe density correction method could minimize the dose and range difference between measurement and RayStation prediction. It should be avoided to simply override the known physical density of the BZ clips for treatment planning owing to overestimation of the range pullback.

Quantitative MRI: Defining repeatability, reproducibility and accuracy for prostate cancer imaging biomarker development

IntroductionQuantitative MRI (qMRI) parameters have been increasingly used to develop predictive models to accurately monitor treatment response in prostate cancer after radiotherapy. To reliably detect changes in signal due to treatment response, predictive models require qMRI parameters with high repeatability and reproducibility. The purpose of this study was to measure qMRI parameter uncertainties in both commercial and in-house developed phantoms to guide the development of robust predictive models for monitoring treatment response. Materials and methodsADC, T1, and R2* values were acquired across three 3 T scanners with a prostate-specific qMRI protocol using the NIST/ISMRM system phantom, RSNA/NIST diffusion phantom, and an in-house phantom. A B1 field map was acquired to correct for flip angle inhomogeneity in T1 maps. All sequences were repeated in each scan to assess within-session repeatability. Weekly scans were acquired on one scanner for three months with the in-house phantom. Between-session repeatability was measured with test-retest scans 6-months apart on all scanners with all phantoms. Accuracy, defined as percentage deviation from reference value for ADC and T1, was evaluated using the system and diffusion phantoms. Repeatability and reproducibility coefficients of variation (%CV) were calculated for all qMRI parameters on all phantoms. ResultsOverall, repeatability CV of ADC was <2.40%, reproducibility CV was <3.98%, and accuracy ranged between −8.0% to 2.7% across all scanners. Applying B1 correction on T1 measurements significantly improved the repeatability and reproducibility (p<0.05) but increased error in accuracy (p<0.001). Repeatability and reproducibility of R2* was <4.5% and <7.3% respectively in the system phantom across all scanners. ConclusionRepeatability, reproducibility, and accuracy in qMRI parameters from a prostate-specific protocol was estimated using both commercial and in-house phantoms. Results from this work will be used to identify robust qMRI parameters for use in the development of predictive models to longitudinally monitor treatment response for prostate cancer in current and future clinical trials.

Assessment of an in-house phantom for the quality control of a clinical gamma camera.

Since in-house phantoms may provide effective quality control for gamma cameras in clinical settings, this study aims to assess an in-house phantom designed to perform quality control tests of a gamma camera using locally available, affordable materials. This is of particular importance in developing countries where scientific support may not be readily available. The phantom was made from cylindrical plexiglass with a diameter of 230 mm and thickness of 60 mm. The phantom design was based on NEMA recommendations and only used materials that are locally available and generally accessible to most nuclear medicine departments and require minimal engineering instruction. The phantom demonstrated high levels of reliability and accuracy. The integral uniformity range was between 1.93% and 2.40%. The differential uniformity ranged between 1.48% and 1.70%. This work demonstrates that in-house phantoms are capable of monitoring gamma camera performance. This approach is particularly useful when scientific support is not easily accessible and when commercial phantoms are not readily available.

In-house-developed phantoms for organ dose measurements using bovine tissues: A comparison study with CT-Expo simulation software

Background: Estimating organ dose from computed tomography (CT) procedures is still ongoing. The aim is to reduce induced cancer risk associated with over dose. Aim and Objectives: The aim of this study was to estimate organ dose using CT-Expo software, to compare obtained values with thermoluminescent dosimeter (TLD) measurements from validated in-house phantoms, and to compare the CT-Expo results with other related studies. Materials and Methods: Four CT diagnostic centers denoted as A, B, C, and D were randomly selected for this study. A CT-Expo software (version 2.5 Germany) was used. A preliminary study was carried out to determine organ dose from the in-house phantoms using bovine tissues. The CT dose parameters used with the in-house phantoms were retrieved from the CT monitor and were used with CT-Expo worksheet to estimate organ dose as well. Results: The CT-Expo mean organ dose to the brain, eye lens, esophagus, and thyroid were 29.05 ± 10.78, 35.65 ± 15.1, 12.45 ± 10.13, and 4.25 ± 2.78 mGy, respectively; to the heart and lungs were 13.08 ± 9.84 and 11.5 ± 7.26 mGy, respectively; and to the liver, stomach, and kidney were 14.42 ± 9.07, 12.78 ± 7.97, and 11.73 ± 7.92 mGy, respectively. There was no statistically significant difference between the TLD measurements and CT-Expo (P = 0.361). The relative difference between CT-Expo and TLD measurements for brain, eye lens, heart, lungs, kidney, liver, and stomach were ≤21%. Investigated organ doses from the software were between 4.25 and 35.65 mGy. There was no difference in mean organ dose when compared to the studies in Thailand, Tanzania, Japan, USA (cadavers 1 and 2), and Nigeria. Conclusion: Large percentage differences were noticed in the thyroid and esophagus which was as a result of the software not recognizing them as organs in the head/neck but rather as organs in the chest; however, there was no difference in organ dose between the CT-Expo and TLD measurement from the in-house-validated phantom.

Breast tumour detection by flexible wearable antenna system

Breast tumour detection using flexible wearable antenna system presented in this paper removes the need for liquid coupling mediums used in conventional systems, leading to a simpler and cost effective imaging device. This is achieved by considering a planar microstrip antenna design on a flexible substrate and optimising the antenna for the skin contact operation. It is shown that systems with a matched coupling medium still have 20% theoretical reflection loss at the skin, which is eliminated in the presented system. Simulation results show three-fold increase in the current densities and electric fields in the tumour. Experimental results with in-house breast and tumour phantoms show that the received signal from a tumour has 33 dB maximum and 19 dB average (over 400 MHz range) amplitude above noise level. Theoretical analysis, simulation models, and experimental results for breast tumour detection using flexible wearable antenna system are presented and discussed.

Estimation of Average Speed of Sound Using Deconvolution of Medical Ultrasound Data

In diagnostic ultrasound imaging the speed of sound is assumed to be 1540 m/s in soft tissues. When the actual speed is different, the mismatch can lead to distortions in the acquired images and so reduce their clinical value. Therefore, the estimation of the true speed has been pursued not only because it enables image correction but also as a way of tissue characterisation. In this article, we present a novel way to measure the average speed of sound concurrently with performing image enhancement by deconvolution. This simultaneous capability, based on a single acquisition of ultrasound data, has not been reported in previous publications. Our algorithm works by conducting non-blind deconvolution of the reflection data with point-spread functions based on different speeds of sound. Using a search strategy, we select the speed that produces the best-possible restoration. The deconvolution operates on the beamformed uncompressed radio-frequency data, without any need to modify the hardware of the ultrasound machine. A conventional handling of the transducer array is all that is required in the data acquisition part of our proposed method: the data can be collected freehand, unlike most other estimation methods. We have tested our algorithm with simulations, in vitro phantoms with known and unknown speeds and in vivo scans. The estimation error was found to be +0.19 ± 8.90 m/s (mean ± standard deviation) for in vitro in-house phantoms whose speeds were also measured independently. In addition to the speed estimation, our method has also proved to be capable of simultaneously producing a better restoration of ultrasound images than deconvolution by an assumed speed of 1540 m/s, when this assumption is incorrect. (E-mail: hs338@cam.ac.uk)