Radiation Therapy Phantom Research Articles

The development and testing of a novel spherical radiotherapy phantom system for the commissioning and patient-specific quality assurance of mono-isocentric multiple mets SRS plans.

To develop a single radiotherapy phantom system capable of performing both patient-specific quality assurance (QA) measurements and commissioning measurements for mono-isocentric LinAc-based stereotactic radiosurgery ("mLSRS") treatment plans. Design A 20-cm diameter spherical phantom was designed which contained within it a film cartridge. The surface of the sphere was machined to display a set of angular markings at both the equator and the meridian representing a spherical coordinate system. A stand was designed which allows for free rotation about any vector passing through the center of the sphere. A program was created using Python 3 to: (a) Compute the measurement setup necessary to intersect exactly one film plane with three user specified dicom points contained within the QA plan; (b) Extract the intersection dose plane from the three dimensional DICOM dose file and; (c) Generate a synthetic computed tomography (CT) in the exact measurement geometry which is subsequently used for phantom positioning during the QA measurement. To assess the functionality of the phantom system dynamic conformal arc mLSRS plans that were generated by a clinically commissioned multiple metastasis treatment planning system (BrainLab Elements version 2.0) using patient-specific data. A total of seven patient plans were created that contained a total of 31 targets {<Volume>=(0.382±0.534)cc: Range [0.051, 2.05]cc, <Off-Axis Distance>=(30±16)mm: Range[0, 55]mm} 27 of which were directly measured with film and analyzed. Each planned isocenter was mapped to the phantom's center and the dose was recomputed. From the phantom dose distribution dicom points of interest were selected in sets of three and input into the provided software. The software computed the plane that intersects with the entered three points and instructed the user on the setup geometry to place the film in the intersecting plane. The software then generated a synthetic CT scan with embedded fiducial markers rotated into the setup orientation. This CT was then used as the setup reference image in ExacTrac image guidance system (tolerance 0.7mm & 0.5deg). All plans were delivered on a Varian Truebeam linear accelerator with HDMLC, Exactrac and a 6 degree of freedom couch. After delivery of each test plan a 10×10 reference field was delivered to a known dose approximately equal to the maximum dose contained within the plan for film calibration. The test film was scanned simultaneously with the 10×10 reference film and a film that received zero dose using an Epson 10000XL flatbed scanner after waiting 24hours. The test film was scaled according to the reference film and analyzed via the gamma analysis (3%, 1mm, 10%) implemented in Ashland Film QA Pro software. The spherical phantom system was able to perform validation measurements on a variety of patient-specific plan geometries. The average gamma pass-rate γ(3%, 1mm,10%) for all measurements was 96.7% (σ=3.6%). A novel spherical radiotherapy phantom system has been designed and tested on clinically relevant test plans.

Preliminary Results on In-Vivo Dose Measurement of Intensity-Modulated Radiotherapy for Cervical Cancer

To investigate the relationship between the results of in-vivo dose (IVD) measurement and setup errors based on Alderson radiotherapy (ART) phantom, and to monitor the IVD changes of intensity-modulated radiotherapy (IMRT) for cervical cancer patients. Electronic portal imaging device (EPID) images and logfile data were collected from ART phantom and 12 patients with cervical cancer, which were used for two-dimensional (2D) IVD verification [evaluation indexes: Gamma analysis (γ) and percent dose difference (DD)] and three-dimensional (3D) IVD verification (evaluation indexes: γ), respectively. The positioning errors with ranges of 0.1∼1 cm and 1∼3cm in the step size of 0.2 cm and 1 cm were artificially introduced in ART phantom. The correlations between IVD results of phantom and its setup errors were analyzed, and the correlations between IVD results of the patients and their treatment fractions were evaluated. The 26 groups of EPID images and corresponding logfiles data from ART phantom and 206 groups from the patients were obtained respectively. The setup errors of ART phantom were not correlated with the corresponding 3D IVD γ1%/1mm (P > 0.05). The 2D IVD averages of ART phantom (γ3%/3mm,mean, γ2%/2mm, mean, γ1%/1mm,mean, DD3%,mean) showed strongly negative correlations with the setup errors (R∈[–0.997, –0.765], P < 0.05). The treatment fractions of all patients were not correlated with their 3D IVD γ1%/1mm (P > 0.05). For 2D IVD verification, DD3%,mean of all patients was negatively correlated with the treatment fractions (R∈[–0.953, –0.499], P < 0.05), among which, γ3%/3mm, mean of 9 patients was more than 89% in all treatment fractions, and γ3%/3mm, mean of the 9 patients was more than 93% for 98.57% treatment fractions. For other 3 patients, γ3%/3mm, mean showed strongly negative correlations with the treatment fractions (R∈[–0.903, –0.824], P < 0.05), with the range of 38% and 100%. Their CBCT images showed that the bladder volume decreased significantly (the relative changes: 82.08%, 84.41% and 73.59%, respectively) and the target retracted significantly (the relative changes: 38.12%, 59.79% and 24.46%, respectively). Conducting IVD verification could monitor the mechanical stability of accelerator and the changes of IVD in patients, and also evaluate the positional deviation of tumors and surrounding organs with IGRT technology, which could improve the safety and quality assurance of radiotherapy for cervical cancer patients and provide guidance for patients with adaptive radiotherapy.

Modelling Curved Contact Flexible Microstrip Applicators for Patient-Specific Superficial Hyperthermia Treatment Planning.

This paper describes a method to reconstruct bendable superficial hyperthermia applicators for routine clinical patient-specific treatment planning. The reconstruction uses a CT scan with a flexible silicone dummy applicator positioned on the patient. The curvature was approximated by two second-degree polynomial functions. A realistic treatment series was mimicked using a standard Alderson radiation therapy phantom and a treatment planning model was reconstructed from a CT scan. The variation among treatment curvatures was compared to the modelled curvature. The mathematical approximation of the applicator curvature was validated for this phantom experiment, as well as for clinical treatments. The average maximum variation among the successive mimicked sessions was 3.67 ± 0.69 mm (range 2.98–4.60 mm). The maximum deviation between the treatment curvature and the modelled curvature was 4.35 mm. Comparing the treatment and approximated curvature yielded a maximum deviation between 2.98 mm and 4.12 mm. For clinical treatments the maximum deviation of the treatment and approximated curvature varied between 0.48 mm and 1.98 mm. These results allow adequate reconstruction of bendable hyperthermia applicators for treatment planning, which can further improve treatment quality, for example by optimizing the water bolus temperature for patient-specific tumor depths. Predictive parameters for hyperthermia treatment outcome can easily be evaluated and compared for various input parameters.

Three-dimensional (3D) scanning using Microsoft® Kinect® Xbox 360® scanner for fabrication of 3D printed radiotherapy head phantom

Radiotherapy phantoms are essential equipment for treatment verification and quality assurance. Recently, development in 3D printing technology provides an opportunity for fabricating patient-specific radiotherapy phantom that has many potential applications in clinical and research. This study investigates the application of Microsoft Kinect® Xbox 360 scanner to model human topography for 3D printed radiotherapy phantom fabrication. The feasibility and performance of the Kinect® scanner were tested on a standard commercial head phantom. The scanned head image was then edited and adapted for 3D printing. The finding suggests that the radiotherapy phantom can potentially be developed using the Kinect® sensor, which is easier and cheaper to operate in comparison to other techniques of fabricating 3D printed radiotherapy phantom.

Gyroid structures for 3D-printed heterogeneous radiotherapy phantoms

The extreme customisation and rapid prototyping capabilities of the 3D printing process allows the manufacture of low-cost and patient-specific radiotherapy phantoms for quality assurance purposes. However, the associated printing techniques and materials are experimentally limited and are yet to be quantified in terms of manufacturability. In addition to this, there lacks research in utilising naturally inspired structures, known as triply periodic minimal surfaces (TPMS), as a structural manufacturing basis for these phantoms, enabling material heterogeneity, which is a significant factor in attaining patient-specificity. We propose the use of Gyroid structures for radiotherapy phantom applications to investigate Gyroid-phantom manufacturability, the mathematical definition of Gyroids and their effects on hounsfield units (HU). The printed Gyroid phantoms were assessed for manufacturability using optical microscopy and micro-computed tomography (µCT), and material hounsfield-equivalence using standard medical CT. A mean HU range of −900 to −390 were achieved from the fabricated Gyroid phantoms with varying standard deviation. Compared to traditional printing infills such as grid and slit structures, the Gyroid phantoms were observed to produce isotropic HU and SD at varied scanning orientations, which optimizes CT attenuations in modulating the hounsfield-equivalence of printed structures. This study not only demonstrates the feasibility of manipulating the structural parameters of Gyroids in simulating tissue imaging attenuations but also opens significant research opportunities in fabricating patient-specific phantoms with added pathological features for end-to-end radiotherapy testing.

Additive Manufacture of Lung Equivalent Anthropomorphic Phantoms: A Method to Control Hounsfield Number Utilizing Partial Volume Effect

Abstract Anthropomorphic radiotherapy phantoms require tissue-equivalent materials to achieve Hounsfield units (HU) that are comparable to those of human tissue. Traditional manufacturing methods are limited by their high-cost and incompatibility with patient-specific customization. Additive manufacture (AM) provides a significant opportunity to enable manufacture of patient-specific geometries at relatively low cost. However, AM technologies are currently limited in terms of available material types, and consequently enable very little variation in achievable HU when standard manufacturing parameters are used. This work demonstrates a novel method whereby the partial volume effect (PVE) is utilized to control the HU of an AM material, in particular, enabling low HU in the range typical of lung tissue. The method enables repeatable design of lung HU and is compatible with commercial machines using standard print parameters. A custom algorithm demonstrates the clinical application of the method, whereby patient-specific computed tomography (CT) data are algorithmically calibrated according to AM print parameters and confirmed to be robust as a custom anthropomorphic radiotherapy phantoms.

Experimental benchmarking of Monte Carlo simulations for radiotherapy dosimetry using monochromatic X-ray beams in the presence of metal-based compounds

The local dose deposition obtained in X-ray radiotherapy can be increased by the presence of metal-based compounds in the irradiated tissues. This finding is strongly enhanced if the radiation energy is chosen in the kiloelectronvolt energy range, due to the proximity to the absorption edge. In this study, we present a MC application developed with the toolkit Geant4 to investigate the dosimetric distribution of a uniform monochromatic X-ray beam, and benchmark it against experimental measurements. Two validation studies were performed, using a commercial PTW RW3 water-equivalent slab phantom for radiotherapy, and a custom-made PMMA phantom conceived to assess the influence of high atomic number compounds on the dose profile, such as iodine and gadolinium at different concentrations. An agreement within 9% among simulations and experimental data was found for the monochromatic energies considered, which were in the range of 30–140 keV; the agreement was better than 5% for depths <60 mm. A dose enhancement was observed in the calculations, corresponding to the regions containing the contrast agents. Dose enhancement factors (DEFs) were calculated, and the highest values were found for energies higher than the corresponding K-edges of iodine and gadolinium. The in-silico results are in line with the empirical findings, which suggest that Geant4 can be satisfactorily used as a tool for the calculation of the percentage depth dose (PDD) at the energies considered in this study in the presence of contrast agents.

Experimental verification of a non-invasive method to monitor the lateral pencil beam position in an anthropomorphic phantom for carbon-ion radiotherapy

The dose conformation and the sparing of neighboring critical healthy structures are improved in carbon-ion beam radiotherapy in comparison to conventional photon radiotherapy. Inter and intrafractional plan adaptation strategies may preclude the quality assurance (QA) of the actually applied treatment plan before the treatment starts. Therefore, independent measurements of the positions of scanned pencil 12C ion beams are of interest in order to monitor the beam application during the treatment and the beam in the isocenter. In this work, secondary ions outgoing from a patient-like phantom are exploited for the assessment of the lateral pencil beam position in a clinic-like 12C treatment fraction. The experiment was performed at the Heidelberg Ion-Beam Therapy Center (HIT) in Germany. A carbon-ion treatment plan was used to treat a 100 cm3 tumor volume in the center of an Alderson head phantom. Two silicon pixel detectors based on the Timepix3 technology developed at CERN were operated in synchronization to detect and to track outgoing secondary ions. We established an analysis of the measured secondary ion track distribution which enabled us to follow the beam scanning movement of the carbon-ion pencil beam by assessing the lateral position of the single beam spots. The precision of the developed method was found to range from 0.84 mm to 2.59 mm. For beam energies greater than 197.58 MeV/n, the mean of absolute distances of the measured lateral pencil beam positions with respect to the pencil beam positions measured by the beam application system (averaged over each energy layer) were smaller than 2 mm. We conclude that the presented method has shown capabilities of monitoring the lateral pencil beam positions by means of secondary ions with precision and sensitivity of clinical interest.

Optimizing MRI sequences and images for MRI-based stereotactic radiosurgery treatment planning.

Development of MRI sequences and processing methods for the production of images appropriate for direct use in stereotactic radiosurgery (SRS) treatment planning. MRI is useful in SRS treatment planning, especially for patients with brain lesions or anatomical targets that are poorly distinguished by CT, but its use requires further refinement. This methodology seeks to optimize MRI sequences to generate distortion-free and clinically relevant MR images for MRI-only SRS treatment planning. We used commercially available SRS MRI-guided radiotherapy phantoms and eight patients to optimize sequences for patient imaging. Workflow involved the choice of correct MRI sequence(s), optimization of the sequence parameters, evaluation of image quality (artifact free and clinically relevant), measurement of geometrical distortion, and evaluation of the accuracy of our offline correction algorithm. CT images showed a maximum deviation of 1.3mm and minimum deviation of 0.4mm from true fiducial position for SRS coordinate definition. Interestingly, uncorrected MR images showed maximum deviation of 1.2mm and minimum of 0.4mm, comparable to CT images used for SRS coordinate definition. After geometrical correction, we observed a maximum deviation of 1.1mm and minimum deviation of only 0.3mm. Our optimized MRI pulse sequences and image correction technique show promising results; MR images produced under these conditions are appropriate for direct use in SRS treatment planning.

ESTIMATION OF EFFECTIVE DOSE OF DENTAL X-RAY DEVICES

This study aims to estimate the effective doses of dental X-ray devices under common scanning protocols. After putting TLDs in the Alderson Radiation Therapy Phantom, we exposed the phantom under common scanning protocols of three dental X-ray devices, namely CBCT, dental panoramic machine and intraoral round cone device. Then effective doses were calculated using the measured absorbed doses of organs and tissues. Tissue weighting factors recommended by the ICRP were adopted in the calculation. Effective doses under common scanning protocols of three Dental X-ray devices were obtained. The effective dose of dental CT was 0.20 mSv, and that of dental panoramic machine and intraoral radiography were 0.013 and 0.0050 mSv, respectively. The tissue absorbed doses of dental CT scan were 0.63 mGy of brain, 7.7 mGy of salivary glands, 8.7 mGy of thyroid and 4.0 mGy of the lens of the eye. The tissue absorbed doses from dental panoramic machine are 0.62 mGy of salivary glands and 0.25 mGy of thyroid. And finally the tissue absorbed dose of intraoral radiography was 0.80 mGy of salivary gland. Among the three dental X-ray devices studied, dental CBCT scan can cause much higher effective dose than the other two. Brain, salivary glands, thyroid and the lens of the eye are tissues receiving relatively higher absorbed doses.

Developing and characterizing MR/CT-visible materials used in QA phantoms for MRgRT systems.

Synthetic tissue equivalent (STE) materials currently used to simulate tumor and surrounding tissues for IROC-Houston's anthropomorphic head and thorax QA phantoms cannot be visualized using magnetic resonance (MR) imaging. The purpose of this study was to characterize dual MR/CT-visible STE materials that can be used in an end-to-end QA phantom for MR-guided radiotherapy (MRgRT) modalities. Over 80 materials' MR, CT, and dosimetric STE properties were investigated for use in MRgRT QA phantoms. The materials tested included homogeneous and heterogeneous materials to simulate soft tissue/tumor and lung tissues. Materials were scanned on a Siemens' Magnetom Espree 1.5T using four sequences, which showed the materials visual contrast between T1- and T2-weighted images. Each material's Hounsfield number and electron density data was collected using a GE's CT Lightspeed Simulator. Dosimetric properties were examined by constructing a 10×10×20cm3 phantom of the selected STE materials that was divided into three sections: anterior, middle, and posterior. Anterior and posterior pieces were composed of polystyrene, whereas the middle section was substituted with the selected STE materials. EBT3 film was inserted into the phantom's midline and was irradiated using an Elekta's Versa 6MV beam with a prescription of 6Gy at 1.5cm and varying field size of: 10×10cm2 , 6×6cm2 , and 3×3cm2 . Measured film PDD curves were compared to planning system calculations and conventional STE materials' percent depth dose (PDD) curves. The majority of the tested materials showed comparable CT attenuation properties to their respective organ site; however, most of the tested materials were not visible on either T1- or T2-weighted MR images. Silicone, hydrocarbon, synthetic gelatin, and liquid PVC plastic-based materials showed good MR image contrast. In-house lung equivalent materials made with either silicone- or hydrocarbon-based materials had HUs ranging from: -978 to -117 and -667 to -593, respectively. Synthetic gelatin and PVC plastic-based materials resembled soft tissue/tumor equivalent materials and had HUs of: -175 to -170 and -29 to 32, respectively. PDD curves of the selected MR/CT-visible materials were comparable to IROC-Houston's conventional phantom STE materials. The smallest field size showed the largest disagreements, where the average discrepancies between calculated and measured PDD curves were 1.8% and 5.9% for homogeneous and heterogeneous testing materials, respectively. Gelatin, liquid plastic, and hydrocarbon-based materials were determined as alternative STE substitutes for MRgRT QA phantoms.

Dual-Energy CT: Balance Between Iodine Attenuation and Artifact Reduction for the Evaluation of Head and Neck Cancer.

Dual-energy computed tomography high energy virtual monochromatic images (VMIs) can reduce artifact but suppress iodine attenuation in enhancing tumor. We investigated this trade-off to identify VMI(s) that strike the best balance between iodine detection and artifact reduction. The study was performed using an Alderson radiation therapy phantom. Different iodine solutions (based on estimated tumor iodine content in situ using dual-energy computed tomography material decomposition) and different dental fillings were investigated. Spectral attenuation curves and quality index (QI: 1/SD) were evaluated. The relationship between iodine attenuation and QI depends on artifact severity and iodine concentration. For low to average concentration solutions degraded by mild to moderate artifact, the iodine attenuation and QI curves crossed at 95 keV. High energy VMIs less than 100 keV can achieve modest artifact reduction while preserving sufficient iodine attenuation and could represent a useful additional reconstruction for evaluation of head and neck cancer.

Abstract ID: 188 Monte Carlo simulation of “out-of-field” distributions in a pediatric phantom in external radiotherapy – Couch top impact

Introduction The scattered radiation from external devices in radiotherapy may cause altered dose distribution among other complications. Although some dose corrections are made for blocking trays, ion chambers, etc. the dose perturbation by the treatment couch top scatter is often overlooked. This out-of-field scattered radiation may induce secondary cancer, especially in pediatric patients, due to biological and geometric factors. Since the out-of-field dosimetric accuracy of treatment planning systems (TPS) is known to decrease, and many of them do not provide the capability of implementing the actual treatment couch top, a PENELOPE based MC code named PRIMO was used to study the couch impact on the out-of-field dose estimation in pediatric irradiation. Material and methods A treatment plan was designed within PRIMO for a hypothetical brain tumor, using two lateral and one cranio-caudal 6MV beam configuration. The plan was created on a CT dataset of 5-year anthropomorphic pediatric phantom. The original dataset was modified with MatlabTM to: keep the original HU values inside the body contour; introduce a real treatment couch HU values and; define the pixel values outside the body and couch as air. Two simulations were performed: with and without the presence of the treatment couch. The PRIMO output data for both simulations were reshaped, manipulated and written as two single multi-frames DICOM files. The dose distribution outside the body contour in both plans was eliminated, and both dose distributions inside the body along the axial plan were compared using 3D gamma function (2%, 2 mm) on PTW-Verisoft. Results Within the treatment field, the results showed good agreement between the two dose distributions (over than 99% of points passed 3D gamma test), indicating that no significant attenuation occurred to the lateral beam crossing the treatment couch. The agreement decreased gradually far away from the isocenter to reach 93% at 20 cm away from isocenter, showing a cranio-caudal back-scattered contribution to dose from the treatment couch. Conclusion For out-of-field scattered dose estimation it is advisable to include the treatment couch in dose calculations.

Abstract ID: 185 Monte Carlo simulation of “Out-of-Field” dose distributions in a pediatric phantom in external radiotherapy – Comparison with Gafchromic film measurements

Introduction Patients undergoing radiotherapy are exposed to out-of-field scattered and leakage radiation, which may induce secondary cancer in long-term survivors. The induction of secondary cancer in pediatric patients is an increased concern, because they have increasingly higher life expectancy, and tend to receive higher secondary organ doses than adults due to geometrical factors. Radiation-induced thyroid and breast cancers have been observed in pediatrics after receiving doses as low as 100 mGy [1] . While the dosimetric accuracy of treatment planning systems (TPS) is known to decrease in the out-of-field region, Monte Carlo (MC) is nowadays the most reliable method in dose calculation. A PENELOPE based MC code named PRIMO was tested for out-of-field dose estimation in pediatric irradiation. Material and methods a 5-year pediatric anthropomorphic phantom was irradiated by Varian Triology linac, using three 6MV static fields beams for a brain tumor. The treatment plan was calculated in Varian Eclipse TPS, using Analytic Anisotropic Algorithm (AAA). The 2D dose distributions at thyroid and lung levels were measured using Gafcromic EBT3 films. The plan was simulated in PRIMO after adjusting the primary beam parameters based on reference data in water phantom. PRIMO output data was reshaped, manipulated and re-written as DICOM files for comparisons with both measured and TPS calculated dose using 2D Gamma Function (3%, 3 mm) on DoseLab Pro software. Results The maximum measured doses per 1 Gy at isocenter (0 cm) were 1.5 cGy and 8 mGy at thyroid (10.25 cm) and lung levels (15.25 cm) respectively. Comparing simulated and measured dose distribution one obtained 82.6% and 88.8% of gamma points 1 at thyroid and lung levels respectively. The difference between measured and TPS calculated dose distributions could easily be accessed visually. Conclusion For secondary induced cancer risk estimation, the present TPS, even using a reliable algorithm as AAA, is not generally satisfactory for out-of-field dosimetry. Alternative tools, like MC simulations are necessary if correct dose estimation must be obtained for risk models application.

Preparation and fabrication of a full-scale, sagittal-sliced, 3D-printed, patient-specific radiotherapy phantom.

PurposePatient‐specific 3D‐printed phantoms have many potential applications, both research and clinical. However, they have been limited in size and complexity because of the small size of most commercially available 3D printers as well as material warping concerns. We aimed to overcome these limitations by developing and testing an effective 3D printing workflow to fabricate a large patient‐specific radiotherapy phantom with minimal warping errors. In doing so, we produced a full‐scale phantom of a real postmastectomy patient.MethodsWe converted a patient's clinical CT DICOM data into a 3D model and then sliced the model into eleven 2.5‐cm‐thick sagittal slices. The slices were printed with a readily available thermoplastic material representing all body tissues at 100% infill, but with air cavities left open. Each slice was printed on an inexpensive and commercially available 3D printer. Once the printing was completed, the slices were placed together for imaging and verification. The original patient CT scan and the assembled phantom CT scan were registered together to assess overall accuracy.ResultsThe materials for the completed phantom cost $524. The printed phantom agreed well with both its design and the actual patient. Individual slices differed from their designs by approximately 2%. Registered CT images of the assembled phantom and original patient showed excellent agreement.ConclusionsThree‐dimensional printing the patient‐specific phantom in sagittal slices allowed a large phantom to be fabricated with high accuracy. Our results demonstrate that our 3D printing workflow can be used to make large, accurate, patient‐specific phantoms at 100% infill with minimal material warping error.

PO-0765: Preparation and Fabrication of a Full-scale Patient-specific 3D-Printed Radiotherapy Phantom

PO-0765: Preparation and Fabrication of a Full-scale Patient-specific 3D-Printed Radiotherapy Phantom

SU‐F‐E‐10: Student‐Driven Exploration of Radiographic Material Properties, Phantom Construction, and Clinical Workflows Or: The Extraordinary Life of CANDY MAN

Purpose:To develop a hands‐on learning experience that explores the radiological and structural properties of everyday items and applies this knowledge to design a simple phantom for radiotherapy exercises.Methods:Students were asked to compile a list of readily available materials thought to have radiation attenuation properties similar to tissues within the human torso. Participants scanned samples of suggested materials and regions of interest (ROIs) were used to characterize bulk attenuation properties. Properties of each material were assessed via comparison to a Gammex Tissue characterization phantom and used to construct a list of inexpensive near‐tissue‐equivalent materials. Critical discussions focusing on samples found to differ from student expectations were used to revise and narrow the comprehensive list. From their newly acquired knowledge, students designed and constructed a simple thoracic phantom for use in a simulated clinical workflow. Students were tasked with setting up the phantom and acquiring planning CT images for use in treatment planning and dose delivery.Results:Under engineer and physicist supervision, students were trained to use a CT simulator and acquired images for approximately 60 different foodstuffs, candies, and household items. Through peer discussion, students gained valuable insights and were made to review preconceptions about radiographic material properties. From a subset of imaged materials, a simple phantom was successfully designed and constructed to represent a human thorax. Students received hands‐on experience with clinical treatment workflows by learning how to perform CT simulation, create a treatment plan for an embedded tumor, align the phantom for treatment, and deliver a treatment fraction.Conclusion:In this activity, students demonstrated their ability to reason through the radiographic material selection process, construct a simple phantom to specifications, and exercise their knowledge of clinical workflows. Furthermore, the enjoyable and inexpensive nature of this project proved to attract participant interest and drive creative exploration.Mahon and Riblett have nothing to disclose; Hugo has a research agreement with Phillips Medical systems, a license agreement with Varian Medical Systems, research grants from the National Institute of Health. Authors do not have any potential conflicts of interest to disclose.

Impact of reduction of flux overlap region on kilovoltage cone-beam computed tomography image quality and patients’ exposure dose

AimIn high-precision radiation therapy, kilovoltage cone-beam computed tomography plays an important role in verifying the position of patient and localization of the target. However, the exposure dose is a problem with kilovoltage cone-beam computed tomography. Flux overlap region increases the patient dose around the center when the scan is performed in a full-scan mode. We assessed the influence of flux overlap region in a full-scan mode to understand the relationship between dose and image quality and investigated methods to achieve a dose reduction. MethodA Catphan phantom was scanned using various flux overlap region patterns in the pelvis on a full-scan mode. We used an intensity-modulated radiation therapy phantom for measuring the central dose. DoseLab was used to perform image analysis and to evaluate the linearity of the computed tomography values, uniformity, high-contrast resolution, and contrast-to-noise ratio. ResultsThe Hounsfield unit value varied by ±40 Hounsfield unit of the acceptance value for the X1 field size of 3.5cm. However, there were no differences in high-contrast resolution and contrast-to-noise ratio among different scan patterns. The absorbed dose decreased by 7% at maximum for the case within the tolerance value. ConclusionDose reduction is possible by reducing the overlap region after calibration and by performing computed tomography in the appropriate overlap region.

Changes in entrance surface dose in relation to the location of shielding material in chest computed tomography

This study examined the effects of entrance surface dose (ESD) on the abdomen and pelvis of the patient when undergoing chest computed tomography (CT) procedure, and evaluated the effects of ESD reduction depending on the location of radiation shield. For CT scanner, the 64-slice multi-detector computed tomography was used. The alderson radiation therapy phantom and optically stimulated luminescence dosimeter (OSLD), which enabled measurement from low to high dose, were also used. For measurement of radiation dose, the slice number from 9 to 21 of the phantom was set as the test range, which included apex up to both costophrenic angles. A total of 10 OSLD nanoDots were attached for measurement of the front and rear ESD. Cyclic tests were performed using the low-dose chest CT and high-resolution CT (HRCT) protocol on the following set-ups: without shielding; shielding only on the front side; shielding only on the rear side; and shielding for both front and rear sides. According to the test results, ESD for both front and rear sides was higher in HRCT than low-dose CT when radiation shielding was not used. It was also determined that, compared to the set-up that did not use the radiation shield, locating the radiation shield on the front side was effective in reducing front ESD, while locating the radiation shield on the rear side reduced rear ESD level. Shielding both the front and rear sides resulted in ESD reduction. In conclusion, it was confirmed that shielding the front and rear sides was the most effective method to reduce the ESD effect caused by scatter ray during radiography.

MO‐B‐BRD‐01: Creation of 3D Printed Phantoms for Clinical Radiation Therapy

This session is designed so that the learning objectives are practical. The intent is that the attendee may take home an understanding of not just the technology, but also the logistical steps necessary to execute these 3D printing techniques in the clinic. Four practical 3D printing topics will be discussed: (i) Creating bolus and compensators for photon machines; (ii) tools for proton therapy; (iii) clinical applications in imaging; (iv) custom phantom design for clinic and research use. The use of 3D printers within the radiation oncology setting is proving to be a useful tool for creating patient specific bolus and compensators with the added benefit of cost savings. Creating the proper protocol is essential to ensuring that the desired effect is achieved and modeled in the treatment planning system. The critical choice of printer material (since it determines the interaction with the radiation) will be discussed. Selection of 3D printer type, design methods, verification of dose calculation, and the printing process will be detailed to give the basis for establishing your own protocol for electron and photon fields. A practical discussion of likely obstacles that may be encountered will be included. The diversity of systems and techniques in proton facilities leads to different facilities having very different requirements for beam modifying hardware and quality assurance devices. Many departments find the need to design and fabricate facility‐specific equipment, making 3D printing an attractive technology. 3D printer applications in proton therapy will be discussed, including beam filters and compensators, and the design of proton therapy specific quality assurance tools. Quality control specific to 3D printing in proton therapy will be addressed. Advantages and disadvantages of different printing technology for these applications will also be discussed. 3D printing applications using high‐resolution radiology‐based imaging data will be presented. This data is used to 3D print individualized physical models of patient's unique anatomy for aid in planning complex and challenging surgical procedures. Methods, techniques and imaging requirements for 3D printing anatomic models from imaging data will be discussed. Specific applications currently being used in the radiology clinic will be detailed. Standardized phantoms for radiation therapy are abundant. However, custom phantom designs can be advantageous for both clinical tasks and research. 3D printing is a useful method of custom fabrication that allows one to construct custom objects relatively quickly. Possibilities for custom radiotherapy phantoms range from 3D printing a hollow shell and filling the shell with tissue equivalent materials to fully printing the entire phantom with materials that are tissue equivalent as well as suitable for 3D printing. A range of materials available for use in radiotherapy phantoms and in the case of phantoms for dosimetric measurements, this choice is critical. The necessary steps required will be discussed including: modalities of 3D model generation, 3D model requirements for 3D printing, generation of machine instructions from the 3D model, and 3D printing techniques, choice of phantoms material, and troubleshooting techniques for each step in the process. Case examples of 3D printed phantoms will be shown. Learning Objectives: Understand the types of 3D modeling software required to design your device, the file formats required for data transfer from design software to 3D printer, and general troubleshooting techniques for each step of the process. Learn the differences between materials and design for photons vs. electrons vs. protons. Understand the importance of material choice and design geometries for your custom phantoms. Learn specific steps of quality assurance and quality control for 3D printed beam filters and compensators for proton therapy. Learn of special 3D printing applications for imaging. Cunha: Research support from Phillips Healthcare.