An anthropomorphic maxillofacial phantom using 3-dimensional printing, polyurethane rubber and epoxy resin for dental imaging and dosimetry.

OBJECTIVE: The aim of this study was to construct an anthropomorphic maxillofacial phantom for dental imaging and dosimetry purposes using three-dimensional (3D) printing technology and materials that simulate the radiographic properties of tissues. METHODS: Stereolithography photoreactive resins, polyurethane rubber and epoxy resin were modified by adding calcium carbonate and strontium carbonate powders or glass bubbles. These additives were used to change the materials' CT numbers to mimic various body tissues. A maxillofacial phantom was designed using CT images of a head. RESULTS: Commercial 3D printing resins were found to have CT numbers near 120 HU and were used to print intervertebral discs and an external skin for the maxillofacial phantom. By adding various amounts of calcium carbonate and strontium carbonate powders the CT number of the resin was raised to 1000 & 1500 HU and used to print bone mimics. Epoxy resin modified by adding glass bubbles was used in assembly and as a cartilaginous mimic. Glass bubbles were added to polyurethane rubber to reduce the CT number to simulate soft tissue and filled spaces between the printed anatomy and external skin of the phantom. CONCLUSION: The maxillofacial phantom designed for dental imaging and dosimetry constructed using 3D printing, polyurethane rubbers and epoxy resins represented a patient anatomically and radiographically. The results of the designed phantom, materials and assembly process can be applied to generate different phantoms that better represent diverse patient types and accommodate different ion chambers.

Modeling the temporal-spatial nature of the readout of an electronic portal imaging device (EPID).

PURPOSE: In real-time electronic portal imaging device (EPID) dosimetry applications where on-treatment measured transmission images are compared to an ideal predicted image, ideally a tight tolerance should be set on the quantitative image comparison in order to detect a wide variety of possible delivery errors. However, this is currently not possible due to the appearance of banding artifacts in individual frames of the measured EPID image sequences. The purpose of this work was to investigate simulating banding artifacts in our cine-EPID predicted image sequences to improve matching of individual image frames to the acquired image sequence. Increased sensitivity of this method to potential treatment delivery errors would represent an improvement in patient safety and treatment accuracy. METHODS: A circuit board was designed and built to capture the target current (TARG-I) and forward power signals produced by the linac to help model the discrete beam-formation process of the linac. To simulate the temporal-spatial nature of the EPID readout, a moving read out mask was applied with the timing of the application of the readout mask synchronized to the TARG-I pulses. Since identifying the timing of the first TARG-I pulse affected the location of the banding artifacts throughout the image sequence, and furthermore the first several TARG-I pulses at the beginning of "beam on" are not at full height yet (i.e., dose rate is ramping up), the forward-power signal was also used to assist in reliable detection of the first radiation pulse of the beam delivery. The predicted EPID cine-image sequence obtained using a comprehensive physics-based model was modified to incorporate the discrete nature of the EPID frame readout. This modified banding predicted EPID (MBP-EPID) image sequence was then compared to its corresponding measured EPID cine-image sequence on a frame-by-frame basis. The EPID was mounted on a Clinac 2100ix linac (Varian Medical Systems, Palo Alto, CA). The field size was set to 21.4  ×  28.6 cm2 with no MLC modulation, beam energy of 6 MV, dose rate of 600 MU/min, and 700 MU were delivered for each clockwise (CW) and counter-clockwise (CCW) arc. No phantoms were placed in the beam. RESULTS: The dose rate ramp up effect was observed at the beginning irradiations, and the identification and timing of the radiation pulses, even during the dose rate ramp up, were able to be quantified using the TARG-I and forward power signals. The approach of capturing individual dose pulses and synchronizing with the mask image applied to the original predicted EPID image sequence was demonstrated to model the actual EPID readout. The MBP-EPID image sequences closely reproduced the location and magnitude of the banding features observed in the acquired (i.e., measured) image sequence, for all test irradiations examined here. CONCLUSIONS: The banding artifacts observed in the measured EPID cine-frame sequences were reproduced in the predicted EPID cine-frames by simulating the discrete temporal-spatial nature of the EPID read out. The MBP-EPID images showed good agreement qualitatively to the corresponding measured EPID frame sequence of a simple square test field, without any phantom in the beam. This approach will lead to improved image comparison tolerances for real-time patient dosimetry applications.

Low-cost optical scanner and 3-dimensional printing technology to create lead shielding for radiation therapy of facial skin cancer: First clinical case series.

PURPOSE: Three-dimensional printing has been implemented at our institution to create customized treatment accessories, including lead shields used during radiation therapy for facial skin cancer. To effectively use 3-dimensional printing, the topography of the patient must first be acquired. We evaluated a low-cost, structured-light, 3-dimensional, optical scanner to assess the clinical viability of this technology. METHODS AND MATERIALS: For ease of use, the scanner was mounted to a simple gantry that guided its motion and maintained an optimum distance between the scanner and the object. To characterize the spatial accuracy of the scanner, we used a geometric phantom and an anthropomorphic head phantom. The geometric phantom was machined from plastic and included hemispherical and tetrahedral protrusions that were roughly the dimensions of an average forehead and nose, respectively. Polygon meshes acquired by the optical scanner were compared with meshes generated from high-resolution computed tomography images. Most optical scans contained minor artifacts. Using an algorithm that calculated the distances between the 2 meshes, we found that most of the optical scanner measurements agreed with those from the computed tomography scanner within approximately 1 mm for the geometric phantom and approximately 2 mm for the head phantom. We used this optical scanner along with 3-dimensional printer technology to create custom lead shields for 10 patients receiving orthovoltage treatments of nonmelanoma skin cancers of the face. Patient, tumor, and treatment data were documented. RESULTS: Lead shields created using this approach were accurate, fitting the contours of each patient's face. This process added to patient convenience and addressed potential claustrophobia and medical inability to lie supine. CONCLUSIONS: The scanner was found to be clinically acceptable, and we suggest that the use of an optical scanner and 3-dimensional printer technology become the new standard of care to generate lead shielding for orthovoltage radiation therapy of nonmelanoma facial skin cancer.

Implant delivering hydroxychloroquine attenuates vaginal T lymphocyte activation and inflammation.

Evidence suggests that women who are naturally resistant to HIV infection exhibit low baseline immune activation at the female genital tract (FGT). This "immune quiescent" state is associated with lower expression of T-cell activation markers, reduced levels of gene transcription and pro-inflammatory cytokine or chemokine production involved in HIV infection while maintaining an intact immune response against pathogens. Therefore, if this unique immune quiescent state can be pharmacologically induced locally, it will provide an excellent women-oriented strategy against HIV infection To our knowledge, this is the first research article evaluating in vivo, an innovative trackable implant that can provide controlled delivery of hydroxychloroquine (HCQ) to successfully attenuate vaginal T lymphocyte activation and inflammation in a rabbit model as a potential strategy to induce an "immune quiescent" state within the FGT for the prevention of HIV infection. This biocompatible implant can deliver HCQ above therapeutic concentrations in a controlled manner, reduce submucosal immune cell recruitment, improve mucosal epithelium integrity, decrease protein and gene expression of T-cell activation markers, and attenuate the induction of key pro-inflammatory mediators. Our results suggest that microbicides designed to maintain a low level of immune activation at the FGT may offer a promising new strategy for reducing HIV infection.

Innovation in respiratory therapy and the use of three-dimensional printing for tracheostomy management.

Technological advances have influenced practice patterns and innovation in many health disciplines, including respiratory therapy. Collaborative approaches and knowledge-sharing environments are vital in addressing problems and adopting emerging technology. This article illustrates how the emergence of low-cost three-dimensional printing technology to physically reproduce the results of computed tomography imaging data can provide ways to assess airway abnormalities and symptomology not explained by traditional diagnostic methods.

Fast analytical scatter estimation using graphics processing units.

PURPOSE: To develop a fast patient-specific analytical estimator of first-order Compton and Rayleigh scatter in cone-beam computed tomography, implemented using graphics processing units. METHODS: The authors developed an analytical estimator for first-order Compton and Rayleigh scatter in a cone-beam computed tomography geometry. The estimator was coded using NVIDIA's CUDA environment for execution on an NVIDIA graphics processing unit. Performance of the analytical estimator was validated by comparison with high-count Monte Carlo simulations for two different numerical phantoms. Monoenergetic analytical simulations were compared with monoenergetic and polyenergetic Monte Carlo simulations. Analytical and Monte Carlo scatter estimates were compared both qualitatively, from visual inspection of images and profiles, and quantitatively, using a scaled root-mean-square difference metric. Reconstruction of simulated cone-beam projection data of an anthropomorphic breast phantom illustrated the potential of this method as a component of a scatter correction algorithm. RESULTS: The monoenergetic analytical and Monte Carlo scatter estimates showed very good agreement. The monoenergetic analytical estimates showed good agreement for Compton single scatter and reasonable agreement for Rayleigh single scatter when compared with polyenergetic Monte Carlo estimates. For a voxelized phantom with dimensions 128 × 128 × 128 voxels and a detector with 256 × 256 pixels, the analytical estimator required 669 seconds for a single projection, using a single NVIDIA 9800 GX2 video card. Accounting for first order scatter in cone-beam image reconstruction improves the contrast to noise ratio of the reconstructed images. CONCLUSION: The analytical scatter estimator, implemented using graphics processing units, provides rapid and accurate estimates of single scatter and with further acceleration and a method to account for multiple scatter may be useful for practical scatter correction schemes.

An investigation of gantry angle data accuracy for cine-mode EPID images acquired during arc IMRT.

EPID images acquired in cine mode during arc therapy have inaccurate gantry angles recorded in their image headers. In this work, methods were developed to assess the accuracy of the gantry potentiometer for linear accelerators. As well, assessments of the accuracy of other, more accessible, sources of gantry angle information (i.e., treatment log files, analysis of EPID image headers) were investigated. The methods used in this study are generally applicable to any linear accelerator unit, and have been demonstrated here with Clinac/Trilogy systems. Gantry angle data were simultaneously acquired using three methods: i) a direct gantry potentiometer measurement, ii) an incremental rotary encoder, and iii) a custom-made radiographic gantry-angle phantom which produced unique wire intersections as a function of gantry angle. All methods were compared to gantry angle data from the EPID image header and the linac MLC DynaLog file. The encoder and gantry-angle phantom were used to validate the accuracy of the linac's potentiometer. The EPID image header gantry angles and the DynaLog file gantry angles were compared to the potentiometer. The encoder and gantry-angle phantom mean angle differences with the potentiometer were 0.13° ± 0.14° and 0.10°± 0.30°, respectively. The EPID image header angles analyzed in this study were within ± 1° of the potentiometer angles only 35% of the time. In some cases, EPID image header gantry angles disagreed by as much as 3° with the potentiometer. A time delay in frame acquisition was determined using the continuous acquisition mode of the EPID. After correcting for this time delay, 75% of the header angles, on average, were within ± 1° of the true gantry angle, compared to an average of only 35% without the correction. Applying a boxcar smoothing filter to the corrected gantry angles further improved the accuracy of the header-derived gantry angles to within ± 1° for almost all images (99.4%). An angle accuracy of 0.11° ± 0.04° was determined using a point-by-point comparison of the gantry angle data in the MLC DynaLog file and the potentiometer data. These simple correction methods can be easily applied to individual treatment EPID images in order to more accurately define the gantry angle.

A quality assurance tool for high-dose-rate brachytherapy.

PURPOSE: The purpose of this work was to develop a quality assurance (QA) tool for high-dose-rate (HDR) brachytherapy that would quickly and easily verify both source positioning (dwell positions) and durations (dwell times). METHODS: The authors constructed a QA tool that combined radiochromic film to verify position with four photodiode detectors to verify dwell times. To characterize the temporal accuracy of the tool, a function generator powered four red light-emitting diodes that were optically coupled to the four photodiode detectors. The QA tool was used to verify the dwell positions and times of a commercial brachytherapy afterloader. Measurements of dwell time were independently verified by a one-dimensional optical camera that acquired 1000 lines/s. RESULTS: The temporal accuracy of the QA tool was found to be about 1 ms. For visual assessment, the source position could be located within about 0.5 mm. Evaluating the accuracy and precision of an HDR brachytherapy afterloader, the authors found that the bias in dwell time can exceed 60 ms and the dwell time associated with the first dwell position had an unexpectedly large standard deviation of 30 ms. They found that the source locations were much easier to locate on the film if a plastic catheter was used instead of a metal treatment tube. Scanning the films enabled the dwell positions to be determined within about 0.2 mm. CONCLUSIONS: For pretreatment QA, the authors found that this tool allowed verification of dwell positions and dwell times in about 6 min.