Electronic portal imaging devices (EPIDs) based on indirect detection, active matrix flat panel imagers (AMFPIs) have become the technology of choice for geometric verification of patient localization and dose delivery in external beam radiotherapy. However, current AMFPI EPIDs, which are based on powdered‐phosphor screens, make use of only of the incident radiation, thus severely limiting their imaging performance as quantified by the detective quantum efficiency (DQE) ( , compared to for kilovoltage AMFPIs). With the rapidly increasing adoption of image‐guided techniques in virtually every aspect of radiotherapy, there exist strong incentives to develop high‐DQE megavoltage x‐ray imagers, capable of providing soft‐tissue contrast at very low doses in megavoltage tomographic and, potentially, projection imaging. In this work we present a systematic theoretical and preliminary empirical evaluation of a promising, high‐quantum‐efficiency, megavoltage x‐ray detector design based on a two‐dimensional matrix of thick, optically isolated, crystalline scintillator elements. The detector is coupled with an indirect detection‐based active matrix array, with the center‐to‐center spacing of the crystalline elements chosen to match the pitch of the underlying array pixels. Such a design enables the utilization of a significantly larger fraction of the incident radiation (up to 80% for a beam), through increases in the thickness of the crystalline elements, without loss of spatial resolution due to the spread of optical photons. Radiation damage studies were performed on test samples of two candidate scintillator materials, CsI(Tl) and BGO, under conditions relevant to radiotherapy imaging. A detailed Monte Carlo‐based study was performed in order to examine the signal, spatial spreading, and noise properties of the absorbed energy for several segmented detector configurations. Parameters studied included scintillator material, septal wall material, detector thickness, and the thickness of the septal walls. The results of the Monte Carlo simulations were used to estimate the upper limits of the modulation transfer function, noise power spectrum and the DQE for a select number of configurations. An exploratory, small‐area prototype segmented detector was fabricated by infusing crystalline CsI(Tl) in a thick tungsten matrix, and the signal response was measured under radiotherapy imaging conditions. Results from the radiation damage studies showed that both CsI(Tl) and BGO exhibited less than reduction in light output after equivalent dose. The prototype CsI(Tl) segmented detector exhibited high uniformity, but a lower‐than‐expected magnitude of signal response. Finally, results from Monte Carlo studies strongly indicate that high scintillator‐fill‐factor configurations, incorporating high‐density scintillator and septal wall materials, could achieve up to 50 times higher DQE compared to current AMFPI EPIDs.
Study goals were to characterize gastrointestinal effects of proton therapy (PT) in a large cohort of patients treated for prostate cancer, identify factors associated with rectal bleeding (RB), and compare RB between patients receiving investigational protocols versus those in outcome-tracking protocols.A total of 1285 consecutive patients were treated with PT between August 2006 and May 2010. Potential pre-existing clinical and treatment-related risk factors for rectal toxicity were recorded. Common Terminology Criteria for Adverse Events version 3.0 was used to score toxicity.Transient RB was the predominant grade 2 or higher (GR2+) toxicity after PT, accounting for 95% of gastrointestinal events. GR1 RB occurred in 217 patients (16.9%), GR2 RB in 187 patients (14.5%), and GR3 in 11 (0.9%) patients. There were no GR4 or GR5 events. Univariate analyses showed correlations between GR2+ RB and anticoagulation therapy (P=.008) and rectal and rectal wall dose-volume histogram (DVH) parameters (P<.001). On multivariate analysis, anticoagulation therapy (P=.0034), relative volume of rectum receiving 75 Gy (V75; P=.0102), and relative rectal wall V75 (P=.0017) were significant predictors for G2+ RB. Patients treated with investigational protocols had toxicity rates similar to those receiving outcome-tracking protocols.PT was associated with a low rate of GR2+ gastrointestinal toxicity, predominantly transient RB, which was highly correlated with anticoagulation and rectal DVH parameters. Techniques that limit rectal exposure should be used when possible.
Lateral migration radiography (LMR) employs scattered photons to acquire detailed images of covered objects. images of plastic encased real mines buried in soil using LMR have shown dramatic differences compared to images generated using simulated mines. The major characteristic that enables the discernibility of land mines to the degree of actual type identification is the presence of voids (air volumes) required for the operation of the fuse assembly or for blast direction control. Air volumes greatly modify the detected field of both once and multiple-scattered photons. The LMR system consists of an x-ray generator and two uncollimated detectors positioned to detect once- scattered photons and two collimated detectors designed to detect primarily multiple-scattered photons. The x-ray generator is located in the gap between symmetrically arranged detectors; the collimated x-ray beam typically has a spot size of 1.5x 1.5 cm with perpendicular incidence on the soil surface. The optimal x-ray spectra for land mine detection with the LMR system range from 130 to 180 kVp with mean x-ray energies of from around 40 to 60 keV. Air volumes modify both exit paths and the position of first-scatter events; they also modify the migration paths of multiple-scattered photons, thus producing different images in the two detector types. The burial mode (below surface or laid on the surface) of the land mine can also be discerned by LMR due to a shadowing effect seen for surfaced-laid land mines. The presence of even a minute amount of metal in the land mine also aids in discerning the mine, because metal produces a signal decrease in both types of detectors. Monte Carlo calculations are performed with the MCNp code to obtain an understanding of the details of the photon lateral migration process. Images generated from these Monte Carlo calculations are in agreement with the experimental measurements. The real mine images confirm that LMR is capable not only of mine detection, but also of mine identification.
In recent years, indirect detection active matrix flat-panel imagers (AMFPIs) have become the gold standard in radiotherapy imaging. The excellent imaging performance of AMFPI-based electronic portal imaging devices (EPIDs) can be attributed to their ability to perform x-ray quantum limited imaging under radiotherapy conditions. However, all current commercial (AMFPI and non-AMFPI) EPIDs use only approximately 1% to 2% of the incident radiation. In this work, strategies to significantly improve the overall performance of indirect detection AMFPI-based EPIDs through novel designs, are presented. Specifically, the focus of this work is on thick, structured scintillators, which achieve high x-ray detection efficiency while simultaneously maintaining spatial resolution. Fundamental signal and noise measurements using prototype, small area, structured scintillators are reported. In addition, theoretical calculations were performed in order to estimate the signal and noise properties of various structured scintillator configurations. Results from theory and experiments were used to estimate the frequency-dependent detective quantum efficiency (DQE). Results suggest that these designs could yield DQE values that are significantly higher than those for current commercial EPID technologies.
The information transmission mechanism of the ground electrode current field uses a very low-frequency electrical signal, which is applied to the two electrodes driven into the soil layer or the collapsed body of the tunnel to form a current field in the rock layer or soil layer. Signal detection is created via the strong penetration of wireless information transmission. This research focuses on various electromagnetic effects, such as polarization, magnetization, and the transmission of electromagnetic waves under the influence of different media, such as rock, sand, reinforced concrete, and air voids. The influence of these adaptive electromagnetic effects on the transmission of electromagnetic waves is mainly reflected in the reflection, refraction, and attenuation of electromagnetic wave signals. The inhomogeneity of the earth medium, the influence of topographic features, and multi-path transmission all cause signal distortion, fading, or changes in the direction of electromagnetic wave propagation. By studying the three physical quantities of magnetic permeability, permittivity, and conductivity, the electromagnetic characteristics of the earth medium are described to research the information transmission characteristics of the earth electrode current field.
Lateral migration radiography (LMR), a new form of Compton backscatter x-ray imaging, is applied to the detection and identification of buried land mines. A mobile LMR land mine detection system was developed and field tested. Weight for this initial system was about 175 kg; weight for a prototype should be about 100 kg. X-ray generator power level was 750 watts; the power level requirement for a prototype should be about 300 watts. An innovative rotating collimator for the x-ray source beam was developed to provide rapid side-to-side scanning of the beam without having to move the x-ray generator in this direction. Acquisition of images of a 40 cm by 40 cm area takes from 30 to 60 seconds, depending on the desired resolution. The imaging capabilities of LMR make it well suited for use as a land mine detection confirmation sensor. This system was employed on the vehicular test lanes at Fort A.P. Hill in October, 2001. High quality images were obtained for a variety of buried land mines. The system was also used to scan 30 locations on one of the test lanes where GPR consistently yielded false alarms. In only two cases did the LMR image sets yield a signature that could be considered to possibly indicate a mine.
A 23-year-old woman with a Masaoka stage III type B2/B3 thymoma was referred to our institution for adjuvant proton therapy after surgical resection. The patient initially presented with chest pain, shortness of breath, and a family history notable for her brother having died from metastatic thymoma at the age of 17 years. A chest computed tomography scan demonstrated a large anterior mediastinal mass. Surgical exploration and resection demonstrated a 16.5 × 8.5 × 3.7 cm mass invading the innominate vein, requiring graft reconstruction, and extending along the right paramediastinal/cardiac border to just above the right hemidiaphragm. Pathology revealed stage III type B2/B3 thymoma with no lymph node involvement, but microscopic positive margins. Because of stage and positive margins, recommendations were made for adjuvant radiation therapy (RT). An RT plan was developed to deliver 50.4 Gy to the postoperative bed with a 10.8 Gy boost to the site that showed microscopic residual disease. Despite advanced disease at presentation, patients with stage III thymoma receiving adjuvant RT do well with a median overall survival of 127 months.1Weksler B Shende M Nason KS Gallagher A Ferson PF Pennathur A The role of adjuvant radiation therapy for resected stage III thymoma: a population-based study.Ann Thorac Surg. 2012; 93 (discussion 1828): 1822-1828Abstract Full Text Full Text PDF PubMed Scopus (50) Google Scholar Because this female patient was quite young, it was important to consider the long-term complications of RT to the chest. Unfortunately, even with the most conformal photon radiation technique, intensity-modulated radiotherapy (IMRT), the mean dose to the organs at risk was quite high. The patient was, therefore, referred to University of Florida Proton Therapy Institute for consideration of treatment with proton therapy. Conventional photon RT, which uses high-energy photons, deposits part of the RT dose throughout the beam's path, causing collateral damage to normal tissue ahead of and behind the actual planned target volume (PTV). Conversely, proton therapy, which uses charged particles, deposits most of the RT dose at the PTV, with a lower entrance dose (ahead of the PTV) and little to no exit dose (behind the PTV) compared with high-energy photons. Our patient underwent treatment planning with IMRT and proton therapy. Figure 1 shows the colorwash isodose plans comparing the dose distributions of both plans. Figure 2 shows dose-volume histograms of the OARs. Table 1 shows mean doses to the OARs.FIGURE 2Dose-volume histograms representing the percentage of each organ irradiated at each radiation dose level with intensity-modulated radiation therapy (dashed line) or proton therapy (solid line).View Large Image Figure ViewerDownload (PPT)TABLE 1Mean Dose to Organs with Intensity-Modulated Radiation Therapy and Proton TherapyOrganIMRT (Gy)Proton (Gy)Absolute Reduction (Gy)Relative Reduction (%)Lungs15.79.95.837Heart28.420.48.028Esophagus36.516.520.055Breasts7.69.72.1−27Nontarget thoraxaNontarget thorax refers to thorax minus planned target volume.8.73.65.159a Nontarget thorax refers to thorax minus planned target volume. Open table in a new tab RT doses as low as 4 to 5 Gy to the lung and/or breast have been associated with an increased risk of secondary lung and breast cancers,2Travis LB Gospodarowicz M Curtis RE et al.Lung cancer following chemotherapy and radiotherapy for Hodgkin's disease.J Natl Cancer Inst. 2002; 94: 182-192Crossref PubMed Scopus (467) Google Scholar,3Travis LB Hill DA Dores GM et al.Breast cancer following radiotherapy and chemotherapy among young women with Hodgkin disease.JAMA. 2003; 290: 465-475Crossref PubMed Scopus (531) Google Scholar whereas RT doses as low as 5 to 15 Gy to the heart have been shown to increase the risk of late cardiac injury, such as myocardial infarction, congestive heart failure, and valvular disease.4Mulrooney DA Yeazel MW Kawashima T et al.Cardiac outcomes in a cohort of adult survivors of childhood and adolescent cancer: retrospective analysis of the Childhood Cancer Survivor Study cohort.BMJ. 2009; 339: b4606Crossref PubMed Scopus (786) Google Scholar,5Tukenova M Guibout C Oberlin O et al.Role of cancer treatment in long-term overall and cardiovascular mortality after childhood cancer.J Clin Oncol. 2010; 28: 1308-1315Crossref PubMed Scopus (335) Google Scholar Our treatment plans showed that, when compared with IMRT, proton therapy reduced the mean dose to the heart by 8 Gy, lungs by 6 Gy, and esophagus by 20 Gy, whereas it increased the dose to the breasts by 2 Gy. Because of the lower doses delivered to most of the OARs and expected lower risk of late toxicity with these lower doses, the patient was treated with proton therapy. Proton therapy should be considered in similar cases of young adults with thymoma, in whom there are concerns of the late toxicity associated with RT.
A series of buried land mine detection measurements were performed at the University of Florida using x-ray lateral migration radiography with 12 difference types of actual antitank and antipersonnel mines. The resulting images posses extraordinarily definitive detail. The signatures are so unique that not only can positive mine detection be accomplished with this technique, but also mine identification. The mine's exterior shape combined with the interior air volumes yield easily recognized image signatures. The emphasis of this paper is on mine-type discrimination from image data. The reported results indicate that the lateral migration radiography technique provides a land mine detection method with the potential of near-zero false positive alarm probability. A practical systems, which is under current design and fabrication, is described and allows for one square meter interrogation in 35 seconds, antitank and antipersonnel mine imaging and recognition in respectively 12.6 and 1.4 seconds. This approximately 75-kilogram system can be attached to a small two-wheel carrier and requires only 140 watts of electric power.
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