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At least 559 records · Page 31
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Scalable Detector Design for a High-Resolution Fast-Neutron Radiography Panel

Development of a scalable flat-panel neutron radiography device is needed to meet the nondestructive testing needs of a growing industrial market. Flood field images from a Cs-137 gamma source and a Cf-252 fission neutron source were generated using a detector composed of a 3-mm-thick sheet of EJ-200, and 3-mm-thick sheet of acrylic light spreader, an 8 $\times$ 8 array of SensL MICROFJ-60035-TSV SiPMs, and an IDEAS ROSSPAD readout module. The readout module can be tiled together with similar systems to create a panel of any size, and is only limited by the number of available Ethernet ports in a switching system. A collimated gamma line image demonstrated a 90% spatial resolution of approximately 0.47 line pairs per centimeter and a 10% spatial resolution of approximately 2.32 line pairs per centimeter. A neutron edge image demonstrated a 90% spatial resolution of approximately 0.70 line pairs per centimeter and a 10% spatial resolution of approximately 3.35 line pairs per centimeter. Both of these images show the ability to generate radiographs with sub-SiPM spatial resolution. Using these readout modules, a large-scale radiographic panel can be developed by tiling ROSSPAD modules together.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Advances in imaging instrumentation for nuclear cardiology

Advances in imaging instrumentation and technology have greatly contributed to nuclear cardiology. Dedicated cardiac SPECT cameras incorporating novel, highly efficient detector, collimator, and system designs have emerged with the expansion of nuclear cardiology. Solid-state radiation detectors incorporating cadmium zinc telluride, which directly convert radiation to electrical signals and yield improved energy resolution and spatial resolution and enhanced count sensitivity geometries, are increasingly gaining favor as the detector of choice for application in dedicated cardiac SPECT systems. Additionally, hybrid imaging systems in which SPECT and PET are combined with X-ray CT are currently widely used, with PET/MRI hybrid systems having also been recently introduced. The improved quantitative SPECT/CT has the potential to measure the absolute quantification of myocardial blood flow and flow reserve. Rapid development of silicon photomultipliers leads to enhancement in PET image quality and count rates. In addition, the reduction of emission–transmission mismatch artifacts via application of accurate time-of-flight information, and cardiac motion de-blurring aided by anatomical images, are emerging techniques for further improvement of cardiac PET. This article reviews recent advances such as these in nuclear cardiology imaging instrumentation and technology, and the corresponding diagnostic benefits.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2017

A Simple Method for Improving the Spatial Resolution in Infrared Laser Ablation Mass Spectrometry Imaging

In mass spectrometry imaging of tissues, the size of structures that can be distinguished is determined by the spatial resolution of the imaging technique. Here, the spatial resolution of IR laser ablation is markedly improved by increasing the distance between the laser and the focusing lens. As the distance between the laser and the lens is increased from 1 to 18 m, the ablation spot size decreases from 440 to 44 μm. This way, only the collimated center of the divergent laser beam is directed on the focusing lens, which results in better focusing of the beam. Part of the laser energy is lost at longer distance, but this is compensated by focusing of the radiation to a smaller area on the sample surface. The long distance can also be achieved by a set of mirrors, between which the radiation travels before it is directed to the focusing lens and the sample. This method for improving the spatial resolution can be utilized in mass spectrometry imaging of tissues by techniques that utilize IR laser ablation, such as laser ablation electrospray ionization, laser ablation atmospheric pressure photoionization, and matrix-assisted laser desorption electrospray ionization. .

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2021

Radiation damage of a two-dimensional carbon fiber composite (CFC)

Carbon fiber composites (CFC) are, among other applications, already in use as low-impedance collimating elements for intercepting TeV-level protons machines, like the CERN Large Hadron Collider. Towards a comprehensive understanding of these materials’ properties and behavior, a series of radiation damage campaigns have been undertaken in order to quantitively investigate the response of AC-150 K CFC to high proton fluences. The CFCs dimensional changes, stability, micro-structural evolution, and structural integrity below and above 5 × 10 20 p/cm 2 fluence threshold were studied. The irradiating particles were protons of kinetic energies in the range of 130–200 MeV. The effects of the irradiation temperature (~90–180°C and 280–500°C) combined with the proton fluence on the dimensional stability and the microstructural evolution of this anisotropic two-dimensional composite structure were studied using precision dilatometry and X-ray diffraction. Our results shed light on the fluence-based limitations for these composite materials. Furthermore, we compare these results with reference unirradiated graphite, and we discuss the similarities and differences in the dimensional changes and post-irradiation annealing properties.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Insight into the BiFeO 3 flash sintering process by in-situ energy dispersive X-ray diffraction (ED-XRD)

The sintering mechanism of BiFeO 3 has been investigated in-situ by energy dispersive X-ray diffraction (ED-XRD) using a high-energy white collimated X-ray beam from the Advanced Photon Source (Argonne National Laboratories). Such radiation is very penetrating thereby allowing measurements of the sample even when placed inside the flash sintering set up. Additionally, the fast ED-XRD measurements permit monitoring the flash sintering process by providing information about phase composition and sample temperature in real time. Moreover, profile scans, obtained by moving the stage vertically while recording the ED-XRD spectra, permit investigating the homogeneity of the flash for the entire length of the sample. All experiments have been complemented by ex-situ studies. Here, it has been concluded that flash sintering of BiFeO 3 is a homogeneous process without any directionality effects. Furthermore, flash sintering takes place at quite low temperatures (below the Tc ≈ 830 °C), which may be related to the high quality of the samples, as pure, highly insulating ceramics without evidence of secondary phases with a homogenous nanostructured grain size distribution are obtained by this technique. Moreover, it is also evidenced that the rapid heating of the sample does not seem to justify, at least by itself, the densification process. Therefore, it appears that the electric current should play a role in the enhanced mobility during the sintering process.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Quantitative investigation of sooting dynamics in droplet combustion using an automated image analysis algorithm

This paper reports an image analysis approach using a newly-developed open-source program to extract quantitative measurements of soot volume fraction (SVF) from digital video images of burning n-heptane droplets. The automated program developed in this work can analyze images of fixed and untethered droplets to quantify sooting dynamics. The images analyzed in the program were taken from experiments carried out in the Multi-user Droplet Combustion Apparatus (MDCA) onboard the International Space Station (ISS). In these experiments, video imaging of burning droplets was obtained using backlighting by a laser diode with a wavelength of 653 nm. Here, the light was collimated before it passed through the droplet and soot-containing region, after which the light was then attenuated and projected onto the camera’s sensors. This technique facilitates the measurements of SVF based on the principles of the full field light extinction method (FFLEM). The measurements provide quantitative data that reveal the sooting dynamics of liquid fuels during droplet combustion processes. The analyses of a soot-attenuating image (ISS n-heptane, untethered droplet) at an instant during the burning show that the SVF distribution has a peak at the soot shell location. It then decreases due to soot oxidation when the location is further away from the burning droplet. Regarding temporal effects on the maximum SVF (SVF max ), results show that SVF max first increases after the burning is initiated until a peak value is reached, after which SVF max decreases. The SVF max values identified in this study for n-heptane are quantitatively consistent with previously reported values for fiber-supported droplets and are reached relatively early in the burning history. n-Heptane images are also analyzed to show the effects of initial droplet sizes on the maximum soot volume fraction. Results show that SVF max decreases with increasing initial droplet size, which is consistent with visual observations of less soot formed and dimmer flame brightness as Do increases.

42 ENGINEERING↗
DOE OSTI2017

A plasma deflagration accelerator as a platform for laboratory astrophysics

The replication of astrophysical flows in the laboratory is critical for isolating particular phenomena and dynamics that appear in complex, highly-coupled natural systems. Particularly, plasma jets are observed in astrophysical contexts at a variety of scales, typically at high magnetic Reynolds number and driven by internal currents. In this paper, we present detailed measurements of the plasma parameters within deflagration-produced plasma jets, the scaling of these parameters against both machine operating conditions and the corresponding astrophysical phenomena. Using optical and spectroscopic diagnostics, including Schlieren cinematography, we demonstrate the production of current-driven plasma jets of »100 km/s and magnetic Reynolds numbers of »100, and discuss the dynamics of their acceleration into vacuum. Finally, the results of this study will contribute to the reproduction of various types of astrophysical jets in the laboratory and indicate the ability to further probe active research areas such as jet collimation, stability, and interaction.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2018

Hard X-ray fluorescence spectroscopy of high pressure cavitating fluids in aluminum nozzles

X-rays are frequently used to study the internal geometry of dense objects, and to measure the density of multiphase flows. However, quantitatively measuring fluid density inside a metallic object such as a high pressure spray nozzle is difficult. X-rays of sufficiently high energy to penetrate a metal object are not appreciably absorbed by the fluid inside. This requires the use of plastic or beryllium test sections, which are not suited to high pressure conditions. We present a high-energy X-ray fluorescence technique which can overcome this problem. The experiments were conducted at the 7-BM beamline of the Advanced Photon Source at Argonne National Laboratory. A hydrocarbon fluid was seeded with cerium nanoparticles. The fluid was pumped at high pressure through aluminum nozzles with inner diameters of 0.36-0.90 mm and wall thicknesses of 2-3 mm. A collimated, monochromatic 42.5 keV X-ray beam excited K-edge fluorescence from the cerium. The K-alpha emission lines at 34-35 keV were recorded by a cryogenic germanium detector. Changes in fluid density due to cavitation of the liquid inside the nozzle were measured by raster scanning the nozzle across the beam. A spatial resolution of 20 x 20 mu m(2) was achieved with a slitted beam, which was improved to 5 x 10 mu m(2) with X-ray focusing mirrors. The uncertainty in the path-integrated vapor fraction was 30-40 mu m at 95% confidence. A limitation of this approach is that for low vapor pressure fluids, the nanoparticles increase the vapor pressure of the fluid and act as additional nucleation sites. These experiments demonstrate a path forward for measurements of multiphase flows inside metal components under conditions that are not feasible in optically accessible materials.

47 OTHER INSTRUMENTATION↗
DOE OSTI2016

Online Magnetic Resonance Image Guided Adaptive Radiation Therapy: First Clinical Applications

Purpose: To demonstrate the feasibility of online adaptive magnetic resonance (MR) image guided radiation therapy (MR-IGRT) through reporting of our initial clinical experience and workflow considerations. Methods and Materials: The first clinically deployed online adaptive MR-IGRT system consisted of a split 0.35T MR scanner straddling a ring gantry with 3 multileaf collimator-equipped {sup 60}Co heads. The unit is supported by a Monte Carlo–based treatment planning system that allows real-time adaptive planning with the patient on the table. All patients undergo computed tomography and MR imaging (MRI) simulation for initial treatment planning. A volumetric MRI scan is acquired for each patient at the daily treatment setup. Deformable registration is performed using the planning computed tomography data set, which allows for the transfer of the initial contours and the electron density map to the daily MRI scan. The deformed electron density map is then used to recalculate the original plan on the daily MRI scan for physician evaluation. Recontouring and plan reoptimization are performed when required, and patient-specific quality assurance (QA) is performed using an independent in-house software system. Results: The first online adaptive MR-IGRT treatments consisted of 5 patients with abdominopelvic malignancies. The clinical setting included neoadjuvant colorectal (n=3), unresectable gastric (n=1), and unresectable pheochromocytoma (n=1). Recontouring and reoptimization were deemed necessary for 3 of 5 patients, and the initial plan was deemed sufficient for 2 of the 5 patients. The reasons for plan adaptation included tumor progression or regression and a change in small bowel anatomy. In a subsequently expanded cohort of 170 fractions (20 patients), 52 fractions (30.6%) were reoptimized online, and 92 fractions (54.1%) were treated with an online-adapted or previously adapted plan. The median time for recontouring, reoptimization, and QA was 26 minutes. Conclusion: Online adaptive MR-IGRT has been successfully implemented with planning and QA workflow suitable for routine clinical application. Clinical trials are in development to formally evaluate adaptive treatments for a variety of disease sites.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2016

Deep Inspiration Breath Hold—Based Radiation Therapy: A Clinical Review

Several recent developments in linear accelerator–based radiation therapy (RT) such as fast multileaf collimators, accelerated intensity modulation paradigms like volumeric modulated arc therapy and flattening filter-free (FFF) high-dose-rate therapy have dramatically shortened the duration of treatment fractions. Deliverable photon dose distributions have approached physical complexity limits as a consequence of precise dose calculation algorithms and online 3-dimensional image guided patient positioning (image guided RT). Simultaneously, beam quality and treatment speed have continuously been improved in particle beam therapy, especially for scanned particle beams. Applying complex treatment plans with steep dose gradients requires strategies to mitigate and compensate for motion effects in general, particularly breathing motion. Intrafractional breathing-related motion results in uncertainties in dose delivery and thus in target coverage. As a consequence, generous margins have been used, which, in turn, increases exposure to organs at risk. Particle therapy, particularly with scanned beams, poses additional problems such as interplay effects and range uncertainties. Among advanced strategies to compensate breathing motion such as beam gating and tracking, deep inspiration breath hold (DIBH) gating is particularly advantageous in several respects, not only for hypofractionated, high single-dose stereotactic body RT of lung, liver, and upper abdominal lesions but also for normofractionated treatment of thoracic tumors such as lung cancer, mediastinal lymphomas, and breast cancer. This review provides an in-depth discussion of the rationale and technical implementation of DIBH gating for hypofractionated and normofractionated RT of intrathoracic and upper abdominal tumors in photon and proton RT.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2016

Exposure Risks Among Children Undergoing Radiation Therapy: Considerations in the Era of Image Guided Radiation Therapy

Recent improvements in toxicity profiles of pediatric oncology patients are attributable, in part, to advances in the field of radiation oncology such as intensity modulated radiation (IMRT) and proton therapy (IMPT). While IMRT and IMPT deliver highly conformal dose to targeted volumes, they commonly demand the addition of 2- or 3-dimensional imaging for precise positioning—a technique known as image guided radiation therapy (IGRT). In this manuscript we address strategies to further minimize exposure risk in children by reducing effective IGRT dose. Portal X rays and cone beam computed tomography (CBCT) are commonly used to verify patient position during IGRT and, because their relative radiation exposure is far less than the radiation absorbed from therapeutic treatment beams, their sometimes significant contribution to cumulative risk can be easily overlooked. Optimizing the conformality of IMRT/IMPT while simultaneously ignoring IGRT dose may result in organs at risk being exposed to a greater proportion of radiation from IGRT than from therapeutic beams. Over a treatment course, cumulative central-axis CBCT effective dose can approach or supersede the amount of radiation absorbed from a single treatment fraction, a theoretical increase of 3% to 5% in mutagenic risk. In select scenarios, this may result in the underprediction of acute and late toxicity risk (such as azoospermia, ovarian dysfunction, or increased lifetime mutagenic risk) in radiation-sensitive organs and patients. Although dependent on variables such as patient age, gender, weight, body habitus, anatomic location, and dose-toxicity thresholds, modifying IGRT use and acquisition parameters such as frequency, imaging modality, beam energy, current, voltage, rotational degree, collimation, field size, reconstruction algorithm, and documentation can reduce exposure, avoid unnecessary toxicity, and achieve doses as low as reasonably achievable, promoting a culture and practice of “gentle IGRT.”.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2016

Agreement Between Institutional Measurements and Treatment Planning System Calculations for Basic Dosimetric Parameters as Measured by the Imaging and Radiation Oncology Core-Houston

Purpose: To compare radiation machine measurement data collected by the Imaging and Radiation Oncology Core at Houston (IROC-H) with institutional treatment planning system (TPS) values, to identify parameters with large differences in agreement; the findings will help institutions focus their efforts to improve the accuracy of their TPS models. Methods and Materials: Between 2000 and 2014, IROC-H visited more than 250 institutions and conducted independent measurements of machine dosimetric data points, including percentage depth dose, output factors, off-axis factors, multileaf collimator small fields, and wedge data. We compared these data with the institutional TPS values for the same points by energy, class, and parameter to identify differences and similarities using criteria involving both the medians and standard deviations for Varian linear accelerators. Distributions of differences between machine measurements and institutional TPS values were generated for basic dosimetric parameters. Results: On average, intensity modulated radiation therapy–style and stereotactic body radiation therapy–style output factors and upper physical wedge output factors were the most problematic. Percentage depth dose, jaw output factors, and enhanced dynamic wedge output factors agreed best between the IROC-H measurements and the TPS values. Although small differences were shown between 2 common TPS systems, neither was superior to the other. Parameter agreement was constant over time from 2000 to 2014. Conclusions: Differences in basic dosimetric parameters between machine measurements and TPS values vary widely depending on the parameter, although agreement does not seem to vary by TPS and has not changed over time. Intensity modulated radiation therapy–style output factors, stereotactic body radiation therapy–style output factors, and upper physical wedge output factors had the largest disagreement and should be carefully modeled to ensure accuracy.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2017

Intercellular Adhesion Molecule-1 and Vascular Cell Adhesion Molecule Are Induced by Ionizing Radiation on Lymphatic Endothelium

Purpose/Objectives: The goal of this study was to assess the effects of ionizing radiation on the expression of the integrin ligands ICAM-1 and VCAM that control leucocyte transit by lymphatic endothelial cells. Materials/Methods: Confluent monolayers of primary human lymphatic endothelial cells (LEC) were irradiated with single dose of 2, 5, 10 or 20 Gy, with 6 MeV-x-rays using a Linear-Accelerator. ICAM-1 and VCAM expression was determined by flow cytometry. Human tissue specimens received a single dose of 20 Gy with 15 MeV-x-rays. MC38, B16-OVA or B16-VEGF-C tumors grown in C57BL/6 mice were irradiated with single dose of 20Gy using a Linear-Accelerator fitted with a 10mm Radiosurgery collimator. Clinical samples were obtained from patients previous and 4 weeks after complete standard radiotherapy. ICAM-1 and VCAM expression was detected in all tissue specimens by confocal microscopy. To understand the role of TGFβ in this process anti-TGFβ blocking mAb were injected i.p. 30min before radiotherapy. Cell adhesion to irradiated LEC was analyzed in adhesion experiments performed in the presence or in the absence of anti- TGFβ and /or anti-ICAM1 blocking mAb. Results: We demonstrate that lymphatic endothelial cells in tumor samples experience induction of surface ICAM-1 and VCAM when exposed to ionizing radiation in a dose- and time-dependent manner. These effects can be recapitulated in cultured LEC, and are in part mediated by TGFβ. These data are consistent with increases in ICAM-1 and VCAM expression on LYVE-1+ endothelial cells in freshly explanted human tumor tissue and in mouse transplanted tumors after radiotherapy. Finally, ICAM-1 and VCAM expression accounts for enhanced adherence of human T lymphocytes to irradiated LEC. Conclusion: Our results show induction of ICAM-1 and VCAM on LVs in irradiated lesions and offer a starting point for elucidating the biological and therapeutic implications of targeting leukocyte traffic in combination to immunotherapy.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2017

Prompt Gamma Imaging for In Vivo Range Verification of Pencil Beam Scanning Proton Therapy

Purpose: To report the first clinical results and value assessment of prompt gamma imaging for in vivo proton range verification in pencil beam scanning mode. Methods and Materials: A stand-alone, trolley-mounted, prototype prompt gamma camera utilizing a knife-edge slit collimator design was used to record the prompt gamma signal emitted along the proton tracks during delivery of proton therapy for a brain cancer patient. The recorded prompt gamma depth detection profiles of individual pencil beam spots were compared with the expected profiles simulated from the treatment plan. Results: In 6 treatment fractions recorded over 3 weeks, the mean (± standard deviation) range shifts aggregated over all spots in 9 energy layers were −0.8 ± 1.3 mm for the lateral field, 1.7 ± 0.7 mm for the right-superior-oblique field, and −0.4 ± 0.9 mm for the vertex field. Conclusions: This study demonstrates the feasibility and illustrates the distinctive benefits of prompt gamma imaging in pencil beam scanning treatment mode. Accuracy in range verification was found in this first clinical case to be better than the range uncertainty margin applied in the treatment plan. These first results lay the foundation for additional work toward tighter integration of the system for in vivo proton range verification and quantification of range uncertainties.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2024

Cobalt-60, Barium-133, Cesium-137, and Europium-152 migration from cementitious sources through sediment under field conditions

Safe and effective storage of radioactive waste is essential to protect human and environmental health. Due to the potential for accidental releases and the severity of the associated risks, it is imperative to further understand radionuclide transport should an accident occur. This study was the second set of measurements conducted in 2022 of an ongoing experiment that has analyzed the vadose zone migration of radionuclides from cementitious wasteforms at the Savannah River Site over the last ten years. The radionuclides introduced within the sources are prominent constituents of radioactive waste or analogs for other groups or series of radionuclides. Lysimeters were first analyzed in 2016 using a collimated high-purity germanium gamma-ray spectrometer to non-destructively measure the concentration of each radionuclide in the sediment column as a function of depth. Following these measurements, the lysimeters were redeployed for another 4 years. All radionuclides in all lysimeters were observed to transport further during the redeployment period; however, the extent of migration varied with the material used for introduction. Except for 137Cs, migration through the sediment control system increased with decreasing ionic potential (ionic charge/radius); migration order: 152Eu<137Cs<60Co<133Ba. Overall, the cementitious wasteforms were observed to decrease radionuclide migration extent relative to natural vadose zone conditions. In both cementitious wasteforms, the migration extent increased in the order 152Eu<133Ba<60Co<137Cs. However, less migration was measured when the radionuclides were incorporated into a reducing grout wasteform. The novelty of this paper is the demonstration of a technique capable of creating non-destructive measurements over decade time scales. Ultimately, this work provides insight into the long-term migration of alkali, alkali earth, divalent transition metal, and trivalent (e.g., lanthanide and actinide element) isotopes.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2023

$In-situ$ synchrotron x-ray diffraction and thermal expansion of TiB2 up to ~3050 °C

There is an increasing interest in understanding the performance and properties of ultra-high temperature ceramics due to their high melting points (<3000 °C) that make them promising for extreme environment applications. In-situ high temperature X-ray diffraction experiments were performed on TiB 2 beads up to ~3050 °C. For these experiments, TiB 2 powders were fabricated into spherical beads via gel casting methods and densified in a high temperature graphite furnace. These sample beads were then levitated in a conical nozzle levitator with reducing atmosphere (3% H 2 -Ar) while being heated using a 400 W CO 2 laser. During levitation a collimated synchrotron X-ray source was used to perform in-situ, temperature-dependent structural characterizations. The anisotropic coefficients of thermal expansion of TiB 2 were characterized as a function of temperature up to ~3050 °C. Elucidation of these properties are critical for the advancement of TiB 2 ceramics and other transition metal di-borides for use in high temperature applications such as hypersonic platforms, nuclear reactors, and atmospheric re-entry.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Linac-based extracranial radiosurgery with Elekta volumetric modulated arc therapy and an anatomy-based treatment planning system: Feasibility and initial experience

We reported our initial experience in using Elekta volumetric modulated arc therapy (VMAT) and an anatomy-based treatment planning system (TPS) for single high-dose radiosurgery (SRS-VMAT) of liver metastases. This study included a cohort of 12 patients treated with a 26-Gy single fraction. Single-arc VMAT plans were generated with Ergo++ TPS. The prescription isodose surface (IDS) was selected to fulfill the 2 following criteria: 95% of planning target volume (PTV) reached 100% of the prescription dose and 99% of PTV reached a minimum of 90% of prescription dose. A 1-mm multileaf collimator (MLC) block margin was added around the PTV. For a comparison of dose distributions with literature data, several conformity indexes (conformity index [CI], conformation number [CN], and gradient index [GI]) were calculated. Treatment efficiency and pretreatment dosimetric verification were assessed. Early clinical data were also reported. Our results reported that target and organ-at-risk objectives were met for all patients. Mean and maximum doses to PTVs were on average 112.9% and 121.5% of prescribed dose, respectively. A very high degree of dose conformity was obtained, with CI, CN, and GI average values equal to 1.29, 0.80, and 3.63, respectively. The beam-on-time was on average 9.3 minutes, i.e., 0.36 min/Gy. The mean number of monitor units was 3162, i.e., 121.6 MU/Gy. Pretreatment verification (3%-3 mm) showed an optimal agreement with calculated values; mean γ value was 0.27 and 98.2% of measured points resulted with γ < 1. With a median follow-up of 16 months complete response was observed in 12/14 (86%) lesions; partial response was observed in 2/14 (14%) lesions. No radiation-induced liver disease (RILD) was observed in any patients as well no duodenal ulceration or esophagitis or gastric hemorrhage. In conclusion, this analysis demonstrated the feasibility and the appropriateness of high-dose single-fraction SRS-VMAT in liver metastases performed with Elekta VMAT and Ergo++ TPS. Preliminary clinical outcomes showed a high rate of local control and minimum incidence of acute toxicity.

61 RADIATION PROTECTION AND DOSIMETRY↗
DOE OSTI2018

A novel IMRT planning study by using the fixed-jaw method in the treatment of peripheral lung cancer with mediastinal lymph node metastasis

Intensity-modulated radiotherapy (IMRT) is an important technology in cancer radiotherapy. In the current planning system, such as in the Pinnacle{sup 3} system, jaw positions are automatically set to cover all target volumes, and many medical centers in developing countries are not equipped with linear accelerators with a jaw tracing function. As solitary lesions are often located in patients, the resulting radiation leakage and transmission increase the dose exposure in surrounding critical organs, although blocked by multileaf collimator (MLC) leaves. We therefore designed a method to manually fix jaw positions, which further reduces doses. We particularly focused on the patients of peripheral lung cancer combined with mediastinal lymph node metastasis, as our medical center mainly targets lung cancer. We designed 2 treatment plans for each patient with the same optimization parameters, i.e., the plan of automatically chosen jaw positions (jaw auto-chosen plan) and the plan of fixed-jaw positions (fixed-jaw plan). In the latter plan, jaws were manually fixed for tumors in lung and in mediastinal lymph node metastases, respectively. We found that both plans met the clinical requirements, and the D{sub 2}, D{sub 98}, conformation number (CN), and homogeneity index (HI) for planning target volume (PTV) had no significant differences between the 2 plans. Importantly, the machine units (MUs) for fixed-jaw plans were 50%~60% more than routine jaw auto-chosen plans, whereas the V{sub 5}, V{sub 10}, V{sub 20}, V{sub 30}, and the mean dose in the total lung and the ipsilateral lung were less than the routine jaw auto-chosen plans. Dose-volume values D{sub 1} for the spinal cord and D{sub 2}, V{sub 40}, V{sub 60} for the heart existed no significant differences for 2 plans. In the fixed-jaw method, the total lung TLV{sub 5}-â–³V{sub ab} and TLV{sub 10}-â–³V{sub ab} values had a moderate positive correlation with the lung radiation leakage and the transmission area reduction. We concluded that the fixed-jaw plan is superior to the routine jaw auto-chosen plan in reducing the radiation exposure of surrounding critical organs, which will benefit the IMRT application.

62 RADIOLOGY AND NUCLEAR MEDICINE↗