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At least 1,207 records · Page 67
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Improved Cumulative Fission Yield Measurements with Fission Spectrum Neutrons on 235 U

Two isotopically-characterized targets of high-purity (99.84±0.03%) 235 U-oxide and a neutron dosimetry package were exposed to a pulsed neutron irradiation using the Godiva critical assembly at the National Criticality Experiments Research Center. Following irradiation, the fissioned targets were counted with a broad-energy germanium detector. Estimates of the total fissions for each target were made using measurements of well-known fission products. The total fission values were then used to measure the fission yields of 21 fission products with half-lives between 636 and 119,700 seconds. Mean values of seventeen of the measured fission products fell within the 95% confidence level of the Evaluated Nuclear Data Files VII.1/b (ENDF/B-VII.1) using the larger of the two uncertainties: 84g Br, 89 Rb, 91 Sr, 93 Y, 97 Zr, 101 Mo, 105 Ru, 128 Sn, 129 Sb, 130g Sb, 131 Sb, 131m Te, 133 I, 135 I, 141 Ba, 142 Ba, and 142 La. Seven isotopes were measured to better precision than is listed in the ENDF/B-VII.1 database: 89 Rb, 93 Y, 128 Sn, 129 Sb, 130g Sb, 131m Te, and 133 I. Four of the measured isotopes were found to be statistically different from the ENDF/B-VII.1 database: 94 Y, 134 Te, 134 I, and 138 Xe. Two of the isotopic analyses conducted in this paper fit the parent and daughter data simultaneously. The parent-daughter pairs measured in this way were the 134 Te/I and 142 Ba/La pairs. The fission yield results obtained in this way are unique, especially for 134 I, because the parent and daughter half-lives are so close. Here, given the limited number of direct measurements of the 134 Te/I pair from fast neutron induced fission and the seemingly high estimate for 134 Te from previous work, it is likely that the value in this paper is more accurate; however, additional measurements of this pair are needed to validate this assertion.

42 ENGINEERING↗
DOE OSTI2015

Improving in vitro to in vivo extrapolation by incorporating toxicokinetic measurements: A case study of lindane-induced neurotoxicity

Approaches for extrapolating in vitro toxicity testing results for prediction of human in vivo outcomes are needed. The purpose of this case study was to employ in vitro toxicokinetics and PBPK modeling to perform in vitro to in vivo extrapolation (IVIVE) of lindane neurotoxicity. Lindane cell and media concentrations in vitro, together with in vitro concentration-response data for lindane effects on neuronal network firing rates, were compared to in vivo data and model simulations as an exercise in extrapolation for chemical-induced neurotoxicity in rodents and humans. Time- and concentration-dependent lindane dosimetry was determined in primary cultures of rat cortical neurons in vitro using “faux” (without electrodes) microelectrode arrays (MEAs). In vivo data were derived from literature values, and physiologically based pharmacokinetic (PBPK) modeling was used to extrapolate from rat to human. The previously determined EC{sub 50} for increased firing rates in primary cultures of cortical neurons was 0.6 μg/ml. Media and cell lindane concentrations at the EC{sub 50} were 0.4 μg/ml and 7.1 μg/ml, respectively, and cellular lindane accumulation was time- and concentration-dependent. Rat blood and brain lindane levels during seizures were 1.7–1.9 μg/ml and 5–11 μg/ml, respectively. Brain lindane levels associated with seizures in rats and those predicted for humans (average = 7 μg/ml) by PBPK modeling were very similar to in vitro concentrations detected in cortical cells at the EC{sub 50} dose. PBPK model predictions matched literature data and timing. These findings indicate that in vitro MEA results are predictive of in vivo responses to lindane and demonstrate a successful modeling approach for IVIVE of rat and human neurotoxicity. - Highlights: • In vitro to in vivo extrapolation for lindane neurotoxicity was performed. • Dosimetry of lindane in a micro-electrode array (MEA) test system was assessed. • Cell concentrations at the MEA EC{sub 50} equaled rat brain levels associated with seizure. • PBPK-predicted human brain levels at seizure also equaled EC{sub 50} cell concentrations. • In vitro MEA results are predictive of lindane in vivo dose–response in rats/humans.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2013

A Multi-Route Model of Nicotine-Cotinine Pharmacokinetics, Pharmacodynamics and Brain Nicotinic Acetylcholine Receptor Binding in Humans

The pharmacokinetics of nicotine, the pharmacologically active alkaloid in tobacco responsible for addiction, are well characterized in humans. We developed a physiologically based pharmacokinetic/pharmacodynamic model of nicotine pharmacokinetics, brain dosimetry and brain nicotinic acetylcholine receptor (nAChRs) occupancy. A Bayesian framework was applied to optimize model parameters against multiple human data sets. The resulting model was consistent with both calibration and test data sets, but in general underestimated variability. A pharmacodynamic model relating nicotine levels to increases in heart rate as a proxy for the pharmacological effects of nicotine accurately described the nicotine related changes in heart rate and the development and decay of tolerance to nicotine. The PBPK model was utilized to quantitatively capture the combined impact of variation in physiological and metabolic parameters, nicotine availability and smoking compensation on the change in number of cigarettes smoked and toxicant exposure in a population of 10,000 people presented with a reduced toxicant (50%), reduced nicotine (50%) cigarette Across the population, toxicant exposure is reduced in some but not all smokers. Reductions are not in proportion to reductions in toxicant yields, largely due to partial compensation in response to reduced nicotine yields. This framework can be used as a key element of a dosimetry-driven risk assessment strategy for cigarette smoke constituents.

Teeguarden, Justin G↗
DOE OSTI2024

Godiva IV central cavity neutron environment characterization with threshold neutron detectors

Godiva IV is a cylindrical fast burst reactor comprised of approximately 65 kg of highly enriched uranium that is operated by Los Alamos National Laboratory and sited at the National Criticality Experiments Research Center at the Nevada National Security Site in Nevada in the United States. Godiva IV is typically operated at delayed critical and in the regime spanning from sub-prompt to super-prompt bursts. Godiva IV is used for sample irradiations, criticality safety demonstrations, dosimetry studies, and for studying super-prompt behavior. In preparation for both an upcoming experiment to reduce uncertainties in the prompt fission spectrum for 235U using threshold neutron detectors, and for future research using Godiva IV, it was desired to exercise the process of the selection of threshold neutron detectors/activation foils, radiation metrology, and the subsequent adjustment of the neutron spectrum. For this exercise, nine high purity threshold neutron detectors/activation foils were irradiated in a Godiva IV burst. The foils were then analyzed using a high-purity germanium detector in the NCERC counting laboratory to determine end of irradiation specific activities for available IRDFF-II reactions. This work summarizes the Godiva IV foil irradiation, radiation metrology results, and adjusted neutron spectrum. The results of this exercise ultimately characterized the neutron environment inside the sample irradiation cavity inside Godiva IV to a higher degree than previously performed, informed decisions for the upcoming larger scale experiment, and will inform future neutron spectrum characterizations at NCERC.

Whitman, Nicholas H.↗
DOE OSTI2021

Using personal monitoring data to derive organ doses for medical radiation workers in the Million Person Study—considerations regarding NCRP Commentary no. 30

The study of low dose and low-dose rate exposure is of central importance in understanding the possible range of health effects from prolonged exposures to radiation. The One Million Person Study of Radiation Workers and Veterans (MPS) of low-dose health effects was designed to evaluate radiation risks among healthy American workers and veterans. The MPS is evaluating low-dose and dose-rate effects, intakes of radioactive elements, cancer and non-cancer outcomes, as well as differences in risks between women and men. Medical radiation workers make up a large group of individuals occupationally exposed to low doses of radiation from external x-ray/gamma exposures. For the MPS, about 100 000 United States medical radiation workers have been selected for study. The approach to the complex dosimetry circumstances for such workers over three to four decades of occupation were initially and broadly described in National Council on Radiation Protection and Measurements (NCRP) Report No. 178. NCRP Commentary No. 30 provides more detail and describes an optimum approach for using personal monitoring data to estimate lung and other organ doses applicable to the cohort and provides specific precautions/considerations applicable to the dosimetry of medical radiation worker organ doses for use in epidemiologic studies. The use of protective aprons creates dosimetric complexity. It is recommended that dose values from dosimeters worn over a protective apron be reduced by a factor of 20 for estimating mean organ doses to tissues located in the torso and that 15% of the marrow should be assumed to remain unshielded for exposure scenarios when aprons are worn. Conversion coefficients relating personal dose equivalent, H p (10) in mSv, to mean absorbed doses to organs and tissues, D T in mGy, for females and males for six exposure scenarios have been determined and presented for use in the MPS. This Memorandum summarises several key points in NCRP Commentary No. 30.

Environmental Sciences & Ecology↗
DOE OSTI2013

Experimental validation of the TOPAS Monte Carlo system for passive scattering proton therapy

Purpose: TOPAS (TOol for PArticle Simulation) is a particle simulation code recently developed with the specific aim of making Monte Carlo simulations user-friendly for research and clinical physicists in the particle therapy community. The authors present a thorough and extensive experimental validation of Monte Carlo simulations performed with TOPAS in a variety of setups relevant for proton therapy applications. The set of validation measurements performed in this work represents an overall end-to-end testing strategy recommended for all clinical centers planning to rely on TOPAS for quality assurance or patient dose calculation and, more generally, for all the institutions using passive-scattering proton therapy systems. Methods: The authors systematically compared TOPAS simulations with measurements that are performed routinely within the quality assurance (QA) program in our institution as well as experiments specifically designed for this validation study. First, the authors compared TOPAS simulations with measurements of depth-dose curves for spread-out Bragg peak (SOBP) fields. Second, absolute dosimetry simulations were benchmarked against measured machine output factors (OFs). Third, the authors simulated and measured 2D dose profiles and analyzed the differences in terms of field flatness and symmetry and usable field size. Fourth, the authors designed a simple experiment using a half-beam shifter to assess the effects of multiple Coulomb scattering, beam divergence, and inverse square attenuation on lateral and longitudinal dose profiles measured and simulated in a water phantom. Fifth, TOPAS’ capabilities to simulate time dependent beam delivery was benchmarked against dose rate functions (i.e., dose per unit time vs time) measured at different depths inside an SOBP field. Sixth, simulations of the charge deposited by protons fully stopping in two different types of multilayer Faraday cups (MLFCs) were compared with measurements to benchmark the nuclear interaction models used in the simulations. Results: SOBPs’ range and modulation width were reproduced, on average, with an accuracy of +1, −2 and ±3 mm, respectively. OF simulations reproduced measured data within ±3%. Simulated 2D dose-profiles show field flatness and average field radius within ±3% of measured profiles. The field symmetry resulted, on average in ±3% agreement with commissioned profiles. TOPAS accuracy in reproducing measured dose profiles downstream the half beam shifter is better than 2%. Dose rate function simulation reproduced the measurements within ∼2% showing that the four-dimensional modeling of the passively modulation system was implement correctly and millimeter accuracy can be achieved in reproducing measured data. For MLFCs simulations, 2% agreement was found between TOPAS and both sets of experimental measurements. The overall results show that TOPAS simulations are within the clinical accepted tolerances for all QA measurements performed at our institution. Conclusions: Our Monte Carlo simulations reproduced accurately the experimental data acquired through all the measurements performed in this study. Thus, TOPAS can reliably be applied to quality assurance for proton therapy and also as an input for commissioning of commercial treatment planning systems. This work also provides the basis for routine clinical dose calculations in patients for all passive scattering proton therapy centers using TOPAS.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2014

Correlation between energy deposition and molecular damage from Auger electrons: A case study of ultra-low energy (5–18 eV) electron interactions with DNA

Purpose: The present study introduces a new method to establish a direct correlation between biologically related physical parameters (i.e., stopping and damaging cross sections, respectively) for an Auger-electron emitting radionuclide decaying within a target molecule (e.g., DNA), so as to evaluate the efficacy of the radionuclide at the molecular level. These parameters can be applied to the dosimetry of Auger electrons and the quantification of their biological effects, which are the main criteria to assess the therapeutic efficacy of Auger-electron emitting radionuclides. Methods: Absorbed dose and stopping cross section for the Auger electrons of 5–18 eV emitted by{sup 125}I within DNA were determined by developing a nanodosimetric model. The molecular damages induced by these Auger electrons were investigated by measuring damaging cross section, including that for the formation of DNA single- and double-strand breaks. Nanoscale films of pure plasmid DNA were prepared via the freeze-drying technique and subsequently irradiated with low-energy electrons at various fluences. The damaging cross sections were determined by employing a molecular survival model to the measured exposure–response curves for induction of DNA strand breaks. Results: For a single decay of{sup 125}I within DNA, the Auger electrons of 5–18 eV deposit the energies of 12.1 and 9.1 eV within a 4.2-nm{sup 3} volume of a hydrated or dry DNA, which results in the absorbed doses of 270 and 210 kGy, respectively. DNA bases have a major contribution to the deposited energies. Ten-electronvolt and high linear energy transfer 100-eV electrons have a similar cross section for the formation of DNA double-strand break, while 100-eV electrons are twice as efficient as 10 eV in the induction of single-strand break. Conclusions: Ultra-low-energy electrons (<18 eV) substantially contribute to the absorbed dose and to the molecular damage from Auger-electron emitting radionuclides; hence, they should be considered in the dosimetry calculation of such radionuclides. Moreover, absorbed dose is not an appropriate physical parameter for nanodosimetry. Instead, stopping cross section, which describes the probability of energy deposition in a target molecule can be an appropriate nanodosimetric parameter. The stopping cross section is correlated with a damaging cross section (e.g., cross section for the double-strand break formation) to quantify the number of each specific lesion in a target molecule for each nuclear decay of a single Auger-electron emitting radionuclide.

63 RADIATION, THERMAL, AND OTHER ENVIRON. POLLUTAN↗
DOE OSTI2014

SU-E-T-89: Comprehensive Quality Assurance Phantom for the Small Animal Radiation Research Platform

Purpose: Use of Small Animal Radiation Research Platform (SARRP) systems for conducting state-of-the-art image guided radiotherapy (IGRT) research on small animals has become more common over the past years. The purpose of this work is to develop and test the suitability and performance of a comprehensive quality assurance (QA) phantom for the SARRP. Methods: A QA phantom was developed for carrying out daily, monthly and annual QA tasks including imaging, dosimetry and treatment planning system (TPS) performance evaluation of the SARRP. The QA phantom consists of nine (60×60×5 mm3) KV-energy tissue equivalent solid water slabs that can be employed for annual dosimetry QA with film. Three of the top slabs are replaceable with ones incorporating Mosfets or OSLDs arranged in a quincunx pattern, or a slab drilled to accommodate an ion chamber insert. These top slabs are designed to facilitate routine daily and monthly QA tasks such as output constancy, isocenter congruency test, treatment planning system (TPS) QA, etc. One slab is designed with inserts for image QA. A prototype of the phantom was applied to test the performance of the imaging, planning and treatment delivery systems. Results: Output constancy test results showed daily variations within 3%. For isocenter congruency test, the phantom could be used to detect 0.3 mm deviations of the CBCT isocenter from the radiation isocenter. Using the Mosfet in phantom as target, the difference between TPS calculations and measurements was within 5%. Image-quality parameters could also be assessed in terms of geometric accuracy, CT number accuracy, linearity, noise and image uniformity, etc. Conclusion: The developed phantom can be employed as a simple tool for comprehensive performance evaluation of the SARRP. The study provides a reference for development of a comprehensive quality assurance program for the SARRP, with proposed tolerances and frequency of required tests.

07 ISOTOPE AND RADIATION SOURCES↗
DOE OSTI2014

SU-E-T-230: Measurement of Proton-Activated Positron Emission with PRESAGE 3-D Dosimeters

Purpose: Measurement of positron emission following proton beam irradiation of a target has been studied as a method of in-vivo dosimetry. Relative dosimetry studies between a phantom and treatment plan are susceptible to range uncertainties from material heterogeneities and setup error. By using the radiochromic polyurethane dosimeter PRESAGE, we can correlate the proton dose distribution to the PET activity measurement within a single detector. The PRESAGE formulation used was developed for high-LET proton radiotherapy, has similar density and RLSP to tissue, and consists of a greater carbon component, which gives it a higher positron signal than many other 3D detectors. Methods: Three cylindrical PRESAGE dosimeters were irradiated semi-uniformly to 500 cGy with 180- MeV protons. The beam was directed along the dosimeter axis and delivered a 2-cm SOBP at the center of the dosimeter. The dosimeters were rushed to a nearby PET/CT where imaging began within 15 minutes, less than a single half-life of 11C. A 3-hr measurement captured the full activation decay. Afterwards, the dose profiles were measured by optical-CT. A direct comparison between the measured dose and the positron emission was performed using CERR software. Results: The correlations between dose distributions and PET activity were consistent with previous studies in that the proximal region of the SOBP displayed the highest activity. The spatial distributions between the dose and activity were similar. Along the central axis of the beam, we found a shift in the distal 80% of 1 cm. The lateral profile showed good agreement between dose and activity. PET imaging times between 30-min and 3-hrs showed <5% discrepancy. Conclusion: PRESAGE dosimeters offer a strong and unique potential to accurately correlate dosimetric and PET activation information. Implementation in an anthropomorphic phantom could be used to study representative treatment plans. NIH grant 5R01CA100835.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2014

SU-E-T-358: Monte Carlo Dose Calculation of Small Field Electron Beams

Purpose: Dynamic radiotherapy involving electron beams such as Dynamic Electron Arc Radiotherapy (DEAR) requires accurate dose modelling of small field sizes, similar to the requirement of IMRT field on the small photon field. The current commercial electron Monte Carlo algorithms such as eMC v11 in Eclipse were developed for standard field sizes and do not support the planning of dynamic therapy yet. The purpose of this study is to develop a method to accurately model small field electron beam dosimetry using Monte Carlo simulations. Methods: Comparison between eMC, phantom measurements (diode), and Monte Carlo (MC) simulations (BEAMnrc/DOSYZnrc) were performed for a Varian TrueBeam linac. MC simulations utilized Varian TrueBeam phase space files which had been validated in another study. Static single small field was assessed by comparing dose distributions in water for a 16 MeV beam for circular (2 cm diameter) and rectangular (1×10 cm{sup 2}) cut-out. MC was performed with a resolution of 2.5×2.5×2 mm{sup 2} and statistical uncertainty < 4%. The dose distribution was averaged over adjacent bins to improve precision. Depth dose and orthogonal profiles were evaluated. Results: Small field PDDs differ from those with standard cones. For both circular and rectangular cutouts, the difference in range R8 0-R1 0 is less than 2 mm and in dose within 2%. For the orthogonal profiles, field size and penumbra differences were within 1 mm at depth of maximum dose. The eMC displayed a distinctive “step” in the out-field dose profile in disagreement with both measurement and MC results and needs further investigation. Conclusion: MC was able to characterize the small field dosimetry with good agreement with the measurement data, and thus offers the opportunity for treatment planning of dynamic radiotherapy. Analyses for all other electron energies and cut-out sizes are under way and results will be included in the presentation.

07 ISOTOPE AND RADIATION SOURCES↗
DOE OSTI2014

SU-E-T-402: Y-90 Microspheres (SIR Spheres) for Treatment of Liver Metastasis : Technique

Purpose: The purpose of this presentation is to discuss the radiation safety and dosimetric technique used for the therapeutic procedure using Y-90 microspheres through intra -arterial administration on patients with liver metastasis Methods: The radiation dosimetry, technique and safety aspects of 14 patients with primary and metastatic liver cancer, treated with Y-90 microsphere (SIR spheres) are discussed. The liver and tumor volumes were determined using the CT and MR scans . The images were imported into the treatment planning system and the liver and tumor volumes and the volume of the liver affected were outlined and the volume calculation was performed using the software. The lung shunt fraction (LSF) and tumor to liver uptake ratio (TLR) were determined using the nuclear medicine SPECT imaging with Tc-99m MAA. The absorbed dose to the target volume in liver was calculated using the following equation:Dose ? (Gy) = C x E? x 5.92 x 10-6 (Gy/s) x T(1/2)(days) x 1.44 x 8.64 x 104 (s) The distribution of activity in the tumor bed was confirmed by post Y-90 administration imaging using the Bremsstrahlung peak at 30% window. The patient and the procedure room were surveyed and radiation safety instructions were given to the patient Results: The tumor volume ranged from 77 cc to 700 cc, tumor to liver uptake ranged from 3 to 12. The lung shunt fraction varied from 1.08% to 9.0%. The activity administered ranged from 1.0GBq to 2.5 GBq, . The radiation survey in contact with the patient ranged from 1.8 mR/hr to 2.5 mR/hr and reading at 1 meter was less than 0.2 mR/hr Conclusion: The technique for radiation dosimetry and radiation safety for Y-90 microsphere therapy is established. The post treatment imaging helped to confirm the distribution of Y-90 microspheres inside the tumor bed.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2014

SU-E-T-633: Dose Differences in Lung Cancer SBRT: The Influences of MLC Width

Purpose: The aim is to compare the plan dose distribution of lung SBRT with MLCs in different width. Methods: Cases with phase INSCLC were enrolled. 9 cases were undergone 4D-CT scanning in the supine position with both arms raised. 3D-CT images without IV contrast were afterwards acquired with 3mm thickness and used for dose calculations. ITV was generated by using the inspiration and expiration images. The ITV can be expanded by geometric set-up uncertainty (5 mm) to generate the PTV. All chest normal tissues including chest wall were contoured by doctors. A total dose of 55 Gy will be given in 5 fractions within 10–14 days with an inter fraction interval of 2–3 days. Guided by the RTOG trial 3502 protocol, 11–13 non-coplanar fields with 6MV photon were arranged. Three types of MLCs with width of 3mm, 5mm and 10mm at isocenter position, were used separately to generate a CRT plan for each case. Monte Carlo algorithm was applied to dose calculation. All plans were adjusted as possible to meet the dose constraints. Dose-volume parameters from plans as followed were compared and analysized: PTV V55Gy, COMPTV D70% (70% of normalization dose), volume A (body minus PTV), and R100% and R50% (the ratio of x% of prescription dose isoline volume to PTV volume). Results: MLCs, 3mm and 5mm wide, played the identical roles on dosimetry of the plans, excluding the parameter volume A (p<0.05). On the contrary, MLC with width of 10mm was significantly inferior to the other two types on most parameters (p<0.05). For R50%, all types contributed equally (p>0.05). Conclusion: For lung cancer SBRT, MLC width had influence to dosimetry, especially in irradiation area. Small size MLC, e.g. 3mm and 5mm, are helpful to generate a high quality treatment plan, which could meet the strict criteria for targets and OAR.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2014

SU-F-19A-05: Experimental and Monte Carlo Characterization of the 1 Cm CivaString 103Pd Brachytherapy Source

Purpose: To determine the in-air azimuthal anisotropy and in-water dose distribution for the 1 cm length of the CivaString {sup 103}Pd brachytherapy source through measurements and Monte Carlo (MC) simulations. American Association of Physicists in Medicine Task Group No. 43 (TG-43) dosimetry parameters were also determined for this source. Methods: The in-air azimuthal anisotropy of the source was measured with a NaI scintillation detector and simulated with the MCNP5 radiation transport code. Measured and simulated results were normalized to their respective mean values and compared. The TG-43 dose-rate constant, line-source radial dose function, and 2D anisotropy function for this source were determined from LiF:Mg,Ti thermoluminescent dosimeter (TLD) measurements and MC simulations. The impact of {sup 103}Pd well-loading variability on the in-water dose distribution was investigated using MC simulations by comparing the dose distribution for a source model with four wells of equal strength to that for a source model with strengths increased by 1% for two of the four wells. Results: NaI scintillation detector measurements and MC simulations of the in-air azimuthal anisotropy showed that ≥95% of the normalized data were within 1.2% of the mean value. TLD measurements and MC simulations of the TG-43 dose-rate constant, line-source radial dose function, and 2D anisotropy function agreed to within the experimental TLD uncertainties (k=2). MC simulations showed that a 1% variability in {sup 103}Pd well-loading resulted in changes of <0.1%, <0.1%, and <0.3% in the TG-43 dose-rate constant, radial dose distribution, and polar dose distribution, respectively. Conclusion: The CivaString source has a high degree of azimuthal symmetry as indicated by the NaI scintillation detector measurements and MC simulations of the in-air azimuthal anisotropy. TG-43 dosimetry parameters for this source were determined from TLD measurements and MC simulations. {sup 103}Pd well-loading variability results in minimal variations in the in-water dose distribution according to MC simulations. This work was partially supported by CivaTech Oncology, Inc. through an educational grant for Joshua Reed, John Micka, Wesley Culberson, and Larry DeWerd and through research support for Mark Rivard.

07 ISOTOPE AND RADIATION SOURCES↗
DOE OSTI2014

TU-F-BRE-01: A High Resolution Micro Fiber Scintillator Detector Optimized for SRS and SBRT in Vivo Real Time Treatment Verification

Purpose: We have built a high resolution real time scintillating fiber detector prototype to determine in real time the accuracy of stereotactic radiosurgery (SRS) and stereotactic body radiotherapy (SBRT) treatments when only a fraction of the planned dose was delivered. The motivation of this work is to enhance dose delivery accuracy and to achieve error free radiosurgery. Methods: A high density array of scintillating fibers and a high speed photo detectors array were integrated to implement a high resolution real time dosimeter that can sample with high resolution pulsed SRS and SBRT beams cross sections. The high efficiency of the developed system allows to read each linac pulse in real time and to compute the accumulated dose and dose errors when only a fraction of the beam was delivered. The fibers are highly packed in a substrate that is directly coupled to two 128 pixel arrays with a pitch matching the fiber spacing to achieve accurate spatial localization. The small cross section of the fiber array allows stacking multiple fiber arrays to measure independent angular profiles that are digitally processed in parallel for real time dosimetry. Results: We implemented a high density array detector prototype with a pitch of 0.5 mm, readout speed of 1.2 msec, and a response time of 0.5 usec. The fast reading speed has the capability to determining the dose in flattening free filter beams. The detector can be installed in transmission mode at the output port of a micro-MLC. Treatment deviations smaller than 3% are detected when less than 1/100 of the planned dose was delivered. Conclusions: We built a prototype of a high resolution fiber scintillator array detector for SRS and SBRT in vivo dosimetry. Results show that the developed detector has the potential to assure error free SRS and SBRT treatments.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2014

WE-A-17A-11: Implanted Brachytherapy Seed Movement Due to Transrectal Ultrasound Probe-Induced Prostate Deformation

Purpose: To characterize the movement of implanted brachytherapy seeds due to transrectal ultrasound probe-induced prostate deformation and to estimate the effects on prostate dosimetry. Methods: Implanted probe-in and probe-removed seed distributions were reconstructed for 10 patients using C-arm fluoroscopy imaging. The prostate was delineated on ultrasound and registered to the fluoroscopy seeds using a visible subset of seeds and residual needle tracks. A linear tensor and shearing model correlated the seed movement with position. The seed movement model was used to infer the underlying prostate deformation and to simulate the prostate contour without probe compression. Changes in prostate and surrogate urethra dosimetry were calculated. Results: Seed movement patterns reflecting elastic decompression, lateral shearing, and rectal bending were observed. Elastic decompression was characterized by anterior-posterior expansion and superior-inferior and lateral contractions. For lateral shearing, anterior movement up to 6 mm was observed for extraprostatic seeds in the lateral peripheral region. The average intra-prostatic seed movement was 1.3 mm, and the residual after linear modeling was 0.6 mm. Prostate D90 increased by 4 Gy on average (8 Gy max) and was correlated with elastic decompression. For selected patients, lateral shearing resulted in differential change in D90 of 7 Gy between anterior and posterior quadrants, and increase in whole prostate D90 of 4 Gy. Urethra D10 increased by 4 Gy. Conclusion: Seed movement upon probe removal was characterized. The proposed model captured the linear correlation between seed movement and position. Whole prostate dose coverage increased slightly, due to the small but systematic seed movement associated with elastic decompression. Lateral shearing movement increased dose coverage in the anterior-lateral region, at the expense of the posterior-lateral region. The effect on whole prostate D90 was smaller due to the subset of peripheral seeds involved, but lateral shearing movement can have greater consequences for local dose coverage.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2014

TH-C-12A-02: Comparison of Two RapidArc Delivery Strategies in Stereotactic Body Radiotherapy of Stage I and II Peripheral Lung Tumors with Unflattened Beams

Purpose: The full arcs strategy used in SBRT with RapidArc and unflattened (FFF) beams in large and heterogeneous peripheral non-smallcell lung cancer (NSCLC) appears to be suboptimal as it increases the disadvantageous dose to the contralateral lung, which potentially increases the toxicity to surrounding tissues. In this study, we investigated, for the first time, the dose delivery strategies using partial arcs (PA) and the fully rotational arcs with avoidance sectors (FAAS) for SBRT with FFF beams in peripheral NSCLC patients. Methods: Eighteen patients with NSCLC (stage I and II) were selected for this study. Nine patients with a GTV <= 10cc were designated as the small tumor group. The remaining nine patients with a GTV between 10 cc and 44 cc were assigned to the large tumor group. The treatment plans were generated in eighteen patients using PA and FAAS, respectively, and delivered with a Varian TrueBeam Linac. Dosimetry of the target and organs at risk (OAR), total MU, out-of-field dose, and delivery time were analyzed. Delta4 and Portal dosimetry were employed to evaluate the delivery accuracy. Results: or the small tumor group, the FAAS plans significantly achieved a better conformity index, the lower total MU and out-of-field dose, a shorter treatment time, and the reduced doses to cord, heart, and lung (p < 0.05). But the target doses were slightly higher than that delivered by PA plans. For the large tumor group, the PA plans significantly attained a better conformity index and a shorter treatment time (p < 0.05). Furthermore, all plans achieved a high pass rate, with all the gamma indices greater than 97% at the Γ{sub 3mm,} {sub 3%} threshold. Conclusion: This study suggests that FAAS strategy is more beneficial for small tumor patients undergoing lung SBRT with FFF beams. However, for large tumor patients, PA strategy is recommended. NIH/NIGMS grant U54 GM104944, Lincy Endowed Assistant Professorship.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2015

Investigating the accuracy of microstereotactic-body-radiotherapy utilizing anatomically accurate 3D printed rodent-morphic dosimeters

Purpose: Sophisticated small animal irradiators, incorporating cone-beam-CT image-guidance, have recently been developed which enable exploration of the efficacy of advanced radiation treatments in the preclinical setting. Microstereotactic-body-radiation-therapy (microSBRT) is one technique of interest, utilizing field sizes in the range of 1–15 mm. Verification of the accuracy of microSBRT treatment delivery is challenging due to the lack of available methods to comprehensively measure dose distributions in representative phantoms with sufficiently high spatial resolution and in 3 dimensions (3D). This work introduces a potential solution in the form of anatomically accurate rodent-morphic 3D dosimeters compatible with ultrahigh resolution (0.3 mm{sup 3}) optical computed tomography (optical-CT) dose read-out. Methods: Rodent-morphic dosimeters were produced by 3D-printing molds of rodent anatomy directly from contours defined on x-ray CT data sets of rats and mice, and using these molds to create tissue-equivalent radiochromic 3D dosimeters from Presage. Anatomically accurate spines were incorporated into some dosimeters, by first 3D printing the spine mold, then forming a high-Z bone equivalent spine insert. This spine insert was then set inside the tissue equivalent body mold. The high-Z spinal insert enabled representative cone-beam CT IGRT targeting. On irradiation, a linear radiochromic change in optical-density occurs in the dosimeter, which is proportional to absorbed dose, and was read out using optical-CT in high-resolution (0.5 mm isotropic voxels). Optical-CT data were converted to absolute dose in two ways: (i) using a calibration curve derived from other Presage dosimeters from the same batch, and (ii) by independent measurement of calibrated dose at a point using a novel detector comprised of a yttrium oxide based nanocrystalline scintillator, with a submillimeter active length. A microSBRT spinal treatment was delivered consisting of a 180° continuous arc at 225 kVp with a 20 × 10 mm field size. Dose response was evaluated using both the Presage/optical-CT 3D dosimetry system described above, and independent verification in select planes using EBT2 radiochromic film placed inside rodent-morphic dosimeters that had been sectioned in half. Results: Rodent-morphic 3D dosimeters were successfully produced from Presage radiochromic material by utilizing 3D printed molds of rat CT contours. The dosimeters were found to be compatible with optical-CT dose readout in high-resolution 3D (0.5 mm isotropic voxels) with minimal artifacts or noise. Cone-beam CT image guidance was possible with these dosimeters due to sufficient contrast between high-Z spinal inserts and tissue equivalent Presage material (CNR ∼10 on CBCT images). Dose at isocenter measured with optical-CT was found to agree with nanoscintillator measurement to within 2.8%. Maximum dose in line profiles taken through Presage and film dose slices agreed within 3%, with FWHM measurements through each profile found to agree within 2%. Conclusions: This work demonstrates the feasibility of using 3D printing technology to make anatomically accurate Presage rodent-morphic dosimeters incorporating spinal-mimicking inserts. High quality optical-CT 3D dosimetry is feasible on these dosimeters, despite the irregular surfaces and implanted inserts. The ability to measure dose distributions in anatomically accurate phantoms represents a powerful useful additional verification tool for preclinical microSBRT.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2015

Quantitative single-particle digital autoradiography with α-particle emitters for targeted radionuclide therapy using the iQID camera

Purpose: Alpha-emitting radionuclides exhibit a potential advantage for cancer treatments because they release large amounts of ionizing energy over a few cell diameters (50–80 μm), causing localized, irreparable double-strand DNA breaks that lead to cell death. Radioimmunotherapy (RIT) approaches using monoclonal antibodies labeled with α emitters may thus inactivate targeted cells with minimal radiation damage to surrounding tissues. Tools are needed to visualize and quantify the radioactivity distribution and absorbed doses to targeted and nontargeted cells for accurate dosimetry of all treatment regimens utilizing α particles, including RIT and others (e.g., Ra-223), especially for organs and tumors with heterogeneous radionuclide distributions. The aim of this study was to evaluate and characterize a novel single-particle digital autoradiography imager, the ionizing-radiation quantum imaging detector (iQID) camera, for use in α-RIT experiments. Methods: The iQID camera is a scintillator-based radiation detection system that images and identifies charged-particle and gamma-ray/x-ray emissions spatially and temporally on an event-by-event basis. It employs CCD-CMOS cameras and high-performance computing hardware for real-time imaging and activity quantification of tissue sections, approaching cellular resolutions. In this work, the authors evaluated its characteristics for α-particle imaging, including measurements of intrinsic detector spatial resolutions and background count rates at various detector configurations and quantification of activity distributions. The technique was assessed for quantitative imaging of astatine-211 ({sup 211}At) activity distributions in cryosections of murine and canine tissue samples. Results: The highest spatial resolution was measured at ∼20 μm full width at half maximum and the α-particle background was measured at a rate as low as (2.6 ± 0.5) × 10{sup −4} cpm/cm{sup 2} (40 mm diameter detector area). Simultaneous imaging of multiple tissue sections was performed using a large-area iQID configuration (ø 11.5 cm). Estimation of the {sup 211}At activity distribution was demonstrated at mBq/μg-levels. Conclusions: Single-particle digital autoradiography of α emitters has advantages over traditional film-based autoradiographic techniques that use phosphor screens, in terms of spatial resolution, sensitivity, and activity quantification capability. The system features and characterization results presented in this study show that the iQID is a promising technology for microdosimetry, because it provides necessary information for interpreting alpha-RIT outcomes and for predicting the therapeutic efficacy of cell-targeted approaches using α emitters.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗