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At least 1,225 records · Page 68
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Dry cask radiation shielding validation and estimation of cask surface dose rate with MAVRIC during long-term storage

The dry storage cask became a semi-permanent solution for spent nuclear fuel since no permanent solution has been finalized over the past three decades. Considering the difficulty of deep geological repository projects in many aspects, prolonging the service life of dry casks longer than a few decades has become an option for spent nuclear fuel storage. It must be ensured that dry cask safety objectives, including radiation shielding, criticality safety, structure health, decay heat removal, and containment be fulfilled during the prolonged service life. This paper presents numerical modeling results of the radiation dose rate distribution on a TN-32 cask surface aged up to 300 years. The numerical modeling method was validated with measurement data, and the difference between the calculated results and measurement data in the total dose rate is 7%. The detailed radiation distribution variations over cask surfaces along the axial and radial directions for 300 years of storage were obtained, and their azimuthal angular dependence was established. The maximum total dose rate over the cask surfaces is less than 10 mrem/hour (9.258 ± 0.212 mrem/hour) after 40 years, and this outcome fulfills all dose rate requirements from 10 CFR 71.47(b). After 300 years of storage, the average total dose rates on the side surface and top surface are 0.150 ± 0.007mremmrem/hour and 0.057 ± 0.003mremmrem/hour, respectively, while the maxima are 0.601 ± 0.014 mrem/hour and 0.112 ± 0.006 mrem/hour, respectively. The variations in the fuel gamma ray, structure gamma ray, neutron and secondary gamma-ray contributions to the total dose rate are presented and analyzed in this work. The neutron and gamma-ray dose rate contributions by energy group are presented and analyzed at the cask top, mid-plane, and bottom at the selected storage times.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2018

Change of cell growth and mitochondrial membrane polarization in the progeny of cells surviving low-dose high-LET irradiation from Ra-226

Highlights: • Chronic low-dose high-LET α-radiation from Ra-226 is effective in inducing lethal mutations. • Decreased clonogenic survival did not occur in descendants of irradiated HaCaT survivors, and hormesis may be induced. • Mitochondrial membrane depolarization may be involved in the induction of lethal mutation. In order to test the delayed effect of radiation on the progeny of irradiated survivors, the human keratinocyte cell line HaCaT and the fish common bluegill embryonic cell line CHSE/F were exposed to low-dose high-LET α-radiation from Ra-226 or γ-rays. The clonogenic survival fraction, mitochondrial membrane polarization (MMP) and reproductive ability of the descendants of the surviving cells were measured. For progeny of irradiated HaCaT survivors, no delayed cell death occurred. On the contrary, progeny at about 47 cell doublings after Ra-226 irradiation and progeny at about 14 cell doublings after γ-irradiation showed increased clonogenic survival. However the total cell number was reduced for progeny of Ra-226-treated cells up to about 47 cell doublings after irradiation and for progeny of γ-irradiated cells up to about 28 doublings after irradiation, which means low reproductive ability had appeared. In addition, α-radiation from Ra-226 had greater impact on the MMP of the HaCaT progeny than γ-rays. MMP of progeny of Ra-226-treated cells decreased at 5 cell doublings after irradiation and increased dose-dependently at 19 cell doublings after treatment, and then decreased dose-dependently at 47 cell doublings, while there was no significant effect on MMP in progeny of γ irradiated cells. The progeny of Ra-226-irradiated CHSE/F survivors showed more serious damage than the offspring of γ-irradiated CHSE/F cells. Significant, dose-dependent delayed cell death occurred in progeny of surviving cells up to about 61 cell doublings after Ra-226 treatment, and the reproductive ability was also significantly reduced. But the MMP increased, which might be because of the increased removal of dead cells. For progeny of CHSE/F cells surviving γ-rays radiation, no significant change in clonogenic survival occurred, except for offspring of cells surviving low dose (0.1 Gy and 0.5 Gy) irradiation, which had higher survival than control up to about 28 cell doublings after irradiation. But the number of cells which were the progeny of γ-irradiated survivors decreased dose-dependently up to about 28 cell doublings after γ-irradiation.

61 RADIATION PROTECTION AND DOSIMETRY↗
DOE OSTI2012

Radiation-Induced Rib Fractures After Hypofractionated Stereotactic Body Radiation Therapy: Risk Factors and Dose-Volume Relationship

Purpose: The purpose of this study was to clarify the incidence, the clinical risk factors, and the dose-volume relationship of radiation-induced rib fracture (RIRF) after hypofractionated stereotactic body radiation therapy (SBRT). Methods and Materials: One hundred sixteen patients treated with SBRT for primary or metastatic lung cancer at our institution, with at least 6 months of follow-up and no previous overlapping radiation exposure, were included in this study. To determine the clinical risk factors associated with RIRF, correlations between the incidence of RIRF and the variables, including age, sex, diagnosis, gross tumor volume diameter, rib-tumor distance, and use of steroid administration, were analyzed. Dose-volume histogram analysis was also conducted. Regarding the maximum dose, V10, V20, V30, and V40 of the rib, and the incidences of RIRF were compared between the two groups divided by the cutoff value determined by the receiver operating characteristic curves. Results: One hundred sixteen patients and 374 ribs met the inclusion criteria. Among the 116 patients, 28 patients (46 ribs) experienced RIRF. The estimated incidence of rib fracture was 37.7% at 3 years. Limited distance from the rib to the tumor (<2.0 cm) was the only significant risk factor for RIRF (p = 0.0001). Among the dosimetric parameters used for receiver operating characteristic analysis, the maximum dose showed the highest area under the curve. The 3-year estimated risk of RIRF and the determined cutoff value were 45.8% vs. 1.4% (maximum dose, {>=}42.4 Gy or less), 51.6% vs. 2.0% (V40, {>=}0.29 cm{sup 3} or less), 45.8% vs. 2.2% (V30, {>=}1.35 cm{sup 3} or less), 42.0% vs. 8.5% (V20, {>=}3.62 cm{sup 3} or less), or 25.9% vs. 10.5% (V10, {>=}5.03 cm{sup 3} or less). Conclusions: The incidence of RIRF after hypofractionated SBRT is relatively high. The maximum dose and high-dose volume are strongly correlated with RIRF.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2013

Increased Subventricular Zone Radiation Dose Correlates With Survival in Glioblastoma Patients After Gross Total Resection

Purpose: Neural progenitor cells in the subventricular zone (SVZ) have a controversial role in glioblastoma multiforme (GBM) as potential tumor-initiating cells. The purpose of this study was to examine the relationship between radiation dose to the SVZ and survival in GBM patients. Methods and Materials: The study included 116 patients with primary GBM treated at the Johns Hopkins Hospital between 2006 and 2009. All patients underwent surgical resection followed by adjuvant radiation therapy with intensity modulated radiation therapy (60 Gy/30 fractions) and concomitant temozolomide. Ipsilateral, contralateral, and bilateral SVZs were contoured on treatment plans by use of coregistered magnetic resonance imaging and computed tomography. Multivariate Cox regression was used to examine the relationship between mean SVZ dose and progression-free survival (PFS), as well as overall survival (OS). Age, Karnofsky Performance Status score, and extent of resection were used as covariates. The median age was 58 years (range, 29-80 years). Results: Of the patients, 12% underwent biopsy, 53% had subtotal resection (STR), and 35% had gross total resection (GTR). The Karnofsky Performance Status score was less than 90 in 54 patients and was 90 or greater in 62 patients. The median ipsilateral, contralateral, and bilateral mean SVZ doses were 48.7 Gy, 34.4 Gy, and 41.5 Gy, respectively. Among patients who underwent GTR, a mean ipsilateral SVZ dose of 40 Gy or greater was associated with a significantly improved PFS compared with patients who received less than 40 Gy (15.1 months vs 10.3 months; P=.028; hazard ratio, 0.385 [95% confidence interval, 0.165-0.901]) but not in patients undergoing STR or biopsy. The subgroup of GTR patients who received an ipsilateral dose of 40 Gy or greater also had a significantly improved OS (17.5 months vs 15.6 months; P=.027; hazard ratio, 0.385 [95% confidence interval, 0.165-0.895]). No association was found between SVZ radiation dose and PFS and OS among patients who underwent STR or biopsy. Conclusion: A mean radiation dose of 40 Gy or greater to the ipsilateral SVZ was associated with a significantly improved PFS and OS in patients with GBM after GTR.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2013

Radiation Dose and Subsequent Risk for Stomach Cancer in Long-term Survivors of Cervical Cancer

Purpose: To assess the dose–response relationship for stomach cancer after radiation therapy for cervical cancer. Methods and Materials: We conducted a nested, matched case–control study of 201 cases and 378 controls among 53,547 5-year survivors of cervical cancer diagnosed from 1943 to 1995, from 5 international, population-based cancer registries. We estimated individual radiation doses to the site of the stomach cancer for all cases and to corresponding sites for the matched controls (overall mean stomach tumor dose, 2.56 Gy, range 0.03-46.1 and after parallel opposed pelvic fields, 1.63 Gy, range 0.12-6.3). Results: More than 90% of women received radiation therapy, mostly with external beam therapy in combination with brachytherapy. Stomach cancer risk was nonsignificantly increased (odds ratio 1.27-2.28) for women receiving between 0.5 and 4.9 Gy to the stomach cancer site and significantly increased at doses ≥5 Gy (odds ratio 4.20, 95% confidence interval 1.41-13.4, P{sub trend}=.047) compared with nonirradiated women. A highly significant radiation dose–response relationship was evident when analyses were restricted to the 131 cases (251 controls) whose stomach cancer was located in the middle and lower portions of the stomach (P{sub trend}=.003), whereas there was no indication of increasing risk with increasing dose for 30 cases (57 controls) whose cancer was located in the upper stomach (P{sub trend}=.23). Conclusions: Our findings show for the first time a significant linear dose–response relationship for risk of stomach cancer in long-term survivors of cervical cancer.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2013

Dosimetric Comparison of 3-Dimensional Planning Techniques Using an Intravaginal Multichannel Balloon Applicator for High-Dose-Rate Gynecologic Brachytherapy

Purpose: To study the dosimetric differences of various channel combinations of the Capri vaginal applicator. Methods and Materials: The Capri consists of a single central channel (R1), an inner array of 6 channels (R2), and an outer array of 6 channels (R3). Three-dimensional plans were simulated for 6 channel arrangements (R1, R2, R12, R13, R23, and R123). Treatment plans were optimized to the applicator surface or 5-mm depth while minimizing dose to organs at risk (OARs: bladder, rectum, sigmoid, and urethra). The clinical target volume (CTV) was defined as a 5-mm circumferential shell extending 4 cm in length around the applicator. Clinical target volume coverage (D{sub mean}, D{sub 90}, V{sub 100}, and V{sub 150}) and OAR doses (D{sub 0.1} {sub cm{sup 3}}, D{sub 1} {sub cm{sup 3}}, D{sub 2} {sub cm{sup 3}}, and D{sub mean}) were compared. A comparison between the Capri (R123) and a conventional single-channel applicator was also done. Statistical significance (P value <.05) was evaluated with a 2-tailed t test. Results: When prescribing to 5-mm depth, CTV coverage using all 13 channels (R123) versus a single channel (R1) was similar; however, when prescribing to the surface there were differences (P<.0001) in all CTV metrics except for the V{sub 150}. The R1 plans had higher doses to all OARs compared with R123 plans (P<.007). Doses to OARs were not significantly different between R23 and R123 plans (P=.05-.95), and CTV coverage differences were on the order of 1%. Capri R123 plans provided slightly lower CTV D{sub 90} and D{sub mean} but equivalent OAR doses with smaller standard deviations compared with conventional cylinder plans for both prescriptions. Conclusions: The Capri multichannel applicator provides equivalent target coverage at 5-mm depth, with significantly reduced dose to OARs relative to using a single channel. Optimal plans can be achieved using R12 (lowest V{sub 150}) or R123 or R23 (lowest OAR doses)

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2013

High-Dose and Extended-Field Intensity Modulated Radiation Therapy for Early-Stage NK/T-Cell Lymphoma of Waldeyer's Ring: Dosimetric Analysis and Clinical Outcome

Purpose: To assess the dosimetric benefit, treatment outcome, and toxicity of high-dose and extended-field intensity modulated radiation therapy (IMRT) in patients with early-stage NK/T-cell lymphoma of Waldeyer's ring (WR-NKTCL). Methods and Materials: Thirty patients with early-stage WR-NKTCL who received extended-field IMRT were retrospectively reviewed. The prescribed dose was 50 Gy to the primary involved regions and positive cervical lymph nodes (planning target volume requiring radical irradiation [PTV{sub 50}]) and 40 Gy to the negative cervical nodes (PTV{sub 40}). Dosimetric parameters for the target volume and critical normal structures were evaluated. Locoregional control (LRC), overall survival (OS), and progression-free survival (PFS) were calculated using the Kaplan-Meier method. Results: The median mean doses to the PTV{sub 50} and PTV{sub 40} were 53.2 Gy and 43.0 Gy, respectively. Only 1.4% of the PTV{sub 50} and 0.9% of the PTV{sub 40} received less than 95% of the prescribed dose, indicating excellent target coverage. The average mean doses to the left and right parotid glands were 27.7 and 28.4 Gy, respectively. The 2-year OS, PFS, and LRC rates were 71.2%, 57.4%, and 87.8%. Most acute toxicities were grade 1 to 2, except for grade ≥3 dysphagia and mucositis. The most common late toxicity was grade 1-2 xerostomia, and no patient developed any ≥grade 3 late toxicities. A correlation between the mean dose to the parotid glands and the degree of late xerostomia was observed. Conclusions: IMRT achieves excellent target coverage and dose conformity, as well as favorable survival and locoregional control rates with acceptable toxicities in patients with WR-NKTCL.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2015

Is Intermediate Radiation Dose Escalation With Concurrent Chemotherapy for Stage III Non–Small-Cell Lung Cancer Beneficial? A Multi-Institutional Propensity Score Matched Analysis

Purpose: The clinical benefits and risks of dose escalation (DE) for stage III non–small-cell lung cancer (NSCLC) remain uncertain despite the results from Radiation Therapy Oncology Group (RTOG) protocol 0617. There is significant heterogeneity of practice, with many clinicians prescribing intermediate dose levels between the 0617 study arms of 60 and 74 Gy. This study investigated whether this strategy is associated with any survival benefits/risks by analyzing a large multi-institutional database. Methods and Materials: An individual patient database of stage III NSCLC patients treated with radical intent concurrent chemoradiation therapy was created (13 institutions, n=1274 patients). Patients were divided into 2 groups based on tumor Biological Effective Dose at 10 Gy (BED 10): those receiving standard dose (SD; n=552), consisting of 72Gy ≤ BED 10 ≤ 76.8 Gy (eg 60-64 Gy/30-32 fractions [fr]), and those receiving intermediate dose (ID; n=497), consisting of 76.8Gy < BED 10 < 100.8 Gy (eg >64 Gy/32 fr and <74 Gy/37 fr), with lower-dose patients (n=225) excluded from consideration. Patients were then matched using propensity scores, leading to 2 matched groups of 196 patients. Outcomes were compared using various statistics including interquartile range (IQR), Kaplan-Meier curves, and adjusted Cox regression analysis. Results: Matched groups were found to be balanced except for N stage (more N3 disease in SD), median treatment year (SD in 2003; ID in 2007), platinum and taxane chemotherapy (SD in 28%; ID in 39%), and median follow-up (SD were 89 months; ID were 40 months). Median dose fractionation was 60 Gy/30 fr in SD (BED 10 IQR: 72.0-75.5 Gy) and 66 Gy/33 fr (BED 10 IQR: 78.6-79.2 Gy) in ID. Survival curves for SD and ID matched cohorts were statistically similar (P=.27); however, a nonstatistically significant trend toward better survival for ID was observed after 15 months (median survival SD: 19.3 months; ID: 21.0 months). There was an increase in grades III to V lung toxicity associated with ID (13.0% vs 4.9%, respectively). Conclusions: No significant overall survival benefits were found with intermediate DE; however, more grade III or greater lung toxicity was observed. The separation of survival curves after 15 months of follow-up suggests that a small overall survival improvement associated with intermediate DE cannot be excluded.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2015

Increasing Radiation Therapy Dose Is Associated With Improved Survival in Patients Undergoing Stereotactic Body Radiation Therapy for Stage I Non–Small-Cell Lung Cancer

Purpose: To determine the comparative effectiveness of different stereotactic body radiation therapy (SBRT) dosing regimens for early-stage non–small-cell lung cancer, using a large national database, focusing on the relative impact of dose as a function of tumor stage. Methods and Materials: The study included patients in the National Cancer Database from 2003 to 2006 with T1-T2N0M0 inoperable lung cancer (n=498). The biologically effective dose (BED) was calculated according to the linear quadratic formula using an α/β ratio of 10. High versus lower-dose (HD vs LD) SBRT was defined as a calculated BED above or below 150 Gy. Overall survival was estimated using Kaplan-Meier methods and Cox proportional hazard regression. Results: The 5 most common dose fractionation schemes (percentage of cohort) used were 20 Gy × 3 (34%), 12 Gy × 4 (16%), 18 Gy × 3 (10%), 15 Gy × 3 (10%), and 16 Gy × 3 (4%). The median calculated BED was 150 Gy (interquartile range 106-166 Gy). The 3-year overall survival (OS) for patients who received HD versus LD was 55% versus 46% (log–rank P=.03). On subset analysis of the T1 cohort there was no association between calculated BED and 3-year OS (61% vs 60% with HD vs LD, P=.9). Among the T2 cohort, patients receiving HD experienced superior 3-year OS (37% vs 24%, P=.01). On multivariable analysis, factors independently prognostic for mortality were female gender (hazard ratio [HR] 0.76, P=.01), T2 tumor (HR 1.99, P=.0001), and HD (HR 0.68, P=.001). Conclusions: This comparative effectiveness analysis of SBRT dose for patients with stage I non–small-cell lung cancer suggests that higher doses (>150 Gy BED) are associated with a significant survival benefit in patients with T2 tumors.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2015

Reducing Dose Uncertainty for Spot-Scanning Proton Beam Therapy of Moving Tumors by Optimizing the Spot Delivery Sequence

Purpose: To develop and validate a novel delivery strategy for reducing the respiratory motion–induced dose uncertainty of spot-scanning proton therapy. Methods and Materials: The spot delivery sequence was optimized to reduce dose uncertainty. The effectiveness of the delivery sequence optimization was evaluated using measurements and patient simulation. One hundred ninety-one 2-dimensional measurements using different delivery sequences of a single-layer uniform pattern were obtained with a detector array on a 1-dimensional moving platform. Intensity modulated proton therapy plans were generated for 10 lung cancer patients, and dose uncertainties for different delivery sequences were evaluated by simulation. Results: Without delivery sequence optimization, the maximum absolute dose error can be up to 97.2% in a single measurement, whereas the optimized delivery sequence results in a maximum absolute dose error of ≤11.8%. In patient simulation, the optimized delivery sequence reduces the mean of fractional maximum absolute dose error compared with the regular delivery sequence by 3.3% to 10.6% (32.5-68.0% relative reduction) for different patients. Conclusions: Optimizing the delivery sequence can reduce dose uncertainty due to respiratory motion in spot-scanning proton therapy, assuming the 4-dimensional CT is a true representation of the patients' breathing patterns.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2016

Dose-Dependent Cortical Thinning After Partial Brain Irradiation in High-Grade Glioma

Purpose: Radiation-induced cognitive deficits may be mediated by tissue damage to cortical regions. Volumetric changes in cortex can be reliably measured using high-resolution magnetic resonance imaging (MRI). We used these methods to study the association between radiation therapy (RT) dose and change in cortical thickness in high-grade glioma (HGG) patients. Methods and Materials: We performed a voxel-wise analysis of MRI from 15 HGG patients who underwent fractionated partial brain RT. Three-dimensional MRI was acquired pre- and 1 year post RT. Cortex was parceled with well-validated segmentation software. Surgical cavities were censored. Each cortical voxel was assigned a change in cortical thickness between time points, RT dose value, and neuroanatomic label by lobe. Effects of dose, neuroanatomic location, age, and chemotherapy on cortical thickness were tested using linear mixed effects (LME) modeling. Results: Cortical atrophy was seen after 1 year post RT with greater effects at higher doses. Estimates from LME modeling showed that cortical thickness decreased by −0.0033 mm (P<.001) for every 1-Gy increase in RT dose. Temporal and limbic cortex exhibited the largest changes in cortical thickness per Gy compared to that in other regions (P<.001). Age and chemotherapy were not significantly associated with change in cortical thickness. Conclusions: We found dose-dependent thinning of the cerebral cortex, with varying neuroanatomical regional sensitivity, 1 year after fractionated partial brain RT. The magnitude of thinning parallels 1-year atrophy rates seen in neurodegenerative diseases and may contribute to cognitive decline following high-dose RT.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2016

Investigating the Implications of a Variable RBE on Proton Dose Fractionation Across a Clinical Pencil Beam Scanned Spread-Out Bragg Peak

Purpose: To investigate the clinical implications of a variable relative biological effectiveness (RBE) on proton dose fractionation. Using acute exposures, the current clinical adoption of a generic, constant cell killing RBE has been shown to underestimate the effect of the sharp increase in linear energy transfer (LET) in the distal regions of the spread-out Bragg peak (SOBP). However, experimental data for the impact of dose fractionation in such scenarios are still limited. Methods and Materials: Human fibroblasts (AG01522) at 4 key depth positions on a clinical SOBP of maximum energy 219.65 MeV were subjected to various fractionation regimens with an interfraction period of 24 hours at Proton Therapy Center in Prague, Czech Republic. Cell killing RBE variations were measured using standard clonogenic assays and were further validated using Monte Carlo simulations and parameterized using a linear quadratic formalism. Results: Significant variations in the cell killing RBE for fractionated exposures along the proton dose profile were observed. RBE increased sharply toward the distal position, corresponding to a reduction in cell sparing effectiveness of fractionated proton exposures at higher LET. The effect was more pronounced at smaller doses per fraction. Experimental survival fractions were adequately predicted using a linear quadratic formalism assuming full repair between fractions. Data were also used to validate a parameterized variable RBE model based on linear α parameter response with LET that showed considerable deviations from clinically predicted isoeffective fractionation regimens. Conclusions: The RBE-weighted absorbed dose calculated using the clinically adopted generic RBE of 1.1 significantly underestimates the biological effective dose from variable RBE, particularly in fractionation regimens with low doses per fraction. Coupled with an increase in effective range in fractionated exposures, our study provides an RBE dataset that can be used by the modeling community for the optimization of fractionated proton therapy.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2017

Clinical Implementation of a Model-Based In Vivo Dose Verification System for Stereotactic Body Radiation Therapy–Volumetric Modulated Arc Therapy Treatments Using the Electronic Portal Imaging Device

Purpose: To report findings from an in vivo dosimetry program implemented for all stereotactic body radiation therapy patients over a 31-month period and discuss the value and challenges of utilizing in vivo electronic portal imaging device (EPID) dosimetry clinically. Methods and Materials: From December 2013 to July 2016, 117 stereotactic body radiation therapy–volumetric modulated arc therapy patients (100 lung, 15 spine, and 2 liver) underwent 602 EPID-based in vivo dose verification events. A developed model-based dose reconstruction algorithm calculates the 3-dimensional dose distribution to the patient by back-projecting the primary fluence measured by the EPID during treatment. The EPID frame-averaging was optimized in June 2015. For each treatment, a 3%/3-mm γ comparison between our EPID-derived dose and the Eclipse AcurosXB–predicted dose to the planning target volume (PTV) and the ≥20% isodose volume were performed. Alert levels were defined as γ pass rates <85% (lung and liver) and <80% (spine). Investigations were carried out for all fractions exceeding the alert level and were classified as follows: EPID-related, algorithmic, patient setup, anatomic change, or unknown/unidentified errors. Results: The percentages of fractions exceeding the alert levels were 22.6% for lung before frame-average optimization and 8.0% for lung, 20.0% for spine, and 10.0% for liver after frame-average optimization. Overall, mean (± standard deviation) planning target volume γ pass rates were 90.7% ± 9.2%, 87.0% ± 9.3%, and 91.2% ± 3.4% for the lung, spine, and liver patients, respectively. Conclusions: Results from the clinical implementation of our model-based in vivo dose verification method using on-treatment EPID images is reported. The method is demonstrated to be valuable for routine clinical use for verifying delivered dose as well as for detecting errors.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2022

Spatial and temporal prediction of radiation dose rates near Fukushima Daiichi Nuclear Power Plant

In this paper, we have developed a methodology to estimate the spatiotemporal distribution of radiation air dose rates around the Fukushima Daiichi Nuclear Power Plant (FDNPP). In our exploratory data analysis, we found that (1) the temporal evolution of dose rates is composed of a log-linear decay trend and fluctuations of air dose rates that are spatially correlated among adjacent monitoring posts; and (2) the slope of the log-linear environmental decay trend can be represented as a function of the apparent initial dose rates, coordinate position, land-use type, and soil type. From these observations, we first estimated the log-linear decay trend at each location based on these predictors, using the random forest method. We then developed a modified Kalman filter coupled with a Gaussian process model to estimate the dose-rate time series at a given location and time. We applied this method to the Fukushima evacuation zone (as of March 2017), which included 17 monitoring post locations (with monitoring datasets collected between 2014 and 2018) and generated a time series of dose-rate maps. Our results show that this approach allows us to produce accurate spatial and temporal predictions of radiation dose-rate maps using limited spatiotemporal measurements.

61 RADIATION PROTECTION AND DOSIMETRY↗
DOE OSTI2016

Cone Beam Computed Tomography: The Challenges and Strategies in Its Application for Dose Accumulation

Online image guidance using cone beam computed tomography (CBCT) has greatly improved the geometric precision of radiotherapy. Changes in anatomy are common during a course of fractionated treatment, resulting in dose deviation from the planned distribution. There is increased interest in performing dose accumulation to compute the actual delivered dose and to adapt the treatment when necessary. This can be achieved by delineating the volume of interest and by generating “dose of the day” through dose computation on the CBCT. However, the image quality and the accuracy of the CT number of CBCT are deemed to be inferior to fan beam CT, which increases the uncertainty associated in this process. A review of literature was conducted to assess the reliability of and to examine strategies for overcoming the challenges in using CBCT for volume delineation and dose computation. The review demonstrates that the uncertainty varies across body sites, and different strategies have been recommended to generate comparable results to images from CT simulators. This facilitates a better understanding of the potential and the limitation of using CBCT for dose accumulation.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2012

Comparison of structural properties of pristine and gamma irradiated single-wall carbon nanotubes: Effects of medium and irradiation dose

A systematic study of the gamma irradiation effects on single wall carbon nanotube (SWCNT) structure was conducted. Nanotubes were exposed to different doses of gamma irradiation in three media. Irradiation was carried out in air, water and aqueous ammonia. Thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR), elemental analysis (EA) and Raman spectroscopy confirmed the changes in the SWCNT structure. TGA measurements showed the highest percentage of introduced groups for the SWCNTs irradiated with 100 kGy. FTIR spectroscopy provided evidence for the attachment of hydroxyl, carboxyl and nitrile functional groups to the SWCNT sidewalls. Those groups were confirmed by EA. All irradiated SWCNTs had hydroxyl and carboxyl groups irrelevant to media used for irradiation, but nitrile functional groups were only identified in SWCNTs irradiated in aqueous ammonia. Raman spectroscopy indicated that the degree of disorder in the carbon nanotube structure correlates with the irradiation dose. For the nanotubes irradiated with the dose of 100 kGy, the Raman I{sub D}/I{sub G} ratio was three times higher than for the pristine ones. Atomic force microscopy showed a 50% decrease in nanotube length at a radiation dose of 100 kGy. Scanning and transmission electron microscopies showed significant changes in the morphology and structure of gamma irradiated SWCNTs. - Highlights: Black-Right-Pointing-Pointer Gamma irradiation causes SWCNT covalent functionalization. Black-Right-Pointing-Pointer Type of covalently attached groups to SWCNT surface depends on irradiation medium. Black-Right-Pointing-Pointer The SWCNT shortening level increases with applied irradiation dose. Black-Right-Pointing-Pointer The average length of carbon nanotubes decreased by 50% at the highest dose. Black-Right-Pointing-Pointer The diameter of SWCNT bundles becomes small as irradiation dose rises.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Circumferential or sectored beam arrangements for stereotactic body radiation therapy (SBRT) of primary lung tumors: Effect on target and normal-structure dose-volume metrics

To compare 2 beam arrangements, sectored (beam entry over ipsilateral hemithorax) vs circumferential (beam entry over both ipsilateral and contralateral lungs), for static-gantry intensity-modulated radiation therapy (IMRT) and volumetric-modulated arc therapy (VMAT) delivery techniques with respect to target and organs-at-risk (OAR) dose-volume metrics, as well as treatment delivery efficiency. Data from 60 consecutive patients treated using stereotactic body radiation therapy (SBRT) for primary non–small-cell lung cancer (NSCLC) formed the basis of this study. Four treatment plans were generated per data set: IMRT/VMAT plans using sectored (-s) and circumferential (-c) configurations. The prescribed dose (PD) was 60 Gy in 5 fractions to 95% of the planning target volume (PTV) (maximum PTV dose ∼ 150% PD) for a 6-MV photon beam. Plan conformality, R{sub 50} (ratio of volume circumscribed by the 50% isodose line and the PTV), and D{sub 2} {sub cm} (D{sub max} at a distance ≥2 cm beyond the PTV) were evaluated. For lungs, mean doses (mean lung dose [MLD]) and percent V{sub 30}/V{sub 20}/V{sub 10}/V{sub 5} Gy were assessed. Spinal cord and esophagus D{sub max} and D{sub 5}/D{sub 50} were computed. Chest wall (CW) D{sub max} and absolute V{sub 30}/V{sub 20}/V{sub 10}/V{sub 5} {sub Gy} were reported. Sectored SBRT planning resulted in significant decrease in contralateral MLD and V{sub 10}/V{sub 5} {sub Gy}, as well as contralateral CW D{sub max} and V{sub 10}/V{sub 5} {sub Gy} (all p < 0.001). Nominal reductions of D{sub max} and D{sub 5}/D{sub 50} for the spinal cord with sectored planning did not reach statistical significance for static-gantry IMRT, although VMAT metrics did show a statistically significant decrease (all p < 0.001). The respective measures for esophageal doses were significantly lower with sectored planning (p < 0.001). Despite comparable dose conformality, irrespective of planning configuration, R{sub 50} significantly improved with IMRT-s/VMAT-c (p < 0.001/p = 0.008), whereas D{sub 2} {sub cm} significantly improved with VMAT-c (p < 0.001). Plan delivery efficiency improved with sectored technique (p < 0.001); mean monitor unit (MU)/cGy of PD decreased from 5.8 ± 1.9 vs 5.3 ± 1.7 (IMRT) and 2.7 ± 0.4 vs 2.4 ± 0.3 (VMAT). The sectored configuration achieves unambiguous dosimetric advantages over circumferential arrangement in terms of esophageal, contralateral CW, and contralateral lung sparing, in addition to being more efficient at delivery.

61 RADIATION PROTECTION AND DOSIMETRY↗
DOE OSTI2013

Evaluating proton stereotactic body radiotherapy to reduce chest wall dose in the treatment of lung cancer

Stereotactic body radiotherapy (SBRT) can produce excellent local control of several types of solid tumor; however, toxicity to nearby critical structures is a concern. We found previously that in SBRT for lung cancer, the chest wall (CW) volume receiving 20, 30, or 40 Gy (V{sub 20}, V{sub 30}, or V{sub 40}) was linked with the development of neuropathy. Here we sought to determine whether the dosimetric advantages of protons could produce lower CW doses than traditional photon-based SBRT. We searched an institutional database to identify patients treated with photon SBRT for lung cancer with tumors within < 2.5 cm of the CW. We found 260 cases; of these, chronic grade ≥ 2 CW pain was identified in 23 patients. We then selected 10 representative patients from this group and generated proton SBRT treatment plans, using the identical dose of 50 Gy in 4 fractions, and assessed potential differences in CW dose between the 2 plans. The proton SBRT plans reduced the CW doses at all dose levels measured. The median CW V{sub 20} was 364.0 cm{sup 3} and 160.0 cm{sup 3} (p < 0.0001), V{sub 30} was 144.6 cm{sup 3}vs 77.0 cm{sup 3} (p = 0.0012), V{sub 35} was 93.9 cm{sup 3}vs 57.9 cm{sup 3} (p = 0.005), V{sub 40} was 66.5 cm{sup 3}vs 45.4 cm{sup 3} (p = 0.0112), and mean lung dose was 5.9 Gy vs 3.8 Gy (p = 0.0001) for photons and protons, respectively. Coverage of the planning target volume (PTV) was comparable between the 2 sets of plans (96.4% for photons and 97% for protons). From a dosimetric standpoint, proton SBRT can achieve the same coverage of the PTV while significantly reducing the dose to the CW and lung relative to photon SBRT and therefore may be beneficial for the treatment of lesions closer to critical structures.

61 RADIATION PROTECTION AND DOSIMETRY↗