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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 199 records · Page 11
All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

SU-E-T-300: Dosimetric Comparision of 4D Radiation Therapy and 3D Radiation Therapy for the Liver Tumor Based On 4D Medical Image

Purpose: The purpose of this work was to determine the dosimetric benefit to normal tissues by tracking liver tumor dose in four dimensional radiation therapy (4DRT) on ten phases of four dimensional computer tomagraphy(4DCT) images. Methods: Target tracking each phase with the beam aperture for ten liver cancer patients were converted to cumulative plan and compared to the 3D plan with a merged target volume based on 4DCT image in radiation treatment planning system (TPS). The change in normal tissue dose was evaluated in the plan by using the parameters V5, V10, V15, V20,V25, V30, V35 and V40 (volumes receiving 5, 10, 15, 20, 25, 30, 35 and 40Gy, respectively) in the dose-volume histogram for the liver; mean dose for the following structures: liver, left kidney and right kidney; and maximum dose for the following structures: bowel, duodenum, esophagus, stomach and heart. Results: There was significant difference between 4D PTV(average 115.71cm3 )and ITV(169.86 cm3). When the planning objective is 95% volume of PTV covered by the prescription dose, the mean dose for the liver, left kidney and right kidney have an average decrease 23.13%, 49.51%, and 54.38%, respectively. The maximum dose for bowel, duodenum,esophagus, stomach and heart have an average decrease 16.77%, 28.07%, 24.28%, 4.89%, and 4.45%, respectively. Compared to 3D RT, radiation volume for the liver V5, V10, V15, V20, V25, V30, V35 and V40 by using the 4D plans have a significant decrease(P≤0.05). Conclusion: The 4D plan method creates plans that permit better sparing of the normal structures than the commonly used ITV method, which delivers the same dosimetric effects to the target.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2015

SU-E-T-369: Evaluating Intensity Modulated Proton Therapy Relative to Passive Scattering Proton Therapy for Increased Vertebral Column Sparing in CSI of Pediatric Patients

Purpose: To investigate the trade-off between vertebral column sparing and thecal-sac target coverage in craniospinal irradiation (CSI) of pediatric patients treated with passive-scattering (PS) and intensity modulated (IMPT) proton therapy. Methods: We selected 2 pediatric patients treated with PS CSI for medulloblastoma. Spinal irradiation was re-planned with IMPT. For all cases, we assumed prescription dose of 23.4 Gy(RBE), with the spinal canal receiving at least 95% of 23.4 Gy(RBE). PS planning was performed using the commercial system XiO. IMPT planning was done using the Astroid planning system. Beam arrangements consisted of (a) PS posterior-anterior (PA) field, PS-PA, (b) IMPT PA field, IMPT-PA, and (c) two posterior oblique IMPT fields, IMPT2 (-35°, 35°). Dose distributions were re-calculated using TOPAS Monte Carlo, along with LET distributions, to investigate LET variations within the target and vertebra anatomy. Variable RBE-weighed dose distributions were also calculated based on a dose and LET-dependent biophysical model. Dosimetric data were compared among the plans for the target volume, spinal cord and adjacent critical organs (thecal-sac and cauda equina). Results: IMPT2 resulted in better sparing of the posterior vertebral column (entrance region posterior to thecal-sac), where planned dose was approximately 6–8Gy(RBE). For IMPT-PA and PS-PA the MC-calculated dose to the posterior vertebral column was, on average, 20Gy and 18Gy respectively. For IMPT2 higher mean-LET (5keV/µm/(g/cm3)) values were observed in anterior vertebral column (beyond the thecal-sac) relative to IMPT-PA and PS-PA, where mean-LET was 3.5keV/µm/(g/cm3) and 2.5keV/µm/(g/cm3) respectively. The higher LET region observed for both IMPT plans was in the distal end of treatment fields, where dose delivered was less 5Gy(RBE). Conclusion: The two-oblique proton beams IMPT2 best spared the spinal column, while reducing the dose to the posterior spinal column from 18–20 to 6–8 Gy(RBE). The best LET distribution was obtained with the PS-PA fields.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2015

SU-E-T-810: Volumetric Modulated Arc Therapy and Conventional Intensity-Modulated Radiotherapy for Non-Small-Cell Lung Cancer with Simultaneously Integrated Boost Radiation Therapy: A Planning Comparison Study

Purpose: To compare and analyze the characteristics of intensity-modulated arc therapy(IMAT) versus fixed-gantry intensity-modulated radiotherapy(IMRT) in treatment of non-small-cell lung cancer. Methods: Twelve patients treated in our radiotherapy center were selected for this study. The patient subsequently underwent 4D-CT simulation.Margins of 5mm and 10mm were added to the ITV to generate the CTV and PTV respectively. Three treatment plans (IMRT,one single arc (RA1),double arcs (RA2))were generated with Eclipse ver.8.6 planning systems. Using a dose level of 75Gy in 15fractions to the ITV,60Gy in 15fractions to the CTV and 45Gy in 15fractions to the PTV respectively. The target and normol tissue volumes were compared,as were the dosimetry parameters. Results: There were no significant differences in CI of ITV,PTV,HI of ITV,CTV and PTV, V5,V10,V15,V20,V25,V30,V45,V50 of total-lung and mean lung dose (all p>0.05). However, the differences were significant in terms of CI of CTV,V5 of B-P (all p<0.05). On the MU, IMRT=1540MU,RA1=1006 MU and RA2=1096 MU. (F=12.00,P=0.000).On the treatment time, IMRT= 13.5min,RA1= 1.5min,and RA2=2.5 min (F= 30.11,P=0.000 ). Conclusion: IMAT is equal to IMRT in dosimetril evaluation. Due to much less Mu and delivery time,IMAT is an ideal technique in treating patients by reduceing the uncomfortable influnce which could effect the treatment.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2015

TU-CD-304-02: Planning and Delivery of Fully Dynamic Trajectory Modulated Arc Therapy On Pituitary Adenoma: Dosimetric Advantages Over Conventional Volumetric Modulated Arc Therapy

Purpose: To assess the potential benefit of trajectory modulated arc therapy (TMAT) for treatments of small benign intracranial tumor, pituitary adenoma. Methods: A TMAT planning platform that incorporates complex source motion trajectory involving synchronized gantry rotation with translational and rotational couch movement was used for the study. The platform couples an interactive trajectory generation tool with a VMAT algorithm that performs multi-resolution, progressive sampling MLC optimization on a user-designed trajectory. A continuous couch rotation of 160° angular span with ±20° mini gantry arcs was used to emulate a non-coplanar horizontal arc-like trajectory. Compared to conventional non-coplanar gantry arcs (60°-100° gantry rotation with couch kicks), TMAT limited the unnecessary low to medium dose spread in the anterior and posterior directions, where primary OARs (e.g., brainstem, optic chiasm, optic nerves, and lens) are in close proximity to the targeted pituitary tumor volume. For 5 standard fractionation pituitary adenoma cases (50.4Gy/28fractions), TMAT and non-coplanar VMAT plans were generated and compared under equivalent objectives/constraints. TMAT delivery was implemented and demonstrated on Varian TrueBeam via XML scripts. Results: Both techniques showed good target coverage while OARs were able to meet the constraints on QUANTEC guidelines. Notably, TMAT decreased the dose deposition in the anterior-to-posterior direction surrounding PTV. TMAT significantly reduced the mean doses on brainstem, optic nerves, eyes and lens by 47.29%±13.17%, 28.51%±8.68%, 80.82%±8.71% and 65.38%±19.99% compared with VMAT, all p≤0.01. Percentage reductions of maximum point dose in eyes and lens were 75.68%±10.30% and 70.72%±18.62% respectively for TMAT versus VMAT, all p≤0.01. A representative isocentric TMAT pituitary plan was delivered via an XML script with 200 control points and 282 MUs. Conclusion: Deliverable TMAT plans were achieved in developer mode in TrueBeam. TMAT was shown to be superior for pituitary adenoma irradiation in terms of OARs sparing.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2015

WE-EF-303-02: BEST IN PHYSICS (JOINT IMAGING- THERAPY): A Comprehensive Simulation of Image Guided Beam Gating for Liver Tumor Treatments Using Scanned Proton Therapy

Purpose: To evaluate the effectiveness of image guided beam gating for PBS liver treatments under realistic breathing conditions. Methods: We have previously proposed a Beams’ Eye View (BEV) X-ray image system as an online motion monitoring device for deriving a gating signal for PBS proton therapy. Using dedicated 4D dose calculations (4DDC), in this work we have simulated gated liver treatments using three amplitude-based gating windows (10/5/3mm) based on motion extracted from BEV imaging of fiducial markers or the diaphragm. In order to improve motion mitigation, BEV guided gating has also been combined with either volumetric (VS) or layered (LS) rescanning. Nine 4DCT(MRI) liver data-sets have been used for the investigation, which not only consider realistic patient geometries but also motion variations between different breathing cycles. All 4D plans have been quantified in terms of plan homogeneity in the PTV (D5-D95), the total estimated treatment time and the beam-on duty cycle. Results: Neither gating nor rescanning can fully retrieve a comparable plan homogeneity to the static case, and considerable reductions of the duty cycle (<10%) were observed as a Result motion variations when small gating windows are used. However, once combined with rescanning, dose homogeneity within 1% of the static plan could be achieved with reasonable prolongation of the treatment time for all 9 subjects. No differences were observed between the efficacy of layered or volumetric re-scanning, or of gating signals extracted from fiducial or diaphragm motions. However, layered rescanning may be preferred over volumetric rescanning when performed in combination with gating as it is generally more time-efficient and dosimetrically robust to patient and motion variations Conclusion Combining BEV beam gating with rescanning is an efficient and effective approach to treating mobile liver tumours, and is equally effective if either the diaphragm or fiducial markers are used as motion surrogates.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2015

Comparison of organ-at-risk sparing and plan robustness for spot-scanning proton therapy and volumetric modulated arc photon therapy in head-and-neck cancer

Purpose: Proton radiotherapy for head-and-neck cancer (HNC) aims to improve organ-at-risk (OAR) sparing over photon radiotherapy. However, it may be less robust for setup and range uncertainties. The authors investigated OAR sparing and plan robustness for spot-scanning proton planning techniques and compared these with volumetric modulated arc therapy (VMAT) photon plans. Methods: Ten HNC patients were replanned using two arc VMAT (RapidArc) and spot-scanning proton techniques. OARs to be spared included the contra- and ipsilateral parotid and submandibular glands and individual swallowing muscles. Proton plans were made using Multifield Optimization (MFO, using three, five, and seven fields) and Single-field Optimization (SFO, using three fields). OAR sparing was evaluated using mean dose to composite salivary glands (Comp{sub Sal}) and composite swallowing muscles (Comp{sub Swal}). Plan robustness was determined for setup and range uncertainties (±3 mm for setup, ±3% HU) evaluating V95% and V107% for clinical target volumes. Results: Averaged over all patients Comp{sub Sal}/Comp{sub Swal} mean doses were lower for the three-field MFO plans (14.6/16.4 Gy) compared to the three-field SFO plans (20.0/23.7 Gy) and VMAT plans (23.0/25.3 Gy). Using more than three fields resulted in differences in OAR sparing of less than 1.5 Gy between plans. SFO plans were significantly more robust than MFO plans. VMAT plans were the most robust. Conclusions: MFO plans had improved OAR sparing but were less robust than SFO and VMAT plans, while SFO plans were more robust than MFO plans but resulted in less OAR sparing. Robustness of the MFO plans did not increase with more fields.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2016

TH-EF-BRB-04: 4π Dynamic Conformal Arc Therapy Dynamic Conformal Arc Therapy (DCAT) for SBRT

Purpose: To develop an efficient and effective trajectory optimization methodology for 4π dynamic conformal arc treatment (4π DCAT) with synchronized gantry and couch motion; and to investigate potential clinical benefits for stereotactic body radiation therapy (SBRT) to breast, lung, liver and spine tumors. Methods: The entire optimization framework for 4π DCAT inverse planning consists of two parts: 1) integer programming algorithm and 2) particle swarm optimization (PSO) algorithm. The integer programming is designed to find an optimal solution for arc delivery trajectory with both couch and gantry rotation, while PSO minimize a non-convex objective function based on the selected trajectory and dose-volume constraints. In this study, control point interaction is explicitly taken into account. Beam trajectory was modeled as a series of control points connected together to form a deliverable path. With linear treatment planning objectives, a mixed-integer program (MIP) was formulated. Under mild assumptions, the MIP is tractable. Assigning monitor units to control points along the path can be integrated into the model and done by PSO. The developed 4π DCAT inverse planning strategy is evaluated on SBRT cases and compared to clinically treated plans. Results: The resultant dose distribution of this technique was evaluated between 3D conformal treatment plan generated by Pinnacle treatment planning system and 4π DCAT on a lung SBRT patient case. Both plans share the same scale of MU, 3038 and 2822 correspondingly to 3D conformal plan and 4π DCAT. The mean doses for most of OARs were greatly reduced at 32% (cord), 70% (esophagus), 2.8% (lung) and 42.4% (stomach). Conclusion: Initial results in this study show the proposed 4π DCAT treatment technique can achieve better OAR sparing and lower MUs, which indicates that the developed technique is promising for high dose SBRT to reduce the risk of secondary cancer.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2016

Sci-Fri PM: Radiation Therapy, Planning, Imaging, and Special Techniques - 01: On the use of proton radiography to reduce beam range uncertainties and improve patient positioning accuracy in proton therapy

To present two related developments of proton radiography (pRad) to minimize range uncertainty in proton therapy. The first combines a pRad with an X-ray CT to produce a patient-specific relative stopping power (RSP) map. The second aims to improve the pRad spatial resolution for accurate registration prior to the first. The enhanced-pRad can also be used in a novel proton-CT reconstruction algorithm. Monte Carlo pRad were computed from three phantoms; the Gammex, the Catphan and an anthropomorphic head. An optimized cubic-spline estimator derives the most likely path. The length crossed by the protons voxel-by-voxel was calculated by combining their estimated paths with the CT. The difference between the theoretical (length×RSP) and measured energy loss was minimized through a least squares optimization (LSO) algorithm yielding the RSP map. To increase pRad spatial resolution for registration with the CT, the phantom was discretized into voxels columns. The average column RSP was optimized to maximize the proton energy loss likelihood (MLE). Simulations showed precise RSP (<0.75%) for Gammex materials except low-density lung (<1.2%). For the head, accurate RSP were obtained (µ=−0.10%1.5σ=1.12%) and the range precision was improved (ΔR80 of −0.20±0.35%). Spatial resolution was increased in pRad (2.75 to 6.71 lp/cm) and pCT from MLE-enhanced pRad (2.83 to 5.86 lp/cm). The LSO decreases the range uncertainty (R80σ<1.0%) while the MLE-enhanced pRad spatial resolution (+244%) and is a great candidate for pCT reconstruction.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2017

Prognostic Factors and Patterns of Locoregional Failure After Surgical Resection in Patients With Cholangiocarcinoma Without Adjuvant Radiation Therapy: Optimal Field Design for Adjuvant Radiation Therapy

Purpose: To identify prognostic factors and patterns of local failure in patients with cholangiocarcinoma (CCA), after surgical resection in the absence of adjuvant radiation, for optimal definition of target volumes encompassing the majority of local recurrences. Methods and Materials: A chart review was performed in patients who underwent resection for primary CCA (intrahepatic, hilar, and distal) between 1999 and 2014. Local failure was defined as recurrence in a theoretical reasonable postoperative radiation volume. This includes the cut surface of liver, biliary anastomosis, hilum, portal nodes, celiac nodes, peri-pancreatic nodes, gastro-hepatic nodes, and retroperitoneal nodes. Patients who received adjuvant radiation were excluded. Results: A total of 189 patients underwent surgical resection for CCA, of whom 145 patients had sufficient follow-up. Median follow-up was 41.6 months (95% confidence interval 35.4-48.7 months). Of the 145 cases, 102 were intrahepatic and 43 were hilar/distal CCA. Adjuvant chemotherapy was given in 38 cases (26%), of which 20 (54%) were gemcitabine-based. Eighty-six patients (59%) had a documented recurrence, of whom 44 (51%) had a locoregional component. Among patients who had a recurrence, 23 (27%) had a recurrence at the biliary anastomosis and/or cut liver surface. Twenty-eight patients (32.6%) had a recurrence in the regional lymph nodes, most prevalent in the portal (16.3%) and retroperitoneal (17.4%) lymph nodes. Univariable analysis identified tumor size, any vascular invasion, presence of satellites, stage/nodal status, and receipt of chemotherapy as significant prognostic factors of overall recurrence among intrahepatic patients. Presence of satellites, and stage 3/Nx status remained statistically significant in multivariable modeling. Conclusions: The areas at highest risk for locoregional recurrence after surgical resection for primary CCA are the biliary anastomosis/cut liver surface, portal lymph nodes, and retroperitoneal lymph nodes. Although these results need to be validated, adjuvant radiation should possibly cover these areas to maximize locoregional control.

62 RADIOLOGY AND NUCLEAR MEDICINE↗