Engineering topics

Stewart, James

Publications and source records attributed to Stewart, James.

23 records · Page 2

DOE OSTI2014

Dosimetrically Triggered Adaptive Intensity Modulated Radiation Therapy for Cervical Cancer

Purpose: The widespread use of intensity modulated radiation therapy (IMRT) for cervical cancer has been limited by internal target and normal tissue motion. Such motion increases the risk of underdosing the target, especially as planning margins are reduced in an effort to reduce toxicity. This study explored 2 adaptive strategies to mitigate this risk and proposes a new, automated method that minimizes replanning workload. Methods and Materials: Thirty patients with cervical cancer participated in a prospective clinical study and underwent pretreatment and weekly magnetic resonance (MR) scans over a 5-week course of daily external beam radiation therapy. Target volumes and organs at risk (OARs) were contoured on each of the scans. Deformable image registration was used to model the accumulated dose (the real dose delivered to the target and OARs) for 2 adaptive replanning scenarios that assumed a very small PTV margin of only 3 mm to account for setup and internal interfractional motion: (1) a preprogrammed, anatomy-driven midtreatment replan (A-IMRT); and (2) a dosimetry-triggered replan driven by target dose accumulation over time (D-IMRT). Results: Across all 30 patients, clinically relevant target dose thresholds failed for 8 patients (27%) if 3-mm margins were used without replanning. A-IMRT failed in only 3 patients and also yielded an additional small reduction in OAR doses at the cost of 30 replans. D-IMRT assured adequate target coverage in all patients, with only 23 replans in 16 patients. Conclusions: A novel, dosimetry-triggered adaptive IMRT strategy for patients with cervical cancer can minimize the risk of target underdosing in the setting of very small margins and substantial interfractional motion while minimizing programmatic workload and cost.

62 RADIOLOGY AND NUCLEAR MEDICINE↗

DOE OSTI2014

First scientific application of the membrane cryostat technology

We report on the design, fabrication, performance and commissioning of the first membrane cryostat to be used for scientific application. The Long Baseline Neutrino Experiment (LBNE) has designed and fabricated a membrane cryostat prototype in collaboration with IHI Corporation (IHI). Original goals of the prototype are: to demonstrate the membrane cryostat technology in terms of thermal performance, feasibility for liquid argon, and leak tightness; to demonstrate that we can remove all the impurities from the vessel and achieve the purity requirements in a membrane cryostat without evacuation and using only a controlled gaseous argon purge; to demonstrate that we can achieve and maintain the purity requirements of the liquid argon during filling, purification, and maintenance mode using mole sieve and copper filters from the Liquid Argon Purity Demonstrator (LAPD) R and D project. The purity requirements of a large liquid argon detector such as LBNE are contaminants below 200 parts per trillion oxygen equivalent. This paper gives the requirements, design, construction, and performance of the LBNE membrane cryostat prototype, with experience and results important to the development of the LBNE detector.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2010

Automated Weekly Replanning for Intensity-Modulated Radiotherapy of Cervix Cancer

Purpose: The adoption of intensity-modulated radiotherapy (IMRT) to treat cervical malignancies has been limited in part by complex organ and tumor motion during treatment. This study explores the limits of a highly adaptive, small-margin treatment scenario to accommodate this motion. In addition, the dosimetric consequences of organ and tumor motion are modeled using a combination of deformable registration and fractional dose accumulation techniques. Methods and Materials: Thirty-three cervix cancer patients had target volumes and organs-at-risk contoured on fused, pretreatment magnetic resonance-computed tomography images and weekly magnetic resonance scans taken during treatment. The dosimetric impact of interfraction organ and target motion was compared for two hypothetical treatment scenarios: a 3-mm margin plan with no replanning, and a 3-mm margin plan with an automated replan performed on the updated weekly patient geometry. Results: Of the 33 patients, 24 (73%) met clinically acceptable target coverage (98% of the clinical target volume receiving at least 95% of the prescription dose) using the 3-mm margin plan without replanning. The range in dose to 98% of the clinical target volume across all patients was 7.9% of the prescription dose if no replanning was performed. After weekly replanning, this range was tightened to 2.6% of the prescription dose and all patients met clinically acceptable target coverage while maintaining organ-at-risk dose sparing. Conclusions: The dosimetric impact of anatomical motion underscores the challenges of applying IMRT to treat cervix cancer. An appropriate adaptive strategy can ensure target coverage for small-margin IMRT treatments and maintain favorable organ-at-risk dose sparing.

62 RADIOLOGY AND NUCLEAR MEDICINE↗

NASA NTRS1993

A neural based intelligent flight control system for the NASA F-15 flight research aircraft

A flight control concept that can identify aircraft stability properties and continually optimize the aircraft flying qualities has been developed by McDonnell Aircraft Company under a contract with the NASA-Dryden Flight Research Facility. This flight concept, termed the Intelligent Flight Control System, utilizes Neural Network technology to identify the host aircraft stability and control properties during flight, and use this information to design on-line the control system feedback gains to provide continuous optimum flight response. This self-repairing capability can provide high performance flight maneuvering response throughout large flight envelopes, such as needed for the National Aerospace Plane. Moreover, achieving this response early in the vehicle's development schedule will save cost.

Urnes, James M.↗

NASA NTRS1990

Flight demonstration of a self repairing flight control system in a NASA F-15 fighter aircraft

Battle damage causing loss of control capability can compromise mission objectives and even result in aircraft loss. The Self Repairing Flight Control System (SRFCS) flight development program directly addresses this issue with a flight control system design that measures the damage and immediately refines the control system commands to preserve mission potential. The system diagnostics process detects in flight the type of faults that are difficult to isolate post flight, and thus cause excessive ground maintenance time and cost. The control systems of fighter aircraft have the control power and surface displacement to maneuver the aircraft in a very large flight envelope with a wide variation in airspeed and g maneuvering conditions, with surplus force capacity available from each control surface. Digital flight control processors are designed to include built-in status of the control system components, as well as sensor information on aircraft control maneuver commands and response. In the event of failure or loss of a control surface, the SRFCS utilizes this capability to reconfigure control commands to the remaining control surfaces, thus preserving maneuvering response. Correct post-flight repair is the key to low maintainability support costs and high aircraft mission readiness. The SRFCS utilizes the large data base available with digital flight control systems to diagnose faults. Built-in-test data and sensor data are used as inputs to an Onboard Expert System process to accurately identify failed components for post-flight maintenance action. This diagnostic technique has the advantage of functioning during flight, and so is especially useful in identifying intermittent faults that are present only during maneuver g loads or high hydraulic flow requirements. A flight system was developed to test the reconfiguration and onboard maintenance diagnostics concepts on a NASA F-15 fighter aircraft.

Urnes, James M.↗