The HI-ART II unit (TomoTherapy Inc., Madison WI) is a modality used by the London Regional Cancer program (LRCP) for radiation therapy. This machine uses the same source of Megavoltage energy radiation to image (3.5 ...
详细信息
The HI-ART II unit (TomoTherapy Inc., Madison WI) is a modality used by the London Regional Cancer program (LRCP) for radiation therapy. This machine uses the same source of Megavoltage energy radiation to image (3.5 MV) and to treat (6MV) patients, combining the functionality of a traditional linear accelerator and CT simulator into one unit. Thus, it is possible to assess patient positioning and adjust for anatomy changes just prior to radiation therapy. Unfortunately, at MV energy levels, the physics of radiation interaction limits image quality, and gives rise to an inherent dose limitation concern that enhances noise levels. Therefore, we propose to quantify the image quality produced by the HI-ART II unit using techniques established for kVCT scanner technology. Our study involved the use of three standard phantoms to test image resolution, noise, uniformity, and linearity for a 512 × 512 reconstruction matrix and three scan pitch settings (0.8, 1.6, and 2.4). Results follow: linearity between MV CT number versus relative electron density was observed, noise calculations ranged from 2.15-2.51%, and a distinct central artifact was revealed during uniformity testing. The linearity between MV CT number versus relative electron density implies that MV CT images are highly suitable for dose calculations. MV CT image quality of uniform phantoms were acceptable and demonstrated noise levels higher than those produced by kVCT simulators. Further study is necessary to correct for the central artifact in MV CT images.
Treating lung cancer with radiation therapy by guaranteed delivery of the prescription dose to the target is difficult due to tumour motion. The standard approach to account for motion effects consists of adding a sub...
详细信息
Treating lung cancer with radiation therapy by guaranteed delivery of the prescription dose to the target is difficult due to tumour motion. The standard approach to account for motion effects consists of adding a substantial margin to a lesion visible on the CT study. Larger irradiated volume results in increased dose deposition in healthy lung and the potential for patient complications. This investigation focuses on determining the optimal choice of planning CT mode for improved radiation delivery in terms of better target coverage and sparing of healthy organs. Dosimetric measurements were performed on a helical tomotherapy unit. A Quasar® (Modus Medical Devices, London, ON) respiratory phantom was imaged while a polystyrene target moved sinusoidally with a period of 4 s and amplitude of 2 cm. For target moving in superior-inferior and lateral directions, conventional fast-CT image studies were created, as well as maximum intensity projection (MIP) and average intensity projection (AveIP) image studies using four-dimensional CT information. All types of CT studies were used to develop treatment plans with a prescription of 2 Gy per fraction to the target outlined according to the imaged data. Measurements of dose deposition were made in four locations within the moving target using an Exradin A1SL ion chamber. Comparing all results to the dose measured at the centre of the static phantom, the MIP plans overdose the target, the fast-CT results vary from case to case, while the AveIP plans provide consistent dose distribution across the target within 2% of the normalization dose.
Intensity Modulated Arc Therapy (IMAT) is a rotational variant of Intensity Modulated Radiation Therapy (IMRT) that can be implemented with or without angular dose rate optimization. The purpose of this study is to de...
详细信息
Intensity Modulated Arc Therapy (IMAT) is a rotational variant of Intensity Modulated Radiation Therapy (IMRT) that can be implemented with or without angular dose rate optimization. The purpose of this study is to determine the inter-relationship among arc range, Multi-Leaf Collimator (MLC) leaf positions and angular dose rate optimizations for IMAT delivery of a concave target. A concave planning target volume (PTV) with central cylindrical organ at risk (OAR) was used in dissecting the inter-relationships. Plans with full and limited arc range were generated using leaf position optimization (LPO) alone, angular dose rate optimization (ADRO) alone or LPO followed by ADRO. Two initial IMAT arcs were conformal avoidance arcs created with 5° angular increments where MLC leaf positions were determined from the beams eye view to irradiate the PTV but avoid the OAR. The objective function value (evaluating dose to PTV and OAR), a conformity index, dose homogeneity index, mean dose to OAR and normal tissues were computed and used to evaluate the treatment plans. Dose rate variations and MLC leaf movements as a function of gantry angle were examined in this approach. The results demonstrate that LPO followed by ADRO provided the lowest objective function values, best conformity and dose homogeneity indices, and third in mean dose to OAR and normal tissues for the complete arc range. Future work will address different strategies for simultaneously optimizing both the MLC leaf positions and the variable angular dose rate for IMAT delivery and compare single and multiple arc plans.
Miniaturization of clinical chemistry analyzers can empower research conducted to better understand, diagnose, manage, and cure diseases such as diabetes. For the last decade, we have been working on the design and de...
详细信息
The Supercritical Water-cooled Reactor (SCWR) and Lead-cooled Fast Reactor (LFR) are among the six reactor concepts identified by the Generation IV initiative for the next generation nuclear reactors. Materials degrad...
详细信息
This paper is based on a collaborative effort between the National Academy of engineering and the National Research Council, with support from the National Science Foundation that was initiated to improve engineering ...
详细信息
The present study describes the recent investigation of boronized surface coating on Steel, Ni super alloy and pure Tantalum. The coatings were produced by thermo-chemical treatment with an original technology powder ...
详细信息
The present study describes the recent investigation of boronized surface coating on Steel, Ni super alloy and pure Tantalum. The coatings were produced by thermo-chemical treatment with an original technology powder mixture at the temperature range of 850-1050°C. Metallographic examination, X-ray diffraction (XRD) and microhardness testing were used to determine the characteristics of the diffusion layer compared with the substrate. The continuous weighting method and the potentiodynamic polarization measurements were used to investigate the corrosion resistance of the specimen surface before and after boronizing. Also, the high temperature oxidation method detected by differential thermal analysis (TGA) was used to observe the oxidation resistance of unboronized and boronized specimens. It was shown that the boronizing process created a boride layer with a thickness of 10-80 μm depending on substrates, temperatures, and times, with microhardness of about 8-10 times greater than that of the substrate. The corrosion resistance of the boronized coating was determined to be 6-10 times higher than that of the substrate. As well, the oxidation resistance of the boronized coating was 3-5 times better than that of the substrate.
Fluorocarbon plasma etching of Si/SiGe heterostructures is demonstrated as a method for fabrication of quantum devices with vertical sidewalls. The heterostructures consist of layers of Si and SiGe, and anisotropic et...
详细信息
暂无评论