38 research outputs found
Hot electron and ion spectra on blow-off plasma free target in GXII-LFEX direct fast ignition experiment
Polystyrene deuteride shell targets with two holes were imploded by the Gekko XII laser and additionally heated by the LFEX laser in a direct fast ignition experiment. In general, when an ultra-intense laser is injected into a blow-off plasma created by the imploding laser, electrons are generated far from the target core and the energies of electrons increase because the electron acceleration distance has been extended. The blow-off plasma moves not only to the vertical direction but to the lateral direction against the target surface. In a shell target with holes, a lower effective electron temperature can be realized by reducing the inflow of the implosion plasma onto the LFEX path, and high coupling efficiency can be expected. The energies of hot electrons and ions absorbed into the target core were calculated from the energy spectra using three electron energy spectrometers and a neutron time-of-flight measurement system, Mandala. The ions have a large contribution of 74% (electron heating of 4.9 J and ion heating of 14.1 J) to target heating in direct fast ignition
Direct fast heating efficiency of a counter-imploded core plasma employing a laser for fast ignition experiments (LFEX)
Fast heating efficiency when a pre-imploded core is directly heated with an ultraintense laser (heating laser) was investigated. \u27Direct heating\u27 means that a heating laser hits a pre-imploded core without applying either a laser guiding cone or an external field. The efficiency, η, is defined as the increase in the internal core energy divided by the energy of the heating laser. Six beams (output of 1.6 kJ) from the GEKKO XII (GXII) green laser system at the Institute of Laser Engineering (ILE), Osaka University were applied to implode a spherical deuterated polystyrene (CD) shell target to form a dense core. The DD-reacted protons and the core x-ray emissions showed a core density of 2.8 ± 0.7 g cm−3, or 2.6 times the solid density. Furthermore, DD-reacted thermal neutrons were utilized to estimate the core temperature between 600 and 750 eV. Thereafter, the core was directly heated by a laser for fast-ignition experiments (LFEX, an extremely energetic ultrashort pulse laser) at ILE with its axis lying along or perpendicular to the GXII bundle axis, respectively. The former and latter laser configurations were termed \u27axial\u27 and \u27transverse modes\u27, respectively. The η was estimated from three independent methods: (1) the core x-ray emission, (2) the thermal neutron yield, and (3) the runaway hot electron spectra. For the axial mode, 0.8%< η <2.1% at low power (low LFEX energy) and 0.4%< η <2.5% at high power (high LFEX energy). For the transverse mode, 2.6%< η <7% at low power and 1.5%< η <7.7% at high power. Their efficiencies were compared with that in the uniform implosion mode using 12 GXII beams, 6% < η <12%, which appeared near to the η for the transverse mode, except that the error bar is very large
Efficacy of butylscopolamine in obtaining clear MR image for intensity-modulated radiotherapy for prostate cancer.
PurposeThe use of butylscopolamine in magnetic resonance imaging (MRI) of the prostate is controversial in the context of diagnostic imaging where local invasion and the presence of metastases are evaluated. However, in radiation oncology, MRI is performed as part of the simulation process, and the objectives differ to the diagnostic setting. MRI is primarily used for accurate target delineation; hence, the use of an agent to reduce intestinal peristalsis and increase image quality may be beneficial. The impact of butylscopolamine on MRI for radiation oncology purposes has not previously been described. The aim of this study was to evaluate the efficacy of butylscopolamine in MRI acquired for radiation oncology simulation of the prostate.Methods and materialsIn total, 67 patients were enrolled in this study. Thirty-five patients received intramuscular injection of butylscopolamine (group A) and 32 patients did not (group B). Visualization of the prostate outline and detection of fiducial gold markers (GMs) in the prostate were evaluated on MRI. Two blinded radiation oncologists (ROs) and one radiation technologist (RT) scored the image quality of the detection of prostate outline and recognition of GMs in the prostate on a scale of 1–5 (1 = poor; 5 = excellent), and the results were evaluated using Mann–Whitney U test and p < 0.05 was considered as statistically significant.ResultsOn MRI, group A was statistically superior to group B in terms of fiducial marker detection by two ROs (p < 0.01). However, there was no significant difference in RT scoring. Furthermore, on MRI, group A was statistically superior to group B in terms of the detection of the prostate outline by an RT.ConclusionsButylscopolamine is effective with respect to detection of the prostate outline and GM recognition (without endorectal coil). The addition of butylscopolamine is simple and cost efficient. We recommend the use of butylscopolamine routinely to obtain good MR images, particularly in the detection of GMs
Visibility of an iron-containing fiducial marker in magnetic resonance imaging for high-precision external beam prostate radiotherapy.
Visualization of fiducial gold markers is critical for registration on computed tomography (CT) and magnetic resonance imaging (MRI) for imaging-guided radiotherapy. Although larger markers provide better visualization on MRI, they tend to generate artifacts on CT. MRI is strongly influenced by the presence of metals, such as iron, in the body. Here we compared efficacies of a 0.5% iron-containing gold marker (GM) and a traditional non-iron-containing marker.Twenty-seven patients underwent CT/MRI fusion-based intensity-modulated radiotherapy. Markers were placed by urologists under local anesthesia. Gold Anchor (GA; diameter: 0.28 mm; length: 10 mm), an iron-containing marker, was placed on the right side of the prostate using a 22-G needle and VISICOIL (VIS; diameter: 0.35 mm; length: 10 mm), a non-iron-containing marker, was placed on the left side using a 19-G needle. T2*-weighted images MRI sequences were obtained. Two radiation oncologists and a radiation technologist evaluated and assigned scores for visual quality on a five-point scale (1, poor; 5, best visibility).Artifact generation on CT was slightly greater with GA than with VIS. The mean marker visualization scores on MRI of all three observers were significantly superior for GA than for VIS (3.5 vs 3.2, 3.9 vs 3.2, and 4.0 vs 2.9). The actual size of the spherical GA was about 2 mm in diameter, but the signal void on MRI was approximately 5 mm.Although both markers were well visualized and can be recommended clinically, the results suggest that GA has some subtle advantages for quantitative visualization that could prove useful in certain situations of stereotactic body radiotherapy and intensity-modulated radiotherapy.Visualization of fiducial gold markers is critical for registration on computed tomography (CT) and magnetic resonance imaging (MRI) for imaging-guided radiotherapy. Although larger markers provide better visualization on MRI, they tend to generate artifacts on CT. MRI is strongly influenced by the presence of metals, such as iron, in the body. Here we compared efficacies of a 0.5% iron-containing gold marker (GM) and a traditional non-iron-containing marker.Twenty-seven patients underwent CT/MRI fusion-based intensity-modulated radiotherapy. Markers were placed by urologists under local anesthesia. Gold Anchor (GA; diameter: 0.28 mm; length: 10 mm), an iron-containing marker, was placed on the right side of the prostate using a 22-G needle and VISICOIL (VIS; diameter: 0.35 mm; length: 10 mm), a non-iron-containing marker, was placed on the left side using a 19-G needle. T2*-weighted images MRI sequences were obtained. Two radiation oncologists and a radiation technologist evaluated and assigned scores for visual quality on a five-point scale (1, poor; 5, best visibility).Artifact generation on CT was slightly greater with GA than with VIS. The mean marker visualization scores on MRI of all three observers were significantly superior for GA than for VIS (3.5 vs 3.2, 3.9 vs 3.2, and 4.0 vs 2.9). The actual size of the spherical GA was about 2 mm in diameter, but the signal void on MRI was approximately 5 mm.Although both markers were well visualized and can be recommended clinically, the results suggest that GA has some subtle advantages for quantitative visualization that could prove useful in certain situations of stereotactic body radiotherapy and intensity-modulated radiotherapy
Comparison of MRI sequences in ideal fiducial maker-based radiotherapy for prostate cancer
AimProstate contouring using CT alone is difficult. To overcome the uncertainty, CT/MRI registration using a fiducial marker is generally performed. However, visualization of the marker itself can be difficult with MRI. This study aimed to determine the optimal MRI pulse sequence for defining the marker as well as the prostate outline among five sequences.Materials and methodsA total of 21 consecutive patients with prostate cancer were enrolled. Two gold fiducial markers were placed before CT/MRI examination. We used the following five sequences: T1-weighted spin-echo (T1WI; TR/TE, 400–650/8[[ce:hsp sp="0.25"/]]ms); T2-weighted fast spin-echo (T2WI; 4000/80); T2*-2D-weighted gradient echo (T2*2D; 700/18); T2*-3D-weighted gradient echo (T2*3D; TR/TE1/deltaTE, 37/14/7.3); and contrast-enhanced T1-weighted spin-echo (CE-T1WI; 400–650/8). Qualitative image analysis of the sequences was performed by three observers. These observers subjectively scored all images on a scale of 1–3 (1[[ce:hsp sp="0.25"/]]=[[ce:hsp sp="0.25"/]]unclear, 2[[ce:hsp sp="0.25"/]]=[[ce:hsp sp="0.25"/]]moderate, 3[[ce:hsp sp="0.25"/]]=[[ce:hsp sp="0.25"/]]well visualized). A higher score indicated better visualization.ResultsT2WI was significantly superior to the other sequences in terms of prostate definition. T2*2D and T2*3D were strongly superior to the other sequences and were significantly superior in terms of fiducial marker definition.ConclusionsT2*2D and T2*3D are superior to the other sequences for prostate contouring and marker identification. Therefore, we recommend initial T2*3D and T2*2D examinations
Comparison of MRI sequences in ideal fiducial maker-based radiotherapy for prostate cancer.
Prostate contouring using CT alone is difficult. To overcome the uncertainty, CT/MRI registration using a fiducial marker is generally performed. However, visualization of the marker itself can be difficult with MRI. This study aimed to determine the optimal MRI pulse sequence for defining the marker as well as the prostate outline among five sequences.A total of 21 consecutive patients with prostate cancer were enrolled. Two gold fiducial markers were placed before CT/MRI examination. We used the following five sequences: T1-weighted spin-echo (T1WI; TR/TE, 400-650/8 ms); T2-weighted fast spin-echo (T2WI; 4000/80); T2*-2D-weighted gradient echo (T2*2D; 700/18); T2*-3D-weighted gradient echo (T2*3D; TR/TE1/deltaTE, 37/14/7.3); and contrast-enhanced T1-weighted spin-echo (CE-T1WI; 400-650/8). Qualitative image analysis of the sequences was performed by three observers. These observers subjectively scored all images on a scale of 1-3 (1 = unclear, 2 = moderate, 3 = well visualized). A higher score indicated better visualization.T2WI was significantly superior to the other sequences in terms of prostate definition. T2*2D and T2*3D were strongly superior to the other sequences and were significantly superior in terms of fiducial marker definition.T2*2D and T2*3D are superior to the other sequences for prostate contouring and marker identification. Therefore, we recommend initial T2*3D and T2*2D examinations.Prostate contouring using CT alone is difficult. To overcome the uncertainty, CT/MRI registration using a fiducial marker is generally performed. However, visualization of the marker itself can be difficult with MRI. This study aimed to determine the optimal MRI pulse sequence for defining the marker as well as the prostate outline among five sequences.A total of 21 consecutive patients with prostate cancer were enrolled. Two gold fiducial markers were placed before CT/MRI examination. We used the following five sequences: T1-weighted spin-echo (T1WI; TR/TE, 400-650/8 ms); T2-weighted fast spin-echo (T2WI; 4000/80); T2*-2D-weighted gradient echo (T2*2D; 700/18); T2*-3D-weighted gradient echo (T2*3D; TR/TE1/deltaTE, 37/14/7.3); and contrast-enhanced T1-weighted spin-echo (CE-T1WI; 400-650/8). Qualitative image analysis of the sequences was performed by three observers. These observers subjectively scored all images on a scale of 1-3 (1 = unclear, 2 = moderate, 3 = well visualized). A higher score indicated better visualization.T2WI was significantly superior to the other sequences in terms of prostate definition. T2*2D and T2*3D were strongly superior to the other sequences and were significantly superior in terms of fiducial marker definition.T2*2D and T2*3D are superior to the other sequences for prostate contouring and marker identification. Therefore, we recommend initial T2*3D and T2*2D examinations