186,603 research outputs found
A phantom study to create synthetic CT from orthogonal twodimensional cine MRI and evaluate the effect of irregular breathing.
No full textAn exciting innovation in radiotherapy is the use of real-time MRI for treatment adaptation. This study proposes an in-silico framework for the generation of 3D synthetic CT (sCT) from orthogonal interleaved 2D cine MRI data to overcome the lack of electron density information in MR images. The method uses pre-treatment data to build a patient breathing motion model. This model is then driven by surrogates extracted from cine MR images during the treatment. The effect of irregular breathing on the motion model is also evaluated by simulating different motion components related to uncorrelated diaphragm, chest and tumor motion. 3D sCT were successfully created for each of the 512 cine MRI pairs in the digital phantom study. The analysis showed that the diaphragm position was a good surrogate to rescale the 3D breathing motion for the current regular breathing phase. However, respiratory and tumor motion were correlated in only 59% of the phases, resulting in tumor position uncertainties of up to 3mm. The inclusion of additional chest and tumor motion information improved the accuracy for irregular changes in breathing pattern and enhanced the tumor position uncertainties to less than 1mm. This study successfully demonstrated a proof-ofprinciple for a digital phantom dataset based on patient parameters, providing a way to create real-time 3D electron density volumes and enhancing the need to account for irregular breathing pattern
A Fountain of Sasanian Age from Ardashir Khwarrah, with a note on the Archaeometric Investigations by Maria Letizia Amadori
No full textThe author describes a peculiar stone object preserved in the stores of Firuzabad UNESCO site base, and tries to interpet and date it as a fountain of the Sasanian period
SU-E-J-235: Audiovisual Biofeedback Improves the Correlation Between Internal and External Respiratory Motion
No full text
Motion prediction in MRI-guided radiotherapy based on interleaved orthogonal cine-MRI
No full textIn-room cine-MRI guidance can provide non-invasive target localization during radiotherapy treatment. However, in order to cope with finite imaging frequency and system latencies between target localization and dose delivery, tumour motion prediction is required. This work proposes a framework for motion prediction dedicated to cine-MRI guidance, aiming at quantifying the geometric uncertainties introduced by this process for both tumour tracking and beam gating. The tumour position, identified through scale invariant features detected in cine-MRI slices, is estimated at high-frequency (25 Hz) using three independent predictors, one for each anatomical coordinate. Linear extrapolation, auto-regressive and support vector machine algorithms are compared against systems that use no prediction or surrogate-based motion estimation. Geometric uncertainties are reported as a function of image acquisition period and system latency. Average results show that the tracking error RMS can be decreased down to a [0.2; 1.2] mm range, for acquisition periods between 250 and 750 ms and system latencies between 50 and 300 ms. Except for the linear extrapolator, tracking and gating prediction errors were, on average, lower than those measured for surrogate-based motion estimation. This finding suggests that cine-MRI guidance, combined with appropriate prediction algorithms, could relevantly decrease geometric uncertainties in motion compensated treatments
Is There a Selection Bias in Radiotherapy Dose-Escalation Protocols?
No full textBackground: To investigate the existence of a selection bias using a virtual radiotherapy dose-escalation trial. In dose-escalation trials, normal tissue constraints generally remain constant while the tumor dose is increased. Since tumor dose and normal tissue constraints are competing demands, a point will be reached at which the tumor dose cannot be increased without exceeding normal tissue constraints. Methods and Materials: In 9 patients with non-small-cell lung cancer, the tumor dose was escalated from 66 Gy to 78 Gy in 4-Gy dose levels using intensity-modulated radiotherapy planning, while the limiting normal tissue dose contraints remained constant. Dosimetric, radiobiologic, and other planning parameters were compared at the 66-Gy dose level :for patients eligible for all dose levels and for those eligible only for lower dose levels. Results: Seven of 9 patients were eligible for all dose levels (Group E). Two of 9 patients ("ineligible" or Group 1) qualified only for lower total doses (95 % confidence interval, 0.075- 0.6, significant). In Group E, mean planning target volumes were smaller (132 vs. 404 cm(3), nonsignificant), monitor units per fraction were significantly lower (448 vs. 802,p = 0.0008), and the average composite score for plan quality was better than in Group I (0.012 vs. 0.068, nonsignificant). Average tumor-control probabilities were higher (0.33 vs. 0.23, nonsignificant), and normal tissue-complication probabilities were lower for Group E than for Group I. Conclusions: Patients eligible for higher dose levels had significantly superior estimated outcome parameters. A method to eliminate this source of error in the interpretation of dose-escalation trials is suggested. (c) 2007 Elsevier Inc.NCI NIH HHS [R01 CA093626-05, R01 CA093626, R01 CA 93626
Electron transport in photon and election beam modelling / Paul J. Keall.
No full textBibliography: p. 185-195.xxii, 195 p. : ill. ; 30 cm.Two rigorous dose calculation methods have been devised to address the deficiencies of currently available dose calculation algorithms. The 1st method incorporates Fermi-Eyges mutiple scattering theory, the 2nd method developed is the Super-Monte Carlo method.Thesis (Ph.D.)--University of Adelaide, Dept. of Physics and Mathematical Physics, 1996
Audiovisual biofeedback improves the correlation between surrogates and tumour motion for lung cancer
No full textAuthor-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
An analysis of 6-MV versus 18-MV photon energy plans for intensity-modulated radiation therapy (IMRT) of lung cancer
No full textPurpose: To analyse the supposed benefits of low over high photon energies for the radiotherapy of lung cancer. Materials and methods: For 13 patients, 6- and 18-MV IMRT planning was performed using identical planning objectives and dose constraints. Plans were compared according to dose-volume histogram (DVH) analysis including conformity and homogeneity indices (Cl and HI) and overall plan quality (composite score CS), considering also magnitude and location of planning target volumes (PTVs). Results: With 6-MV plans, CSs were better in 11/13, His in 10/13 and Cls in 6/13 patients compared with 18-MV plans. Six-MV plans resulted in,a better normal tissue sparing except for specified dose levels to the thorax and spinal cord. On average differences between 6 and 18 MV both for the PTV and normal tissues were not statistically significant (p > 0.05). Considering size and location of the PTVs as well as their relative position to normal tissue, overall no significant differences between 6 and 18 MV were observed. Conclusions: On average no clinically or statistically significant differences between 6- and 18-MV plans were observed. High photon energies should therefore not be excluded a priori when a dose-calculation algorithm is utilized that accurately accounts for heterogeneities. (c) 2006 Elsevier Ireland Ltd. All rights reserved.NCI NIH HHS [R01 CA093626, R01 CA 93626, R01 CA 98524
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