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Posterior Direction (posterior + direction)
Selected AbstractsEffect of lateral target motion on image registration accuracy in CT-guided helical tomotherapy: A phantom studyJOURNAL OF MEDICAL IMAGING AND RADIATION ONCOLOGY, Issue 3 2010J Medwig Summary Optimisation of imaging modes for kilovoltage CT (kVCT) used for treatment planning and megavoltage CT (MVCT) image guidance used in ungated helical tomotherapy was investigated for laterally moving targets. Computed tomography images of the QUASARÔ Respiratory Motion Phantom were acquired without target motion and for lateral motion of the target, with 2-cm peak-to-peak amplitude and a period of 4 s. Reference kVCT images were obtained using a 16-slice CT scanner in standard fast helical CT mode, untagged average CT mode and various post-processed 4D-CT modes (0% phase, average and maximum intensity projection). Three sets of MVCT images with different inter-slice spacings of were obtained on a Hi-Art tomotherapy system with the phantom displaced by a known offset position. Eight radiation therapists performed co-registration of MVCT obtained with 2-, 4- and 6-mm slice spacing and kVCT studies independently for all 15 CT imaging combinations. In the investigated case, the untagged average kVCT and 4-mm slice spacing for the MVCT yielded more accurate registration in the transverse plane. The average residual uncertainty of this combination of imaging procedures was 0.61 ± 0.16 mm in the longitudinal direction, 0.45 ± 0.14 mm in the anterior,posterior direction and insignificant in the lateral direction. Manual registration of MVCT,kVCT study pairs is necessary to account for a target in significant lateral motion with respect to bony structures. [source] Mechanisms of Postural Control in Alcoholic Men and Women: Biomechanical Analysis of Musculoskeletal Coordination During Quiet StandingALCOHOLISM, Issue 3 2010Edith V. Sullivan Background:, Excessive sway during quiet standing is a common sequela of chronic alcoholism even with prolonged sobriety. Whether alcoholic men and women who have remained abstinent from alcohol for weeks to months differ from each other in the degree of residual postural instability and biomechanical control mechanisms has not been directly tested. Method:, We used a force platform to characterize center-of-pressure biomechanical features of postural sway, with and without stabilizing conditions from touch, vision, and stance, in 34 alcoholic men, 15 alcoholic women, 22 control men, and 29 control women. Groups were matched in age (49.4 years), general intelligence, socioeconomic status, and handedness. Each alcoholic group was sober for an average of 75 days. Results:, Analysis of postural sway when using all 3 stabilizing conditions versus none revealed diagnosis and sex differences in ability to balance. Alcoholics had significantly longer sway paths, especially in the anterior,posterior direction, than controls when maintaining erect posture without balance aids. With stabilizing conditions the sway paths of all groups shortened significantly, especially those of alcoholic men, who demonstrated a 3.1-fold improvement in sway path difference between the easiest and most challenging conditions; the remaining 3 groups, each showed a ,2.4-fold improvement. Application of a mechanical model to partition sway paths into open-loop and closed-loop postural control systems revealed that the sway paths of the alcoholic men but not alcoholic women were characterized by greater short-term (open-loop) diffusion coefficients without aids, often associated with muscle stiffening response. With stabilizing factors, all 4 groups showed similar long-term (closed loop) postural control. Correlations between cognitive abilities and closed-loop sway indices were more robust in alcoholic men than alcoholic women. Conclusions:, Reduction in sway and closed-loop activity during quiet standing with stabilizing factors shows some differential expression in men and women with histories of alcohol dependence. Nonetheless, enduring deficits in postural instability of both alcoholic men and alcoholic women suggest persisting liability for falling. [source] Evaluation of megavoltage CT imaging protocols in patients with lung cancerJOURNAL OF MEDICAL IMAGING AND RADIATION ONCOLOGY, Issue 1 2010S Smith Summary Currently, megavoltage CT studies in most centres with tomotherapy units are performed prior to every treatment for patient set-up verification and position correction. However, daily imaging adds to the total treatment time, which may cause patient discomfort as well as results in increased imaging dose. In this study, four alternative megavoltage CT imaging protocols (images obtained: during the first five fractions, once per week, alternating fractions and daily on alternative weeks) were evaluated retrospectively using the daily position correction data for 42 patients with lung cancer. The additional uncertainty introduced by using a specific protocol with respect to the daily imaging, or residual uncertainty, was analysed on a patient and population bases. The impact of less frequent imaging schedules on treatment margin calculation was also analysed. Systematic deviations were reduced with increased imaging frequency, while random deviations were largely unaffected. Mean population systematic errors were small for all protocols evaluated. In the protocol showing the greatest error, the treatment margins necessary to accommodate residual errors were 1.2, 1.3 and 1.7 mm larger in the left,right, superior,inferior and anterior,posterior directions, respectively, compared with the margins calculated using the daily imaging data. The increased uncertainty because of the use of less frequent imaging protocols may be acceptable when compared with other sources of uncertainty in lung cancer cases, such as target volume delineation and motion because of respiration. Further work needs to be carried out to establish the impact of increased residual errors on dose distribution. [source] The role of M. popliteus in unpredictable and in self-initiated balance provocationsJOURNAL OF ORTHOPAEDIC RESEARCH, Issue 3 2006Ann-Katrin Stensdotter Abstract The purpose of this study was to determine whether m. popliteus (POP) activity would contribute to the control of knee joint position in unpredictable and in self-initiated provocations of standing balance. Ten healthy women (age 25.2,±,4.5 years, means and SD) without known knee pathology were tested for postural reactions (1) to unpredictable support surface translations in anterior and posterior directions, and (2) in self-initiated balance provocations in a reaction time (RT) forward reach-and-grip task. Electromyographic activity was recorded from POP and other leg muscles plus the deltoid muscle. Three-dimensional kinematics were captured for the knee joint and the body centre of mass was calculated. POP was active first of all the muscles recorded, regardless of translation direction, and knee joint movements elicited were either knee extension or external rotation of the tibia. In the RT task, the POP was active after initiation of reaching movement, and there was little consistency in the kinematic response. POP activity was not direction specific in response to support surface translation, but appeared triggered from reactive knee joint movement. The response to the support-surface translation suggests that POP served to control knee joint position rather than posture. In the RT task, we could not deduce whether POP activity was attributed to knee joint control or to postural control. © 2006 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 24:524,530, 2006 [source] | ||||||||||