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To evaluate in an objective way the effect of leaf interdigitation and leaf width on volumetric modulated arc therapy plans in Pinnacle. Three multileaf collimators (MLCs) were modeled: two 10 mm leaf width MLCs, with and without interdigitating leafs, and a 5 mm leaf width MLC with interdigitating leafs. Three rectum patients and three prostate patients were used for the planning study. In order to compare treatment techniques in an objective way, a Pareto front comparison was carried out. 200 plans were generated in an automated way, per patient per MLC model, resulting in a total of 3600 plans. From these plans, Pareto-optimal plans were selected which were evaluated for various dosimetric variables. The capability of leaf interdigitation showed little dosimetric impact on the treatment plans, when comparing the 10 mm leaf width MLC with and without leaf interdigitation. When comparing the 10 mm leaf widthMLC with the 5 mm leaf widthMLC, both with interdigitating leafs, improvement in plan quality was observed. For both patient groups, the integral dose was reduced by 0.6 J for the thin MLC. For the prostate patients, the mean dose to the anal sphincter was reduced by 1.8 Gy and the conformity of the V95% was reduced by 0.02 using the thin MLC. The V65% of the rectum was reduced by 0.1% and the dose homogeneity with 1.5%. For rectum patients, the mean dose to the bowel was reduced by 1.4 Gy and the mean dose to the bladder with 0.8 Gy for the thin MLC. The conformity of the V95% was equivalent for the 10 and 5 mm leaf width MLCs for the rectum patients. We have objectively compared three types of MLCs in a planning study for prostate and rectum patients by analyzing Pareto-optimal plans which were generated in an automated way. Interdigitation of MLC leafs does not generate better plans using the SmartArc algorithm in Pinnacle. Changing the MLC leaf width from [ABSTRACT FROM AUTHOR]

Purpose: lower lobe lung tumors move with amplitudes of up to 2 cm due to respiration. To reduce respiration imaging artifacts in planning CT scans, 4D imaging techniques are used. Currently, we use a single (midventilation) frame of the 4D data set for clinical delineation of structures and radiotherapy planning. A single frame, however, often contains artifacts due to breathing irregularities, and is noisier than a conventional CT scan since the exposure per frame is lower. Moreover, the tumor may be displaced from the mean tumor position due to hysteresis. The aim of this work is to develop a framework for the acquisition of a good quality scan representing all scanned anatomy in the mean position by averaging transformed (deformed) CT frames, i.e., canceling out motion. A nonrigid registration method is necessary since motion varies over the lung. Methods and Materials: 4D and inspiration breath-hold (BH) CT scans were acquired for 13 patients. An iterative multiscale motion estimation technique was applied to the 4D CT scan, similar to optical flow but using image phase (gray-value transitions from bright to dark and vice versa) instead. From the (4D) deformation vector field (DVF) derived, the local mean position in the respiratory cycle was computed and the 4D DVF was modified to deform all structures of the original 4D CT scan to this mean position. A 3D midposition (MidP) CT scan was then obtained by (arithmetic or median) averaging of the deformed 4D CT scan. Image registration accuracy, tumor shape deviation with respect to the BH CT scan, and noise were determined to evaluate the image fidelity of the MidP CT scan and the performance of the technique. Results: Accuracy of the used deformable image registration method was comparable to established automated locally rigid registration and to manual landmark registration (average difference to both methods <0.5 mm for all directions) for the tumor region. From visual assessment, the registration was good for the clearly visible features (e.g., tumor and diaphragm). The shape of the tumor, with respect to that of the BH CT scan, was better represented by the MidP reconstructions than any of the 4D CT frames (including MidV; reduction of “shape differences” was 66%). The MidP scans contained about one-third the noise of individual 4D CT scan frames. Conclusions: We implemented an accurate method to estimate the motion of structures in a 4D CT scan. Subsequently, a novel method to create a midposition CT scan (time-weighted average of the anatomy) for treatment planning with reduced noise and artifacts was introduced. Tumor shape and position in the MidP CT scan represents that of the BH CT scan better than MidV CT scan and, therefore, was found to be appropriate for treatment planning. [ABSTRACT FROM AUTHOR]

Obrist's cardiac-somatic coupling hypothesis predicts a widespread inhibition of heart rate and task-irrelevant muscle activity during expectancy situations. This hypothesis was tested by measuring heart rate and pericranial electromyographic (EMG) activity during a warned simple reaction time task with visual or auditory reaction signals and hand or foot responses. In each of three groups of 24 participants, EMG activity of three different facial, masticatory, or neck muscles was recorded. During the warning interval preceding the presentation of the reaction signal, masticatory and lower facial muscles predominantly showed a gradual inhibition in activity concomitant with heart rate deceleration. In contrast, two upper facial muscles showed increasing activity. Pericranial EMG responses were little affected by reaction signal modality and were independent of responding limb. Greater heart rate deceleration was associated with greater inhibition and weaker facilitation of EMG responses. The results suggest a functional role of inhibitory EMG responses in increasing the perceptual sensitivity to expected signals. [ABSTRACT FROM AUTHOR]

Based on previous research, it was hypothesized that both the final cardiac deceleration and the late wave of the Contingent Negative Variation (CNV) at the end of the foreperiod of a simple reaction time task are composed of a movement-related component and a stimulus-anticipation component. Forty right-handed adult female and male subjects performed a time estimation task. They had to press a button with the index-finger at intervals of 20 to 22 seconds. After the button-press a visual stimulus was presented, which provided Knowledge of Results (KR) about the correctness of the timing. For half the subjects the delay between button-press and stimulus presentation was 2 s, for the other half it was 4 s. Recordings of both the electrocardiogram (ECG) and the electroencephalogram (EEG) were obtained, the latter being derived bilaterally From precentral, postcentral, and parietal sites. As was expected, cardiac deceleration was found both prior to the movement and prior to stimulus presentation in both delays. At the cortical level the movement was preceded by a Readiness Potential (RP). Stimulus presentation was preceded by a cortical negative wave, the Stimulus-Preceding Negativity (SPN), at all positions. Precentrally and postcentrally the Stimulus-Preceding Negativity exhibited a larger right hemisphere preponderance in the 2-s delay than in the 4-s delay. [ABSTRACT FROM AUTHOR]

Background & Purpose: Stereotactic radiosurgery (SRS) is an increasingly important treatment modality for pain relief of spinal oligometastases. Considering the dose (16-24Gy) and proximity to the spinal cord, good governance of total geometric treatment accuracy is imperative. When using MRI for spinal cord delineation in SRS treatment planning, the cerebrospinal fluid (CSF) no longer serves as an implicit organ-at-risk margin. In this study, spinal cord motion within CSF was investigated with MRI to estimate its potential influence on geometric accuracy of SRS spine treatment. Method: MRI series of 8 volunteers were collected at different spine locations (C7, T8 or L2). Data were acquired on a 1.5T scanner; resolutions 0.5x0.5x2mm³ (T1, T2 weighted) and 0.6x0.6x10mm3 (cine MRI). To assess the influence of subject positioning, spine orientation was changed with cushions and subjects were repositioned. Analysis involved rigid, grey value, vertebral body registration, followed by translations-only spinal cord registration. The difference between translations of vertebral and spinal cord registrations was analyzed in three directions (LR, AP, CC) as a measure for spinal cord movement within CSF. In some scans, the water-fat shift (WFS) direction was altered to determine the impact on (perceived) spinal cord location. Respiration effects were evaluated on free breathing cine MRI. Results: Evaluation of the registration procedure showed that, on average at T8, reproducibility of the differences was 0.03±0.1mm in LR, AP directions and -0.2±0.4mm in CC direction. Effects of spine orientation and repositioning could not be distinguished within that reproducibility for C7, T8 and L2 (figure 1). For L2 however (equina cauda), the reproducibility in CC direction (SD 1.5mm) was poorer. In two participants, this resulted in spurious larger registration differences in AP and CC directions. Opposing small WFS parameters (LR, AP; 2x0.3mm; T2) could not be detected, whereas larger parameters (LR, AP; 2x1.1mm; T1) translate into corresponding registration differences of 1.7±0.1mm. The cine MR images at T8 did not show spinal cord movement due to respiration. Conclusion: MRI parameters (e.g. WFS) for sequences used in SRS treatment planning can be optimized to minimize geometric uncertainties. With respect to respiration and subject positioning, spinal cord position was found to be stable within a voxel. This implies that geometric accuracy in spine SRS with MRI for spinal cord delineation is uncompromised by spinal cord movement. Disclosure: No significant relationships. [ABSTRACT FROM AUTHOR]