Extracting global and local dynamics from the stochastics of rhythmic forearm movements.

The authors examined the dynamics governing rhythmic forearm movements that 9 participants performed under a variety of task constraints by using a generic, unbiased analysis technique for extracting the drift coefficients of Fokker-Planck equations from stochastic data. From those coefficients, they reconstructed and analyzed vector fields and phase portraits to identify characteristic, task-dependent kinematic and dynamical features. They first directly estimated the parameters of weakly nonlinear self-sustaining oscillators from the extracted drift coefficients. The estimated parameters that the authors had selected instinctively and then particularized by using averaging methods largely confirmed previously derived limit-cycle models. Next, they ventured beyond limit-cycle models to examine global and local dynamical features that those models cannot adequately address, particularly task-dependent changes in flow strength and curvature and distinct dynamical features associated with flexion and extension. The authors argue that those features should be focal points of researchers' future modeling efforts to formulate a more adequate and encompassing account of the dynamics of rhythmic movement.

Significant tumor shift in patients treated with stereotactic radiosurgery for brain metastasis.

INTRODUCTION: Linac-based stereotactic radiosurgery (SRS) for brain metastases may be influenced by the time interval between treatment preparation and delivery, related to risk of anatomical changes. We studied tumor position shifts and its relations to peritumoral volume edema changes over time, as seen on MRI. METHODS: Twenty-six patients who underwent SRS for brain metastases in our institution were included. We evaluated the occurrence of a tumor shift between the diagnostic MRI and radiotherapy planning MRI. For 42 brain metastases the tumor and peritumoral edema were delineated on the contrast enhanced T1weighted and FLAIR images of both the diagnostic MRI and planning MRI examinations. Centre of Mass (CoM) shifts and tumor borders were evaluated. We evaluated the influence of steroids on peritumoral edema and tumor volume and the correlation with CoM and tumor border changes. RESULTS: The median values of the CoM shifts and of the maximum distances between the tumor borders obtained from the diagnostic MRI and radiotherapy planning MRI were 1.3 mm (maximum shift of 5.0 mm) and 1.9 mm (maximum distance of 7.4 mm), respectively. We found significant correlations between the absolute change in edema volume and the tumor shift of the CoM (p < 0.001) and tumor border (p = 0.040). Patients who received steroids did not only had a decrease in peritumoral edema, but also had a median decrease in tumor volume of 0.02 cc while patients who did not receive steroids had a median increase of 0.06 cc in tumor volume (p = 0.035). CONCLUSION: Our results show that large tumor shifts of brain metastases can occur over time. Because shifts may have a significant impact on the local dose coverage, we recommend minimizing the time between treatment preparation and delivery for Linac based SRS.

Discrete and cyclical movements: unified dynamics or separate control?

In the literature on motor control, three theoretical perspectives on the relation between discrete and cyclical movements may be discerned: (a) cyclical movements are concatenated discrete movements; (b) discrete movements are a limiting case of cyclical movements, and (c) discrete and cyclical movements are motor primitives that may be combined but are irreducible to each other. To examine the tenability of these perspectives, 16 participants performed cyclical and discrete (flexion and extension) reaching movements of various amplitudes to differently sized targets. The kinematic properties of the recorded movements were analyzed and compared in detail. The cyclical, ongoing movements differed markedly from the discrete movements as well as from the first and last half-cycles of a bout of cyclical movements, especially in terms of their symmetry ratio. These effects were largely independent of amplitude, target size and movement direction (flexion-extension). The results obtained ruled out perspective (a) and, in principle, left open perspectives (b) and (c). However, the observed kinematic features were not readily accounted for by the specific dynamical models that have been proposed under perspectives (b) and (c). Future modeling attempts should explicate the dynamics of initiation and abortion of both discrete and cyclical movements.

Reproducibility of the MRI-defined spinal cord position in stereotactic radiotherapy for spinal oligometastases.

PURPOSE: To establish the reproducibility of the MRI-defined spinal cord position within the spinal canal. MATERIALS AND METHODS: We acquired T1- and T2-weighted MRI scans of 15 volunteers on spine levels C7, T8 or L2. The scan protocol was repeated several times for different postures and time intervals. We determined the spinal cord shift (LR, AP, CC) using a rigid, grey value, vertebral body registration, followed by a spinal cord registration. We tested the sensitivity of our method, introducing artificial spinal cord shifts by varying the size and direction of the water-fat-shift (WFS) of the MR sequences. RESULTS: The spinal cord position on MRI is reproducible within approximately 0.2mm SD (LR, AP) and 0.7mm SD (CC) when reproducing the posture on the same day, as well as several weeks later. However, when comparing different postures, shifts of ∼1.5mm were found. Varying the WFS difference between scans (0.6-3.0mm) induced equivalent virtual spinal cord shifts (0.5-2.5mm). CONCLUSIONS: Displacement of the spinal cord inside the spinal canal may occur as a result of posture change. Considering the total geometric accuracy of spine SBRT, MRI-defined spinal cord position is sufficiently reproducible and requires no addition to the typical setup-and-intrafraction motion PRV margin if posture is identical throughout the RT process.

Dosimetric impact of post-operative seroma reduction during radiotherapy after breast-conserving surgery.

PURPOSE: Three boost radiotherapy (RT) techniques were compared to evaluate the dosimetric effect of seroma reduction during RT after breast-conserving surgery (BCS). MATERIALS AND METHODS: Twenty-one patients who developed seroma after BCS were included. Each patient underwent three CT scans: one week before RT (CT(-1)), in the third (CT(3)) and fifth (CT(5)) week of RT. For each patient, three plans were generated. (1) SEQ: whole breast irradiation planned on CT(-1,) sequential boost planned on CT(5), (2) SIB: simultaneous integrated boost planned on CT(-1), (3) SIB adaptive radiation therapy (SIB-ART): planned on CT(-1) and re-planned on CT(3). Irradiated volumes, mean lung (MLD) and maximum heart dose (HD(max)) were projected and compared on CT(5). RESULTS: On average 62% seroma reduction during RT was observed. Volumes receiving ≥ 107% of prescribed whole breast dose were significantly smaller with SIB-ART compared to SEQ and SIB. The undesired volume receiving ≥ 95% of prescribed total dose was also significantly smaller with SIB-ART. For SEQ, SIB-ART and SIB, respectively, small but significant differences were found in MLD (4.2 vs. 4.6 vs. 4.7 Gy) and in HD(max) for patients with left-sided breast cancer (39.9 vs. 35.8 vs. 36.9 Gy). CONCLUSIONS: This study demonstrates a dosimetric advantage for patients with seroma when simultaneous integrated boost is used with re-planning halfway through treatment.

Multiinstitutional study on target volume delineation variation in breast radiotherapy in the presence of guidelines.

PURPOSE: This study aims to determine magnitude, causes and consequences of post-operative breast tumour target volume delineation variation among radiation oncologists in the presence of guidelines. MATERIALS AND METHODS: Excision cavities, CTVs and PTVs of eight breast cancer patients were delineated on CT scans by 13 Dutch radiation oncologists (observers) from 12 Dutch institutes participating in the international Young Boost Trial. Delineated volumes and conformity indices were determined. CTV delineation variation (SD) was determined for anatomically relevant regions. Non-parametric statistics were performed to establish effects of observers, patient characteristics and regions on delineation variation. RESULTS: Even in the presence of delineation guidelines considerable delineation variation is present (0.24

Clinical applicability of cone-beam computed tomography in monitoring seroma volume change during breast irradiation.

PURPOSE: To determine whether cone-beam CT (CBCT) is effective in monitoring seroma reduction during breast irradiation when compared with conventional CT. PATIENTS AND METHODS: This study included 19 women with Stage T1-2 breast cancer treated with breast-conserving therapy. Each patient underwent two to four CT and multiple CBCT scans (mean, 8; range, 7-13 scans) at various time intervals during radiotherapy. Seroma were contoured by two observers on all scans and checked by one radiation oncologist. Seroma clarity was determined according to The British Columbia Cancer Agency Seroma Clarity Score scale, and conformity index (CI) of the two observers was evaluated. Correlations in seroma contours and seroma characteristics between CBCT and CT, as well as interobserver variation, were examined. RESULTS: The mean differences in seroma volume between CT and CBCT (3%, p = 0.3) and between the two observers (6%, p = 0.2) were not statistically significant. Seroma clarity correlated significantly with CI for both CT and CBCT (p = 0.02 and p = 0.001, respectively), indicating the higher the seroma clarity score, the greater the CI between the observers. With seroma clarity 3 or higher for CT and CBCT, a high level of observer concordance was shown (all CI of these scans were >or=50%). CONCLUSION: Volume discrepancy between CBCT and CT and between the two observers was not statistically significant. Seroma clarity influenced observers' ability to contour on CT or CBCT equally. Therefore, CBCT is a good clinical surrogate for CT in monitoring seroma reduction during breast radiotherapy, especially for patients with seroma clarity score 3 or higher.

Clinical factors associated with seroma volume reduction in breast-Conserving Therapy for early-stage breast cancer: a multi-institutional analysis.

PURPOSE: To correlate clinical factors with seroma volume and reduction; and to determine whether cone-beam CT (CBCT) could be used clinically to monitor seroma reduction. PATIENTS AND METHODS: This investigation included 102 women from five institutions with stage T1-2 breast cancer treated with breast-conserving therapy. Two CT scans were acquired: the planning CT (CT1) and a second CT (CT2) during radiotherapy (RT). Seroma was contoured on all scans, and correlations between seroma characteristics and clinical factors were investigated by univariate and multivariate analyses. In a substudy, 10 of the 102 patients received multiple CBCT scans during RT. Seroma were contoured by two observers in the substudy. Fifteen time points at which CT and CBCT were performed within 2 days were identified. The levels of correlation in seroma contours between CBCT and CT and between the two observers were examined. RESULTS: The mean relative seroma reduction from CT1 to CT2 was 54% (p < 0.001). A significant inverse relationship was found between relative seroma reduction per week and number of RT fractions given by univariate and multivariate analyses (p = 0.01, 0.03). The mean difference in contoured seroma volumes between CT and CBCT was 12% (3.3 cm(3)). When assessing the relative difference in seroma contours between Observer 1 and Observer 2, an interobserver difference of 12% was demonstrated. Neither discrepancy was clinically significant. CONCLUSIONS: Radiotherapy seems to hinder seroma reduction. Volume discrepancies between CBCT and CT were minor, with low interobserver variation, indicating that CBCT might be useful in monitoring seroma reduction.

Deterministic and stochastic features of rhythmic human movement.

The dynamics of rhythmic movement has both deterministic and stochastic features. We advocate a recently established analysis method that allows for an unbiased identification of both types of system components. The deterministic components are revealed in terms of drift coefficients and vector fields, while the stochastic components are assessed in terms of diffusion coefficients and ellipse fields. The general principles of the procedure and its application are explained and illustrated using simulated data from known dynamical systems. Subsequently, we exemplify the method's merits in extracting deterministic and stochastic aspects of various instances of rhythmic movement, including tapping, wrist cycling and forearm oscillations. In particular, it is shown how the extracted numerical forms can be analysed to gain insight into the dependence of dynamical properties on experimental conditions.