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Antonio Pedotti

Publications and source records attributed to Antonio Pedotti.

15 recordsLinked to original sources
PubMed2006

Patient set-up verification by infrared optical localization and body surface sensing in breast radiation therapy.

BACKGROUND AND PURPOSE: The aim of the study was to investigate the clinical application of a technique for patient set-up verification in breast cancer radiotherapy, based on the 3D localization of a hybrid configuration of surface control points. MATERIALS AND METHODS: An infrared optical tracker provided the 3D position of two passive markers and 10 laser spots placed around and within the irradiation field on nine patients. A fast iterative constrained minimization procedure was applied to detect and compensate patient set-up errors, through the control points registration with reference data coming from treatment plan (markers reference position, CT-based surface model). RESULTS: The application of the corrective spatial transformation estimated by the registration procedure led to significant improvement of patient set-up. Median value of 3D errors affecting three additional verification markers within the irradiation field decreased from 5.7 to 3.5 mm. Errors variability (25-75%) decreased from 3.2 to 2.1 mm. Laser spots registration on the reference surface model was documented to contribute substantially to set-up errors compensation. CONCLUSIONS: Patient set-up verification through a hybrid set of control points and constrained surface minimization algorithm was confirmed to be feasible in clinical practice and to provide valuable information for the improvement of the quality of patient set-up, with minimal requirement of operator-dependant procedures. The technique combines conveniently the advantages of passive markers based methods and surface registration techniques, by featuring immediate and robust estimation of the set-up accuracy from a redundant dataset.

Breast Neoplasms↗
PubMed2006

Robust frameless stereotactic localization in extra-cranial radiotherapy.

In the field of extra-cranial radiotherapy, several inaccuracies can make the application of frameless stereotactic localization techniques error-prone. When optical tracking systems based on surface fiducials are used, inter- and intra-fractional uncertainties in marker three-dimensional (3D) detection may lead to inexact tumor position estimation, resulting in erroneous patient setup. This is due to the fact that external fiducials misdetection results in deformation effects that are poorly handled in a rigid-body approach. In this work, the performance of two frameless stereotactic localization algorithms for 3D tumor position reconstruction in extra-cranial radiotherapy has been specifically tested. Two strategies, unweighted versus weighted, for stereotactic tumor localization were examined by exploiting data coming from 46 patients treated for extra-cranial lesions. Measured isocenter displacements and rotations were combined to define isocentric procedures, featuring 6 degrees of freedom, for correcting patient alignment (isocentric positioning correction). The sensitivity of the algorithms to uncertainties in the 3D localization of fiducials was investigated by means of 184 numerical simulations. The performance of the implemented isocentric positioning correction was compared to conventional point-based registration. The isocentric positioning correction algorithm was tested on a clinical dataset of inter-fractional and intra-fractional setup errors, which was collected by means of an optical tracker on the same group of patients. The weighted strategy exhibited a lower sensitivity to fiducial localization errors in simulated misalignments than those of the unweighted strategy. Isocenter 3D displacements provided by the weighted strategy were consistently smaller than those featured by the unweighted strategy. The peak decrease in median and quartile values of isocenter 3D displacements were 1.4 and 2.7 mm, respectively. Concerning clinical data, the weighted strategy isocentric positioning correction provided the reduction of fiducial registration errors, featuring up to 61.7% decrease in median values (versus 46.8% for the unweighted strategy) of initial displacements. The weighted strategy proved high performance in minimizing the effects of fiducial localization errors, showing a great potential in improving patient setup. The clinical data analysis revealed that the application of a robust reconstruction algorithm may provide high-quality results in patient setup verification, by properly managing external fiducials localization errors.

Algorithms↗
PubMed2006

Chest wall mechanics during pressure support ventilation.

INTRODUCTION: During pressure support ventilation (PSV) a part of the breathing pattern is controlled by the patient, and synchronization of respiratory muscle action and the resulting chest wall kinematics is a valid indicator of the patient's adaptation to the ventilator. The aim of the present study was to analyze the effects of different PSV settings on ventilatory pattern, total and compartmental chest wall kinematics and dynamics, muscle pressures and work of breathing in patients with acute lung injury. METHOD: In nine patients four different levels of PSV (5, 10, 15 and 25 cmH2O) were randomly applied with the same level of positive end-expiratory pressure (10 cmH2O). Flow, airway opening, and oesophageal and gastric pressures were measured, and volume variations for the entire chest wall, the ribcage and abdominal compartments were recorded by opto-electronic plethysmography. The pressure and the work generated by the diaphragm, rib cage and abdominal muscles were determined using dynamic pressure-volume loops in the various phases of each respiratory cycle: pre-triggering, post-triggering with the patient's effort combining with the action of the ventilator, pressurization and expiration. The complete breathing pattern was measured and correlated with chest wall kinematics and dynamics. RESULTS: At the various levels of pressure support applied, minute ventilation was constant, with large variations in breathing frequency/ tidal volume ratio. At pressure support levels below 15 cmH2O the following increased: the pressure developed by the inspiratory muscles, the contribution of the rib cage compartment to the total tidal volume, the phase shift between rib cage and abdominal compartments, the post-inspiratory action of the inspiratory rib cage muscles, and the expiratory muscle activity. CONCLUSION: During PSV, the ventilatory pattern is very different at different levels of pressure support; in patients with acute lung injury pressure support greater than 10 cmH2O permits homogeneous recruitment of respiratory muscles, with resulting synchronous thoraco-abdominal expansion.

Adult↗
PubMed2005

3D optoelectronic analysis of interfractional patient setup variability in frameless extracranial stereotactic radiotherapy.

PURPOSE: To investigate size and frequency of interfractional patient setup variability in hypofractionated stereotactic extracranial radiotherapy. METHODS AND MATERIALS: Infrared optical 3D tracking of surface markers was applied to quantify setup variability on 51 patients. Isocenter position repeatability was assessed by means of frameless anatomic calibration and was compared with portal image evaluation. Specific data analysis allowed for compensation of patients' breathing movements and for separation of the effects of operator-dependent misalignments and respiration-induced displacements. Effects of patient position (supine vs. prone) and treatment table configuration were investigated. RESULTS: Patient positioning assisted by the optical tracking device allowed reducing displacements of surface control points within the 3-mm range. Errors in isocenter localization were in the range of a few millimeters. This was in agreement with the portal image evaluation. Breathing motion introduced appreciable errors, which increased control points and isocenter 3D variability. This effect was significantly higher than those related to other investigated factors. CONCLUSIONS: The role of infrared optical tracking devices for patient positioning is assessed on a large patient population. Their use in the frame of high-precision radiotherapy is emphasized by the application of related methodologies for breathing phase detection and frameless isocenter localization.

Abdominal Neoplasms↗
PubMed2005

Inverse dynamic investigation of voluntary leg lateral movements in weightlessness: a new microgravity-specific strategy.

This study deals with the quantitative assessment of exchanged forces and torques at the restraint point during whole body posture perturbation movements in long-term microgravity. The work was based on the results of a previous study focused on trunk bending protocol, which suggested that the minimization of the torques exchanged at the restraint point could be a strategy for movement planning in microgravity (J. Biomech. 36(11) (2003) 1691). Torques minimization would lead to the optimization of muscles activity, to the minimization of energy expenditure and, ultimately, to higher movement control capabilities. Here, we focus on leg lateral abduction from anchored stance. The analysis was based on inverse dynamic modelling, leading to the estimation of the total angular momentum at the supporting ankle joint. Results agree with those obtained for trunk bending movements and point out a consistent minimization of the torques exchanged at the restraint point in weightlessness. Given the kinematic features of the examined motor task, this strategy was interpreted as a way to master the rotational dynamic effects on the frontal plane produced by leg lateral abduction. This postural stabilizing effects was the result of a multi-segmental compensation strategy, consisting of the counter rotation of the supporting limb and trunk accompanying the leg raising. The observed consistency of movement-posture co-ordination patterns among lateral leg raising and trunk bending is put forward as a novel interpretative issue of the adaptation mechanisms of the motor system to sustained microgravity, especially if one considers the completely different kinematics of the centre of mass, which was observed in weightlessness for these two motor tasks.

Adult↗
PubMed2005

Redundant system of passive markers for ultrasound scanhead tracking.

Scanhead tracking by opto-electronic (OE) systems allows high accuracy in three-dimensional (3-D) freehand ultrasound imaging. In this paper, a new set of methods is proposed and compared with the standard approach [Gram-Schmidt method (GS)]. Three redundancy-based algorithms are introduced to compensate for possible loss of markers during data acquisition: regression plane (RP), multiple Gram-Schmidt (MGS), and center of mass least square (CMLS). When combined with the ultrasound instrument, the root-mean-squared (RMS) uncertainty in locating target points, over a working volume of 420 mm x 490 mm x 100 mm, improved by 7% and 24% using MGS and CMLS method respectively, compared to GS. A lower improvement was obtained with RP methods (5%), using the best marker configuration. In conclusion, CMLS method provides a robust and accurate procedure for 3-D freehand ultrasound scanhead tracking, able to manage possible loss of markers, with interesting perspectives for image fusion and body referenced 3-D ultrasound.

Algorithms↗
PubMed2004

Dosimetric effects within target and organs at risk of interfractional patient mispositioning in left breast cancer radiotherapy.

PURPOSE: To investigate the effects of interfraction setup uncertainties on the dose distribution within the clinical target volume (CTV) and the organs at risk (OAR) of left-sided breast cancer patients undergoing external radiotherapy. METHODS AND MATERIALS: Interfractional setup errors were assessed by measuring surface control points displacements during 89 irradiation sessions in 4 patients, by means of opto-electronic localization. The measured position deviations were fed back to the treatment planning system for the evaluation of the corresponding dosimetric effects within CTV and OARs (lung, heart). RESULTS: Results revealed errors above 5 mm on some of the control points, but corresponding volumetric variations were on average below 2% for both the CTV within the 95-105% dose range and the OARs receiving more than 50% and 90% of the prescribed dose. A specific sensitivity to the setup errors was found as a function of the treatment plan design, leading to isolated cases exhibiting volumetric variations of CTV and OARs exceeding 2%. CONCLUSIONS: This study confirms the potential increase of treatment quality provided by the systematic patient position verification and highlights the role of opto-electronic position detection systems for the real-time check of patient setup errors and the evaluation of the corresponding dosimetric consequences, as a way to achieve consistent dose delivery.

Analysis of Variance↗
PubMed2004

Effects of posture and bronchoconstriction on low-frequency input and transfer impedances in humans.

We simultaneously evaluated the mechanical response of the total respiratory system, lung, and chest wall to changes in posture and to bronchoconstriction. We synthesized the optimal ventilation waveform (OVW) approach, which simultaneously provides ventilation and multifrequency forcing, with optoelectronic plethysmography (OEP) to measure chest wall flow globally and locally. We applied an OVW containing six frequencies from 0.156 to 4.6 Hz to the mouth of six healthy men in the seated and supine positions, before and after methacholine challenge. We measured mouth, esophageal, and transpulmonary pressures, airway flow by pneumotachometry, and total chest wall, pulmonary rib cage, and abdominal volumes by OEP. We computed total respiratory, lung, and chest wall input impedances and the total and regional transfer impedances (Ztr). These data were appropriately sensitive to changes in posture, showing added resistance in supine vs. seated position. The Ztr were also highly sensitive to lung constriction, more so than input impedance, as the former is minimally distorted by shunting of flow into alveolar gas compression and airway walls. Local impedances show that, during bronchoconstriction and at typical breathing frequencies, the contribution of the abdomen becomes amplified relative to the rib cage. A similar redistribution occurs when passing from seated to supine. These data suggest that the OEP-OVW approach for measuring Ztr could noninvasively track important lung and respiratory conditions, even in subjects who cannot cooperate. Applications might range from routine evaluation of airway hyperreactivity in asthmatic subjects to critical conditions in the supine position during mechanical ventilation.

Adult↗
PubMed2003

The densitometric physical fractionator for counting neuronal populations: application to a mouse model of familial amyotrophic lateral sclerosis.

The method of the 'densitometric physical fractionator' presented here realizes an accurate and reproducible stereological quantification, not requiring a motorized or controlled z-axis, of cell populations. It includes a special software for the calibration of the optics alignment of the microscope and a semi-automatic procedure that integrates specific densitometric functions for image analysis, to identify the reference volume and the particle profiles. This improves the identification of the cells significantly, reduces variability in the subjective choice of the particles by the operators, and allows a consistent saving of time during the analysis. The method is proved to be unbiased and the accuracy and reproducibility of the results has been validated through intra- and inter-operator analyses. Furthermore, it has been applied to calculate the loss of spinal motor neurons during pathology progression in transgenic mice for superoxide-dismutase Cu/Zn dependent (SOD1) mutants, a model of amyotrophic lateral sclerosis (ALS).

Amyotrophic Lateral Sclerosis↗
PubMed2003

Inverse dynamic investigation of voluntary trunk movements in weightlessness: a new microgravity-specific strategy.

Present investigation faces the question of quantitative assessment of exchanged forces and torques at the restraints during whole body posture exercises in long-term microgravity. Inverse dynamic modelling and total angular momentum at the ankle joint were used in order to reconstruct movement dynamics at the restraining point, represented by the ankle joint. The hypothesis is that the minimisation of the torques at the interface point assumes a key role in movement planning in 0 g. This hypothesis would respond to an optimisation of muscles activity, a minimisation of energy expenditure and therefore an accurate control of body movement. Results show that the 0 g movement strategy adopted ensures that the integral of the net ankle moment between the beginning and the end of the movement is zero. This expected mechanical constraint is not satisfied when 0 g movement dynamics is simulated using terrestrial kinematics. This accounts for a significant imposed change of movement strategy. Particularly, the efficient compensation of the inertial effects of the segments in terms of total angular momentum at the ankle joint was evidenced. These results explain the exaggerated axial synergies, observed on kinematics and which moved centre of mass (CM) backward from its already backward initial positioning, as a tool for enhancing the compensation and achieving the desired minimisation of the torques exchanges at the restraints.

Abdomen↗
PubMed2002

Absence of center of mass control for leg abduction in long-term weightlessness in humans.

The present investigation describes for the first time leg lateral abduction performance during long-term microgravity exposure. Two astronauts took part in the experiments, starting 2 weeks into the mission and lasting for 5 months. Results on joint angles kinematics confirm previous investigations on parabolic flights, showing good task fulfillment for both subjects. Special interest was focused on whole body center of mass (CM) positioning. As in short-term microgravity, no initial CM lateral shift toward the 'supporting' leg was observed. In contrast with short-term microgravity and ground-based experiments, no stabilization of the CM medio-lateral position was found but a significant shift of CM toward the moving leg was observed. This suggests that the adaptation to sustained weightlessness might have led to a microgravity-specific motor strategy for leg abduction, which was not focused on CM strategy.

Adult↗
PubMed2002

Method for the analysis of posture and interface pressure of car drivers.

Biomechanical study of car driver posture is one of the most referenced aspects for the ergonomic design process of the whole vehicle. The aim of this work is to present a multi-factor method for the analysis of sitting posture and the resulting interactions of the car driver body with the cushion and the backrest. The proposed method, based on the combined use of an optoelectronic system for motion capture and suitable matrices of pressure sensors, has allowed the measurement of a large set of car driver posture parameters and the identification of specific sitting strategies characterising the driving posture, despite the different behaviours of the analysed subjects.

Adult↗
PubMed2002

Determinants of exercise performance in normal men with externally imposed expiratory flow limitation.

To understand how externally applied expiratory flow limitation (EFL) leads to impaired exercise performance and dyspnea, we studied six healthy males during control incremental exercise to exhaustion (C) and with EFL at approximately 1. We measured volume at the mouth (Vm), esophageal, gastric and transdiaphragmatic (Pdi) pressures, maximal exercise power (W(max)) and the difference (Delta) in Borg scale ratings of breathlessness between C and EFL exercise. Optoelectronic plethysmography measured chest wall and lung volume (VL). From Campbell diagrams, we measured alveolar (PA) and expiratory muscle (Pmus) pressures, and from Pdi and abdominal motion, an index of diaphragmatic power (W(di)). Four subjects hyperinflated and two did not. EFL limited performance equally to 65% W(max) with Borg = 9-10 in both. At EFL W(max), inspiratory time (TI) was 0.66s +/- 0.08, expiratory time (TE) 2.12 +/- 0.26 s, Pmus approximately 40 cmH2O and DeltaVL-DeltaVm = 488.7 +/- 74.1 ml. From PA and VL, we calculated compressed gas volume (VC) = 163.0 +/- 4.6 ml. The difference, DeltaVL-DeltaVm-VC (estimated blood volume shift) was 326 ml +/- 66 or 7.2 ml/cmH2O PA. The high Pmus and long TE mimicked a Valsalva maneuver from which the short TI did not allow recovery. Multiple stepwise linear regression revealed that the difference between C and EFL Pmus accounted for 70.3% of the variance in DeltaBorg. DeltaW(di) added 12.5%. We conclude that high expiratory pressures cause severe dyspnea and the possibility of adverse circulatory events, both of which would impair exercise performance.

Adult↗
PubMed2002

Respiratory muscle dynamics and control during exercise with externally imposed expiratory flow limitation.

To determine how decreasing velocity of shortening (U) of expiratory muscles affects breathing during exercise, six normal men performed incremental exercise with externally imposed expiratory flow limitation (EFLe) at approximately 1 l/s. We measured volumes of chest wall, lung- and diaphragm-apposed rib cage (Vrc,p and Vrc,a, respectively), and abdomen (Vab) by optoelectronic plethysmography; esophageal, gastric, and transdiaphragmatic pressures (Pdi); and end-tidal CO2 concentration. From these, we calculated velocity of shortening and power (W) of diaphragm, rib cage, and abdominal muscles (di, rcm, ab, respectively). EFLe forced a decrease in Uab, which increased Pab and which lasted well into inspiration. This imposed a load, overcome by preinspiratory diaphragm contraction. Udi and inspiratory Urcm increased, reducing their ability to generate pressure. Pdi, Prcm, and Wab increased, indicating an increased central drive to all muscle groups secondary to hypercapnia, which developed in all subjects. These results suggest a vicious cycle in which EFLe decreases Uab, increasing Pab and exacerbating the hypercapnia, which increases central drive increasing Pab even more, leading to further CO2 retention, and so forth.

Abdominal Muscles↗