Proton Beam Therapy in the Reirradiation Setting of Brain and Base of Skull Tumour Recurrences.

The therapeutic management of local tumour recurrence after a first course of radical radiotherapy is always complex. Surgery and reirradiation carry increased morbidity due to radiation-induced tissue changes. Proton beam therapy (PBT) might be advantageous in the reirradiation setting, thanks to its distinct physical characteristics. Here we systematically reviewed the use of PBT in the management of recurrent central nervous system (CNS) and base of skull (BoS) tumours, as published in the literature. The research question was framed following the Population, Intervention, Comparison and Outcomes (PICO) criteria: the population of the study was cancer patients with local disease recurrence in the CNS or BoS; the intervention was radiation treatment with PBT; the outcomes of the study focused on the clinical outcomes of PBT in the reirradiation setting of local tumour recurrences of the CNS or BoS. The identification stage resulted in 222 records in Embase and 79 in Medline as of March 2023. Sixty-eight duplicates were excluded at this stage and 56 were excluded after screening as not relevant, not in English or not full-text articles. Twelve full-text articles were included in the review and are presented according to the site of disease, namely BoS, brain or both brain and BoS. This review showed that reirradiation of brain/BoS tumour recurrences with PBT can provide good local control with acceptable toxicity rates. However, reirradiation of tumour recurrences in the CNS or BoS setting needs to consider several factors that can increase the risk of toxicities. Therefore, patient selection is crucial. Randomised evidence is needed to select the best radiation modality in this group of patients.

In vitro study of a physiological type flow in a bifurcated vascular prosthesis.

Using a cardiovascular simulator allowing the production of physiological conditions, velocity field and pressure-diameter relationship were determined in a bifurcated arterial graft for two geometric configurations of implantation. Velocity measurements give the surgeon attractive and useful information for finding out the best way to implant the graft. The study of the pressure-diameter relationship showed a particular behaviour of the graft; the wall motion of the graft, compared with the pressure wave, being different both in the mother branch at the upstream anastomosis and in the daughter branch.

Velocity distribution along an elastic model of human arterial tree.

An experimental investigation of an elastic model of the human arterial tree, has been performed for physiological type flow by pulsed Doppler ultrasonic velocimetry. The arterial tree model, fabricated in clear polyurethane, includes the aortic arch, with a Starr-Edwards ball valve mounted in the root of the aorta, the descending aorta and the iliac bifurcation. Our study showed that the velocity profile, a few centimeters beyond the valve, is skewed, with higher velocities towards the top and the inner wall (anatomically the posterior and left lateral wall). An inward shift of the maximum velocity and reverse flow are denoted along the inner wall of the aortic arch. The velocity profiles in the descending aorta are blunted. Downstream from the vertex of the iliac bifurcation, there is vorticity creation, but the branching effect is quickly damped by the pulsatility of the flow and the elasticity of the wall.

The effect of unsteadiness on the flow through stenoses and bifurcations.

This paper is concerned with the influence of a stenosis or a bifurcation on the flow through a tube. In particular the effect of unsteadiness is investigated using simple pulsatile and physiological type flows (Fig. 1). The experimental investigations reported herein are concerned with velocity measurements and flow visualizations. (see formula in text) These measurements, performed in a 60 degrees bifurcation, have permitted the reconstruction of the three-dimensional velocity profiles. The importance of the secondary flow in the branching is analyzed for various values of the flow parameters. Results of tests show a strong influence of unsteadiness on flow characteristics and then on hemodynamic factors. One conclusion is the following: if hemodynamic factors play an important role in the problems of atherosclerosis, then, for macrocirculation studies, it is necessary to take into account unsteadiness and, in particular, the actual shape of the flow-time forcing function.

Hemodynamics of endovascular prostheses.

A surgical study (Bergeron et al., 1991, International Angiology 10(3), 182-186) picked out that re-endothelialization of implanted expandable stents, frequently used to reduce the recurrent stenosis rate after balloon angioplasty, was correct and more rapid in femoro-popliteal arteries (quasi-straight vessels) than in iliac arteries (bifurcated vessels). Since it is now well known that local hemodynamics are considered to be an important atherogenic factor, we decided to compare and optimize the shape of the existing equipment, in order to further give some informations to surgeons about the optimal stenting at the site of bifurcation. Therefore, we studied in vitro (1) the influence of the protruding part of a stent on the flow patterns in the branches of an aorto-iliac bifurcation model, and (2) the possibility of reducing or preventing this impact. Qualitative information was obtained from visualizations in the horizontal median plane of the bifurcation model, while Doppler ultrasonic velocimetry provided quantitative data, at different points of the cardiac cycle. Results showed that a standard stent implanted in a daughter branch of the bifurcation may have a considerable influence on flow behaviour when it is sticking out of the daughter branch. A new design of stent, with a bevelled shape, showed a significant reduction of flow disturbance.

In-vitro measurements of the regurgitation of mechanical mitral heart valve prostheses in case of atrial fibrillation.

BACKGROUND AND AIM OF THE STUDY: The characterization of heart valve prostheses requires regurgitation tests to be conducted in pulsatile flow. Although tests are generally conducted in accordance with hemodynamic conditions of a healthy young man, heart valve implantation is often associated with other pathology, such as atrial fibrillation. To run more realistic trials, four mechanical heart valve prostheses were tested with, and then without, atrial contraction. METHODS: The dual activation simulator (DAS) allow simulation of physiologically normal and pathological flows through the mitral valve. The DAS comprises silicon-based cavities, is activated by pumps, and was equipped successively with monoleaflet (Björk-Shiley, Medtronic Hall) and bileaflet (St. Jude Medical, CarboMedics) valves. Each valve (mitral, size 27 mm) was tested under two conditions (with and without atrial contraction) at a mean flow rate of 3 l/min of glycerol/water solution (analog blood viscosity). RESULTS: Leakage volumes were of the same magnitude as the precision of the instruments. Respectively, closing volumes increased from normal conditions to atrial fibrillation from 3.2 to 5.1 ml for Björk-Shiley, from 4.6 to 6.3 ml for Medtronic Hall, from 5 to 6.6 ml for St. Jude Medical, and from 5.2 to 5.4 ml for CarboMedics. The standard deviation was below the precision of measurements (+/- 0.5 ml). CONCLUSION: Without atrial contraction, the valves seemed to be closed by backward flow only, thus confirming earlier reports. This study showed that different heart valves behave differently in pathological situations with regard to their design; this must be considered when selecting a valve for implantation.

Ex vivo evaluation of side-perforated needles by injection of anesthetic solutions into the mandibular bone and the periodontal ligament of pigs.

New 27-gauge side-perforated needles were compared with conventional needles during injection in dense tissues on the basis of (a) the force to be applied on the syringe plunger and (b) the frequency of complete needle clogging. A miniaturized force transducer was used to measure the forces applied to the syringe plunger. One hundred intraosseous injections and one hundred intraligamentary injections were performed in fresh pig mandibles, using both types of needles. Results showed that (a) less force was required when performing injections with the side-perforated needles and (b) side-perforated needles got clogged less frequently than conventional ones. This result is of special interest for routine dental practice.

Injection pressure of anesthetics using 30-gauge needles with or without side perforation.

A testing bench was designed and constructed to simulate resistance by living tissues to the injection of dental anesthetics. A full series of pressure measurements were made on that bench using 30-gauge dental needles: (a) without side perforation; (b) with side perforation; and (c) with side perforation, the axial perforation being clogged at the tip of the needle. The results obtained in this physical model suggest that (a) the injection pressure at the tip of the needles is essentially the same whether there exists a side perforation on the needle wall or not and (b) when the axial perforation is clogged, the anesthetic solution can flow into the tissues through the side perforation under approximately the same pressure as that measured with unclogged needles. The latter result may be of special interest for intraosseous and intraligamentary (periodontal ligament) injections.

Effects of pulsatile versus non-pulsatile pulpal pressure simulations on diffusional transport across human dentine in vitro.

The influence of a simulated pulsatile pulpal pressure on the diffusion of NaCl through slices of human dentine (n = 12) was evaluated in vitro. The average hydraulic conductance of the slices of dentine was 0.0131 +/- 0.0031 microliter/cm2 per min per cmH2O(x +/- SD). A 1 mol/l NaCl solution was placed on one side of the slices of dentine and deionized water on the other side. The time needed to reach a steady state and the quantity of NaCl that diffused through the slice were successively measured on the same slice of dentine, under three conditions: without pressure simulation, with a static pressure of 1.5 kPa, and with a pulsatile pressure varying from 1.2 to 1.8 kPa. The pressure was applied to the deionized water. When a static pressure was applied, the time required to reach a steady state increased from 24 to 30 h. When a pulsatile pressure was applied the time required to reach a steady state decreased from 24 to 12 h. No statistically significant difference was found between the quantity of NaCl that had diffused when the steady state was reached.

Influence of tooth cryopreservation on human dentin permeability, in vitro.

OBJECTIVES: In order to use cryopreserved teeth in laboratory studies, cryopreservation must not modify the functional properties of teeth, in particular dentin permeability. The purpose of this study was to evaluate the effects of tooth cryopreservation on human dentin permeability. METHODS: Three hundred and sixty freshly extracted human noncarious third molars were used. The teeth were randomly assigned to two groups: 180 teeth were stored in phosphate-buffered saline at 4 degrees C and tested within 4 h of collection; 180 teeth were cryopreserved. Hydraulic conductance was calculated according to the method developed by Pashley (Outhwaite et al., 1976). RESULTS: Cryopreserved teeth presented a hydraulic conductance of 8.97 x 10(-3) +/- 4.21 x 10(-3) microL.cm-2.min-1.cm.H(2)0(-1) slightly higher than the hydraulic conductance of the freshly extracted teeth of 8.03 x 10(-3) +/- 3.87 x 10(-3) microL.cm-2.min-1.cm.H(2)0(-1). No statistically significant difference was found between the two groups. SIGNIFICANCE: Under the conditions of this study, cryopreservation did not modify dentin permeability.

In vitro cytotoxicity of dental adhesive systems under simulated pulpal pressure.

OBJECTIVES: Most of the devices used to evaluate the cytotoxicity of resin-based composites in vitro use a dentin barrier test. However, it is difficult to obtain the number of freshly extracted teeth, all on the same day, that is necessary for powerful statistical analysis. Tooth cryopreservation provides a way to build up a supply of teeth. This in vitro study compared cryopreserved teeth and freshly extracted teeth in an evaluation of the cytotoxicity of resin-based composites. In addition, this study also evaluated the effects of pulsatile pressure and the importance of dentin permeability on the cytotoxic response to bonding resins. METHODS: Forty freshly extracted and forty cryopreserved third molars were used. A standardized Class I cavity was prepared within the dentin. The hydraulic conductance of each tooth was recorded. The cavities were filled either with Scotchbond Multi-Purpose Plus and Z 100 (3M Dental Products) or with Optibond and Herculite (Kerr). A plexiglas device was designed to permit 24 h long contact between culture medium and the roof of the pulp chamber while a pulsatile pulpal pressure was simulated. The viability of L 929 cells cultured with a control medium and evaluated by an MTT assay was compared to that of L 929 cells cultured with medium which remained for 24 h in contact with the pulp chamber of restored teeth. A three-way ANOVA was used to compare the cytotoxicity among the different groups. A simple least-squares linear regression was used to seek a relationship between the hydraulic conductance of dentin and the cytotoxicity of composite restorative materials. RESULTS: No significant differences in cytotoxicity were found between the freshly extracted teeth and the cryopreserved teeth (p = 0.53). The cytotoxicity of the resin adhesives was statistically higher when a pulsatile pulpal pressure was simulated (p = 0.04). A significant relationship was found between the hydraulic conductance of dentin and the cytotoxicity of resin-based composites (p = 0.02). SIGNIFICANCE: Cryopreserved teeth can be used for in vitro evaluation of the cytotoxicity of resin adhesives. Pulsatile pulpal pressure simulations increased the in vitro cytotoxicity of the tested materials.

Accuracy of the simplified Bernoulli relationship in measuring pressure gradients across stenosis.

In order to test the validity of the modified Bernoulli equation in predicting pressure gradients across stenotic regions, we have constructed an in-vitro model and studied the influence of the length and of the severity of the stenosis. Under physiological conditions, simultaneous pressure gradients are estimated by both Doppler and direct pressure manometer techniques. Measurements of the pressure gradients (in the range 10-150 mmHg) by the two techniques show that the Doppler estimation using the modified Bernoulli equation underestimated the pressure transducer gradient measurements for every length of stenosis, this underestimation being greater than 45% for very severe stenosis.

Influence of the haemodynamic parameters on the repartition of the flow between an artery and its graft.

The aim of this study was to investigate the repartition of the flow between an artery and its graft for several values of the geometric and dynamic parameters (length and severity of the stenosis, Reynolds number and frequency pulse value). The model, fabricated in silicone, was included in an hydrodynamic test bench, allowing to reproduce physiological conditions. Our study showed that the severity of the stenosis was the most influent parameter on the repartition of the flow; in particular, a 75% severity was necessary to obtain a repartition 70-30% between the graft and the artery.

A new dual activation simulator of the left heart that reproduces physiological and pathological conditions.

Heart valve replacements are often associated with cardiac pathologies, but valvular prostheses are still tested in vitro under the same physiological conditions as for a healthy young man. Therefore a new mock circulatory system of the left heart, the dual activation simulator (DAS), has been built. The DAS allows atrial and ventricular dynamics to be controlled with pumps that activate anatomically shaped silicon models of the cavities. The mitral flow is a two-peak waveform. The E/A ratio can be changed, and the A-wave can be suppressed to simulate, for instance, atrial fibrillation. The cardiac rhythm and the mean flow-rate can be changed at will. The ability of the DAS to reproduce physiological flow is assessed by computation of the aortic input impedance and by harmonic analysis of left ventricular and atrial pressures. It allows the behaviour of valve prostheses to be studied in various conditions of concern to clinicians and can be a useful tool for engineers to improve valve prostheses or validate diagnostic tools such as 3D colour Doppler. The DAS and its capacities are described.

Time-frequency analysis of the noise produced by the closing of artificial heart valves: an in vitro study.

Clinical investigations showed that patients with an implanted mechanical heart valve are sometimes disturbed by the noise produced by the valve closing. The aim of this study was to investigate the noise generated by mechanical artificial heart valves with reference to the one produced by biological valves. This type of biological valve was used as a standard because it does not disturb the patient. We used an in vitro approach with a cardiovascular simulator. The noise signal was recorded simultaneously using a hydrophone and an accelerometer. During each cardiac cycle, because of the shortness of the signal (15-25 ms) and of the transient state, rapid frequency dynamics limited the usefulness of stationary analysis techniques for the first heart sound. Therefore, a time-frequency technique was much more convenient than a classic Fourier analysis. We used a discrete wavelet transform that pointed out the time fluctuation of each frequency component. Globally, mechanical valves produced a high sound level within the octave bandwidths centered on 64 Hz up to 512 Hz, while the amplitude of these components decreased rapidly for the biological valve.

Near velocity field downstream prosthetic valves in aortic position.

Using a cardiovascular simulator to duplicate in vitro the flow conditions through valves in aortic position, bidimensional velocity maps very near the valve are reconstructed, from an ultrasonic 8 Mhz doppler system, in an elastic model of the ascending aortic arch. Three mechanical heart valves representative of the different types of commercial models (a tilting disc, a ball in cage and a two-leaflet valve) and a new bileaflet prototype were investigated. From examination of the velocity field, it is possible to define the main characteristics of the valve wake and to observe the development of negative velocities associated with regurgitant flows. From a comparison with tests in rigid tubes, the role played by the arch elasticity is analysed.

Ventricular flow dynamic past bileaflet prosthetic heart valves.

To characterise hydrodynamic properties of prosthetic heart valves in mitral position, ultrasonic velocity measurements were performed using a cardiovascular simulator. A Duromedics and a Saint-Jude Medical bileaflet heart valve were tested. The Saint-Jude valve was oriented first in an anatomical position, i.e. the tilt axis parallel to the septal wall, and then in an anti-anatomical position. In the anti-anatomical position, from mid diastole to mid systole, two contrarotative vortices are generated in the ventricle by the interaction between the flow directed by the leaflets downstream from the lateral orifices and the ventricular wall motions. In the anatomical position, the mitral flow penetrates the ventricle principally through the lateral orifice proximal to the septal wall, due to the vortex in the atrial chamber. The mitral inflow then circulates along the septal wall to the apex, and produces a large ventricular vortex during systole. In the anatomical position, the Saint-Jude thus provides a better ventricular washout during this phase. The mitral inflow through the Duromedics in the anti-anatomical position produces two contrarotative vortices in the ventricle, but in the opposite sense than downstream the Saint-Jude valve; the flows that penetrate through the lateral orifices are directed to the ventricular walls and then recirculate to the centre of the ventricle, providing a very fluctuating flow near the apex. Thus, a slight difference in valve design produces a significant difference in the ventricular flow fields.

[Prostheto-prosthetic and aorto-prosthetic anastomosis using stents, threads, clips and staples. In vitro comparative study]. / Anastomoses prothéto-prothétiques et aorto-prothétiques par stents, fils de suture, clips et agrafes. Etude comparative sur banc d'essai.

OBJECTIVE: --To evaluate mechanical strength of new potential systems of vascular prostheses anastomosis versus usual suture (4.0 yarn), --To advance objective quantified data in order to establish the specifications of a new quick and reliable mechanical anastomosis device for laparoscopic surgery. MATERIAL AND METHODS: Two experimental studies were conducted in order to quantify the mechanical resistance of anastomoses between two Dacron vascular prostheses and anastomoses between one Dacron vascular prosthesis and one cadaver abdominal aorta segment. Existing materials, which have generally used for other types of surgery, were applied for these studies (clips, staples, stents). These systems of anastomosis were compared to usual suture, used as reference. RESULTS: The mechanical strength of an anastomosis between two Dacron vascular prostheses performed with staples or the same number of stitches is of equivalent magnitude. Anastomoses made with clips or stent are ten to fifteen times weaker than those made with stitches. We did not succeed in performing an anastomosis with staples on cadaver aorta segments because aorta segments tear when staples are applied. In the experiments with a hand-sewn graft, the aorta always tor before the suture, without breakage of the suture. CONCLUSION: From these in vitro trials, we can advance that a continuous suture is probably far too resistant in relation to the aorta own resistance. As we do not know accurately the physiologic strength applied to a vascular prosthesis in vivo, one acceptance criterion from a safety point of view for a new anastomosis system must be that its strength will be equal to the well-proven continuous suture (greater than 150 N) or to the aorta breaking point (between 100 and 160 N). From that point of view, anastomoses performed with clips or a stent are not convenient, unless special clips or stents can be developed for this application. The mechanical strength is of staples sufficient but their design has to be adapted to this particular type of anastomosis.

[Reliability and perspectives in peroperative flowmetry. An original computer-assisted ultrasonic technic]. / Fiabilité et perspectives de la débimétrie per opératoire. Une technique ultrasonore informatisée originale.

To mitigate the lack of reliability of currently used flowmetry technics, an original method was developed based on a single window 15 MHz Doppler flowmeter and an Apple IIe computer with data acquisition system. Eleven successive measurements of instantaneous rate were made in an arterial section. A mean flow was determined by integration of mean rate in section. The reliability of the method was evaluated by an experimental study on a hydrodynamic bench reproducing physiologic flow conditions with an error always less than 8%. An in vivo study in 30 patients provided 100 measurements of arterial flow before and after surgical arterial reconstruction. The mean error value was less than 10%. Among the risks of error, those due to the probe was reduced by specially conceived probes. The most important factor was that of respiration, this latter factor imposing an integration time of rate of signal of 30 seconds to eliminate errors due to respiration. The conventional measurement time for other configurations is 6 seconds but this leads to a mean error of 25% which can attain 60%. The perspective of miniaturization of the apparatus in the near future with acceleration of measurements using a multi-window Doppler should allow flow measurement in 30 seconds and control of surgical reconstructions (on healthy arteries, vein grafts and prostheses but excluding PTFE). Similarly, it should be possible to improve evaluation of so-called vasoactive drugs.