Commissioning dose computation models for spot scanning proton beams in water for a commercially available treatment planning system.

PURPOSE: To present our method and experience in commissioning dose models in water for spot scanning proton therapy in a commercial treatment planning system (TPS). METHODS: The input data required by the TPS included in-air transverse profiles and integral depth doses (IDDs). All input data were obtained from Monte Carlo (MC) simulations that had been validated by measurements. MC-generated IDDs were converted to units of Gy mm(2)/MU using the measured IDDs at a depth of 2 cm employing the largest commercially available parallel-plate ionization chamber. The sensitive area of the chamber was insufficient to fully encompass the entire lateral dose deposited at depth by a pencil beam (spot). To correct for the detector size, correction factors as a function of proton energy were defined and determined using MC. The fluence of individual spots was initially modeled as a single Gaussian (SG) function and later as a double Gaussian (DG) function. The DG fluence model was introduced to account for the spot fluence due to contributions of large angle scattering from the devices within the scanning nozzle, especially from the spot profile monitor. To validate the DG fluence model, we compared calculations and measurements, including doses at the center of spread out Bragg peaks (SOBPs) as a function of nominal field size, range, and SOBP width, lateral dose profiles, and depth doses for different widths of SOBP. Dose models were validated extensively with patient treatment field-specific measurements. RESULTS: We demonstrated that the DG fluence model is necessary for predicting the field size dependence of dose distributions. With this model, the calculated doses at the center of SOBPs as a function of nominal field size, range, and SOBP width, lateral dose profiles and depth doses for rectangular target volumes agreed well with respective measured values. With the DG fluence model for our scanning proton beam line, we successfully treated more than 500 patients from March 2010 through June 2012 with acceptable agreement between TPS calculated and measured dose distributions. However, the current dose model still has limitations in predicting field size dependence of doses at some intermediate depths of proton beams with high energies. CONCLUSIONS: We have commissioned a DG fluence model for clinical use. It is demonstrated that the DG fluence model is significantly more accurate than the SG fluence model. However, some deficiencies in modeling the low-dose envelope in the current dose algorithm still exist. Further improvements to the current dose algorithm are needed. The method presented here should be useful for commissioning pencil beam dose algorithms in new versions of TPS in the future.

Gravity-driven fingers in fractures: experimental study and dispersion analysis by moment method for a point-source injection.

In this study, we investigate the behavior of a dense contaminant injected from a point-source in a fracture. Our experimental model is a transparent Hele-Shaw cell, 0.5 mm of aperture. A saline solution is injected locally representing the point-source pollution. A Laser Induced Fluorescence (LIF) method provides concentration measurement of the pollution plume. Two propagation patterns have been observed: one and two-finger plumes. If the upper part of the plume is stable over time regardless of the second configuration, the moment when the plume separates into two fingers is highly dependent on both injection flow-rate and contaminant concentration. To further investigate the dispersion process inside the fracture, experimental results are interpreted by the spatial and time moment methods. Resulting dispersivities and plume propagation mean velocity are compared to theoretical values derived from a modified Taylor-Aris dispersion tensor. The longitudinal macro-dispersion obtained suggests an asymptotical behavior of the plume spread regardless of the studied configurations. Experimental local dispersivities derived from time and space moments proved to be close at large times to theoretical values predicted by the density-dependent dispersion tensor (Oltéan et al., 2004). Based on those observations the mechanism behind the separation of the plume into two fingers is believed to be significantly impacted by the pre-asymptotic behavior of the dispersion tensor.

Experimental validation of a Monte Carlo proton therapy nozzle model incorporating magnetically steered protons.

The purpose of this study is to validate the accuracy of a Monte Carlo calculation model of a proton magnetic beam scanning delivery nozzle developed using the Geant4 toolkit. The Monte Carlo model was used to produce depth dose and lateral profiles, which were compared to data measured in the clinical scanning treatment nozzle at several energies. Comparisons were also made between measured and simulated off-axis profiles to test the accuracy of the model's magnetic steering. Comparison of the 80% distal dose fall-off values for the measured and simulated depth dose profiles agreed to within 1 mm for the beam energies evaluated. Agreement of the full width at half maximum values for the measured and simulated lateral fluence profiles was within 1.3 mm for all energies. The position of measured and simulated spot positions for the magnetically steered beams agreed to within 0.7 mm of each other. Based on these results, we found that the Geant4 Monte Carlo model of the beam scanning nozzle has the ability to accurately predict depth dose profiles, lateral profiles perpendicular to the beam axis and magnetic steering of a proton beam during beam scanning proton therapy.

Therapeutic step and shoot proton beam spot-scanning with a multi-leaf collimator: a Monte Carlo study.

In step and shoot spot-scanning, a small-diameter proton beam is magnetically swept and varied in energy in order to cover the tumour. Initial estimates of the beam size indicate that additional collimating hardware will be needed for lower energy proton beams in order to achieve a clinically acceptable lateral dose falloff at the edge of the proton beam. In this report, we present dosimetric data from Monte Carlo simulations with a model of a simple multileaf collimator which indicate that such a device may be used to improve the lateral dose falloff. The dosimetric quantities relevant to the clinical usefulness of the device are studied, including lateral penumbra, leaf transmission and scalloping effect. Multileaf collimation is compared with a differential spot-weighting technique of sharpening the lateral dose falloff.

Advantage of protons compared to conventional X-ray or IMRT in the treatment of a pediatric patient with medulloblastoma.

PURPOSE: To compare treatment plans from standard photon therapy to intensity modulated X-rays (IMRT) and protons for craniospinal axis irradiation and posterior fossa boost in a patient with medulloblastoma. METHODS: Proton planning was accomplished using an in-house 3D planning system. IMRT plans were developed using the KonRad treatment planning system with 6-MV photons. RESULTS: Substantial normal-tissue dose sparing was realized with IMRT and proton treatment of the posterior fossa and spinal column. For example, the dose to 90% of the cochlea was reduced from 101.2% of the prescribed posterior fossa boost dose from conventional X-rays to 33.4% and 2.4% from IMRT and protons, respectively. Dose to 50% of the heart volume was reduced from 72.2% for conventional X-rays to 29.5% for IMRT and 0.5% for protons. Long-term toxicity with emphasis on hearing and endocrine and cardiac function should be substantially improved secondary to nontarget tissue sparing achieved with protons. CONCLUSION: The present study clearly demonstrates the advantage of conformal radiation methods for the treatment of posterior fossa and spinal column in children with medulloblastoma, when compared to conventional X-rays. Of the two conformal treatment methods evaluated, protons were found to be superior to IMRT.

Optimised immunofluorescence procedure for enumeration of Cryptosporidium parvum oocyst suspensions.

The aim of this study was to evaluate an optimised immunofluorescence assay in terms of the variability of sets of counts for Cryptosporidium parvum oocyst suspensions and data recovery and the reliability of the procedure. A coefficient of variation (CV) of 10% was determined to be the maximum value acceptable for count variability. It was found that the optimised IFA tested provided a high precision for the sets of enumerations for suspensions containing 800-20,000 oocysts/mL. The procedure was found to be robust and providing high recovery level (96.3%). In terms of counting precision, the technique described here approaches the performance of flow cytometry and surpasses other manual techniques with a CV of 10% for a concentration close to 800 oocysts/mL. The procedure described is particularly suitable for the production of seed doses and for other applications requiring the titration of oocyst suspensions with a high degree of precision and accuracy.

Experimental investigations and numerical modelling of Cryptosporidium parvum transport behaviour in aquifers.

The purpose of this study was to improve understanding of the potential for transfer of the protozoan pathogen Cryptosporidium parvum through aquifers to drinking water wells. Therefore, the factors characterising this transport were experimentally determined. We have developed a continuously recirculating column assay. The latter allows small amounts of C. parvum oocysts to be manipulated providing as much protection as possible from the risks of contamination. As the analysis of oocyst samples is time consuming, a numerical model, simulating the transport phenomena of oocysts under the experimental conditions of assays, was developed to establish the whole experimental curve of results using a small number of experimental points. The comparisons drawn between analytic solutions, experimental results with tracer (NaCl solution) and numerical simulation were in good agreement. A continuously recirculating column assay was performed using oocysts in suspension (flow rate = 1.43 mL/min). Treated sand was used as previous experiments had shown that no adsorption occurs. We observed almost total filtration (99.85%). To check this result, an assay with an open column was carried out under the same conditions. We observed a filtration value of 97%. Consequently, we may say that the continuously recirculating column assay provides satisfactory results.

[Adaptation of amikacin dosages for the premature infant]. / Adaptation des posologies de l'amikacine chez le prématuré.

Pharmacokinetic studies of amikacin were investigated concomitant with the kidney and auditory function and with the minimal inhibitory concentrations on the causal bacteria in 23 premature neonates with confirmed or suspected infections. It appears that the usual doses administered to newborns or preterm neonates must be decreased and calculated in function to the gestational ages and life's days. Every preterm neonates received a first infusion of 7.5 mg/kg. When premature have less than 14 days of life, amikacin was given at a dose of 3.75 mg/kg every 12 hr for a gestational age less than 32 weeks, or 5 mg/kg every 12 hr for a gestational age between 32 and 37 weeks. After 14 days of life, considering our results it must be necessary to administer 5 or 7.5 mg/kg every 12 hr.

Morphological changes in the operated stomach under the influence of duodenogastric reflux. Clinical follow-up over 20 years.

The chronic changes in the gastric mucosa arising years or even decades after surgery and interpreted as a precancerous state are causally related to the unphysiological irritation due to duodenogastric reflux. It was the objective of our study to determine whether there is an increase in alterations in the gastric mucosa of the operated stomach, as a function of postoperative interval and the particular surgical procedure performed, with consideration for the varying degrees of resultant duodenogastric reflux. Specifically, there were 320 patients and three different operative procedures studied with postoperative follow-up averaging a period of up to 20 years. The synopsis of the results shows not only a progression of the premalignancy apparent in the morphology of the mucosa, but also provides an indication of the varying intensity of duodenogastric reflux associated with each of the operative methods.

When is a corrective procedure indicated for the operated stomach?

Disease occurring as a direct consequence of the surgical treatment of ulcers is not infrequently an indication for remedial surgical intervention. Most frequently it is necessary, on the one hand, to refer to objective information such as the histological findings as well as a gastric function analysis, and, on the other hand, to the clinical picture of the illness. Therefore, we have attempted to summarize the symptoms, the morphology, and the function into a synopsis, which would make it possible t match the severity of gastric disease with a particular mode of therapy. The sum of the three parameters provides a point value between three and twelve. It is our belief that surgical intervention is to be seriously considered above a point score of seven (SFM-Index).

Cell-kinetic investigations in the operated rat stomach to show the influence of duodenogastric reflux. An experimental long-term study.

In has been proven in our own studies that the frequency of carcinoma is closely correlated with the varying intensity of duodenogastric reflux occurring as a result of surgery. Now it was our objective to provide information regarding the changes in cell proliferation kinetics in support of the already established relation, toward which end we conducted an additional autoradiographic study on the gastric mucosa of the same operated animals. Five different operative procedures were performed on the stomachs of 265 female Wistar rats. 3H-Thymidine was used for labeling. Comparison of the labeling rates with the type of operative procedure used revealed an average labeling value typical for each particular procedure. It became evident that increased reflux quite obviously leads to an increase in cell proliferation.

[The ultrastructure of ganglia and newly formed tendon sheaths]. / Zur Ultrastruktur von Ganglien und neugebildeten Sehnenscheiden.

Comparative electron microscopic examination of ganglions (from the tendon sheaths and joint capsules of the hand) as well as that of newly formed tendon sheaths (after resection of digital flexors and their tendon sheaths) indicate that both are the result of an adaptive effect of the mesenchyma which enables the formation of a new synovial organ in the presence of an adequate stimulus.