Variations in proton scanned beam dose delivery due to uncertainties in magnetic beam steering.

The purpose of this work was to develop a method to calculate and study the impact of fluctuations in the magnetic field strengths within the steering magnets in a proton scanning beam treatment nozzle on the dose delivered to the patient during a proton therapy treatment. First, an analytical relationship between magnetic field uncertainties in the steering magnets and the resulting lateral displacements in the position of the delivered scanned beam "dose spot" was established. Next, using a simple 3D dose calculation code and data from a validated Monte Carlo model of the proton scanning beam treatment nozzle, the uniform dose delivery to a 3D treatment volume was calculated. The dose distribution was then recalculated using the calculated lateral displacements due to magnetic field fluctuations to the proton pencil beam position. Using these two calculated dose distributions, the clinical effects of the magnetic field fluctuations were determined. A deliberate displacement of four adjacent spots either toward or away from each other was used to determine the "maximum" dose impact, while a random displacement of all spots was used to establish a more realistic clinical dose impact. Changes in the dose volume histogram (DVH) and the presence of hot and cold spots in the treatment volume were used to quantify the impact of dose-spot displacement. A general analytical relationship between magnetic field uncertainty and final dose-spot position is presented. This analytical relationship was developed such that it can be applied to study magnetic beam steering for any scanned beam nozzle design. Using this relationship the authors found for the example beam steering nozzle used in this study that deliberate lateral displacements of 0.5 mm or random lateral displacements of up to 1.0 mm produced a noticeable dose impact (5% hot spot) in the treatment volume. A noticeable impact (3% decrease in treatment volume coverage) on the DVH was observed for random displacements of up to 1.5 mm. For the scanning nozzle studied in this work, these displacement values correlated with an uncertainty value of 2.04% in the magnetic field values of the nozzle steering magnets. The authors conclude that fluctuations in the dose-spot delivery caused by uncertainty in the magnet fields used for beam steering could have clinically significant effects on the delivered dose distribution. Due to differences in the design and implementation of proton beam scanning nozzles at different treatment facilities, the effects of magnetic field fluctuations of dose delivery should be evaluated and understood for each specific nozzle design during clinical commissioning of the treatment nozzle.

Vendors: part of the supply chain solution.

St. Joseph Health System in Bryan, Texas, recently undertook a formal performance improvement process in which vendors were treated as partners rather than adversaries. The health system established three systemwide initiatives-vendor summit, a vendor of the year award, and a vendor survey-to improve vendor relationships. Engaging vendors in dialogue to help reduce supply costs ultimately helped St. Joseph save nearly $8 million within just six months.

Neonatal percutaneous central venous lines: fit to burst.

OBJECTIVE: To examine pressure changes in neonatal percutaneous central venous catheters under varying laboratory conditions and to quantify the risks of rupture in clinical practice. DESIGN: We tested 27-gauge polyurethane Premicath and 24-gauge silicone ECC (both Vygon, Norristown, PA) catheters. Burst pressures were determined by applying a slowly ramped pressure to catheters that were occluded at the tip. Flow-pressure relationships were defined by increasing flow rates through patent catheters from 5 to 499 ml/h. Pressure changes during the manual flushing of catheters were determined for patent and occluded catheters and with different syringe sizes. RESULTS: The mean burst pressure for polyurethane catheters (1730.8 kPa, 95% CI 1634.7 to 1826.8) was higher than for silicone catheters (275.6 kPa, 95% CI 240.4 to 310.8). Polyurethane catheters demonstrated an approximately fivefold greater margin of safety above manufacturer recommended operating pressures before burst compared to silicone catheters. Pressures remained at safe levels in both catheters over the range of flows generally used in neonatal practice. Hand-flushing of obstructed silicone catheters caused rupture in 5/6 silicone catheters tested, in comparison to 0/16 polyurethane catheters. CONCLUSIONS: Polyurethane central venous catheters have a greater pressure tolerance than silicone catheters and are less likely to rupture under experimental conditions. Obstructed silicone catheters rupture easily when flushed. Catheters were not tested in human infants.