Quasi-VMAT in high-grade glioma radiation therapy.

PURPOSE: To compare a quasi-volumetric modulated arc therapy (qVMAT) with three-dimensional conformal radiation therapy (3D-CRT) and intensity-modulated radiation therapy (IMRT) for the treatment of high-grade gliomas. The qVMAT technique is a fast method of radiation therapy in which multiple equispaced beams analogous to those in rotation therapy are radiated in succession. PATIENTS AND METHODS: This study included 12 patients with a planning target volume (PTV) that overlapped at least one organ at risk (OAR). 3D-CRT was planned using 2-3 non-coplanar beams, whereby the field-in-field technique (FIF) was used to divide each field into 1-3 subfields to shield the OAR. The qVMAT strategy was planned with 15 equispaced beams and IMRT was planned using 9 beams with a total of 80 segments. Inverse planning for qVMAT and IMRT was performed by direct machine parameter optimization (DMPO) to deliver a homogenous dose distribution of 60 Gy within the PTV and simultaneously limit the dose received by the OARs to the recommended values. Finally, the effect of introducing a maximum dose objective (max. dose < 54 Gy) for a virtual OAR in the form of a 0.5 cm ring around the PTV was investigated. RESULTS: The qVMAT method gave rise to significantly improved PTV95% and conformity index (CI) values in comparison to 3D-CRT (PTV95% = 90.7 % vs. 82.0 %; CI = 0.79 vs. 0.74, respectively). A further improvement was achieved by IMRT (PTV95% = 94.4 %, CI = 0.78). In qVMAT and IMRT, the addition of a 0.5 cm ring around the PTV produced a significant increase in CI (0.87 and 0.88, respectively), but dosage homogeneity within the PTV was considerably reduced (PTV95% = 88.5 % and 92.3 %, respectively). The time required for qVMAT dose delivery was similar to that required using 3D-CRT. CONCLUSION: These findings suggest that qVMAT should be preferred to 3D-CRT for the treatment of high-grade gliomas. The qVMAT method could be applied in hospitals, for example, which have limited departmental resources and are not equipped with systems capable of VMAT delivery.

Dynamic system for the calibration of semi-volatile carbonyl compounds in air.

A dynamic calibration system designed for generating accurate and precise concentrations of semi-volatile carbonyls in the ppb (v/v) (ppbv)-ppt (v/v) (pptv) range has been developed and tested. Alkanals from C6 to C9 were used as test compounds. Diffusion rates of their vapours from capillary tubes were determined theoretically and with two methods whose accuracy was independently evaluated with liquid standard solutions. Methods selected for testing the calibration system were those commonly used for the selective quantification of carbonyls in air. One is based on the well-known reaction with 2,4-dinitrophenylhydrazine (DNPH), followed by the analysis of formed hydrazones by HPLC-UV. The other is based on the retention of carbonyls on graphitic carbon adsorbents, followed by MS detection of the sample injected into a capillary column by thermal desorption. A good consistency was found between the values of the diffusion rates determined by the two methods. The scatter between the two methods was in the range of +/-10% when diffusion rates of ca. 1 ng/s were attained. Experimental values closely approached those calculated by applying the equation describing the diffusion of a vapour in equilibrium with the liquid through a capillary tube.

Distribution of n-alkanes, polynuclear aromatic hydrocarbons and nitrated polynuclear aromatic hydrocarbons between the fine and coarse fractions of inhalable atmospheric particulates.

The distribution ratios of n-alkanes, polynuclear aromatic hydrocarbons (PAHs) and nitrated PAH components between fine and coarse fractions of soot has been investigated in downtown Rome through three field campaigns carried out at different times of the year. The preferential accumulation of almost all species investigated onto fine particles has been observed in all field experiments performed. Moreover, nitrated PAHs had varied distributions, according to the origin of their occurrence in the atmosphere; in fact, congeners of photochemical origin accumulated more in fine particles than those released by primary sources.

Characterization of a rural area in terms of dry and wet deposition.

Atmospheric gaseous pollutants (NO2, SO2, NH3, HNO3) and related ionic species in water-soluble fine particulates and rainwater were monitored from September 1986 to January 1987 with the aim of estimating the acid deposition over a rural area near Rome. A wet-only rain collector and an annular denuder-filter pack sampling system for gases and aerosols were employed to avoid chemical artifact formation. A comparison of the wet and dry deposition rates indicates that atmospheric removal by precipitation was the dominant sink for sulfate and nitrate at the sampling site. Ion balance analysis showed that the main compounds present in aerosols were (NH4)2SO4 and NH4NO3, since the ammonium neutralization factor approached 100% and the acidity content was very low. The marked enrichment of H+, SO4(2-) and NO3- in precipitation compared with NH4+ could be explained by assuming either that SO2 and NO2 are oxidized in cloud droplets or that acidic sulfate and nitrate are scavenged directly in-cloud or below-cloud.

The determination of tetraalkyl lead in air by a denuder diffusion technique.

A diffusion method for the selective determination of tetraalkyl lead (TAL) in air is proposed. Separation from inorganic lead takes place on an ICl-coated annular denuder, where only TAL is removed during sampling. A differential technique making use of two denuders in series prevents any interference from particulate lead. Analysis of denuder acid extracts by flameless atomic absorption spectrometry provides a direct measure of organic lead thus avoiding a complex solvent extraction procedure.

[Determination of the acidity of particulate matter in the urban and industrial atmospheres]. / Determinazione dell'acidità del materiale particolato in atmosfere urbane ed industriali.

A new method is described for the determination of the strong acidity of particulate matter. The method consists in the volumetric titration of an aqueous extract by means of a strong acid. The titration is performed potentiometrically using a glass electrode and the end point is obtained by extrapolation using a Gran's plot. The lowest concentration of strong acid detectable in a sample is about 0.5 microgram/ml expressed as H2SO4. The method has been applied for the determination of the strong acidity content in airborne particulate matter samples and in dusts emitted from industrial sources.

Ozone measurement with silica cartidges and HRGC-MS analysis.

Ozone in ambient air is collected onto silica gel cartridges impregnated with pentafluorophenylhydrazine (PFPH) and 1,2-di(4-pyridyl)ethylene (DPE), so that the pyridine-4 aldehyde formed by DPE oxidation is converted into the corresponding PFPH derivative (PPH). The latter product is determined by HRGC/MS. Since the ozonolysis reaction proceeds stoichiometrically on the cartridge, there is no need for calibration in the gas phase with a standardized ozone source. When compared with UV photometry analyzers, this active chromatographic method (ACM) demonstrates a very good accuracy (ACM/UV photometer = 0.97) and precision (12.0-14.0%) under both laboratory and field sampling conditions at ozone concentrations of 20-200 microg m(-3) and exposure times of 1-3 h. The sampling performance was found to be insensitive to relative humidity (r.h.) variations in the 25-90% range and any interference effects could not be observed from various agents, except light, which can be eliminated by using an aluminium shelter. The detection limit for ozone achievable with the ACM in air samples collected at 0.5 L min(-1) for 1 h was found better than 0.5 microg m(-3).