Polystyrene Slabs Research Articles

SU‐FF‐T‐36: MammoSite Dosimetry Under Condition of Insufficient Buildup and the Proximity of the Balloon to the Lung

Purpose: Brachytherapy dose planning for MammoSite assumes full scatter buildup. Clinically, MammoSite dosimetry is affected by the buildup condition between the balloon and the skin and the reduced backscatter contribution from the lung. We attempted to answer the following questions: what is the effect of insufficient buildup? What is the dose to the lung? Method and Materials: A breast phantom consisting of polystyrene slabs and Styrofoam blocks is constructed. The thickness of slabs may vary to simulate the varying tissues thickness between the balloon surface and skin. Kodak EDR2 films are mounted parallel to the MammoSite catheter between the polystyrene slabs and the Styrofoam blocks. For each thickness of polystyrene slab above the base, the films are irradiated with the same dose. The films are scanned and analyzed by the RIT software. Results: The insufficient dose buildup and the lack of backscatter contribution may lead to underdosage at the prescription depth. With only 1 cm tissue above the balloon surface, the minimum dose at the prescription depth is only 75% of the dose under full scatter buildup. Even with 3.5 cm tissue, the dose at 10 mm is only 85%. The lung dose, on the other hand, exhibits a buildup behavior, which varies with the thickness of tissue. As much as 180% of the prescribed dose may be delivered to the lung in the vicinity to the balloon surface. Conclusion: The insufficient dose buildup and the presence of lung lead to undersage at the prescription distance which is not revealed in all existing planning system since full scatter buildup without heterogeneity correction is assumed. For correct MammoSite dosimetry, the above issues should be addressed properly. The excessive lung dose even under insufficient dose buildup is may be avoided in some cases by careful placement of the balloon.

TU‐C‐T‐6E‐06: First Clinical Experience with Pre‐Treatment and in Vivo IMRT Verification Using EPID Dosimetry

Purpose: The aim of this study was to verify the first IMRT prostate plans made in our clinic with a newly commissioned treatment planning system (TPS, Pinnacle 7.4f) using an amorphous silicon electronic portal imaging device (a‐Si EPID, Elekta iViewGT), both pre‐treatment and in vivo. Method and Materials: For pre‐treatment verification, the plans of 8 patients were re‐calculated on a polystyrene slab phantom. An in‐house developed back‐projection algorithm was used to estimate the dose distribution at the phantom/patient isocentric mid‐plane (perpendicular to the beam‐axis) with the EPID. Each plan was also validated at the isocentre with ionization chamber measurements. Separate fields were measured with film and EPID, with gantry angle =0°. The in vivo mid‐plane dose was estimated with the EPID for the first 3 fractions and weekly thereafter. γ‐evaluation was used to assess 2D dose distributions with criteria of 3% dose difference (of maximum dose) and 3mm distance‐to‐agreement. The evaluated area included all points within the 20% isodose line of each EPID field. Anatomy changes for in vivo measurements were assessed using cone‐beam CT acquired prior to each verified fraction. Results: For pre‐treatment verification, the dose distributions of EPID vs. plan and EPID vs. film agreed within 3% or 3mm for 99.2% and 100% of points, respectively. The average ratio of the measured and planned isocentre dose was 0.987 ±0.003(SD) for ionization chamber and 0.997 ±0.009(SD) for EPID. For the in vivoyfields, 96.7% of dose points were in agreement. Examples of discrepancies were due to variation in gas pockets during treatment and problems calculating the dose distribution in a small area of overlapping segments (1cm2). Conclusion: These results show that an a‐Si EPID can be used to accurately verify IMRT prostate treatments in the mid‐plane of the phantom or patient, both pre‐treatment and in vivo.

Interfacial fracture toughness between glassy polymer networks

AbstractThe interfacial fracture energy, Gc, between glassy crosslinked polystyrene samples was studied with the symmetric double‐cantilever beam test. Compression‐molded polystyrene slabs were crosslinked by γ irradiation in vacuo. The fracture samples were prepared by the welding of two crosslinked polystyrene slabs under contact pressure for 1 h at 150 °C, which was above the glass‐transition temperature for polystyrene (≅104 °C). The fracture toughness tests were performed at room temperature. The interfacial fracture energy was studied as a function of the crosslink density of the slabs. It was found that the interfacial fracture energy decreased with increasing crosslink density. A least‐squares fit of the data showed that the interfacial fracture energy scaled as N, where Nc is the weight‐average chain length between crosslinks (in number of monomer units). A comparison with the predictions made by different models on weak interfaces was made. It was found that if the loops of the network were identified as the connectors responsible for adhesion at the glassy network‐network interfaces, the model by Xu et al. predicted that Gc would scale as N, consistent with the trends in the data. Using the expression for Gc from this model to fit the data the value for the static friction constant per monomer for polystyrene was found to be fmono = 3.5 ± 0.7 × 10−12 N/monomer, in good agreement with the values found in the literature. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1902–1908, 2003

THE EQUILIBRIUM MOISTURE CONTENT OF LOW-DENSITY THERMAL INSULATING MATERIALS/LENGVŲ TERMOIZOLIACINIŲ MEDŽIAGŲ NUOSTOVUSIS DRĖGNIS

Data about water vapour sorption by modern low-density thermal insulating materials are very scarce. The isothermal sorption of water vapour dependent on relative air humidity was investigated for rock and glass wool products in this paper as well as for expanded and extruded polystyrene slabs and cellulose fibre produced in Lithuania, Poland and Estonia. The moisture in these materials is bound by several ways, therefore it is not possibile to express the equilibrium moisture Wp dependency on relative air humidity ϕ by an exact analytical equation [1, 6]. These dependencies were expressed by a two-constant empiric equation (1) for interval ϕ from 0 to 0,97 based on BET equations [1, 7, 8]. The experimental data are given in Figs 1–9, statistical treatment of this data results are given in Tables 1–3. The two fields are typical for all isothermal sorption curves: 0<ϕ<0,8 moisture bound as adsorbate) and 0,8<ϕ<0,97 (capillary bound moisture). The hygroscopicity of investigated glass wool products is higher than for rock wool products and depends on their density. This value is very small for expanded polystyrene and is considerable for cellulose fibre.

Analysis of butyl acrylate diffusion in a glassy polystyrene matrix to predict gradient structure

AbstractTo be able to control composition structure in gradient polymers prepared by sequential polymerization, diffusion phenomena has to be considered, particularly for the first 100% weight increment in a glassy polymer matrix. With that purpose, an analytical model to predict diffusion in that region has been developed for amorphous polymers. The inclusion of a relaxation time to estimate surface concentration changes during sorption led to diffusion coefficients one order of magnitude higher than Fickian coefficients. However, adding a volume increment term to account for polymer swelling, diffusion coefficients went up to 48 times the Fickian values. Experimentally, butyl acrylate with a small amount of photosensitizer was diffused into a slightly crosslinked polystyrene slab matrix at different temperatures in the glassy region. After fixing the gradient composition by photopolymerization, chemical structures throughout the slab were determined by FTIR. The proposed model was confronted with experimental sorption showing a close fit at the different temperatures in the region of interest. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 1343–1348, 2001

THE EQUILIBRIUM MOISTURE CONTENT OF LOW-DENSITY THERMAL INSULATING MATERIALS

Summary Data about water vapour sorption by modern low-density thermal insulating materials are very scarce. The isothermal sorption of water vapour dependent on relative air humidity was investigated for rock and glass wool products in this paper as well as for expanded and extruded polystyrene slabs and cellulose fibre produced in Lithuania, Poland and Estonia. The moisture in these materials is bound by several ways, therefore it is not possibile to express the equilibrium moisture W p dependency on relative air humidity ϕ by an exact analytical equation [1, 6]. These dependencies were expressed by a two-constant empiric equation (1) for interval ϕ from 0 to 0,97 based on BET equations [1, 7, 8]. The experimental data are given in Figs 1–9, statistical treatment of this data results are given in Tables 1–3. The two fields are typical for all isothermal sorption curves: 0<ϕ<0,8 moisture bound as adsorbate) and 0,8<ϕ<0,97 (capillary bound moisture). The hygroscopicity of investigated glass wool products ...

THE INFLUENCE OF NATURAL CONVECTION ON THERMAL PROPERTIES OF BUILDING ENCLOSURE WITH POLYSTYRENE BOARDS/PUTŲ POLISTIRENO PLOKŠTĖMIS IZOLIUOTŲ PASTATŲ SIENŲ ŠILUMINIŲ SAVYBIŲ PRIKLAUSOMYBĖ NUO NATŪRALIOS KONVEKCIJOS

Building insulating materials with good insulation properties usually are porous, because they contain large amounts of air or other gas inside. The pore system can be closed, as in many cellular plastics, or open as in fibre materials. The mechanisms of heat transfer in porous material are: conduction in solid phase, radiation within material and conduction due to the gas confined in the insulation. In an open-pore material, like lightweight mineral wool, the transportation of heat can be further increased by air movement (convection) through the permeable material. Convection is impossible in a closed porous materials like polystyrene (EPS, XPS) boards. But heat losses can be increased by air movement if there are cracks between boards and other building envelope structures. The airflow velocity and direction may vary strongly due to the changing boundary condition. However, at the present time in Lithuania convection in insulating materials is considered as non-existent, when calculating heat transmission and designing building structures. Because of the lack of knowledge concerning air movement in external building structures, and how it is affecting the heat transfer, this investigation has been carried out. For research an equipment (Fig 2) was made, assigned for exploring both vertical and horizontal structures (height 2100 mm, width 1100 mm and thickness up to 300 mm). For reducing heat losses through the sides up to minimum, an equipment was built from slabs (thickness 150 mm). As the hot side of equipment gypsum board was applied to the surface of which 8 heat flow sensors and 9 thermocouples were attached. For maintaining constant and isothermal temperature of the surface of this partition (Θi, =+20°C), heating elements and ventilators were mounted inside the equipment. The cold surface of the equipment was of the same construction as the warm one only with the regulated slide valve with an area of 0,02 m2. It allows exploring the so-called not-ventilated structures. During the test, temperature was measured at different places and depths. The research was performed on the foam polystyrene plates of 3×50 mm of thickness with 3–5 mm air gaps. Measurements were conducted in the following sequence: Two basic measurements of closed structure were performed for constant values of temperatures Θe=0°C and Θe=10°C. In this case the structure was held horizontally and heat flow was directed from top to bottom. Therefore it could be assumed that heat was transferred by conduction and radiation. Measurements of the closed structure were performed on the equipment being in vertical position and for external temperature Θe=0°C and Θe=10°C. Measurements of the opened structure. The measurement carried out for the same external environment conditions, the ventilating orifice being opened. The results of laboratory experiments allowed to assess the heat losses of the enclosure being arranged in the form of wall with air gaps applying foam polystyrene slabs. Different types of structures being investigated are shown in Fig 1. The Nu numbers for closed and ventilated structures are presented in Figs 8 and 9. The research results could be applied to enclosures with hard type insulation too. Although the natural convection does not occur inside the ideal material, but it takes place inside enclosure with air gaps. Thus, actual U-value depends on structural solutions and air tightness on building envelope. If wind barrier is permeable, then air filtration through the structure may cause even critical values for heat losses.

THE INFLUENCE OF NATURAL CONVECTION ON THERMAL PROPERTIES OF BUILDING ENCLOSURE WITH POLYSTYRENE BOARDS

Summary Building insulating materials with good insulation properties usually are porous, because they contain large amounts of air or other gas inside. The pore system can be closed, as in many cellular plastics, or open as in fibre materials. The mechanisms of heat transfer in porous material are: conduction in solid phase, radiation within material and conduction due to the gas confined in the insulation. In an open-pore material, like lightweight mineral wool, the transportation of heat can be further increased by air movement (convection) through the permeable material. Convection is impossible in a closed porous materials like polystyrene (EPS, XPS) boards. But heat losses can be increased by air movement if there are cracks between boards and other building envelope structures. The airflow velocity and direction may vary strongly due to the changing boundary condition. However, at the present time in Lithuania convection in insulating materials is considered as non-existent, when calculating heat transmission and designing building structures. Because of the lack of knowledge concerning air movement in external building structures, and how it is affecting the heat transfer, this investigation has been carried out. For research an equipment (Fig 2) was made, assigned for exploring both vertical and horizontal structures (height 2100 mm, width 1100 mm and thickness up to 300 mm). For reducing heat losses through the sides up to minimum, an equipment was built from slabs (thickness 150 mm). As the hot side of equipment gypsum board was applied to the surface of which 8 heat flow sensors and 9 thermocouples were attached. For maintaining constant and isothermal temperature of the surface of this partition (Θi, =+20°C), heating elements and ventilators were mounted inside the equipment. The cold surface of the equipment was of the same construction as the warm one only with the regulated slide valve with an area of 0,02 m2. It allows exploring the so-called not-ventilated structures. During the test, temperature was measured at different places and depths. The research was performed on the foam polystyrene plates of 3×50 mm of thickness with 3–5 mm air gaps. Measurements were conducted in the following sequence: 1. Two basic measurements of closed structure were performed for constant values of temperatures Θe=0°C and Θe=10°C. In this case the structure was held horizontally and heat flow was directed from top to bottom. Therefore it could be assumed that heat was transferred by conduction and radiation.2. Measurements of the closed structure were performed on the equipment being in vertical position and for external temperature Θe=0°C and Θe=10°C.3. Measurements of the opened structure. The measurement carried out for the same external environment conditions, the ventilating orifice being opened. The results of laboratory experiments allowed to assess the heat losses of the enclosure being arranged in the form of wall with air gaps applying foam polystyrene slabs. Different types of structures being investigated are shown in Fig 1. The Nu numbers for closed and ventilated structures are presented in Figs 8 and 9. The research results could be applied to enclosures with hard type insulation too. Although the natural convection does not occur inside the ideal material, but it takes place inside enclosure with air gaps. Thus, actual U-value depends on structural solutions and air tightness on building envelope. If wind barrier is permeable, then air filtration through the structure may cause even critical values for heat losses.

Effect of low-density lateral interfaces on soft-tissue doses

Purpose : Doses at the interface between tissue and low-density inhomogeneities with the interface positioned perpendicular to the beam direction have been well studied. When the inhomogeneity lies parallel to the beam direction (i.e., a lateral interface), the resulting dose distribution is not as well known. Lateral lung-soft-tissue interfaces are common in many fields used to treat malignancies in the thorax region including tangential breast fields and anteroposterior fields for lung and esophageal cancer. The purpose of this study was to evaluate the dose distribution along lateral interfaces and to determine the implications for treatment. Methods and Materials : A polystyrene and cork slab phantom was irradiated from the side to simulate treatment fields with lateral lung-soft-tissue interfaces. The beam was positioned with the isocenter in polystyrene and the field edge in cork. Cork slabs (0.6-2.5 cm) were used to simulate different thicknesses of lung between the field edge and the target volume. Measurements were made using a parallel plate ionization chamber. With the chamber position held constant, polystyrene slabs were added between the cork and the chamber to study the dose distribution in the interface region. Interface doses were studied as a function of the amount of cork in the field, field size, beam energy (6–18 MV), and depth. Results : Doses in the interface region were lower by as much as 10% compared to doses in a homogeneous phantom. For a given cork width and field size, the magnitude of the underdose increased by several percent as the x-ray energy increased from 6 to 18 MV. The underdose at the interface was 5% for 6 MV and 8% for 18 MV X-rays with a 1-cm cork width. For a 2.5-cm cork width, underdoses of 2.5% and 3% at distances up to 2.5 and 4 mm lateral to the interface were observed for 6- and 18-MV X-rays, respectively. However, doses right at the interface were 1% greater for 6 MV and 3% less for 18 MV than doses in a homogeneous phantom. For a given cork width, the interface doses were not significantly dependent on field width but decreased by an additional 2–3% as the length decreased to 4 cm. Additional decreases were also observed when the measurement depth decreased to 3 cm. With a 1-cm width of cork in the field, a lateral distance of 3–4 mm from the interface was necessary to ensure doses of at least 98% of the homogenous dose with 6-MV X-rays. A lateral distance of 6–7 mm was necessary for 10- and 18-MV X rays. Conclusion : Underdosing will occur in the soft tissues adjacent to low-density inhomogeneities. The magnitude depends primarily on the width of the inhomogeneity seen in the treatment field, but also on field size, depth, and beam energy. For treatment fields with a lateral lung interface, a segment of tissue approximately 3–4 mm thick for 6 MV and 6–7 mm thick for higher-energy beams may be underdosed. Lung widths of ⩾ 1.75 cm as observed on film will generally guarantee doses of at least 96% of those calculated with no inhomogeneity corrections. High-energy beams are often used to treat sites in the thorax or breast to improve dose homogeneity throughout the treatment volume. Potential underdosing due to the presence of lung should be considered and may require a decrease in beam energy or an increase in the margin between the target volume and the field edge to ensure adequate treatment.

Simple calculation of the electron-backscatter factor.

The authors have studied the dependence of the electron-backscatter factor (EBF) on mean electron energy and on backscatterer atomic number by using the semiempirical depth-dose code EDMULT. A plane-parallel electron beam is assumed to be normally incident on a polystyrene slab, which is backed with a layer (backscatterer) of different materials of effectively semi-infinite thickness. A small air cavity to measure ionization is embedded in the polystyrene slab at the boundary facing the backscatterer. The EBF is defined as the ratio of the ionization with the backscatterer to the ionization with a full polystyrene medium, and is approximated by the ratio of the doses computed at the depth of the cavity. Values of EBF obtained show trends similar to the experimental data of Klevenhagen et al. [Phys. Med. Biol. 27, 263-373 (1982)], although the former are generally lower than the latter. When the typical energy spread of clinical electron beams is taken into account, the difference between the experimental and the calculated values is reduced. The present results also show the same trend of increase of the backscatter factor with increasing energy as observed by Klevenhagen et al. in some series of measurements for the lead backscatterer at the lowest energies. This is explained by the rapid buildup of the dose with depth for electrons of low initial energies incident on the full polystyrene medium.

Parallel-plate ionization chamber response in cobalt-60 irradiated transition zones.

The authors study the acceptance of a Capintec parallel-plate ionization chamber. The Capintec chamber is used for dose measurements in a lead and polystyrene slab phantom irradiated with cobalt-60 gamma rays. The authors define an enhancement ratio to quantify the dose measurements. The enhancement ratio equals the ratio of dose measured with the lead slab present to dose measured under equilibrium conditions in polystyrene at equal primary beam attenuation. The measured enhancement ratio at the exit side of the lead/polystyrene interface is 25% lower than the Monte Carlo predicted enhancement ratio. The authors propose that geometric acceptance limitations of the Capintec chamber to large-angle, low-energy electrons are the cause for this difference. A Monte Carlo simulation of the Capintec chamber acceptance confirms the hypothesis.

Anomalous penetrant transport in glassy polymers VI. Effect of temperature on transport

AbstractTransport of liquid cyclohexane through well characterised, initially glassy, crosslinked polystyrene slabs was Investigated at 20, 30, 40, and 50°C. The samples used were produced by bulk polymerization of styrene and divinyl benzene (DVB) at 90°C for 43 hr using benzoyl peroxide as an initiator. The samples tested had initial cross‐linking ratios, X, between 5 and 25 × 10−3 mol DVB/mol styrene. The initial thickness of the samples tested varied from 0.25 mm to 1.80 mm, and the aspect ratio (length to thickness ratio) was maintained above 10;1 in order to analyze the results by one‐dimensional transport equations. Cyclohexane uptake was followed as a function of time along with dimensional changes in the thickness and area of the samples. The results of penetrant uptake as a function of time were analyzed using a simplified exponential expression and employing all the data points from the beginning of the experiment until the time of observation of the maximum in uptake. Good correlations were established between the penetrant uptake and the transport temperature. These results were interpreted in terms of competitive relaxational and diffusional mechanisms.

Anomalous penetrant transport in glassy polymers V. Cyclohexane transport in polystyrene

Transport of liquid cyclohexane through well characterized, initially glassy, crosslinked polystyrene slabs was investigated. The samples were produced by bulk polymerization of styrene and divinyl benzene using benzoyl peroxide as an initiator at 90°C for 48 h; they had initial crosslinking ratios, X, between 0.005 and 0.025 mol DVB/mol styrene, initial thickness of 0.25 mm to 1.80 mm, and the aspect ratio was maintained above 10 to achieve one-dimensional transport. The results of cyclohexane uptake as a function of time were used to elucidate the effects of degree of crosslinking and sample geometry on the mechanisms of penetrant transport. These results were interpreted in terms of relaxational and diffusional mechanisms.

Coupled electron/photon Monte Carlo calculations of X-ray scattering with application to industrial radiography

Abstract Monte Carlo transport methods are used to simulate the scattering of X-rays in polystyrene and iron slabs. The calculations are made with monoenergetic X-ray sources in the energy region from 30 keV (100 keV for iron) to 20 MeV. This energy range includes the energy regions for diagnostic radiology (0.03–0.15 MeV), nuclear medicine (0.1–2.0 MeV) and industrial radiography (0.2–20 MeV). slab thicknesses for polystyrene were 53, 100, and 210 mm and for iron 7 and 14 mm. The present calculations include the effects of secondary electron/positron radiation which become quite important at high energies. As a function of the incident photon energy, the ratio of the scattered to the total radiation (scatter fraction) was found to have a characteristic ‘N’ shape. Increasing the atomic number of the scattering media has the effect of ‘squeezing the N’.

Pressure‐Induced densification in injection molding

AbstractThe effect of pressure on the densification of amorphous polymers in the Injection‐molding process is examined. Density distributions in molded polystyrene slabs were measured for several well‐defined molding histories. In all cases the density of the molded part was spatially inhomogeneous, and its distribution in the slab was closely related to the pressure and temperature histories that prevailed in the molding cavity during the process cycle. The density profile in the gapwise direction followed a characteristic “parabolic” pattern with a minimum at the midplane of the slab. A simple phenomenological model, based on the pressure‐induced densification effect, was constructed to explain the observed density profiles, and close agreement with experimental data was found. Annealing of the molded article at a high temperature (&lt;Tg) caused the density to decrease overall and become more uniform across the part. This is generally consistent with volume‐recovery data for the densified material, which were generated independently in a controlled pressure‐densification experiment.

Anomalous penetrant transport in glassy polymers

Transport of liquid cyclohexane through well characterized, initially glassy, crosslinked polystyrene slabs was investigated as a function of time at 20, 30, 40, and 50 ° C. The samples used were produced by bulk polymerization of styrene and divinyl benzene using benzoyl peroxide as an initiator at 90 ° C for 48 hrs. The samples tested had initial crosslinking ratios, X, between 0.005 and 0.0250 mol DVB/mol styrene, their thickness varied from 0.025 to 0.180 cm, and the aspect ratio was maintained above 10 to achieve one-dimensional transport. A cyclohexane uptake overshoot was observed as a function of time. This overshoot was analyzed as a function of crosslinking ratio and geometric characteristics of the samples and it was attributed to molecular changes of polystyrene during swelling.

Emission of energetic electrons from a Nd-laser-produced plasma

Absolute spectral measurements of 50–500-keV electrons emitted from a Nd-laser-produced plasma are presented. For normally incident irradiation (1015–1016 W/cm2) onto polystyrene slab targets a total emitted energy of ∼1010 electrons is inferred with a total emitted energy of ∼0.2 mJ. The electron emission is observed to be almost the same both in and out of the plane of polarization. Properties of the emitted spectrum, such as spectral hardness and intensity, are observed to be dependent on the pulse shape and the target material.

Electron Depth-Dose Distribution Measurements in Finite Polystyrene Slabs

Experimental depth-dose curves for 2.00-MeV electrons incident on layers of polystyrene were obtained for broad-beam geometry as a function of slab thickness and incident beam angle. Calibrated radiochromic dye films were used as dosimeters. Continuous spatial absorbance changes in the irradiated film were recorded with the aid of a scanning densitometer. Data were obtained for the following conditions: (a) polystyrene thicknesses 0.42, 0.63, and 1.5 times the electron range, and (b) electron-beam incidence angles of 0°, 15°, 30°, 45°, 60°, and 75° to the normal. Comparisons were made with theoretical depth-dose histograms generated by the Monte Carlo computer code ETRAN. Close agreement was found for the two thicker slabs, but energy absorption in the thin slab was observed to be lower than that predicted by the calculations by 5–15%.

A new waveguide method for measuring the permittivity of dielectric slabs

The paper describes a new waveguide method for measuring the complex relative permittivity of dielectric slabs. The slab is mounted in rectangular waveguide either on the waveguide axis or in contact with the side wall. One end of the slab contacts a fixed short-circuit plate. By using a standing-wave detector, the condition is found for the guide wavelength in the dielectric section to equal the free-space wavelength. A simple expression enables the real part of the permittivity to be calculated. From observations of the standing-wave ratio, the attenuation coefficient in the dielectric-loaded waveguide is determined. Another simple expression then enables the imaginary part of the permittivity to be calculated. The theory of the method is developed and illustrated with results obtained using a polystyrene slab.