Tissue-equivalent Phantom Material Research Articles

Dosimetric Characterization of DSF/NaOH/IA-PAE/R. spp. Phantom Material for Radiation Therapy

Background: Different compositions of DSF/NaOH/IA-PAE/R. spp. composite particleboard phantoms were constructed. Methods: Photon attenuation characteristics were ascertained using gamma rays from 137Cs and 60Co. Absorbed doses at the location of an ionization chamber and Gafchromic EBT3 radiochromic films were calculated for high-energy photons (6 and 10 MV) and electrons (6, 9, 12, and 15 MeV). Results: The calculated TPR20,10 values indicate that the percentage discrepancy for 6 and 10 MV was in the range of 0.29-0.72% and 0.26-0.65%. It was also found that the relative difference in the dmax to water and solid water phantoms was between 1.08-1.28% and 5.42-6.70%. The discrepancies in the determination of PDD curves with 6, 9, 12, and 15 MeV, and those of water and solid water phantoms, ranged from 2.40-4.84%. Comparable results were found using the EBT3 films with variations of 2.0-7.0% for 6 and 10 MV photons. Likewise, the discrepancies for 6, 9, 12, and 15 MeV electrons were within an acceptable range of 2.0-4.5%. Conclusions: On the basis of these findings, the DSF/NaOH/IA-PAE/R. spp. particleboard phantoms with 15 wt% IA-PAE addition level can be effectively used as alternative tissue-equivalent phantom material for radiation therapy applications.

Fabrication and characterization of epoxy resin-added Rhizophora spp. particleboards as phantom materials for computer tomography (CT) applications

ABSTRACT This study aims to evaluate the average density, mechanical stability, and the suitability of Rhizophora spp. particleboard bonded with epoxy resin as tissue-equivalent phantom materials. The particleboards were fabricated with added epoxy at levels of 0%, 5%, 10%, and 15%. CT scan was used to evaluate the epoxy distribution. The sample with 15% epoxy level complied with the Japanese Industrial Standards. Moreover, the crystallinity was measured by microscopic analysis and X-ray diffraction (XRD). The results showed that the values of mass density and effective atomic number of the studied samples were well agreed and close to the value of water. Both microscopic analysis and XRD results showed the utility of epoxy in filling up the gaps and increasing the crystallinity. In addition, the standard deviation (SD) value of fabricated particleboard bonded with 15% epoxy resin provided a good matching with the SD value of Catphan 600 phantom. Furthermore, 15% of epoxy, as a binder material, was considered the best percentage to achieve high performance and to enhance the mechanical stability of Rhizophora particleboards. In conclusion, epoxy resin improves the mechanical and physical properties of Rhizophora spp. particleboards to be performed as a phantom material.

Characterization of Rhizophora SPP. particleboards with SOY protein isolate modified with NaOH/IA-PAE adhesive for use as phantom material at photon energies of 16.59–25.26 keV

In this work, Rhizophora spp. particleboard phantoms were made using SPI-based adhesives, modified with sodium hydroxide and itaconic acid polyamidoamine-epichlorohydrin (0, 5, 10, and 15 wt%). An X-ray computed tomography (CT) imaging system was used to ascertain the CT numbers and density distribution profiles of the particleboards. The SPI-based/NaOH/IA-PAE/Rhizophora spp. particleboard phantoms with 15 wt% IA-PAE addition level had the highest solid content, flexural strength, flexural modulus, and internal bonding strength of 36.06 ± 1.08%, 18.61 ± 0.38 Nmm−2, 7605.76 ± 0.89 Nmm−2, and 0.463 ± 0.053 Nmm−2, respectively. The moisture content, mass density, water absorption, and dimensional stability were 6.93 ± 0.27%, 0.962 ± 0.037 gcm−3, 22.36 ± 2.47%, and 10.90 ± 0.86%, respectively. The results revealed that the mass attenuation coefficients and effective atomic number values within the 16.59–25.26 keV photon energy region, were close to the calculated XCOM values in water, with a p-value of 0.077. Moreover, the CT images showed that the dissimilarities in the discrepancy of the profile density decreased as the IA-PAE concentrations increased. Therefore, these results support the appropriateness of the SPI-based/NaOH/IA-PAE/Rhizophora spp. particleboard with 15 wt% IA-PAE adhesive as a suitable tissue-equivalent phantom material for medical health applications.

Physical and mechanical properties of soy-lignin bonded Rhizophora spp. particleboard as a tissue-equivalent phantom material

Experimental binderless and adhesive-bonded particleboards were made from three different sample sizes, 0 to 103 µm, 104 to 210 µm, and 211 to 500 µm from Rhizophora spp. wood trunk at 1.0 g cm-3. The objective was to evaluate the physical and mechanical properties of the particleboards. The binderless and soy-lignin bonded particleboards were fabricated and studied based on the density, internal bonding, modulus of rupture, water absorption, and thickness swelling. Microstructure study using scanning electron microscopy (SEM) and elemental analysis by carbon hydrogen nitrogen (CHN) analyser were also performed. Particleboards with adhesives improved the internal bond strength. Smaller particle sizes also were shown to be able to improve the thickness swelling outcomes, with lower hygroscopic properties. The SEM images showed that smaller particle size allowed better bonding with adhesives and provided superior strength in the fabrication of tissue equivalent phantom material. The CHN ratio demonstrated by soy flour and lignin revealed no major difference when compared with the Rhizophora spp. samples, showing basic chemical composition of natural adhesives, which was crucial in the fabrication of tissue-mimicking phantom. The study revealed the potential of soy flour and lignin as adhesives for the fabrication of Rhizophora spp. particleboard as a tissue equivalent phantom material.

TISSUE EQUIVALENT MATERIALS FROM SPC-SPI/NAOH/IA-PAE BONDED MANGROVE WOOD CHARACTERIZED FOR RADIATION THERAPY DOSIMETRY

This research focuses on dosimetric measurements in bio-based tissue equivalent phantom materials, designed using soy protein concentrate (SPC), soy protein isolate (SPI), Rhizophora spp. wood, sodium hydroxide, and itaconic acid polyamidoamine-epichlorohydrin resin with an ionization chamber and GafchromicTH EBT3 film dosimeters. The measurements were performed under exposure to 6 MV and 10 MV photon, and 6 MeV and 15 MeV electron beams. The particleboard samples were exposed to a dose of 100 cGy and 10 x 10 cm2 field size at a source-to-surface distance of 100 cm. The dosimeters were irradiated at measurement depths of 1.5, 2.5 and 3.0 cm, respectively, inside the phantom slabs. The particleboards presented superior physical and mechanical properties. The dose measurements revealed excellent agreement with that of water and solid water phantoms. In addition, comparison between the measured dosimetric properties is well within 2%, 2%, 10% and 5.5% for 6 MV, 6 MeV, 10 MV and 15 MeV energies of the maximum dose for the field size tested. This study had successfully shown that SPC-SPI/NaOH/IA-PAE bonded Rhizophora spp. particleboards are promising tissue equivalent phantom materials with merit for medical applications.

Evaluation of raw-data-based and calculated electron density for contrast media with a dual-energy CT technique.

The aim of the current study is to evaluate the accuracy and the precision of raw-data-based relative electron density (REDraw) and the calibration-based RED (REDcal) at a range of low-RED to high-RED for tissue-equivalent phantom materials by comparing them with reference RED (REDref) and to present the difference of REDraw and REDcal for the contrast medium using dual-energy CT (DECT). The REDraw images were reconstructed by raw-data-based decomposition using DECT. For evaluation of the accuracy of the REDraw, REDref was calculated for the tissue-equivalent phantom materials based on their specified density and elemental composition. The REDcal images were calculated using three models: Lung-Bone model, Lung-Ti model and Lung-Ti (SEMAR) model which used single-energy metal artifact reduction (SEMAR). The difference between REDraw and REDcal was calculated. In the titanium rod core, the deviations of REDraw and REDcal (Lung-Bone model, Lung-Ti model and Lung-Ti model with SEMAR) from REDref were 0.45%, 50.8%, 15.4% and 15.0%, respectively. The largest differences between REDraw and REDcal (Lung-Bone model, Lung-Ti model and Lung-Ti model with SEMAR) in the contrast medium phantom were 8.2%, -23.7%, and 28.7%, respectively. However, the differences between REDraw and REDcal values were within 10% at 20mg/ml. The standard deviation of the REDraw was significantly smaller than the REDcal with three models in the titanium and the materials that had low CT numbers. The REDcal values could be affected by beam hardening artifacts and the REDcal was less accurate than REDraw for high-Z materials as titanium. The raw-data-based reconstruction method could reduce the beam hardening artifact compared with image-based reconstruction and increase the accuracy for the RED estimation in high-Z materials, such as titanium and iodinated contrast medium.

Evaluation of image quality and recovery coefficient of corn starch-bonded Rhizophora spp. particleboards as phantom for SPECT/CT imaging

The aim of this study was to evaluate the performance of corn starch-bonded Rhizophora spp. particleboards as phantom for SPECT/CT including the image contrast, source dimension ratio and recovery coefficient values. Phantom set made of the Rhizophora spp. particleboards was constructed according to the Jaszczak phantom commonly used in SPECT/CT with external dimension of 22 and 18 cm diameter and length respectively. Cylindrical vials with different diameter sizes filled with 99mTc unsealed source were inserted in drilled holes of the constructed particleboards phantom. The particleboards phantom was scanned by using SPECT/CT scanning mode and the SPECT images were reconstructed using clinical protocol. The results showed that the contrast value, source dimension ratio and recovery coefficient of Rhizophora spp. particleboards in good agreement with Jaszczak phantom. The overall results showed an excellent agreement of performance between corn starch-bonded Rhizophora spp. particleboards to the Jaszczak (water) as standard phantom material. The overall results indicated that the corn starch-bonded Rhizophora spp. can be highly recommended to be used as tissue-equivalent phantom material for Quality Assurance and dosimetry works in SPECT/CT imaging.

Measurement of attenuation coefficients and CT numbers of epoxy resin and epoxy-based Rhizophora spp particleboards in computed tomography energy range

This study aims to evaluate the attenuation properties of epoxy resin and Rhizophora spp. particleboards bonded with epoxy resin as tissue equivalent phantom materials. The calculated linear and mass attenuation coefficients of epoxy resin and Rhizophora spp. particleboards bonded with three different weight percentages of the epoxy resin (5%, 10% and 15%) were compared with theoretical (XCOM) and experimental measurements of human liver tissue and water at the same energy levels. The 241Am and 109Cd point sources were used to measure the linear and mass attenuation coefficients of the samples at gamma energies; 26.3, 59.5 and 88.0 keV. The computed tomography (CT) scanner was employed to determine the mean attenuation values (CT number) for the fabricated samples and water at CT tube energy 120 kVp. The linear and mass attenuation coefficients of epoxy resin and fabricated Rhizophora spp. particleboard bonded with 15% of epoxy resin provided excellent agreement to the values of XCOM calculated in the human liver tissue and water, respectively. The CT number results showed that the epoxy resin and the Rhizophora spp. particleboard bonded with15% epoxy were in a good agreement with those of human liver tissue and water, respectively. Therefore, the overall attenuation measurements of this study verify the applicability of epoxy resin as a phantom material to mimic the human liver in CT examinations and the epoxy–Rhizophora spp. particleboard fabricated with 15% epoxy resin can be used as a tissue equivalent material corresponding to CT energy range.

A scintillator-based approach to monitor secondary neutron production during proton therapy.

The primary objective of this work is to measure the secondary neutron field produced by an uncollimated proton pencil beam impinging on different tissue-equivalent phantom materials using organic scintillation detectors. Additionally, the Monte Carlo code mcnpx-PoliMi was used to simulate the detector response for comparison to the measured data. Comparison of the measured and simulated data will validate this approach for monitoring secondary neutron dose during proton therapy. Proton beams of 155- and 200-MeV were used to irradiate a variety of phantom materials and secondary particles were detected using organic liquid scintillators. These detectors are sensitive to fast neutrons and gamma rays: pulse shape discrimination was used to classify each detected pulse as either a neutron or a gamma ray. The mcnpx-PoliMi code was used to simulate the secondary neutron field produced during proton irradiation of the same tissue-equivalent phantom materials. An experiment was performed at the Loma Linda University Medical Center proton therapy research beam line and corresponding models were created using the mcnpx-PoliMi code. The authors' analysis showed agreement between the simulations and the measurements. The simulated detector response can be used to validate the simulations of neutron and gamma doses on a particular beam line with or without a phantom. The authors have demonstrated a method of monitoring the neutron component of the secondary radiation field produced by therapeutic protons. The method relies on direct detection of secondary neutrons and gamma rays using organic scintillation detectors. These detectors are sensitive over the full range of biologically relevant neutron energies above 0.5 MeV and allow effective discrimination between neutron and photon dose. Because the detector system is portable, the described system could be used in the future to evaluate secondary neutron and gamma doses on various clinical beam lines for commissioning and prospective data collection in pediatric patients treated with proton therapy.

TH-AB-204-01: Cherenkov- Excited Luminescence Scanned Imaging (CELSI) for High-Resolution, Deep-Tissue, in Vivo Optical Molecular Imaging with Limited Radiation Dose

Purpose: A new imaging modality Cherenkov-excited luminescence scanned imaging (CELSI) is demonstrated illustrating that LINAC beams induce Cherenkov emission within tissue, and that in-turn can excite luminescence of optical probes. This is achieved in a highly spatially confined fashion thereby allowing scanned imaging of distributions of luminescent sources. Methods: A 5 mm thick line-excitation megavoltage X-ray beam (6 MV) was collimated and moved by the multi-leaf collimator (MLC) of a linear accelerator (LINAC), to scan in 3 orthogonal directions. The scan in this demonstration was through a rat abdomen for lymph node imaging. The node was injected with oxygen-sensitive phosphor (Oxyphor PtG4), having strong luminescence lifetime, which is sensitive to the local oxygen concentration. During the scanning, Cherenkov-excited luminescence was continuously integrated by an intensified charge-coupled device (ICCD) synchronized to radiation pulses, and the position of the total signal was back-projected to the position of the scanning beam. Results: The lymph node was accurately located in the axillary region by CELSI imaging. Through lifetime measurement of the luminescence signal from within the lymph node, the pO2 was found to be reporting the true oxygenation level. Phantom studies validated that an inclusion with size below 1 mm could be reconstructed through a layer of 20 mm thick tissue equivalent phantom material. Concentrations of PtG4 down to 100 nM were detectable and capillary tubes containing the probe with diameters down to 200 µm could be resolved by CELSI, at 5 mm depth in tissue equivalent phantoms. Conclusion: CELSI is reported here for the first time, as an innovative optical molecular imaging technique by utilizing the LINAC as an optical scanning and excitation device. Potential applications of CELSI include reconstructions of interested optical probes and recoveries of local physiological information with relatively high spatial resolution.

Characterization of the rhizophora particleboard as a tissue-equivalent phantom material bonded with bio-based adhesive

In this study, some characteristics of Rhizophora spp. particleboards bonded with Serishoom (traditional animal–based adhesive) as a phantom material was investigated. The Rhizophora spp. particleboards were fabricated in two Serishoom adhesive treatment levels (6% and 12%) with three Rhizophora spp. particle sizes (≤ 149 µm, 149 µm – 500 µm, and 500 µm – 1000 µm) at 1 g.cm-3 of the target density. The internal bond strength and the dimensional stability of the Serishoom-bonded Rhizophora spp. particleboards were improved by using the smaller Rhizophora spp. particle size and the higher Serishoom adhesive treatment level. The effective atomic numbers of the Serishoom-bonded Rhizophora spp. particleboards were determineted to be 7,56 to 7,58 by an energy dispersive X-ray, which is in good agreement with those of water and breast tissue. In addition, the density distribution profiles of the fabricated Serishoom-bonded Rhizophora spp. particleboards were determined by the Kriging method with the use Surfer8 computer software, which indicated that there was good density homogeneity throughout the Serishoom-bonded Rhizophora spp. particleboards. The results showed a potential of the Serishoom-bonded Rhizophora spp. particleboard bonded with Serishoom to be used as a phantom material.

Some properties of particleboards produced from Rhizophora spp. as a tissue-equivalent phantom material bonded with Eremurus spp.

The objective of this study is to evaluate the mechanical and physical properties of the particleboard manufactured from Rhizophora spp. in three particle sizes bonded with powdered Eremurus spp. root as a bio-based adhesive in two adhesive treatment levels. The samples acquired high internal bond strength values when the Rhizphora spp. particle size was reduced and the adhesive treatment level was increased. Dimensional stability normally increased with the reduced Rhizophora spp. wood particle size. The hydrophilic property of Eremurus spp. indicates that dimensional stability also increased with decreased adhesive treatment level. However, dimensional stability is affected by the adhesive treatment level when the wood particle size is smaller than that of the adhesive particle. The density distributions of the fabricated particleboards were evaluated using Surfer8 software, which showed significant homogeneity in all samples. The microstructures of the fabricated particleboards were investigated by field emission scanning electron microscopy, which refers to the better surrounding adhesive with bigger particles than Rhizophora spp. particles. This study indicates the potential of Eremurus spp. root as a bio-adhesive, which improved the characterization of Rhizophora spp. particleboard.

Dedicated phantom materials for spectral radiography and CT

As x-ray imaging technology moves from conventional radiography and computed tomography (CT) to spectral radiography and CT, dedicated phantom materials are needed for spectral imaging. The spectral phantom materials should accurately represent the energy-dependent mass-attenuation coefficients of different types of tissues. Although tissue-equivalent phantom materials were previously developed for CT and radiation therapy applications, these materials are suboptimal for spectral radiography and CT; they are not compatible with contrast agents, do not represent many of the tissue types and do not provide accurate values of attenuation characteristics of tissue. This work provides theoretical framework and a practical method for developing tissue-equivalent spectral phantom materials with a required set of parameters. The samples of the tissue-equivalent spectral phantom materials were developed, tested and characterized. The spectral phantom materials were mixed with iodine, gold and calcium contrast agents and evaluated. The materials were characterized by CT imaging and x-ray transmission experiments. The fabricated materials had nearly identical densities, mass attenuation coefficients, effective atomic numbers and electron densities as compared to corresponding tissue materials presented in the ICRU-44 report. The experimental results have shown good volume uniformity and inter-sample uniformity (repeatability of sample fabrication) of the fabricated materials. The spectral phantom materials were fabricated under laboratory conditions from readily available and inexpensive components. It was concluded that the presented theoretical framework and fabrication method of dedicated spectral phantom materials could be useful for researchers and developers working in the new area of spectral radiography and CT. Independently, the results could also be useful for other applications, such as radiation therapy.

SU-GG-T-265: Stopping Power for Tissue Equivalent Materials and Hounsfield Numbers for Proton Radiation Treatment Planning: Calculation and Measurements

Purpose: To generate a proton stopping power calibration curve from tissue equivalent materials combined with Hounsfield Unit (HU) values measured by an in house CT scanner for use in proton treatment planning. Method and Materials: Tissue equivalent phantom materials (Gammex Model 467) used for CT calibration were placed at the center of a water tank (40×30×30 cm3) and scanned with the CT scanner to measure their HU values. Image reconstruction was done with 5 mm slice thickness. In addition, the tissue equivalent phantom material relative stopping powers were measured with 197.1 MeV protons whose defining range was 18.28 cm. Ten phantom materials were individually placed in front of a water tank. A PPCO5 parallel plate chamber was used to measure pristine Bragg peaks in water. Results: A stoichiometric calibration method was used to characterize the CT scanner by fitting the measured HU values to the equation HU = ρerel (A Z3.86 + B Z1.86 + C). Parameter A, B, and C are specific to the CT scanner used in this measurement and they correspond to photoelectric, Rayleigh and Compton cross sections. These fit parameters were used to calculate the HU values for the tissues whose compositions are listed in ICRP (1975). In addition, proton relative stopping powers for these materials were calculated by the Bethe-Bloch formula. The relative stopping power for each phantom material was also measured from the difference of the pulled back Bragg peak compared to that of water, and the results were compared. Conclusion: A stopping power versus HU value calibration curve for the proton treatment planning system was generated.

SU‐FF‐T‐280: Evaluation of the Accuracy, and Energy Dependence of the Nano‐Dot Dosimeters

Purpose: Characteristics and clinical application of the diode, TLD, and Nano‐dot have been studied by various investigators. However, there is a limited publication on clinical application of the Nano‐dot detectors (Landauer®)1. Despite the detailed investigations on characteristics of Nano‐dot, such as time, temperature, and depth, there is no data on energy dependence and accuracy of this dosimeter. The goal of this project is to evaluate the accuracy, energy dependence, and also positional dependence of the Nano‐dots in their clinical applications. Material and method: Accuracy and energy dependence of the Nano‐dot response have been investigated using the megavoltage photon and electron beams from Varian Clinac 2100/EX2 Linear Accelerator. The irradiated in tissue equivalent phantom material were read using a MircoStar reader. The responses of the Nano‐dots were converted to absorbed dose by calibrating the reader using a set of calibrated Nano‐dots which were irradiated in the calibration condition for doses ranging from 0.0 to 400 cGy. The measured absorbed doses for other irradiated Nano‐dots were analyzed as a function of beam energy and dose. Results: The results of these investigations show that the response of the Nano‐dots are very reproduceable (<0.2%). However, up to 5% variation among different Nano‐dots exposed to the same dose and the same beam energy has been observed. These dosimeters are less sensitive to higher energy photon beams. Accurate localization of the Nano‐dots on the patient is a significant factor on clinical application of this detector. Conclusion: Nano‐dots must be carefully calibrated for the different beam energy. Therefore, using the same calibration factors on the MicroStar reader, one has to verify that the results to be corrected appropriately, if it is used for other beam energies.1. Paul A. Jursinic, “Characterization of optically stimulated luminescent dosimeters, OSLDs, for clinical dosimetric measurements, Med. Phys. 34 (12) 4594–4604 (2007).

Dosimetric evaluation of a newly designed low dose rate brachytherapy applicator for treatment of cervical cancer with extension into the lower vagina

Currently, patients having cervical cancer with extension into the lower vagina are being treated with a combination of the Fletcher–Suit applicator, which treats the cervix, and a vaginal cylinder, which treats the lower vagina. With this method, patients receive two separate implants—a procedure that creates greater uncertainty in the dose distribution and unnecessary patient inconvenience.To reduce the uncertainty of the dose delivery and to eliminate patient inconvenience, a new applicator was designed and fabricated at the University of Kentucky for treatment of cervical cancer extending into the lower vagina. In addition, the geometric design of the new device allows for treatment of cervical cancer without extension into the lower vagina and simultaneously provides advantages relative to the commonly used Fletcher–Suit applicator.The dosimetric characteristics of this new applicator (hereafter called Meigooni applicator) were determined using experimental procedures. The measurements were performed using tissue‐equivalent phantom material (Solid Water: Gammex RMI, Middleton, WI) that was machined to accommodate the applicator and LiF thermoluminescent dosimetry chips. The applicator was loaded with C137s brachytherapy sources in a standard loading scheme. A similar experimental procedure was performed using the currently available Fletcher–Suit mini‐ovoid applicator. The results obtained with each applicator were compared with the values calculated by two commercially available treatment planning systems.The experiments showed that the Meigooni applicator allows for safe single treatment of cervical cancer that has extended into the lower vagina, eliminating the need for two separate treatment techniques. Moreover, the Meigooni applicator can function as an alternative to the Fletcher–Suit applicator for the treatment of patients with cervical cancer.PACS number: 87.53.Jw

SU‐FF‐I‐26: Tissue Equivalent Phantoms for the Evaluation of Tube Current Modulated CT Dose and Image Quality

Purpose: To develop and test new, flexible, tissue‐equivalent phantoms for the evaluation of tube current modulation dose reduction and image quality in CT. The developed phantom material also has applications for mammographic and 4‐D time varying phantoms. Method and Materials: A compressible, flexible, urethane‐based tissue equivalent phantom material was developed and utilized in the production of ellipsoid shaped phantoms for CT imaging. Multiple phantoms were created, each with different major (26–40 cm) and minor (18–28 cm) axes, in order to model patients of varying dimensions and thicknesses. All phantoms were made to be integrated with a Catphan CT image quality phantom as well as CTDI dose assessment phantoms. Image evaluation software was utilized in order to evaluate several image quality parameters in CT images taken using the phantoms in order to quantify the effects of tube current modulation in CT scanners for varying techniques. Ion chamber and gated fiber optically coupled dosimeters were also used with the phantoms in order to evaluate the effects of tube current modulation on dose to patients of varying dimensions. Results: It was found that the use of ellipsoid shaped phantoms allowed for more accurate observation of dose and image quality effects of tube current modulation in CT scanners over traditional circular acrylic phantoms. Patient doses were found the be less for studies in which tube current modulation was in use as compared to standard CT techniques, however the degree of dose reduction was found to be largely influenced by the major and minor axes of the ellipse. Conclusion: This work shows potential of ellipsoid phantoms to aid in dose reduction in CT scanning through tube current modulation by allowing more accurate modeling of actual patient dimensions.

Theoretical modelling, experimental studies and clinical simulations of urethral cooling catheters for use during prostate thermal therapy

Urethral cooling catheters are used to prevent thermal damage to the urethra during thermal therapy of the prostate. Quantification of a catheter's heat transfer characteristics is necessary for prediction of the catheter's influence on the temperature and thermal dose distribution in periurethral tissue. Two cooling catheters with different designs were examined: the Dornier Urowave catheter and a prototype device from BSD Medical Corp. A convection coefficient, h, was used to characterize the cooling ability of each catheter. The value of the convection coefficient (h = 330 W m−2 °C−1 for the Dornier catheter, h = 160 W m−2 °C−1 for the BSD device) was obtained by comparing temperatures measured in a tissue-equivalent phantom material to temperatures predicted by a finite element method simulation of the phantom experiments. The coefficient was found to be insensitive to the rate of coolant flow inside the catheter between 40 and 120 ml min−1. The convection coefficient method for modelling urethral catheters was incorporated into simulations of microwave heating of the prostate. Results from these simulations indicate that the Dornier device is significantly more effective than the BSD catheter at cooling the tissue surrounding the urethra.

A 915-MHz antenna for microwave thermal ablation treatment: physical design, computer modeling and experimental measurement.

A 915-MHz antenna design that produces specific absorption rate distributions with preferential power deposition in tissues surrounding and including the distal end of the catheter antenna is described. The design features minimal reflected microwave current from the antenna flowing up the transmission line. This cap-choke antenna consists of an annular cap and a coaxial choke which matches the antenna to the coaxial transmission line. The design minimizes heating of the coaxial cable and its performance is not affected by the depth of insertion of the antenna into tissue. The paper provides a comparison of results obtained from computer modeling and experimental measurements made in tissue equivalent phantom materials. There is excellent agreement between numerical modeling and experimental measurement. The cap-choke, matched-dipole type antenna is suitable for intracavitary microwave thermal ablation therapy.

Experimental evaluation of the thermal properties of two tissue equivalent phantom materials

Tissue equivalent radio frequency (RF) phantoms provide a means for measuring the power deposition of various hyperthermia therapy applicators. Temperature measurements made in phantoms are used to verify the accuracy of various numerical approaches for computing the power and/or temperature distributions. For the numerical simulations to be accurate, the electrical and thermal properties of the materials that form the phantom should be accurately characterized. This paper reports on the experimentally measured thermal properties of two commonly used phantom materials, i.e. a rigid material with the electrical properties of human fat, and a low concentration polymer gel with the electrical properties of human muscle. Particularities of the two samples required the design of alternative measuring techniques for the specific heat and thermal conductivity. For the specific heat, a calorimeter method is used. For the thermal diffusivity, a method derived from the standard guarded comparative-longitudinal heat flow technique was used for both materials. For the 'muscle'-like material, the thermal conductivity, density and specific heat at constant pressure were measured as: k = 0:31 0:001W(mK)-1, rho = 1026 7kgm-3, and c p = 4584 107J(kgK)-1. For the 'fat'-like material, the literature reports on the density and specific heat such that only the thermal conductivity was measured as k = 0:55W(mK)-1.