Tissue-equivalent Phantom Material Research Articles

Intracavitary hyperthermia: Construction and heat patterns of individualized vaginal prototype applicators

Patients who have inoperable or previously irradiated cervical recurrences, especially if very confined and alone, pose a challenging problem to the clinician. Low-dose irradiation and hyperthermia seems to be a promising method for salvage treatments in previously treated patients. In order to heat the vaginal apex, individualized prototype applicators utilizing commercial microwave antennas were constructed and tested in muscle equivalent phantom. The technical construction of vaginal applicators followed Pierquin's procedure for gynaecological brachy-therapy moulds: (1) a true negative vaginal print in alginate was made; (2) a positive mould in plaster of Paris was then constructed; (3) a negative vaginal print was produced in plaster of Paris and (4) heat moulding of a 0.1 cm thick sheet of cellulose acetate on the plaster mould was accomplished. Interstitial microwave antennas were inserted within the applicator and kept in place using silk wires or Teflon rings. The external part of the applicator was thermally sealed and protected with silicone. This was particularly useful in cases where an inner cooling system was required. Heat patterns in tissue equivalent phantom materials were determined using non-perturbing probes and infrared thermography. An illustrative clinical case is described.

Continuous three-dimensional radiation dosimetry in tissue-equivalent phantoms using electron paramagnetic resonance in L-alpha-alanine.

A new tissue-equivalent phantom material has been developed which also acts as a dosimeter. The new phantom material has a similar elemental composition to that of soft tissue and has a density 1.1 g/cm3. The phantom has an agar-gel base, and contains crystallized L-alpha-alanine which traps radiation-induced free radicals. Samples from the phantom were analyzed by an electron paramagnetic resonance (EPR) spectrometer and the intensity of the EPR signal was related to the absorbed dose. When calibrated, the phantom material acts as a dosimeter, with applications in radiation therapy.

Agarose as a tissue equivalent phantom material for NMR imaging

Phantoms for evaluation of nuclear magnetic resonance (NMR) imaging systems were made from water-based agarose gels, according to a standard procedure herein described. Copper sulfate (CuSO 4) was included in the gels to further affect their proton relaxation characteristics. The proton relaxation rates of each batch of gel are dependent on the concentrations of agarose and copper ions in it, with T1 depending more on copper than on agarose, and T2 depending more strongly on agarose than on copper. The wide range of T1 and T2 which can be covered, and the stability and physical characteristics of the agarose gel material make it well-suited for phantom use.

Thermal properties of tissue equivalent phantom materials.

Thermal conductivity, specific heat, density, and thermal diffusivity were determined for standard RF and microwave phantom materials. Thermal conductivity data for seven phantom materials of varying aluminum content were analyzed using mixture theories. With the thermal diffusivity values obtained, worst case errors in SAR determination due to thermal conduction for adipose-muscle planar phantoms were estimated.

Change in oxygen enhancement ratio with depth in tissue-equivalent material for a collimated beam of fast neutrons

Survival of reproductive capacity of murine leukaemia P-388 cells was assayed in vivo after the cells had been irradiated in vitro under aerobic or hypoxic conditions with collimated beams of X rays or 16 MeV D-Be fast neutrons at various depths in tissue-equivalent phantom material. The response to X-irradiation was the same in the absence of the phantom and at 8-7 cm depth. The response to fast neutrons under aerobic conditions was unchanged from 0 to 23 cm depth within the phantom. However, under hypoxic conditions, the dose-response curve for fast neutrons became significantly steeper with increasing depth in the phantom. The OER decreased from 2-0 in the absence of the phantom to 1-5 at 15 cm deep.

Continuing report on the deterioration of x-ray fluoroscopic screens.

At the annual meeting of this Society in 1967, a preliminary report was presented on the deterioration of x-ray fluoroscopic screens (1). This paper constitutes a report on findings since that time. Equipment and Methodology Twenty-eight fluoroscopic screens are being used in this study, 14 each from two manufacturers. All screens are of the zinc-cadmium sulfide phosphor type with the phosphor bonded to plastic backing material. The screens have been divided into test groups and are being exposed to x rays, light from sun lamps, incandescent lamps, and fluorescent lamps. Most of the conditions were designed to be related to some realistic exposure to which the screen in a diagnostic x-ray unit might be subjected. Although it is known that light output of fluoroscopic and radiographic screens is influenced by temperature, no attempt has been made to stabilize the temperature since a set of controls is used for comparison. In normal use temperature would be expected to vary and this should be kept in mind in assessing screen quality when no control is available. The light output of all the screens is measured with a special x-ray unit and a direct-reading light meter employing a photomultiplier tube as the detector. By use of a direct-reading instrument, calibrated in foot-lamberts, measurements are made independently of the sensitivity of the observer's eye and require no time-consuming matching of brightness. Calibration of the light meter is maintained by means of a regulated brightness source. When measurements of the luminescent response of the fluoroscopic screens are made, three sheets of one-half-inch-thick MIX-D, a tissue-equivalent phantom material, are placed at the table-top position. A fixed geometry has been used since the initiation of the study. All screens are covered by lead glass, having an equivalent of 2.0 mm of lead at 150 kVp, so that all light readings are taken under normal conditions of viewing. The light output of the screens is measured for an exposure rate of 0.5 R/min. when the x-ray unit is operated at 100 kVp. The grouping of the screens is shown in TABLE 1. Each of the test conditions listed was chosen to investigate one of the agents reported to cause or suspected of causing screen deterioration. The exposure of the screens to light from fluorescent, tungsten, and sun lamps is made through lead glass. An additional set of screens in the sun lamp group is being exposed without being covered by lead glass. All x-ray exposures are made with the screens covered by lead glass so that back-scatter conditions would be the same as those experienced by a fluoroscopic screen in a fluoroscopic screen assembly. Test Conditions3 A. Control Group: Screens kept in a darkened storage box at room temperature and exposed to x rays only when periodic measurements (approximately once a month) of all the screens are made.

REPRODUCTIVE CAPACITY OF MAMMALIAN TUMOUR CELLS IRRADIATED IN VIVO WITH CYCLOTRON-PRODUCED FAST NEUTRONS.

The reproductive capacity of isologous P–388 leukaemic cells has been determined in vivo after irradiation with fast neutrons from the M.R.C. cyclotron, Hammersmith Hospital. When tumour-bearing donor animals are irradiated at 10 cm depth in tissue-equivalent phantom material, using a relatively narrow fast neutron beam, the results are indistinguishable from results when donor animals are irradiated in air using a wide neutron beam. Implications of this finding for radiotherapy of human tumours are discussed.

RBE and Quality of Electromagnetic Radiation at Depths in a Water Phantom

The biological effectiveness of electromagnetic radiation in the Xand y-ray regions has been investigated quite extensively along with that of many other types of radiation (1, 2). These studies have resulted in the determination of an RBE for these radiations compared to a standard X-radiation. Although the RBE is known to depend on a great number of factors, it is strongly dependent on the linear energy transfer (LET); LET, in turn, varies with the type and quality of radiation being considered. The biological indicators used in most RBE investigations have been small animals or organisms or the surfaces of larger animals. As a result of thris, little o no attenuation and subsequent energy degradation of the radiation has taken place prior to the production of the biological effect. It is of great interest to know whether the biological effectiveness of a given primary type of radiation is affected by the degradation that takes place when this beam of radiation passes through material that overlies the site of biological interest. Very little information is available at the present time regarding the RBE of radiation in depth (3-5). There has, however, been an interest in the change in radiation quality which takes place when Xor -y-rays pass through tissue or tissue-equivalent material, and several papers have been written on this subject. In 1932 Quimby and McNattin (6) measured changes in radiation quality by measuring absorption within tissue-equivalent phantom material, using spherical ionization chambers with surrounding spherical copper filters. This absorption method of studying radiation quality was further pursued by Greening (7) in 1951. Another physical line of attack was initiated by Clarkson and Mayneord in 1939 (8). They used a pair of coaxial ionization chambers which were identical except for inner wall material, one chamber having a