The modification of specific absorption rates in interstitial microwave hyperthermia via tissue-equivalent material bolus.

Patterns of specific absorption rates generated by interstitial, microwave antenna arrays must be experimentally ascertained and quantified to facilitate their clinical incorporation. Phantom studies involved the use of four single-gap, coaxial antennas oriented in a 2 cm square array. These dipoles were driven in phase by a microwave generator at a frequency of 915 MHz. The inherent limitations in modifying the specific absorption rate patterns were addressed with the addition of bolus to the phantom. These additions of Guy's muscle tissue-equivalent material were made either proximal or distal to the phantom proper. Experiments conducted in the presence and absence of tissue-equivalent material bolus showed the ability to achieve broader bands of 50% power deposition in certain bolus conditions. These heating patterns were sufficiently reproducible and predictable to warrant clinical application of the bolus addition. A through-and-through method of catheter implantation allowed for bolus addition when deemed necessary. Treatments with veterinary and human patients using the bolus method to modify heating patterns yielded augmented patterns of power deposition. The effective length of the antennas that would radiate efficiently was essentially broadened via introduction of a microwave-interacting medium. As a result of the tissue equivalent material's ability to absorb microwave power, it was necessary to interpose minimally-interactive styrofoam spacers to limit heat transfer effects at the tissue-bolus interfaces.

Adjustable portal film cassette holder for radiation therapy.

An adjustable portal film cassette holder has been designed and constructed. The holder provides for: holding portal film perpendicular to and centered with the central axis of the beam film-to-patient distance to minimize magnification; angling (swivel) film to match collimator angle; and ease of correct repositioning of arrangement when frequent filming is required. This device has now been in use for several months with good results.

Nuclear medicine from Becquerel to the present.

During a period of a little over ninety years, the use of radioactive materials has moved from the discovery of natural radioactivity by Becquerel to the use of highly sophisticated equipment for in-house production of biologically important molecules labeled with radionuclides, for the measurement of body functions. Radiation detectors have progressed from photographic plates and the gold leaf electroscope to the routine use of improved scintillation detectors for imaging the three-dimensional distribution of radioactive materials in the body as a function of space and time. It is expected that future improvements will be along the line of instruments with better spatial resolution, contrast, and sensitivity. Advances in hardware and software will be more than matched by developments in radiopharmaceuticals, including the use of monoclonal antibodies and receptor mapping agents which promise the exquisite specificity and sensitivity of radioimmunoassay procedures.

A comparative study of indium-111 DTPA radionuclide and iothalamate meglumine roentgenographic arthrography in the evaluation of painful total hip arthroplasty.

Fifteen patients with painful total hip prostheses were referred for nuclear medicine and roentgenographic arthrography studies to exclude loosening of the acetabular and/or the femoral component. A new radioisotopic technique suitable for the evaluation of both components was developed using dual-isotope single-photon tomography with 99mtechnetium methylene diphosphonate bone imaging and indium-111 diethylenetriaminepentacetic acid arthrography. Thirteen of the 15 subjects were subsequently treated with additional surgery. The surgical findings were compared with the nuclear medicine and roentgenographic results. The overall diagnostic accuracy of both arthrographic procedures was approximately 80%, but the roentgenographic arthrogram was more sensitive and the radionuclide arthrogram was more specific.

Evaluation of a low-dose neonatal chest radiographic system.

A new low-dose chest radiographic system for use in the neonatal nursery was evaluated. This test system, composed of a Du Pont Kevlar fiber-front cassette, Quanta fast-detail screen, Cronex 4L film (wide latitude), and additional yttrium filtration (0.1 mm), reduced the radiation dose in neonatal chest radiography by 69% (0.9 vs 2.9 mrad [0.009 vs 0.029 mGy]) as compared with a conventional system without added yttrium filtration; the thyroid dose was reduced by 76% (0.9 vs 3.7 mrad [0.009 vs 0.037 mGy]). The cumulative dose reduction was achieved through a combination of factors, including (1) beam hardening by the added yttrium filter, (2) increased X-ray transmission through the Kevlar cassette, and (3) a fast film-screen combination. Scatter radiation at distances of 1 and 6 ft. (0.3 and 1.8 m) was negligible for both systems. Image sharpness was compared for the conventional system with and without added yttrium filtration and for the Kevlar system with yttrium. Although sharpness of bony detail was unchanged by adding yttrium filtration to the conventional system, a decrease in sharpness was noted with the Kevlar system. Because image sharpness was affected in the test system, we are not using the Kevlar-Cronex 4L system for mobile chest radiography in the neonatal intensive care unit, despite dose reductions. However, further study is recommended to determine if there is a slower film-screen combination with yttrium filtration that will not degrade image sharpness.

The distribution of power and heat produced by interstitial microwave antenna arrays: II. The role of antenna spacing and insertion depth.

The distribution of power and temperature generated by 915 MHz interstitial microwave antenna arrays was studied in static muscle-equivalent phantoms and both perfused and non-perfused canine thigh muscle. These arrays, which would form the geometric basis of larger volume implants, consisted of four parallel antennas oriented such that transverse to their long axes they formed the corners of a square. Arrays with 2 and 3 cm sides were compared at various depths of insertion where the nodes for all four antennas were coincident at the same depth. The position relative to the antenna nodes of the maximum power and highest temperature within the array volume varied with the depth of insertion of the antennas. Though power dropped rapidly distal to the nodes at all depths, a shift in the location of the maximum power proximal to the nodes resulted in an increase in the effective heating volume at certain insertion depths. For 2 cm array spacing the highest power and temperature were measured along the central axis of the array at all insertion depths. However, arrays using 3 cm spacing generated their maximum power adjacent to the antennas with only 50% of this level occurring along the central axis. When the temperature produced by 3 cm arrays was measured in phantoms midway through simulated 30-minute hyperthermia treatments, the effect of thermal conduction on the temperature distribution was evident. Though power was only 50% centrally, the highest temperatures occurred there. This same pattern of central heating occurred in perfused canine muscle demonstrating the importance of conductive and convective heat redistribution in reducing thermal gradients within the array volume.

Specific absorption rates in simulated tissue media for a 10 x 10 cm 915-MHz waveguide applicator.

The use of hyperthermia in combination with radiotherapy is currently being investigated at many cancer treatment facilities. Several different types of heating modalities are presently being used and for each of these systems it is important to determine the power distributions of their hyperthermia applicators in tissue-equivalent phantoms. This information will be used for treatment planning, routine quality assurance, and acceptance testing as well as for comparison between these various modalities and systems. This report describes the power distribution characteristics of the Clini-Therm 10 x 10 cm 915-MHz waveguide applicator measured within muscle tissue phantom materials arranged in several clinically relevant treatment configurations. The net increase in temperature that resulted from 20-s pulses of microwave power was measured at various points within each phantom by the system's implantable fiberoptic temperature sensors. From these temperature measurements the distribution of power was calculated as specific absorption rates (SAR). The results are displayed as two-dimensional ISO-SAR maps which relate power levels throughout the irradiated volume to those obtained on the central axis of the applicator. When the applicator was in direct contact with the muscle phantom the highest SAR measured was 2 cm lateral to its central axis along the muscle surface. On the central axis approximately 50% of the power was attenuated by each centimeter of muscle material. The introduction of either fat, bone, or a water-filled pad between the applicator and the muscle altered the pattern of power distribution within the irradiated volume without substantially altering the relative distribution of power along the central axis.(ABSTRACT TRUNCATED AT 250 WORDS)

The reactor accident at Chernobyl: a nuclear medicine practitioner's perspective.

The radiation incident at Chernobyl, USSR, on April 26, 1986 was first detected in Sweden on April 29, when increased radioactivity was observed at a nuclear facility in that country. Subsequently, higher levels of radioactivity were observed in most of Eastern Europe and then in Western Europe. Increased radioactivity was eventually noted in the United States beginning about May 5. The three-day interval between the incident and its discovery outside the USSR caused great apprehension. This chain of events indicates the very important role for the nuclear medicine physician, the medical physicist and their colleagues. It is likely that this medical specialty area is staffed by personnel who are best qualified to interpret these findings and to determine the necessary course of action both for patients and the general public. The nuclear medicine specialist can provide valuable input in estimating the radiation dose impact resulting from such an incident. This estimate may be accomplished either by combining measured activity levels with the physiological and physical factors involved; or by actual in vivo counting and quantitation of radioactivity in individuals exposed to radionuclides. From the measured activities in air, water and food, and assumed intakes for various age groups, doses can be estimated both for inhalation and ingestion of radionuclides. In vivo measurements of radionuclides can be performed with conventional instrumentation used routinely in nuclear medicine laboratories.

Indium 111 toxicity in the human lymphocyte.

Indium-labeled lymphocytes were examined for response to a variety of mitogens, ability to synthesize immunoglobulins, mitotic index, and presence of chromosome aberrations at a range of exposures from 0.2 to 500 muCi/10(8) cells. Results of all four tests were found to be abnormal when the lymphocytes were labeled with 111In activities well within those employed for diagnostic testing.

Response to ionizing radiation of human bladder transitional cell carcinomas grown in the nude mouse.

The sensitivity to ionizing radiation of three human bladder transitional cell carcinomas grown in the nude mouse was investigated at four different radiation levels, 500, 1,000, 2,000 and 4,000 rad. Each tumor line exhibited a response pattern which reflected to a certain degree tumor differentiation and growth rate in the nude mouse. Exposure to 1,000 rad was the minimum amount of radiation required to produce a distinct, although transient, tumor response in all three tumor lines characterized by a growth delay of 3-4 weeks, whereas maximum tumor response was observed at the 4,000 rad radiation level. These studies would permit a better understanding of the behavior of human bladder cancer to ionizing radiation and may further facilitate efforts at identifying effective radiosensitizing agents that may result in maximizing tumor response.

Practical aspects involved in the design and set up of a 0.15 T, 6-coil resistive magnet, whole body NMR imaging facility.

Many technical and logistical questions must be addressed when planning the installation of an NMR imaging system. These considerations become particularly significant when the facility is being established within an existing medical center complex. This paper presents a report on the practical aspects and experience obtained in siting a 6-coil 0.15 T resistive magnet system. The topics discussed include: floor loading; ferromagnetic environment; the effect of iron on the magnet field strength and homogeneity characteristics; shimming procedures; temperature stability requirements; rf shielding; and effects of the magnetic field on common medical instrumentation and magnetic media. It was found that the field shift as a function of the distance of a steel mass from the center of the magnet exhibited an (1/r)5.2 +/- 0.5 to (1/r) 4.2 +/- 0.3 dependence for axial and radial positions respectively which, as expected, is somewhat weaker than the (1/r)6 dependence expected by point dipole approximations. Field distortions caused by the presence of ferromagnetic material in radial positions may be essentially fully compensated with first order transverse shim coils (most conveniently, the x and y imaging gradient coils could be used). Axially distributed material requires, in addition to first order z-gradient correction, higher order axial shim compensation. The temperature stability of the magnet system over the scan period must be better than 0.2 degrees C to insure that temperature-induced field fluctuations are less than the intrinsic static inhomogeneity: and, ideally, below 0.01 degrees C to reduce these fluctuations to less than those caused by power supply instability.

Relation between effective radiation dose and outcome of radioiodine therapy for thyroid cancer.

We used a combination of radioiodine scanning and quantitative radiation dosimetry to evaluate responses to therapeutic irradiation with 131I in 76 patients with thyroid adenocarcinoma. Fifty patients received 131I treatment for ablation of residual thyroid tissue after surgical thyroidectomy, and 26 had 131I treatment for metastatic thyroid cancer. Successful ablation was observed in patients receiving higher radiation doses to the thyroid--about 4.4 times those in patients whose lesions were not ablated--largely because of a longer effective half-life of 131I in residual thyroid tissue in the patients with ablated lesions. Patients with metastases that persisted after 131I therapy tended to have more advanced disease and received significantly lower radiation doses per millicurie of administered 131I than did persons whose lesions responded to treatment. Initial 131I treatment resulting in radiation doses of at least 30,000 rad to thyroid remnants and 8000 rad to metastases was associated with a significant increase in the rate of response to therapy.

Experimental studies on the radiation-modifying effect of cis-diamminedichloroplatinum II (DDP) in human bladder transitional cell carcinomas grown in nude mice.

The effect of cis-diamminedichloroplatinum II (DDP) and ionizing radiation on human bladder transitional cell carcinoma (TCC) was evaluated in nude mouse-grown human tumors following administration of single-agent and combination treatment. Combination of DDP and radiation resulted in accelerated tumor regression and substantially delayed tumor regrowth. The potentiating effect of DDP on ionizing radiation was related to timing and sequence of treatments and was independent of tumor sensitivity to DDP. Best results, as judged by tumor growth curve characteristics, histopathologic changes, and absence of tumor metastases, were obtained when DDP was administered at an early stage following radiation treatment.

Radiation absorbed-dose estimates for the liver, spleen, and metaphyseal growth complexes in children undergoing gallium-67 citrate scanning.

Quantitative conjugate-view external counting techniques were applied to estimate the radiation dose to the liver, spleen, and metaphyseal growth complexes (distal femur and proximal tibia) for ten pediatric patients undergoing gallium-67 scanning procedures. The effective half-life of Ga 67 in these organs was approximately 78 hours. The dose per unit of administered activity for the liver and spleen was between 0.3 and 4.0 rad/mCi (0.08 to 1.08 Gy/GBq) and 0.5 and 7.0 rad/mCi (0.13 to 1.89 Gy/GBq), respectively. For the metaphyseal growth plates, the range was 2.3 to 14.3 rad/mCi (0.62 to 3.86 Gy/GBq).

Characteristics of extrafocal radiation and its potential significance in pediatric radiology.

Extrafocal radiation was investigated using four different rotating-anode radiographic units currently employed in a pediatric hospital. It was found to exhibit significant penetration, with an effective energy only slightly lower than that of the primary radiation. The percentage of extrafocal relative to focal radiation in pediatric procedures involving rare-earth screens ranged from 2 to 15%. The ratio of extrafocal to focal radiation tended to increase with increasing kVp, mA, and field size but was independent of focal spot size. Since extrafocal radiation may extend significantly outside of the primary collimated field, radiosensitive organs such as the gonads, thyroid, and eyes which are assumed to be shielded may actually receive as much as 25 mR per radiograph.

Histopathologic evaluation of response to treatment of human tumors grown in the nude mouse.

The histopathologic changes following chemotherapy treatment of a number of human tumors grown in nude mice were evaluated. On the basis of the histopathologic profile, three response levels were recognized--a mild response, a moderate response and a severe response. Severe response was characterized by arrest of cell division and profound nuclear-cytoplasmic degenerative changes. Regrowth of effectively treated tumors originated in clusters of cells most probably representing resistant tumor cell clones. Histopathologic changes represent a sensitive indicator of the response of nude mouse grown human tumors to anticancer agents. Availability and correct interpretation of the post-treatment histopathologic picture is of importance in selecting the proper combination treatment which would maximize tumor response.

Nuclear magnetic resonance imaging techniques as developed modestly within a university medical center environment: what can the small system contribute at this point?

This paper describes a geometrically small NMR imaging system which has been developed and assembled within a university medical center environment. Consideration is given to the technical specifications and basic economics for the magnet system, NMR spectrometer, and computer configuration. Initial research objectives for the system are outlined which include (1) the signal-to-noise improvement potential of rotational gradient imaging, and (2) 19F tracer imaging considerations with a detailed discussion concerning the feasibility of in vivo NMR imaging of 19F-fluorodeoxyglucose (2-FDG and 3-FDG). Finally, potentially significant areas for research within the constraints of a small NMR imaging system are described.