Estrogen modulation of osteoblastic cell-to-cell communication

Chitosan has potential biomedical applications that may require the final products to be sterilized before use. The gamma irradiation of purified and highly deacetylated chitosan fibers and films at sterilizing doses (up to 25 kGy) caused main chain scissions. The viscosity average molecular weight of the polymer decreased with increasing irradiation dose, the radiation yields of scission being 1.16 in air and 1.53 in anoxia. Preirradiation application of a negative pressure of 100 kPa disrupted the network structure, which may have contributed to the greater radiation yield obtained by chitosan fibers in anoxia. Radiation induced scission of the chitosan chains resulted in a lower glass transition temperature (Tg), indicative of higher segmental mobility. The Tg was below ambient at an irradiation dose of 25 kGy in air. Irradiation in air improved the tensile strength of the chitosan film, probably due to changes in chain interaction and rearrangement. Irradiation in anoxia did not affect film properties significantly, partly because the preirradiation application of negative pressure had a negligible effect on the structure of the chitosan film. Polymer network structure and the irradiation conditions are therefore important determinants of the extent of radiation induced reactions in chitosan.     

Transformation of health care through innovative use of information technology: challenges for health and medical informatics education

Matrices loaded with cytarabine were prepared by compression of the tailor made triblock copolymers C17E227C17 and C17E454C17 (where C=methylene and E=oxyethylene). Observations of the swelling characteristics of copolymer matrices on immersion in distilled water indicated an increase in the thickness of the gel layer around the matrices following ingress of water into the matrices. The in vitro release of cytarabine was characterised from matrices of different molar mass and with different known drug loadings. The release of cytarabine from the copolymer matrices was predominantly by a Fickian diffusion mechanism; the release rate was dependent on drug loading and independent of copolymer molar mass.     

Gamma sterilization of a semi-solid poly(ortho ester) designed for controlled drug delivery--validation and radiation effects

Radiation sterilization is becoming increasingly popular for the sterilization of many pharmaceutical products. Although this technique is not limited to the sterilization of polymers, it is probably the most suitable method for such materials. This method however suffers several drawbacks. The sterilization of a product must lead to a safety level of 10(-6), i.e. one chance in a million to find a contaminated sample. In many cases, this assurance of sterility can be achieved by using a uniform treatment dose of 2.5 Mrad, recommended by the pharmacopeia. We investigated the possibility of using doses of radiation inferior to 2.5 Mrad to sterilize a semi-solid poly(ortho ester) (POE) developed for use as carrier in controlled drug delivery. After determination of the initial bioburden, the polymer was intentionally contaminated with the bioindicator Bacillus pumilus E 601. Following exposure to gamma irradiation, the D10 value of the radio resistant bioindicator was determined. Using the initial contamination value, the reduction factor D10 and the safety level, it is possible to calculate an optimal sterilizing dose for POE. All polymers are affected by ionizing radiation and the amount of radiation which produces a significant change in properties may vary from one polymer to the other. A molecular weight and dynamic viscosity decrease resulting from backbone cleavage was observed for this POE at a dose lower than 2.0 Mrad. Evaluation of the structure using 1H-NMR, 13C-NMR and IR analysis shows that for doses higher than 2.0 Mrad, another degredation process takes place.(ABSTRACT TRUNCATED AT 250 WORDS)     

Inactivation of Escherichia coli O157:H7 in apple juice by irradiation

Three strains (932, Ent-C9490, and SEA13B88) of Escherichia coli O157:H7 were used to determine the effectiveness of low-dose gamma irradiation for eliminating E. coli O157:H7 from apple juice or cider and to characterize the effect of inducing pH-dependent, stationary-phase acid resistance on radiation resistance. The strains were grown in tryptic soy broth with or without 1% dextrose for 18 h to produce cells that were or were not induced to pH-dependent stationary-phase acid resistance. The bacteria were then transferred to clarified apple juice and irradiated at 2 degrees C with a cesium-137 irradiator. Non-acid-adapted cells had radiation D values (radiation doses needed to decrease a microbial population by 90%) ranging from 0.12 to 0.21 kGy. D values increased to 0.22 to 0.31 kGy for acid-adapted cells. When acid-adapted SEA13B88 cells were tested in five apple juice brands having different levels of suspended solids (absorbances ranging from 0.04 to 2.01 at 550 nm), radiation resistance increased with increasing levels of suspended solids, with D values ranging from 0.26 to 0.35 kGy. Based on these results, a dose of 1.8 kGy should be sufficient to achieve the 5D inactivation of E. coli recommended by the National Advisory Committee for Microbiological Criteria for Foods.     

Gamma irradiation and ozone treatment for inactivation of Escherichia coli O157:H7 in culture media

A study was conducted to investigate the reduction and elimination of Escherichia coli O157:H7 by the effects of gamma irradiation and ozone treatment. Log phase cells were found to be more sensitive to gamma irradiation than stationary phase cells. E. coli O157:H7 was found to be considerably more resistant to irradiation at -18 degrees C than at 20 degrees C. The D values for this organism for treatment with ozone in tryptic soy agar were higher than those for treatment with ozone in phosphate buffer. Gamma irradiation at a dose of 1.5 kGy or ozone treatment at a concentration of 3 to 18 ppm for 20 to 50 min was required to assure the elimination of E. coli O157:H7.     

Method to identify products induced by radiosterilization. A study of cefotaxime sodium

Before the use of radiations to sterilize cefotaxime sodium powder, four new products radioinduced must be identified and qualified. They have an apparent level of or above 0.1%, at the sterilization dose of 25 kGy and are potentially toxic. Their identification is difficult because these products are formed at very low concentrations and generally have a structure similar as that of the main compound. The method proposed is to irradiate the drug in aqueous solution in order to increase the yields in radiolysis products, to compare the retention time of the new products, measured by high performance liquid chromatography, with those obtained after the irradiation of the solid drug and to identify from the aqueous solution the products which are common. One common product was found after the irradiation of cefotaxime in solid state and in aqueous solution. It was easily identified from the irradiated aqueous solution as anticefotaxime. This new product induced by the radiosterilization treatment, is not toxic but less active.     

Radiation-enhanced expression of E6/E7 transforming oncogenes of human papillomavirus-16 in human cervical carcinoma

BACKGROUND: Human papillomavirus (HPV) infection represents the most important risk factor for cervical carcinoma. Levels of expression of E6 and E7 transforming oncoproteins of high risk HPV genotypes (i.e., HPV-16 and HPV-18) have been linked specifically to the mitotic activity of cervical carcinoma and appear to be necessary for maintaining the malignant phenotype. However, E6/E7 viral proteins recently have been reported to be effective tumor rejection antigens in animal models and humans. Radiation treatment represents a standardized and effective modality for contemporary cervical carcinoma therapy. However, although the physiologic and cellular changes associated with high doses of irradiation have been well documented it has been shown only recently that an increased synthesis of specific cellular proteins is observed after irradiation. In this study, the authors analyzed the effects of high doses of gamma irradiation on the expression of E6/E7 oncoproteins in HPV-16-infected cervical carcinoma cell lines. In addition, the effects of radiation on major histocompatibility complex (MHC) restriction elements also were studied. METHODS: The effect of high doses of gamma irradiation (i.e., 1250, 2500, 5000, and 10,000 centigray [cGy]) on the kinetics of E6/E7 oncoprotein expression in two HPV-16 positive cervical carcinoma cell lines (i.e., CaSki and SiHa) was evaluated by Northern blot analysis. In addition, the effect of radiation on the expression of MHC molecules also was studied by Northern blot and fluorescence activator cell sorter (FACS) analysis. RESULTS: Dose ranging from 1250 (sublethal) to 10,000 (lethal) cGy significantly increased the expression of E6/E7 oncoproteins as well as MHC Class I molecules in CaSki and SiHa cell lines when compared with untreated tumor cells. Both cell lines showed increased mRNA expression for MHC Class I molecules in a dose-dependent manner. E6/E7 oncoproteins also were up-regulated in a dose-dependent manner in the CaSki cell line, whereas in the SiHa cell line their expression plateau at 5000 cGy. When the kinetics of radiation-induced up-regulation of E6/E7 were studied, persistent up-regulation of the viral oncoproteins was noted for all doses of irradiation, with the lower and sublethal doses (i.e., 1250-2500 cGy) inducing the most significant enhancement. CONCLUSIONS: High doses of irradiation can induce a significant and long-lasting up-regulation of E6/E7 oncogenes and MHC Class I restriction elements on HPV positive cervical carcinoma cell lines. These effects by themselves suggest that irradiation could enhance local tumor immunogenicity in patients receiving radiation therapy. However, in contrast to this possible beneficial effect, sublethal tumor irradiation (up-regulating E6/E7 transforming oncoproteins) also could confer a significant growth advantage to radiation-resistant tumor cells. These findings, combined with the previously reported acquisition of a radiation-induced drug resistance, could provide a biologic basis for the poor prognosis of patients with cervical carcinoma recurrence after radiation therapy.     

Oxidation of low-density lipoproteins by OH. and OH./O2-. free radicals produced by gamma radiolysis

The aim of this study was to analyze quantitatively the oxidative modification of low-density lipoproteins (LDLs) induced by OH. free radicals produced by gamma radiolysis, in the absence or in the presence of oxygen (action of OH. free radicals, or simultaneous action of OH. and O2-. free radicals, respectively). The effects of increasing radiation doses on aqueous LDL solutions have been monitored by several parameters: a decrease in endogenous vitamin E, the formation of thiobarbituric acid-reactive substances (TBARS) and conjugated dienes, the appearance of a differential fluorescence (excitation wavelength = 360 nm), and an increase in the relative electrophoretic mobility. Initial radiation yields (decrease in vitamin E, formation of TBARS) have been determined at pH 7 as a function of LDL concentration (from 0.75 to 9 g liter-1). From the comparison of these yields with those of OH. and O2-. free radicals produced by water radiolysis, we have deduced reaction mechanisms for the initiation of oxidation of LDLs by OH. and OH./O2-. free radicals.     

Poly(anhydride-co-imides): in vivo biocompatibility in a rat model

The degradation and tissue compatibility characteristics of a novel class of biodegradable poly(anhydride-co-imide) polymers: poly[trimellitylimidoglycine-co-1,6-bis(carboxyphenoxy)hexan e] (TMA-gly: CPH) (in 10:90; 30:70 and 50: 50 molar ratios) and poly[pyromellitylimidoalanine-co-1,6-bis(carboxyphenoxy)hexa ne] (PMA-ala:CPH) (in 10:90 and 30:70 molar ratios) were investigated and compared with control poly(lactic acid/glycolic acid) (PLAGA in 50:50 molar ratio) matrices, a well-characterized biocompatible polymer, in rat subcutaneous tissues for 60 days. Polymers were compression-molded into circular discs of 14 mm x 1 mm in diameter. On post-operative days 7, 14, 28 and 60, histological tissue samples were removed, prepared by fixation and staining, and analyzed by light microscopy. PLAGA matrices produced mild inflammatory reactions and were completely degraded at the end of 60 days, leaving implant tissues that were similar to surgical wounds without implants. TMA-gly:CPH (10:90 and 30:70) matrices produced mild inflammatory reactions by the end of 60 days, similar to those seen with PLAGA. TMA-gly: CPH (50: 50) produced moderate inflammatory reactions characterized by macrophages and edema. PMA-ala:CPH matrices elicited minimal inflammatory reactions that were characterized by fibrous encapsulation by the end of 60 days. In vivo degradation rates of poly(anhydride-co-imides) were similar to PLAGA. Both PMA-ala:CPH and TMA-gly: CPH matrices maintained their shapes and degraded at a constant rate over the period of two months. These polymers, possessing good mechanical properties and tissue compatibility, may be useful in weight-bearing applications in bone.     

Atopic sensitization during the first year of life in relation to long chain polyunsaturated fatty acid levels in human milk

The influence of low (0.39-1.1%), medium (4.25%) and high (7.1-32.5%) fat levels in fish on radiation inactivation of four food-borne pathogens was investigated. Cells of Listeria monocytogenes 036, Yersinia enterocolitica F5692, Bacillus cereus and Salmonella typhimurium at logarithmic phase were inoculated in 10% fish homogenates and subjected to gamma irradiation at ice temperature (0-1 degree C) with doses ranging from 0.05 to 0.8 kGy. The radiation survival curves of L. monocytogenes and B. cereus were characterized by shoulders, while a tailing effect was depicted by cells of Y. enterocolitica and B. cereus. The D10 values in kGy calculated on the exponential part of the curve ranged from 0.2 to 0.3, 0.15 to 0.25, 0.1 to 0.15 and 0.09 to 0.1 for L. monocytogenes 036, B. cereus, Salm. typhimurium and Y. enterocolitica F5692, respectively. This order (D10) of radiation resistance of each organism was not affected by the fat content of the fish. Inoculated pack studies carried out separately with each pathogen in fatty (Indian sardine, 7.1%) and lean (Golden anchovy, 0.39%) fish showed no difference in their survival after exposure to 1 kGy and 3 kGy doses, which corroborated the above observation. The practical significance of these results in the application of the technology is discussed.     

The impact of sterilization method on wear in knee arthroplasty

Sterilization by gamma irradiation in air has been shown to have the potential to accelerate the oxidation of polyethylene components resulting in reduced mechanical properties. In the hip, it has been reported that the occurrence of delamination and cracking in retrieved bearings is significantly different when comparing components sterilized with gamma irradiation in air with components sterilized with ethylene oxide. Using a collection of 1635 retrieved polyethylene knee bearings, this study pursues a similar comparison of sterilization method with clinical wear in the knee. It confirms that retrieved polyethylene knee components that were gamma irradiated in air have a high incidence of delamination and cracking, leading at times to complete wear through of the bearing. Knee components sterilized with ethylene oxide showed no evidence of fatigue damage even after in vivo durations in excess of 15 years.     

Overview of polyethylene as a bearing material: comparison of sterilization methods

Polyethylene has been used for more than 30 years as an orthopaedic bearing material; however, there has been recent concern regarding the early failure of a small percentage of the polyethylene bearings. The damage seen in some retrieved polyethylene components has been linked to gamma radiation sterilization in air, which was widely used by the industry for years. Gamma radiation in air has been documented to cause an increase in oxidation and degradation of mechanical properties with time. The degradation of polyethylene initiated by gamma sterilization in air has led the orthopaedic industry toward alternative sterilization methods, including gamma radiation in an inert gas or vacuum environment, ethylene oxide gas sterilization, and gas plasma sterilization. For many of these alternative techniques, little clinical performance data exist. This study is a comparative evaluation of sterilization methods using the same analytic techniques that have been used to document the effects of gamma sterilization in air on polyethylene. Fourier transform infrared spectroscopy, electron spin resonance, and uniaxial tensile testing are used to compare, respectively, the oxidation levels, free radical concentration, and mechanical properties of material sterilized by each method. The polyethylene is evaluated before sterilization, poststerilization, and postartificial aging. All examined alternative sterilization methods, when compared with gamma sterilization in air, caused less material degradation during a component's preimplantation shelf life.     

Shelf life of ground beef patties treated by gamma radiation

The effects of irradiation on microbial populations in ground beef patties vacuum package and irradiated frozen at target doses of 0.0, 1.0, 3.0, 5.0, and 7.0 kGy were determined. Irradiated samples were stored at 4 or -18 degrees C for 42 days, and mesophilic aerobic plate counts (APCs) were periodically determined. Fresh ground beef (initial APC of 10(2) CFU/g) treated with 3.0, 5.0, and 7.0 kGy was acceptable (< 10(7) CFU/g) for 42 days at 4 degrees C. The 1.0 kGy-treated beef samples were acceptable microbiologically (< 10(7) CFU/g) after 42 days but developed an unacceptable off-odor after 21 days. Shelf life diminished in fresh ground beef patties with an initial APC of 10(4) CFU/g. Only beef patties treated with 7.0 kGy were found to be acceptable at 42 days. Beef patties treated at 1.0 and 3.0 kGy reached spoilage APC levels (> 10(7) CFU/g) by day 14 and 21, respectively, whereas patties treated at 5.0 kGy did not spoil until 42 days. The nonirradiated control samples for both batches of ground beef spoiled within 7 days. Microbial counts in ground beef patties stored at -18 degrees C did not change over the 42-day period. Shelf life of ground beef patties stored at 4 degrees C may be extended with gamma radiation, especially at 5.0 and 7.0 kGy. Initial microbial load in ground beef samples was an important shelf life factor.     

Diagnosis of acute localized irradiation lesions: review of the French experimental experience

In the last 50 years several radiation accidents occurred in which industrial radiographers and others suffered severe radiation injuries from inadvertent contact with radiation sources. Such accidents involving acute localized injuries are characterized by a severe initial reaction progressing through erythema to skin necrosis with a spontaneous resolution of the lesion over a 2-mo period for the lower doses. However, the early symptoms observed on the skin give no indication as to the in-depth pathology, and cutaneous and muscular radionecrosis started generally from early epithelial, microvascular, and vascular lesions and from delayed muscular and connective tissue lesions. In a case of acute localized irradiation, different biophysical techniques are able to give real responses in biological dosimetry. More numerous are the methods, especially imaging methods, that make it possible for the clinician to evaluate the extent of the early injuries and to manage the medical intervention. We have developed animal experimental models of acute localized irradiation: overexposure to the gamma rays of a 192Ir industrial radiographic collimated source (in the pig and the rabbit) and overexposure to the beta rays of a 90Sr-90Y collimated source (in the pig). In these experimental models, most of the imaging techniques used in clinical practice, as infra-red thermography, microwave thermography, cutaneous and tissular vascular scintigraphy (beta or gamma emitters), cutaneous blood flow measurements by cutaneous laser Doppler, x ray computed tomography, nuclear magnetic resonance imaging, and skin topography, were correlated with clinical evaluation and histopathological observations, after high doses of gamma or beta irradiations ranging from 4 to 340 Gy at the skin surface. All these techniques are not for isolated use and the present review indicates that their combination is necessary to give an improved diagnostic and prognostic picture of early and late delayed radiation damage to the skin and subcutaneous tissues.     

Radiation induced color centers in cerium-doped and cerium-free multicomponent silicate glasses

The effect of doped cerium on the radiation-resistance behavior of silicate glass was investigated in our work. The ultraviolet-visible absorption spectra and electron paramagnetic resonance（EPR） spectra were obtained after the cerium-rich and cerium-free multicomponent silicate glasses（K509 and K9） were irradiated by gamma rays with a dose range from 10 to 1000 kGy. The results showed that E’ center, oxygen deficient center（ODC） and non-bridging oxygen hole center（HC1 and HC2） were induced in K9 and K509 glasses after radiation. The concentrations of all color centers presented an exponential growth with the increase of the gamma dose. Moreover, the concentration of HC1 and HC2 in cerium-doped K509 glass was much lower than that in cerium-free K9 glass at the same dose of radiation, which could be attributed to the following mechanism： Ce3＋ ions capturing holes then forming Ce3＋＋ centers inhibited the formation of hole trapped color centers（HC1 and HC2） and Ce4＋ ions capturing electrons to form Ce3＋ centers suppressed the formation of electron trapped color centers like E’ center.     

Shelf life and in vivo duration. Impacts on performance of tibial bearings

Polyethylene has been used for more than 30 years as an orthopaedic bearing material; however, recently concern has been focused on the early failure of some polyethylene bearings. The damage seen in some bearings has been linked to gamma radiation sterilization performed in an air environment. Gamma sterilization in air has been documented to cause an increase in oxidation and degradation of mechanical properties that continue with time. However, not all retrieved bearings that are gamma sterilized in air exhibit the elevated oxidation and mechanical property degradation that lead to early component failure. Bearings that are gamma sterilized in air oxidize while sitting in inventory before implantation. Shelf oxidation rate was estimated based on analysis of a series of never implanted tibial bearings. This shelf oxidation rate allowed estimation of in vivo oxidation for retrieved tibial bearings of known sterilization date. Bearings with less than 1 year of shelf life after gamma sterilization in air had lower in vivo oxidation and better in vivo performance than did those with longer shelf life before implantation. Shelf time before implantation appears to be a significant factor in the success or failure of bearings that are gamma sterilized in air.     

Amino acid residue 200 on the alpha1 subunit of GABA(A) receptors affects the interaction with selected benzodiazepine binding site ligands

Mutant alph1 subunits of the GABA(A) receptor were coexpressed in combination with the wild-type beta2 and gamma2 subunits in human embryonic kidney (HEK) 293 cells. The binding properties of various benzodiazepine site ligands were determined by displacement of ethyl-8-fluoro-5,6-dihydro-5-methyl-6-oxo-4H-imidazo[1,5a]-[1,4]benzodia zepine-3-carboxylate ([3H]Ro 15-1788). The mutation G200E led to a decrease in zolpidem and 3-methyl-6-[3-(trifluoromethyl)phenyl]-1,2,4-triazolo[4,3-b]pyridazine (CL 218872) affinity amounting to 16- and 8-fold. Receptors containing a conservative T206V substitution showed a 41- and 38-fold increase in methyl-6,7-dimethoxy-4-ethyl-beta-carboline-3-carboxylate (DMCM) and CL 218872 affinity combined with a decrease in diazepam and zolpidem affinity, amounting to 7- and 10-fold. Two mutations, Q203A and Q203S showed almost no effects on the binding of benzodiazepine site ligands, indicating that this residue is not involved in the binding of benzodiazepines and related compounds.     

Effects of irradiation on the expression of major histocompatibility complex class I antigen and adhesion costimulation molecules ICAM-1 in human cervical cancer

PURPOSE: We initiated studies to analyze the effects of high doses of gamma irradiation on the surface antigen expression of MHC Class I, Class II, and ICAM-1 on human cervical carcinoma cell lines. METHODS AND MATERIALS: The expression of surface antigens (MHC Class I, Class II, and ICAM-1) was evaluated by FACS analysis on two cervical cell lines at different time points, following their exposure to high doses of gamma irradiation (i.e., 25.00, 50.00, and 100.00 Gy). RESULTS: The CaSki and SiHa cervical cancer cells we analyzed in this study expressed variable levels of MHC Class I and ICAM-1 antigens, while Class II surface antigens were not detectable. Whereas irradiation doses of 25.00 Gy were not sufficient to totally block cell replication in both cell lines, exposure to 50.00 or 100.00 Gy was able to completely inhibit cell replication. Range doses from 25.00 to 100.00 Gy significantly and consistently increased the expression of all surface antigens present on the cells prior to irradiation but were unable to induce neoexpression of antigens previously not expressed by these cells (i.e., MHC Class II). Importantly, such upregulation was shown to be dose dependent, with higher radiation doses associated with increased antigen expression. Moreover, when the kinetic of this upregulation was studied after 2 and 6 days after irradiation, it was shown to be persistent and lasted until all the cells died. CONCLUSIONS: These findings may partially explain the increased immunogenicity of tumor cells following irradiation and may suggest enhanced immune recognition in tumor tissue in patients receiving radiation therapy.     

Development of Chronomers tm for narcotic antagonists

The object of this program is to prepare a bioerodable naltrexone delivery system which can be implanted subcutaneously in humans and which can relieve the narcotic antagonist over 1-6 months at relatively constant and sufficient rates to block the euphoric effect of morphine based drugs. The system is composed of naltrexone uniformly dispered in a solid hydropholic CHRONOMER TM matrix which undergoes predictable surface erosion when exposed to an aqueous medium. Kinetic studies in vitro have been carried out during the course of the program to determine the best composition for the system. Toxilogical studies conducted at ALZA during the past 2 years have not revealed limiting adverse effects of either the CHRONOMER TM materials or their hydrolysis products. The tail-flick test procedure was used to measure the effectiveness of naltrexone to antagonize the analgesis of morphine in rats. Naltrexone infused intravenously at doses of 4 and 16 ug/kg/hr resulted in, after 6 hours, 54 and 89% antagonism, respectively, against a 63.5% effective dose of morphine. Perliminary sterilization studies showed that no adverse effects to CHRONOMER TM/naltrexone systems occurred after exposure to 2.5 or 5.0 mrads of 60CO irradiation.     

Radiosurgical lesions in the normal human brain 17 years after gamma knife capsulotomy

OBJECTIVE: To our knowledge, this is the first long-term follow-up study of high-dose single-session irradiation to the human brain and provides new data concerning late tissue reactions after irradiation to small target volumes. The long-term lesional brain changes in 14 patients subjected to bilateral gamma knife capsulotomy for otherwise intractable anxiety disorders were retrospectively analyzed by magnetic resonance imaging. METHODS: The prototype gamma unit was used for the radiosurgical procedure, and the collimators provided rectangular cross-sectional fields with an anteroposterior diameter of 3 mm and a transverse diameter of 5 or 11 mm. Maximum target doses were 120 to 180 Gy. Magnetic resonance imaging was performed 15 to 18 years (mean, 17 yr) after treatment, and dose-volume histograms were calculated for the dose distributions. RESULTS: One patient had been irradiated twice on one side. In all but one of the remaining 27 targets, lesions with a volume of less than 100 mm3 were revealed by magnetic resonance imaging. The volumes of the lesions were confined within the volume corresponding to a minimum dose of approximately 110 Gy, with one exception. In one of three targets receiving a maximum dose of 120 Gy, no lesion was detected. There were no late radiation effects such as cyst formations, telangiectasias, hemorrhagic infarctions, or neoplasms. CONCLUSION: This investigation indicates that a minimum dose of 110 Gy, with the currently used 4-mm collimator, to the edge of the target volume is required to create a lesion. The results prove that gamma knife surgery can be used in functional neurosurgery for producing small permanent lesions in the normal human brain.