Comparison of I-125 sources used for permanent interstitial implants.

The increase in the number of manufacturers of 125I sources used in prostate brachytherapy has generated many questions in the radiation oncology community. In this investigation, the physical and dosimetric characteristics were evaluated for the following sources listed by marketing company and source model: Nycomed-Amersham 6711 (OncoSeed), Nycomed-Amersham 6702, Mentor IoGold, UroMed Symmetra, Imagyn IsoSTAR, UroCor, (PSA, Mallincrkrodt) ProstaSeed, Syncor PharmaSeed, SourceTech Medical, (BARD) 125Implant (BrachySource), Med-Tec I-Plant, Best Medical Model 2301, DraxImage BrachySeed, and International Brachytherapy, Inc. (IBT) InterSource125. The investigation examined the differences in design, construction, and the dosimetric characteristics created from each source. The dosimetric characteristics of the new sources were compared to that of the Amersham 6711 source. Parameter studies have led to the development of a simple equation that can be used to clinically convert the standard 6711 source strength to an equivalent strength of a new source.

Fitting and benchmarking of dosimetry data for new brachytherapy sources.

New source designs of encapsulated low-energy gamma emitting nuclides for permanent implants require dosimetric analysis and calibration standardization. The dosimetry measurements can be incorporated into a treatment planning system by fitting the data. The use of a fitting function whose behavior at range limits mimics the physical phenomena, using as few parameters as possible, eliminates noisy outliers and lends credence to calculations beyond the measured range. Clinical implementation of the new sources also requires benchmarking against existing sources, where the current clinical experience lies. We present an analysis of measured dosimetry data for three brachytherapy sources recently available from North American Scientific, Inc. (North Hollywood, CA): 103Pd source model MED3633 ("PdGold"), 125I source models MED3631-A/M ("IoGold-AM") and MED3631-A/S ("IoGold-AS"). Using the formalism of the Interstitial Collaborative Working Group (ICWG) the radial dose function, g(r), the anisotropy function, F(r, theta), and the anisotropy factor, phi an(r), were previously evaluated from measurements of each source design. In this report we use fitting functions whose forms are chosen to approach reasonable values at data limits. These forms are quite similar to those used in a previous analysis of TG43 Iodine and palladium compendium data. Fitting parameter results for each function are provided for each brachytherapy source model. Fit-data discrepancies are smaller than measurement uncertainties, meaning that incorporation into treatment planning systems will not introduce significant errors in clinical use. Current clinical experience is based on the Theragenics (Norcross, GA) 103Pd seed ("PdThera"), and the Nycomed-Amersham (Arlington Heights, IL) 125I seed models 6711 ("6711") and 6702 ("6702"). The new sources are benchmarked against these seeds.

Empirical dosimetric characterization of model I125-SL 125iodine brachytherapy source in phantom.

Low-energy photon emitting radionuclides encapsulated for a permanent implant are routinely applied in prostate cancer brachytherapy. Before clinical use, a new source design requires full dosimetric analysis and calibration standardization. The results of one such experimental measurement and analysis are reported here for a new design of 125I source, model I125-SL. Dose measurements were made using standard methods employing thermoluminscent dosimeters in a water equivalent plastic phantom, in accord with the AAPM Task Group #43 recommendation of liquid water reference material. Precision machined bores in the phantom located dosimeters and source(s) in a reproducible fixed geometry providing for transverse-axis and angular dose profiles over a range of distances from 0.17 to 10 cm. The data were analyzed in terms of parameters recommended by AAPM TG43. The dose-rate constant, lambda, was evaluated by two methods, the first with reference to a 60Cobalt standard, accounting for response variation with photon energy spectrum. Second, the dose-rate constant was determined with reference to phantom measurements using NIST traceable calibrated model 6702 and 6711 sources. The radial dose function, g(r), the anisotropy function, F(r,theta), the anisotropy factor, phi(an)(r), and the point-source approximation anisotropy constant, phi(an), were derived from one- and two-dimensional dose distribution data measured in the phantom, accounting for finite dosimeter volume and with attention to interchip effects. The results are compared to TG43 and other existing data for 125I sources. The new source is comparable to the model 6711 source design.

Dosimetric characterization of a new design 103 palladium brachytherapy source.

Low-energy gamma emitting isotopes encapsulated for permanent implant are in routine use in the treatment of prostate cancer. New source designs require full dosimetric analysis and calibration standardization before responsible clinical application. The results of one such experimental measurement and analysis are here reported for a new design of 103palladium source, model MED3633 (North American Scientific, Inc.). By AAMP Task Group #43 recommendations, the reference material for brachytherapy dosimetry is liquid water. The dose measurements were made using standard methods employing thermoluminescent dosimeters in a water equivalent plastic phantom. Precision machined bores in the phantom located dosimeters and source(s) in a reproducible fixed geometry providing for transverse-axis and angular dose profiles over a range of distances from 0.17 to 7 cm. The data were analyzed in terms of parameters recommended by AAPM TG43. The dose-rate constant, lambda, was evaluated with reference to a 60 cobalt standard, accounting for response variation with isotope energy spectrum. The radial dose function, g(r), the anisotropy function, F(r, theta), the anisotropy factor, phi,un(r), and the point-source approximation anisotropy constant, phi(un), were derived from one- and two-dimensional dose distribution data measured in the phantom, accounting for finite dosimeter volume and with attention to interchip effects. The results are compared to TG43 and other existing data for 103Pd sources. The new source is comparable to the model 200 103Pd source design, demonstrating equivalent radial dose function, g(r). The dose surrounding a MED3633 source may be slightly more isotropic than for the model 200 source. The air-kerma strength of the MED3633 source used in this study was provided by the manufacturer and is traceable to the NIST 1999 standard. The evaluated dose-rate constant, lambda, with NIST traceable strength calibration is lower than that of the model 200 source, with that manufacturer's strength calibration.

Report on the dosimetry of a new design 125Iodine brachytherapy source.

Dosimetric measurements were performed to characterize a new 125I source that is a variant design of an existing source, designated as MED3631-A/S, and that has application in interstitial brachytherapy. The new source, designated as MED3631-A/M, has centralized radio-opaque markers. In the original MED3631-A/S source, the radio-opaque markers are separated. Thermoluminescent dosimeters were placed in phantom to measure transverse axis and angular dose profiles over a range of distances from 0.5 to 7 cm. The data were analyzed in terms of parameters recommended by AAPM Task Group No. 43. Tabular data evaluated in liquid water are provided for the dose-rate constant, lambda, radial dose function, g(r), the anisotropy function, F(r,theta), the anisotropy factor, phi(an)(r), the point-source approximation anisotropy constant, phi(an). The dose-rate constant was determined by an absolute method using a Cobalt-60 reference and by relative measurements using calibrated 125I source(s). Values of the dose-rate constant are provided for both the 1985 and 1999 NIST air-kerma strength standards. The new source is comparable to both the MED3631-A/S and the model 6702 125I source designs, demonstrating equivalent radial dose function, g(r). Differences in the value of the dose-rate constant, lambda, and the anisotropy of the dose distributions in phantom are discussed in light of the improved isotropy of the new design, the MED3631-A/M source, and the uncertainty involved in the dose measurement using a Cobalt-60 reference.

Evaluation of a new brachytherapy iodine-125 source by AAPM TG43 formalism.

Dosimetric measurements were performed to characterize a new 125I source that is similar in design to existing sources and that has application in interstitial brachytherapy. Thermoluminescent dosimeters were placed in phantom to measure transverse-axis and angular dose profiles over a range of distances from 0.5 to 7 cm. The data were analyzed in terms of parameters recommended by AAPM Task Group #43. Tabular data evaluated in liquid water are provided for the dose-rate constant, lambda, radial dose function, g(r), the anisotropy function, F(r, theta), the anisotropy factor, phi an(r), the point-source approximation anisotropy constant, phi an, and the point-source average dose rate times the square of distance for unit air kerma strength, r2D(r). The new source is compared to the model 6702 125I source design, demonstrating similar dose-rate constant, lambda, and radial dose function, g(r). Differences in the anisotropy of the dose distributions are discussed. Finally, a comparison of the radial dose distribution is made between liquid water and tissue equivalent materials.

Expression of human group II PLA2 in transgenic mice results in epidermal hyperplasia in the absence of inflammatory infiltrate.

Group II PLA2 has been implicated in inflammatory processes in both man and other animals and has been shown to be involved in inflammatory conditions, such as arthritis and sepsis. Transgenic mice expressing the human group II PLA2 gene have been generated using a 6.2-kb genomic fragment. These mice express the group II PLA2 gene abundantly in liver, lung, kidney, and skin, and have serum PLA2 activity levels approximately eightfold higher than nontransgenic littermates. The group II PLA2 transgenic mice reported here exhibit epidermal and adnexal hyperplasia, hyperkeratosis, and almost total alopecia. The chronic epidermal hyperplasia and hyperkeratosis seen in these mice is similar to that seen in a variety of dermatopathies, including psoriasis. However, unlike what is seen with these dermatopathies, no significant inflammatory-cell influx was observed in the skin of these animals, or in any other tissue examined. These mice provide an important tool for examining group II PLA2 expression, and for determining the role of group II PLA2 in normal and disease physiology. They serve as an in vivo model for identifying inhibitors of group II PLA2 activity and gene expression.

Mutant and native human beta-amyloid precursor proteins in transgenic mouse brain.

Human beta-amyloid precursor protein (beta APP) has been targeted to transgenic neurons using synapsin I promoter-based chimeric transgenes. Native human beta APP was introduced as well as beta APP containing mutations genetically linked to familial Alzheimer's disease (AD) and to hereditary cerebral hemorrhage with amyloidosis-Dutch type. In mouse brain, human beta APP RNA was up to 60% as abundant as total endogenous beta APP RNA. Human beta APP gene expression was most abundant in the CA subfields of the hippocampus and in the piriform cortex. Correct processing of human beta APP at the beta-secretase cleavage site was demonstrated in transgenic mouse brains. Despite a 40% increase in total beta APP immunoreactivity in lines expressing mutant human beta APP, no evidence of amyloid deposition was found in brains of mice up to 14 months in age. Higher levels of mutant human beta APP, increased age, or other factors may be necessary to elicit beta-amyloid-related neuropathologies in the rodent brain.

Transgenic mice expressing both human apolipoprotein B and human CETP have a lipoprotein cholesterol distribution similar to that of normolipidemic humans.

Transgenic mice expressing both human apolipoprotein (apo) B and human cholesteryl ester transfer protein (CETP) have been developed. When fed a normal mouse chow diet, the apoB/CETP double transgenic animals had threefold higher serum CETP activity than humans and had human apoB levels that were similar to those of normolipidemic humans. When compared with nontransgenic mice, the total serum cholesterol levels in the female apoB/CETP transgenic animals were increased significantly. Serum HDL cholesterol levels were decreased significantly in both male and female apoB/CETP transgenic animals. The percentages of the total cholesterol within the HDL, LDL, and VLDL fractions of the apoB/CETP animals were approximately 30%, 65%, and 5%, respectively, similar to the distribution of cholesterol in the plasma of normolipidemic humans. Thus, by expressing both human apoB and human CETP, the lipoprotein cholesterol distribution in the serum of a chow-fed mouse was transformed into one that resembles a human profile.

Implications of tissue heterogeneity for radiosurgery in head and neck tumors.

PURPOSE: This study was undertaken to investigate the perturbation of small radiation beams by low density heterogeneities and to evaluate the ability of a Monte Carlo code to account for such perturbation. Performance of an inexpensive film scanning system was also evaluated. METHODS AND MATERIALS: Film and diode measurements were made in an acrylic phantom in which the size and position of an air gap were varied. Monte Carlo analysis was used to obtain additional verification of the measurements, to provide insight into photon and electron transport phenomena not directly measurable, and as a benchmark for the code. RESULTS: With 10 MV photons and a 1 cm circular field, a small 3-mm air cavity placed 2.6 cm deep in acrylic (full buildup) results in a reduction in central axis dose of 21% immediately following the cavity. Equilibrium is then reestablished over the next centimeter, after which the dose exceeds that of the homogeneous case by 3-4%. The loss in central axis equilibrium is highly field-size dependent, with some loss occurring even for the largest (32 mm) collimator. In addition, the presence of the air cavity produces a significant increase in dose up to 2 cm lateral and outside the primary field. CONCLUSIONS: Tissue heterogeneities are not presently accounted for in radiosurgery calculations, yet have the ability to perturb dose significantly. Targets may potentially be underdosed, and adjacent critical structures overdosed. Inability to account for tissue heterogeneities may limit the use of the radiosurgery approach in some areas. A Monte Carlo approach may be the method of choice for small field dose calculation when tissue heterogeneities are encountered.

Mineralization of mono- and dichlorobenzenes and simultaneous degradation of chloro- and methyl-substituted benzenes by the white rot fungus Phanerochaete chrysosporium.

Phanerochaete chrysosporium extensively degraded and mineralized chlorobenzene and o-, m-, and p-dichlorobenzenes. The rate of degradation was in the following order: monochlorobenzene > m-dichlorobenzene > o-dichlorobenzene > p-dichlorobenzene. Net level of degradation was generally higher than mineralization. Maximal degradation and mineralization of chlorobenzenes were observed in malt extract cultures in which the lignin peroxidases and manganese peroxidases are not known to be produced. The fungus degraded both chlorobenzene and toluene when presented as a mixture, indicating its ability to simultaneously degrade chloro-substituted and methyl-substituted benzenes.

A verification of the Monte Carlo code MCNP for thick target bremsstrahlung calculations.

The bremsstrahlung spectra from thick targets of Be, Al, and Pb are calculated using the Monte Carlo code MCNP (Monte Carlo N-particle). The current version of MCNP (v.4A) incorporates a coupled electron-photon transport scheme that allows the user to estimate the photon fluence produced from primary electron interactions. The simulation parameters are based on bremsstrahlung measurements of 15 MeV electrons incident on thick targets of Be, Al, and Pb at various angles between 0 degree and 90 degrees. The integrated yield and mean energy of each bremsstrahlung spectrum is calculated for the three targets at these angles. For angles less than 60 degrees the integrated yield calculated by MCNP4A is within 6% of measured values for the three targets. Furthermore, predicted mean energy is within 7% of the values derived from measurement for all angles tested. Also compared are the performances of two MCNP4A fluence tallies; a next-event estimator (detector tally) and a track length estimator (cell tally). Timing studies indicate the detector tally will perform the integrated yield calculations to a precision of 1% approximately 10 to 50 times faster than the conventional cell tally for an emission angle of 0 degree.

Mutational spectrum of revertants in the hisD3052 allele of Salmonella typhimurium induced by hydrogen peroxide-activated benzidine.

Benzidine is mutagenic in a modified Ames (Salmonella typhimurium) assay, which uses hydrogen peroxide-dependent peroxidative activation. The mutational specificity of benzidine was investigated in tester strain TA98, which reverts by frameshifts of the hisD3052 allele. The most frequently observed mutation is a deletion of two bases from a (CG)4 run. This deletion was elevated in frequency among benzidine-induced revertants, relative to spontaneous revertants. Many other mutations were also observed, including additions, deletions, and complex events. Only small frameshifts were observed among the benzidine-induced revertants, whereas some larger deletions were observed among the spontaneous revertants.

A new family of water-soluble, third generation antitumor platinum complexes.

[1,1-Cyclobutanedicarboxylato(2)-O,O'](1,3-dioxane-5,5-dimethan amine- N,N')platinum(II), 3a, a third generation, very water-soluble platinum complex, has been synthesized along with several of its analogues. All members of the new family contain a 1,3-dioxane or 1,3-dioxolane-1,3-diamine as their basic ligand, a moiety which contributes to their increased water solubility, and a bidentate acid ligand, which is responsible for their good stability. They were all easily crystallized and characterized by 1H NMR and elemental analysis, and the parent complex 3a was further characterized by 13C NMR. Their very desirable physical properties combined with their broad spectrum of antitumor activity and reduced toxicity make them good candidates of further development.

Arabinofuranosyl-5-azacytosine: activity against human tumors in athymic mice.

Arabinofuranosyl-5-azacytosine (Ara-AC), a new compound structurally related to arabinofuranosylcytosine (Ara-C) and 5-azacytidine (5-AC), has demonstrated significant therapeutic activity against a wide spectrum of murine tumors and three human tumor xenografts in the NCI tumor panel. Studies on the activity of Ara-AC in these and other human tumor xenograft models were undertaken to define its potential anti-human-tumor profile more completely. Ara-AC demonstrated marked antitumor activity against human tumor xenografts, including leukemias and solid tumors that do not respond to Ara-C or 5-AC. An important finding was the demonstration that Ara-AC was as effective by the oral route as when given intraperitoneally. Furthermore, the compound demonstrated synergism when combined with cisplatin in the treatment of refractory solid tumors and also induced monocyte-type differentiation of promyelocytic leukemia (HL-60) cells in vitro. Ara-AC is a promising new compound that may have utility in the treatment of human cancer beyond that anticipated for a cytotoxic nucleoside.

Characterization of Vero cells.

A cell line used in the production of biologicals should be free of infectious agents, and 'described with respect to cytogenetic characteristics and tumorigenicity'. Vero, a continuous cell line derived from a normal African green monkey kidney, was examined for the presence of retroviruses and for tumorigenic potential. We were unable to detect the presence of retroviruses by reverse transcriptase assay, electron microscopy or hybridization of cellular genomic DNA with Mason-Pfizer monkey virus DNA probes. In addition, passage 156 Vero cells did not form progressively growing tumors in nude mice or grow with high efficiency in soft agarose.

Development of resistance and characteristics of a human colon carcinoma subline resistant to mitoxantrone in vitro.

A subline of human colon carcinoma cells (WiDr/R) resistant to the cytotoxic effects of mitoxantrone in vitro, was developed by continuous exposure to increasing concentrations of drug. After 16 culture passages in the presence of mitoxantrone, a cell population emerged which was 30-40 times more resistant to the cytolytic effect of mitoxantrone than the mitoxantrone-sensitive parent (WiDr/S) line. Resistance to mitoxantrone was retained by WiDr/R cells propagated for more than 40 cell generations in mitoxantrone-free medium. Decreased drug sensitivity was strongly associated with reduced intracellular accumulation of mitoxantrone. Moderate differences in drug retention by sensitive and resistant cells were demonstrated. However, decreased uptake due to alterations at the cell membrane which impair transport of drug into the cell, reducing interaction with DNA, appears to be the principal basis of resistance in these cells.

Modulation of the immune response to tumors by a novel synthetic compound, N-[4-[(4-fluorophenyl)sulfonyl]phenyl] acetamide (CL 259,763).

CL 259,763, N-[4-[(4-fluorophenyl)sulfonyl]phenyl] acetamide, is an orally active compound capable of modifying the reactivity of certain lymphoid cell populations affected by the growth of a tumor. The compound augmented the response of lymphocytes from tumor-primed animals to syngeneic tumor cells, resulting in a marked increase in tumor cell destruction. Likewise, it enhanced macrophage inhibitory effects on the growth of tumor cells in vitro. These "activated" macrophages were detectable in peritoneal exudates of treated mice 4 to 12 days after receiving a single oral dose of CL 259,763, with peak activity being demonstrable by day 7. The compound also restored the alloreactivity of lymphocytes from immunodepressed mice bearing the Lieberman plasma cell tumor, possibly by interfering with suppressor cells. Macrophages and lymphocytes from treated mice released significantly more IL-1 and IL-2-like factors in culture than did the control counterparts. Sera from treated mice also possessed more colony stimulating factor than those from normal mice. Immunoadjuvant effects were evident when the compound was administered with an inactivated L1210 leukemia vaccine and it enhanced the effectiveness of cytotoxic chemotherapy when given to mice challenged with P388 murine leukemia. These immunomodulating effects of CL 259,763 may hopefully be exploited in efforts to augment the immune response of the host to a progressively growing tumor.