Dose rate constant and energy spectrum of interstitial brachytherapy sources

In the past two years, several new manufacturers have begun to market low-energy interstitial brachytherapy seeds containing 125I and 103Pd. Parallel to this development, the National Institute of Standards and Technology (NIST) has implemented a modification to the air-kerma strength (S(K)) standard for 125I seeds and has also established an S(K) standard for 103Pd seeds. These events have generated a considerable number of investigations on the determination of the dose rate constants (inverted V) of interstitial brachytherapy seeds. The aim of this work is to study the general properties underlying the determination of dose rate constant and to develop a simple method for a quick and accurate estimation of dose rate constant. As the dose rate constant of clinical seeds is defined at a fixed reference point, we postulated that dose rate constant may be calculated by treating the seed as an effective point source when the seed's source strength is specified in S(K) and its source characteristics are specified by the photon energy spectrum measured in air at the reference point. Using a semi-analytic approach, an analytic expression for dose rate constant was derived for point sources with known photon energy spectra. This approach enabled a systematic study of dose rate constant as a function of energy. Using the measured energy spectra, the calculated dose rate constant for 125I model 6711 and 6702 seeds and for 192Ir seed agreed with the AAPM recommended values within +/-1%. For the 103Pd model 200 seed, the agreement was 5% with a recently measured value (within the +/-7% experimental uncertainty) and was within 1% with the Monte Carlo simulations. The analytic expression for dose rate constant proposed here can be evaluated using a programmable calculator or a simple spreadsheet and it provides an efficient method for checking the measured dose rate constant for any interstitial brachytherapy seed once the energy spectrum of the seed is known.     

Dose distributions produced by shielded applicators using 241Am for intracavitary irradiation of tumors in the vagina.

Dosimetric characteristics of shielded vaginal applicators containing encapsulated 241Am sources are investigated in this work. Encapsulated 241Am sources emit primarily 60-keV photons which are more effectively shielded by thin layers of high atomic number materials than the 662-keV photons from 137Cs sources. With 241Am, it is possible to achieve almost unidirectional irradiation of localized vaginal tumors. The drastic decrease in irradiation volume on the contralateral side (uninvolved with tumor) is observed to decrease dose by up to 20%, even in the forward direction (unshielded side toward the tumor) of the applicator. A possible explanation for the observed effects of shields in both the forward and backward directions is the reduction of scattered photon fluence due to absorption of photons in the lead shield via photoelectric effect. Current theoretical models do not include this perturbation effect caused by shields on brachytherapy applicators.     

Immunoglobulin level in donor blood reactive for antibodies to human immunodeficiency virus.

Blood samples from 98 asymptomatic volunteer blood donors, including 55 that were reactive for antibodies to human immunodeficiency virus (HIV) in Western blot (WB) assay, were tested for levels of immunoglobulin G (IgG), IgM, and titer of antibodies to HIV, cytomegalovirus, and herpes simplex virus. Levels of IgG were significantly elevated (P less than or equal to 0.001) in donors with specific anti-HIV reactivity. A total of 69% of donors with anti-HIV had IgG levels of greater than or equal to 12 mg/ml, and 44% had IgG levels of greater than or equal to 14.5 mg/ml. Levels of IgM were not significantly different among WB-reactive and nonreactive donors. The titer of anti-HIV was significantly (P less than 0.02) correlated with IgG levels among donors reactive in the WB assay. Elevation of IgG, however, was not significantly associated with the presence of anticytomegalovirus or anti-herpes simplex virus antibodies. The data show that elevation of IgG may represent an early manifestation of HIV infection before the development of clinical symptoms of acquired immunodeficiency syndrome.     

Experimental determination of the anisotropy function for the model 200 103Pd "light seed" and derivation of the anisotropy constant based upon the linear quadratic model

Since the publication of the AAPM Task Group 43 report in 1995, Model 200 103Pd seed, which has been widely used in prostate seed implants and other brachytherapy procedures, has undergone some changes in its internal geometry resulting from the manufacturer's transition from lower specific activity reactor-produced 103Pd ("heavy seeds") to higher specific activity accelerator-produced radioactive material ("light seeds"). Based on previously reported theoretical calculations and measurements, the dose rate constants and the radial dose functions of the two types of seeds are nearly the same and have already been reported. In this work, the anisotropy function of the "light seed" was experimentally measured and an averaging method for the determination of the anisotropy constant from distance-dependent values of anisotropy factors is presented based upon the continuous low dose rate irradiation linear quadratic model for cell killing. The anisotropy function of Model 200 103Pd "light seeds" was measured in a Solid Water phantom using 1 X 1 x 1 mm micro LiF TLD chips at radial distances of 1, 2, 3, 4, 5, and 6 cm and at angles from 0 to 90 degrees with respect to the longitudinal axis of the seeds. At a radial distance of 1 cm, the measured anisotropy function of the 103Pd "light seed" is considerably lower than that of the 103Pd "heavy seed" reported in the TG 43 report. Our measured values at all radial distances are in excellent agreement with the results of a Monte Carlo simulation reported by Weaver, except for points along and near the seed longitudinal axis. The anisotropy constant of the 103Pd "light seed" was calculated using the linear quadratic biological model for cell killing in 30 clinical implants. For the model 200 "light seed," it has a value of 0.865. However, our biological model calculations lead us to conclude that if the anisotropy factors of an interstitial brachytherapy seed vary significantly over radial distances anisotropy constant should not be used as an approximation for anisotropy characteristics of a brachytherapy seed.     

Ameliorating effect of microdoses of a potentized homeopathic drug,Arsenicum Album,on arsenic-induced toxicity in mice

Background  

Arsenic in groundwater and its accumulation in plants and animals have assumed a menacing proportion in a large part of West Bengal, India and adjoining areas of Bangladesh. Because of the tremendous magnitude of the problem, there seems to be no way to tackle the problem overnight. Efforts to provide arsenic free water to the millions of people living in these dreaded zones are being made, but are awfully inadequate. In our quest for finding out an easy, safe and affordable means to combat this problem, a homeopathic drug, Arsenicum Album-30, appears to yield promising results in mice. The relative efficacies of two micro doses of this drug, namely, Arsenicum Album-30 and Arsenicum Album-200, in combating arsenic toxicity have been determined in the present study on the basis of some accepted biochemical protocols.     

Leishmania promastigote membrane antigen-based enzyme-linked immunosorbent assay and immunoblotting for differential diagnosis of Indian post-kala-azar dermal leishmaniasis

Diagnosis of post-kala-azar dermal leishmaniasis (PKDL), caused by Leishmania donovani, is difficult, as the dermal lesions are of several types and resemble those caused by other skin diseases, especially leprosy. Since the disease generally appears very late after the clinical cure of kala-azar in India, it is also difficult to correlate PKDL with a previous exposure to L. donovani. Very few attempts have been made so far to diagnose PKDL serologically, and the diagnostic methods vary in their sensitivities and specificities. Diagnosis of PKDL through sophisticated PCR methods, although highly sensitive, has limited practical use. We have developed a serodiagnostic method using an enzyme-linked immunosorbent assay to detect specific immunoglobulin (Ig) isotypes and IgG subclass antibodies in the sera of Indian PKDL patients. Our assay, which uses L. donovani promastigote membrane antigens, was 100% sensitive for the detection of IgG and 96.7% specific for the detection of IgG and IgG1. Optical density values for individual patients, however, demonstrated wide variations. Western blot analysis based on IgG reactivity could differentiate patients with PKDL from control subjects, which included patients with leprosy, patients from areas where kala-azar is endemic, and healthy subjects, by the detection of polypeptides of 67, 72, and 120 kDa. The recognition patterns of the majority of serum samples from patients with PKDL were also distinct from those of the serum samples from patients with visceral leishmaniasis (VL), at least for a 31-kDa polypeptide. To further differentiate patients with PKDL from those with active and cured VL, we analyzed the specific titers of the Ig isotypes and IgG subclasses. High levels of IgG, IgG1, IgG2, and IgG3 antibodies significantly differentiated patients with PKDL from patients cured of VL. The absence of antileishmanial IgE and IgG4 in patients with PKDL differentiated these patients from those with active VL. These results imply intrinsic differences in the antibodies generated in the sera from patients with PKDL and VL.     

Clinical implementation of AAPM Task Group 32 recommendations on brachytherapy source strength specification

Historically the strength of sealed brachytherapy sources has been described by many physical quantities, including true activity, apparent activity, and equivalent mass of radium. Recently, the AAPM Task Group 32 recommended that these quantities be replaced by a single quantity, air-kerma strength, with units of muGy m2h-1. A set of equations has been developed for unambiguously converting source strength estimates and renormalizing published dose-rate tables, which assume traditional quantities and units, into forms consistent with air-kerma strength. For commonly used brachytherapy sources, multiplicative conversion factors for each source-strength formalism and set of units are given. To convert equivalent mass of radium to air-kerma strength requires a single multiplicative factor, 7.23 muGy m2h-1/mgRaEq, applicable to all sources. Based upon a review of vendor source specification practices, the factors for converting source strength of 198Au, 103Pd, and 125I seeds from apparent mCi to air-kerma strength are 2.06, 1.29, and 1.27 muGy m2h-1/mCi(apparent), respectively. These factors are independent of source geometry but depend on the nominal exposure rate constant value selected by the vendor. Conversion factors applicable to mass of radium or true activity depend upon both source geometry and radionuclide identity. Because many of these conversion factors depend upon vendor choices of physical constants and exposure rate constants, readers are cautioned to carefully review vendor source strength specification practices before adopting these values clinically. Finally, the relationships between the various source strength quantities and absorbed dose rate in the medium surrounding the source are elucidated.     

The characterization of Gardnerella vaginalis DNA using non-radioactive DNA probes

DNA restriction profiles of various Gardnerella vaginalis isolates, generated by BamHI, EcoRI, PstI and other restriction enzymes, varied considerably. Only a few DNA fragments were identified as common in ethidium bromide fluorescence profile and Southern-blot hybridization patterns (employing a digoxigenin-labelled G. vaginalis DNA probe and an enzyme-linked immunoassay detection method). While the efficiencies of Southern-blot hybridization appeared inconsistent, in dot-blot assays, DNA from each isolate hybridized readily, enabling the detection of at least 10 ng DNA. A 5.7-kb DNA fragment from G. vaginalis ATCC 14018 genomic library, cloned in the BamHI site of pBR322, could replace the total genomic DNA probe. This specific DNA fragment was present in different sizes in 12 analysed G. vaginalis strains, describing a restriction fragment length polymorphism. In control studies, none of the DNA from bacteria other than G. vaginalis (including some genitourinary tract residents) hybridized with the G. vaginalis total or specific DNA probes. Non-radioactive G. vaginalis DNA probes can thus form the basis of a useful detection method for further studies of this organism.