Backscatter dose perturbation in kilovoltage photon beams at high atomic number interfaces.

Dose perturbations at tissue interfaces have been of significant concern since the beginning of this century. However, comprehensive studies related to the backscatter perturbation in kilovoltage beams are still limited. The dose perturbation depends on various parameters, including beam energy, field size, and the thickness, width, position, and atomic number, Z, of the inhomogeneity creating the interface with soft tissue. Using a thin window parallel plate ion chamber having relatively flat response at low energies, the dose perturbation was measured as backscatter dose perturbation factor, BSDF, at various interfaces in kilovoltage x-ray beams. The BSDF is defined as the ratio of doses with and without an interface for identical setup conditions. Results indicate that the BSDF is strongly dependent on beam energy, like the backscatter factor. Contrary to its behavior in megavoltage beams, BSDF in kilovoltage beams does depend on the field size, suggesting a contribution from scattered photons and fluorescent radiation, originating in the high-Z material. The thickness of the high-Z medium is not critical, since a fraction of a millimeter is sufficient to provide full backscatter. The interface effect with wide inhomogeneity has two distinct regions: the high dose region (BSDF > 1.0), which is very localized and disappears within a fraction of a millimeter, and the low dose region (BSDF < 1.0), which is observed up to 10 cm. The dependence of BSDF is neither a quadratic function of Z nor a cube root of beam energy, indicating that the interface effect is complex and not predominantly due to photoelectron transport.

Intravenous streptokinase in acute evolving myocardial infarction--six to thirty-six months follow up.

270 consecutive patients who presented within six hours of the onset of acute myocardial infarction (AMI) and had no contraindication to thrombolytic therapy received intravenous infusion of 750,000 units of streptokinase (STK) in thirty minutes followed by heparin and oral anticoagulants. Treatment was instituted within 210 +/- 64 minutes after the onset of symptoms and reperfusion was achieved in 44 +/- 21 minutes. Reperfusion was recognised by indirect criteria in 249 patients, (92.2%) in the 0-6 hours group and 100% in the 0-3 hours group in all 72 patients. 2D echo LV ejection fraction (LVEF) improved from 51.6% +/- 9.4% at 0 hours to 60.61 +/- 8.4% at first week. In 40 patients (14.8%) there was early reocclusion in mean time of 36 +/- 13 hours of treatment. The incidence of reocclusion was higher in patients with anterior wall AMI than with inferior wall AMI. Reocclusion was also more frequent in patients who were administered adjuvant Dipyridamole therapy. In 36 of these patients reperfusion was achieved with an additional dose of streptokinase. During the last thirty-six months follow up, treadmill stress test was positive in 15 out of 80 (18.8%) streptokinase group subjected to it as compared to 42.2% conventionally managed patients. No LV thrombus, aneurysm or papillary muscle dysfunction was seen. 25 patients (9.2%) underwent coronary angiography six weeks later. CABG was undertaken in only 18 patients (6.6%) along with endarterectomy in one (.37%). None of the patients required additional aneurysmectomy or valve replacement. Elderly patients (above 75 years) suffered major haemorrhagic complications (.37%) and 17% of patients had minor bleeds. In-hospital mortality was 4.8% as compared to 10.2% in the control group (P less than .05). A long-term follow-up (6-36 months) revealed 11 patients that (4.07%) had reinfarction at mean time of 18 +/- 11 months (P less than .05). The late mortality rate in 6-36 months follow up was was 1.8% (P less than .05). It was concluded that intravenous streptokinase in acute myocardial infarction along with long-term anticoagulants is safe and effective. It reduces early and late mortality and morbidity significantly. A conservative strategy of subjecting patients to CABG after effective thrombolysis was found satisfactory during six to thirty-six months follow-up.

Pentoxifylline--a new drug for the treatment of intermittent claudication.

Pentoxifylline, a xanthine analogue was evaluated for efficacy, safety and tolerance in the treatment of intermittent claudication in a pilot study. Evaluation was performed in 35 cases. 20 patients were given Pentoxifylline in doses of 1200 mg daily, and 15 patients were given placebo for a period of 8 weeks respectively. Pentoxifylline given in doses of 1200 mg was significantly more effective than the placebo in increasing both the initial and absolute claudication distance (ICD & ACD) in patients with chronic occlusive arterial disease. The subjective parameters, such as paraesthesias, muscular cramps and sensation of heaviness in the legs paralleled the course of walking parameters. These results support the hypothesis that Pentoxifylline in doses of 400 mg TDS reduces blood viscosity by improving red cell flexibility, and thereby enhances blood flow in patients with COAD (Fontaine Stage II or Stage III). Pentoxifylline is thus regarded as a promising drug for circulatory ischaemic disorders, especially in intermittent claudication. It was well tolerated with minimal untoward effects.

Smoking, a great health hazard.

PIP: Positive and substantial steps need to be taken to discourage smoking. If steps are not taken, smoking could create a coronary health problem of epidemic proportion. It has been observed that 80% of deaths from heart attack in individuals under 45 are directly related to smoking. The chances of heart attack are twice as likely among those who smoke compared to those who do not. When a smoker stops smoking, his chances of heart attack decline to those of a non-smoker in about 6 months. A recent Soviet study concludes that smoking reduces the human life span by 2250 days or more than 6 years. Other serious diseases related to smoking include lung cancer and bronchitis. However, as the number of persons who have heart disease continues to rise, the major risk factors of heart attack are examined. Smoking is not only a major risk factor but also a highly preventable one. Passive smoking or inhalation of smoke by a non-smoker in the presence of someone who is smoking is also dangerous and can lead to heart disease as well. There needs to be no governmental tolerance of smokers and smoking with bans of smoking instituted in all public places. Moreover, cigarette advertising and sponsorship should be prohibited. Campaigns that educate the public about the hazards of smoking should be initiated, and the use of medication to reduce stress and control smoking should be considered as a viable deterrent and substitution for smoking.^ieng

Pentoxifylline (Trental)--a new drug for the treatment of peripheral chronic occlusive arterial disease.

Pentoxifylline (Trental), a xanthine analog, was evaluated for tolerance, safety and efficacy in the treatment of chronic arterial disease in a pilot study. Evaluation was performed in 35 cases. Twenty patients (Fontaine stage II or stage III severity) were given pentoxifylline in a daily dose of 1200 mg (Trental 400 t.i.d.) and 15 patients were given placebo for a period of eight weeks, respectively. Pentoxifylline was significantly more effective than the placebo in increasing both the initial and absolute claudication distance (ICD and ACD) in patients with peripheral chronic occlusive arterial disease (COAD). The subjective parameters such as paresthesias, muscular cramps and sensation of heaviness in the legs paralled the course of walking parameters. These results support the hypothesis that pentoxifylline in doses of 400 mg (slow release tablets) t.i.d. enhances blood flow via reducing blood viscosity and improving red cell flexibility in patients with intermittent claudication due to COAD. Pentoxifylline is thus regarded as a promising drug for the treatment of circulatory ischemic disorders, especially in intermittent claudication. It was well tolerated with minimal untoward effects.

Structural and ir properties of Pb(1-x)Hg(x)S thin films.

Electron diffraction, DTA, and optical absorption studies carried on thin films of PbS-HgS prepared by the solution growth technique developed by us suggest the formation of a uniphase ternary alloy with f.c.c. symmetry. The lattice parameter of the Pb(1-x)Hg(x)S alloy films can be made to increase or decrease with increasing concentrations of Hg depending on the choice of growth conditions. In the case of films where the lattice parameter increases with Hg concentration, alloying of PbS with alpha-HgS takes place, and the optical absorption edge shifts continuously toward higher energies. On the other hand, in the films for which the lattice parameter decreases with increasing Hg concentration, alloying of PbS with beta-HgS takes place, and the optical absorption edge shifts to lower energies. Thus the optical gap of the composite material can be varied from 0.2 eV to 1.2 eV by changing the growth conditions.