Application of the scaling factor method to estimation of beta dose distributions for dissimilar media separated by a planar interface

Reliable methods of estimating doses are essential for the use of beta emitting radionuclides for radiotherapy. The passage of electrons through matter is a very complex phenomenon due to the large number of elastic and inelastic interactions resulting in scattering and energy losses. The analytical solution for the electron transport being intractable, the problem has been addressed by the Monte Carlo technique. Empirical or semiempirical less time consuming methods, such as the scaling factor method, may appear more preferable in practice when dealing with complicated source distributions. The method, proposed by Cross and co-workers [AECL Report Nos. AECL-1617 (1982), AECL 10521 (1992)] consists in the derivation of beta-ray dose distribution in other media from those in water by using a "scaling factor" or "relative attenuation factor" on distance and a closely related renormalization factor imposed by the energy conservation. This work investigates the accuracy of the scaling factor method using a statistical approach, a generalized chi 2 test, focusing on the particular case of potential interest, the scaling factor for water to bone. The direct comparison of the shapes of the depth dose deposition curves in the two media indicates discrepancies of less than 5% up to at least 60% of the range in bone, a depth within which 95% of the initial energy is deposited. The scaling factor derived by this method, 0.9720 +/- 0.0012, confirms the existing experimentally determined value of 0.973 +/- 1% [AECL Report No. AECL-10521 (1992)]. The accuracy of the determination is increased by almost a factor of 10. A way of improving the scaling method, especially for depth over the 60% continuous slowing down approximation range, by using a modulation function is also proposed.     

Surgical preparation of miniature swine for atherosclerosis research

A 2-stage surgical procedure for chronic intestinal, vascular, and lymphatic sampling in miniature swine is described. Cannulas were placed in the jejunum and ileum, followed by a 2nd implantation of indwelling catheters in the portal and hepatic veins, caudal vena cava, abdominal aorta, and cisterna chyli. The techniques used proved that miniature swine can be surgically adapted to meet experimental requirements.     

多媒体数据流实时传输技术研究

随着人们对实时业务需求的不断扩大,多媒体实时传输技术得到了蓬勃发展。文章研究了关于多媒体数据流实时传输的关键技术——资源预留协议、实时传输协议、实时流化协议、IPv6协议,具体分析了这些技术的原理及功能,最后给出了网络实时传输技术的实现与展望。     

Cardiovascular risk during ECT: managing the managers

Although atrophie blanche is classified as a vasculitis, its presentation and management differ from the classical vasculitis. We present a patient with idiopathic atrophie blanche and discuss its management.     

Prostate enlargement in mice due to fetal exposure to low doses of estradiol or diethylstilbestrol and opposite effects at high doses

On the basis of results of studies using high doses of estrogens, exposure to estrogen during fetal life is known to inhibit prostate development. However, it is recognized in endocrinology that low concentrations of a hormone can stimulate a tissue, while high concentrations can have the opposite effect. We report here that a 50% increase in free-serum estradiol in male mouse fetuses (released by a maternal Silastic estradiol implant) induced a 40% increase in the number of developing prostatic glands during fetal life; subsequently, in adulthood, the number of prostatic androgen receptors per cell was permanently increased by 2-fold, and the prostate was enlarged by 30% (due to hyperplasia) relative to untreated males. However, as the free serum estradiol concentration in male fetuses was increased from 2- to 8-fold, adult prostate weight decreased relative to males exposed to the 50% increase in estradiol. As a model for fetal exposure to man-made estrogens, pregnant mice were fed diethylstilbestrol (DES) from gestation days 11 to 17. Relative to controls, DES doses of 0.02, 0.2, and 2.0 ng per g of body weight per day increased adult prostate weight, whereas a 200-ng-per-g dose decreased adult prostate weight in male offspring. Our findings suggest that a small increase in estrogen may modulate the action of androgen in regulating prostate differentiation, resulting in a permanent increase in prostatic androgen receptors and prostate size. For both estradiol and DES, prostate weight first increased then decreased with dose, resulting in an inverted-U dose-response relationship.     

Alternative strategies for the long-term preservation of spermatozoa

The thermodynamics of RNA secondary structure formation in small model systems provides a database for predicting RNA structure from sequence. Methods for making these measurements are reviewed with emphasis on optical methods and treatment of experimental errors. Analysis of experimental results in terms of simple nearest-neighbor models is presented. Some measured sequence dependences of non-Watson-Crick motifs are discussed.     

Comparing the severity of obstructive sleep apnea in patients referred by urban and rural physicians

The occurrence of a subdural hematoma caused by the rupture of an intracranial aneurysm is rare. In our case, the patient is a 43-year-old woman who suffered from sudden onset of severe headache. Computed tomographic (CT) scan disclosed a subdural hematoma associated with subarachnoid hemorrhage. CT angiography and digital subtraction angiography revealed an elongated aneurysm adhering to the dura in the left Sylvian fissure. The subdural hematoma was evacuated and the aneurysm clipped. The patient made a full recovery.