Biomedical subjects

Y C Lo

Publications and source records attributed to Y C Lo.

60 records · Page 4Linked to original sources

PubMed1990

[Evaluation of dose distribution in the region of small air space in human body by Co-60 and 10 MV X-ray beams].

In many parts of human body, air-filled spaces are components of normal anatomical structures, such as nasopharynx and paranasal sinuses, and the inclusion of these spaces in radiation treatment fields may create inhomogeneous dose distribution, due to the loss of scattering electron equilibrium, the lack of backscatter and the alteration in primary beam attenuation. Accurate determination or measurement of dose in the region of irregular air spaces has been experimentally difficult. However, tumors growing on the surface of the air cavities do cause serious concern by conscientious radiation therapists and physicist about the possibility of underdose. Using the models of simulated air cavities, combined air cavity and air channel, and taking measurement with a small window parallel plate ionization chamber in solid phantoms, it is found that the air spaces in the human body will cause underdose or overdose at the exit air space surface for 10MV X-ray and Co-60 r-ray. Surface dose were evaluated by a gain/loss factors (G/L) which was defined as the ratio of exit air space surface dose and the dose measured in a same but homogeneous phantom. The G/L factors are greater than 1.0 (overdose) where the air spaces are much smaller than radiation field sizes and are less than 1.0 (underdose) in extreme situations where the air spaces are larger than radiation field sizes and where the scattered volume of cavity wall in the treatment fields in also small. In addition, these effects of overdose and underdose are enhanced by increasing air space thickness and higher photon energy. We suggest that the radiation therapists and clinical physicists be cautious in applying these useful guidelines for treatment planning.

Cobalt Radioisotopes↗

PubMed1989

Practical neutron dosimetry with superheated drops.

The Superheated Drop Detector (SDD) is a new kind of neutron detector based on the same principle as that of the bubble chamber, except the superheated material is in drop form suspended by a gel or polymer as first described by Apfel (U.S. Patent 4,143,274). Previously, we have developed a theoretical model for the prediction of the threshold neutron energy to nucleate bubbles in our superheated materials and a model for the calculation of the energy dependent response function of SDD. The results of the theoretical calculations agree with the experimental measurements reasonably well. We found the measured response curve of one of our SDDs follows the same trend as the ideal ICRP dose equivalent response curve within 40% for neutrons of energy above 100 keV and within a factor of 10 below 100 keV. Therefore, it is possible to make a rem-response Superheated Drop Detector. We have further calibrated our SDD with 252Cf neutron sources (both bare and D2O moderated). The results are in reasonable agreement with our theoretical predictions, which proves that our model is valid not only for monoenergetic neutrons but also for neutrons from a radioactive source. The principles of operation of our detector, which can be used in neutron dosimetry, area monitoring, and neutron spectrometry, are discussed.

Neutrons↗

PubMed1989

Dosimetry of high dose rate intracavitary radiation therapy using Co-60 and Ir-192 sources.

For decades, the high dose rate sources of Co-60 and Ir-192 have been used in remote controlled afterloading brachytherapy. A small volume ion chamber was used to measure the dose rate in varying distances from the sources. The entire dose distribution around the source was tabulated and the data were used to calculate the treatment time for individualized patient setting. A solid diode detector was used to plot the relative distance dose and the symmetrical dose distribution of the sources. Thermoluminescence dosimetry (TLD) was used for spot-checking of the dose. The dose distribution in the clinically useful range of 2-5 cm was carefully estimated. When normalized at 2.0 cm from the source, the dose rate at 5.0 cm was 17.1% for the Co-60 source and 18.4% for the Ir-192 source. It is clearly demonstrated that Ir-192 offers no dosimetric advantages, which is contrary to what used to be believed by some clinicians. The parameters of the computer treatment planning system have to be corrected and then adopted into clinical application.

Brachytherapy↗

PubMedDate not supplied

Albedos for 4-, 10-, and 18-MV bremsstrahlung x-ray beams on concrete, iron, and lead--normally incident.

Backscattering of radiation incident on a solid medium has been treated with some success as a reflection phenomenon. The concept of albedo has been used in the literature to deal with this problem. A Monte Carlo program has been used in this study to simulate the generation of bremsstrahlung beams from medical linear accelerators. The accuracy of the calculated spectra have been checked indirectly by calculating TPRs and comparing them with measured values. The dose albedos for 60Co and 137Cs beams normally incident on concrete have been calculated and compared with experimentally determined values in the literature. The generated energy spectra are then used to calculate the albedo factors for 4-, 10-, and 18-MV bremsstrahlung x-ray beams normally incident on concrete, iron, and lead. The number albedo decreases with increase in the atomic number of the reflecting medium. However, for high-energy photons, the dose albedo increases with increase in the atomic number of the medium. This is an important factor that needs to be considered in the design of shielding. The calculated energy spectra can be used in other problems and the albedo factors can be applied in practical shielding design for medical linear accelerators.

Cesium Radioisotopes↗

PubMedDate not supplied

Condom use among female commercial sex workers and male clients in Hong Kong.

The use of condoms is an aid to protection against human immunodeficiency virus (HIV) infection and other sexually transmitted diseases (STDs). In a one-and-a-half month period in mid-1993, 190 commercial female sex workers and 633 male clients of 8 Social Hygiene Clinics in Hong Kong were interviewed on their practice in condom usage. For both sex workers and clients, 18.5% and 22.8% never and 55.3% and 50.3% seldom used condoms during sexual contacts with paying partners and non-paying partners respectively. The majority (86%) of male clients claimed that they would use a condom if they knew it could reduce risk of contracting HIV and other STD. Condom promotion activities are necessary, particularly for those at higher risk of infection because of their sexual behaviour.

Adult↗

PubMedDate not supplied

StAR protein is expressed in both medulla and cortex of the bovine and rat adrenal gland.

We have employed polyclonal antibodies to a peptide sequence of bovine steroidogenic acute regulatory (StAR) protein and human placental 3beta-hydroxysteroid dehydrogenase (3beta-HSD) to determine the localisation and distribution of these proteins in rat and bovine adrenal glands. Immunohistochemical staining demonstrated the presence of StAR protein in the zona glomerulosa (ZG), zona fasciculata (ZF), zona reticularis (ZR) and in the medulla of both species. For 3beta-HSD, immunostaining was observed in the ZG, ZF and ZR of the rat adrenal and was absent in the medulla. Immunoblotting experiments showed intense bands for StAR protein (30 kDa, 37 kDa) in the mitochondria of bovine ZG, ZF and medulla and a less intense band (30 kDa) in the microsomes. In rat ZG and ZF/R mitochondria only the 30 kDa protein was present. For 3beta-HSD, an intense band (42 kDa) was found in microsomes and mitochondria of rat and bovine ZG and ZFR. A very faint signal for 3beta-HSD was seen in adrenal medulla. In conclusion, StAR (or a closely related) protein is present throughout the adrenal gland in rat and bovine species in contrast to 3beta-HSD which is confined to the steroidogenic zones. The possible function of StAR protein in the adrenal medulla merits investigation.

3-Hydroxysteroid Dehydrogenases↗