Biomedical subjects

J C Chu

Publications and source records attributed to J C Chu.

40 records · Page 3Linked to original sources

PubMed1981

Treatment of asthmatic patients sensitive to mites (Dermatophagoides farinae); a four-year study of immunotherapy with an extract of Dermatophagoides farinae.

Dermatophagoides farinae (D.F.) is considered by many to be one of the main allergens in house dust. The present report is a four-year study with an extract of D.F. in 518 patients with extrinsic asthma. The extract was clinically effective in 315 out of 474 patients (66.5%) after the first course of therapy (20 weeks). It was even better (P less than 0.001) after more than two courses (76.5%). About 10% of the patients become almost entirely asymptomatic. The individuals whose skin reactions decreased after treatment showed the best results (P less than 0.05). After therapy the skin reaction and degranulation of mast cells were inhibited. Side effects were mild and transient. The results suggest that immunotherapy with D. farinae might be an acceptable measure of treatment for many patients with extrinsic asthma.

Antibodies↗

PubMed1980

A liquid ionisation chamber for neutron dosimetry.

Theories of ionisation in liquid and the use of liquid ionisation chambers in mixed neutron field dosimetry have been studied. Theoretical models developed by Jaffe and by Onsager were used for comparison with the experimental measurements. The Jaffe method predicts a higher collecting efficiency than does the Onsager model. Gamma and neutron sensitivities of a liquid chamber can be calculated by the Bragg-Gray principle and Onsager's theory. The calculation is subject to relatively large uncertainties, mainly due to insufficient knowledge of the ion distribution in ionisation tracks and of W/e values for iso-octane. The chamber constructed for clinical use should work best for mixed neutron fields with gamma-neutron ratios of 10-20%; however, it would be difficult to use a liquid ionisation chamber to detect small neutron variations in mixed fields with large gamma components.

Energy Transfer↗

PubMedDate not supplied

Use of a tungsten filter to improve beam uniformity.

A general method for calculating the dose distribution in an irradiated volume is to evaluate the primary and scatter components separately according to the method described by Clarkson and Cunningham. It was found, however, that for a 6 MV Siemens accelerator the calculated dose overestimated the peripheral dose at depths beyond 10 cm by 3%-6%. The difference was attributed to the varying beam quality across the field. This beam quality variation was decreased by hardening the beam with a permanently installed 1/3 in. tungsten filter inserted between the beam flattening filter and the mirror base assembly. The tungsten filter had a more pronounced beam hardening effect at the beam edge than along the central ray. For example, the dose rate in air at the beam edge for a 30 x 30 cm2 field was 13% higher than along the central ray without the tungsten filter. The addition of the 1/8 in. filter decreased this horn to 6%. The beam quality along the central ray also increased. The tissue-air ratio for zero field size along the central ray increased by 2% with the addition of the tungsten filter. The scatter-air ratio, however, did not change with the added filter. Agreement within 1%-2% was achieved between the calculated and measured beam profiles at all depths in a phantom when the tungsten filter was added.

Filtration↗

PubMedDate not supplied

Static multileaf collimator for fast-neutron therapy.

This paper describes a multileaf collimator, designed to obtain irregularly shaped neutron fields, that fits into an existing fixed field-size collimator system. The shape of the desired portal field is obtained by appropriately setting the position of each leaf of the collimator. The collimator consists of 40 polyethylene leaves to produce fields of irregular shape of up to 400 cm2. The leaves are interlaced with grooves to prevent neutron leakage. The measured penumbra defined by the multileaf collimator is similar to that defined by the same length fixed field-size water extended polyester (WEP) collimator. The multileaf collimator has a lower neutron transmission due to its higher hydrogen concentration.

Fast Neutrons↗