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Biomedical subjects

D E Wrede

Publications and source records attributed to D E Wrede.

10 recordsLinked to original sources
PubMed1979

An analysis of the dosimetry for mantle field therapy using 4 MV X-rays and its routine application.

There are several different methods in vogue at present in determining patient midplane doses in the "mantle" treatment for Hodgkin's disease and malignant lymphomas. A method of determining midplane doses in individual cases using thermoluminescent dosimetry is presented. It shows excellent agreement with the midplane doses measured in an Alderson-Rando phantom treated as a hypothetical "mantle" patient.

Hodgkin Disease↗
PubMed1976

Approaches to optimization of dose in radiation therapy of cervix carcinoma.

A treatment planning approach to radiation therapy for carcinoma of the cervix which attempts to maximize tumor dose and minimize the effect on normal tissue must include additonal dose reference points besides the standard ones (Manchester points A and B, mg-hrs.) A variety of loading configurations can be used to treat the tumor volume to a specified dose. In order to avoid inappropriate loading arrangements, dose at the tumor and at the vault must be carried to required therapeutic levels.

Female↗
PubMed1975

Evaluation of radiochemical protectors using urinary deoxycytidine levels.

It is customary to use the LD50 response as a criterion for the evaluation of chemical radioprotection. The increased urinary excretion of deoxycytidine (CdR) in irradiated rats has been shown to be a linear dose--response relationship up to 200 R, thus making it possible to consider such a response as a criterion for chemical radioprotection evaluation at sub-lethal irradiation levels. Rats were subjected to 200 R X-irradiation with various chemical protectors and without chemical protectors, urine was collected 24 hours after irradiation, and the CdR levels in the urine analysed. A dose-reduction factor (DRF) was determined for 24-hour urinary excretions of CdR for chemically protected and non-protected rats. The DRF values are within 6 per cent of those reported by other investigators using LD50 as the response criterion for serotonin, cysteine, MEA and PAPP but differ for WR-2721 and WR-2823. Agreement using WR-2721 and WR-2823 compounds is only obtained when the toxicity effect of the compound is taken into consideration.

Animals↗
PubMed1975

Calvarial-scalp compensator for radiotherapy.

A universal compensator for megavoltage cobalt-60 radiotherapy of the skull was constructed and applied to clinical radiotherapy use. This compensator allows the skull to be treated with a more uniform dose.

Adult↗
PubMed1975

Computer dosimetry based on pelvic simulation.

A technique is described which shows a good correlation between computer dose rates based on a simulated pelvic irradiation system and dose rates measured in patients using a probe monitor. With radiation sources in position, the system described permits a rapid check of computer dosimetry output in a clinical situation. As a dual dose monitor system greater confidence in the accuracy of implant dose distribution is possible.

Computers↗
PubMed1975

Experimental investigation of source-block distance to source-surface distance ratios for cuboid and beam-divergence-shaped shadow blocks for cobalt-60 teletherapy.

The partial transmission zone (PTZ) measured in air and its radiation shadow components are identified quantitatively and qualitatively for both cuboid and beam-divergence-shaped blocks. Source-block distance (SBD) and source-surface distance (SSD) are varied to produce SBD/SSD ratios from 0.71 to 0.86. The variation of the magnitude of the radiation shadow components as a function of SBD/SSD is explained in terms of a radiation shadow model. The clinical significance of PTZ minimization and a comparison between PTZs of 'shaped' and 'nonshaped' blocks is discussed. For small ratios of SBD/SSD the beam-divergence-shaped blocks produce smaller medial and lateral PTZs, whereas for larger ratios in the order of 0.9 the medial PTZ is also small for the cuboid blocks. Both PTZs, in general, decrease with increasing SBD/SSD ratios and for both cuboid and beam-divergence-shaped blocks.

Cobalt Radioisotopes↗
PubMedDate not supplied

Dosimetric considerations of symmetric and asymmetric 60Co teletherapy split fields.

Split fields are commonly used for a variety of treatments for which local shielding is desired; a single field is split into two fields by means of lead blocks placed in the beam. The condition for assuming independence of the two fields is investigated by using the area over perimeter calculational method and comparing this to experimental depth-dose data measured in a water phantom using a Shonka ionization chamber. Two principal variations affecting dose distributions are examined: block width and position of the block expressed as the fractional perpendicular distance between the central ray of the overall field and the center of the block. An intercomparison between calculation and experimental data shows that the right and left sides of the split field behave as independent fields giving TAR values in agreement with experimental data to within +/-1%. If the fields are asymmetric and if the larger field is less than 70% of the total area including the blocked part, then the dosimetry should be based on average TARs, off-center ratios, and backscatter factors for the two fields. If the larger area is greater than 70% of the total area, then the treatment time can be calculated from the larger field only.

Cobalt Radioisotopes↗