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Biomedical subjects

D E Wrede

Publications and source records attributed to D E Wrede.

14 recordsLinked to original sources
PubMed1980

Simple experimentally derived algorithm for computer calculated dose rates associated with 137Cs gynecologic insertions.

A simple mathematical algorithm is derived from experimental data for dose rates from 137Cs sources in a finite tissue equivalent medium corresponding to the female pelvis. An analytical expression for a point source of 137Cs along with a simple numerical integration routine allows for rapid as well as accurate dose rate calculations at points of interest for gynecologic insertions. When compared with theoretical models assuming an infinite unit density medium, the measured dose rates are found to be systematically lower at distances away from a single source; 5 per cent at 2 cm and 10 per cent at 7 cm along the transverse axis. Allowance in the program for print out of dose rates from individual sources to a given point and the feature of source strength modification allows for optimization in terms of increasing the difference in dose rate between reference treatment points and sensitive structures such as the bladder, rectum and colon.

Brachytherapy↗
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↗
PubMedDate not supplied

A useful algorithm for calculating central ray TAR and TMR values.

An algorithm utilizing a two-dimensional polynomial power functions least squares fit has been applied to the calculations of TAR in the case of CO-60 teletherapy and TMR in the case of an 8MV LS75/10 linear accelerator giving less than +/- 1/2% errors respectively between calculated and measured values. The TAR and TMR algorithms are used as subroutines in pocket sized and table top programmable calculators or computers and thus provide rapid calculation of treatment time or monitor units as well as given dose.

Cobalt Radioisotopes↗
PubMedDate not supplied

Shaped field electron dosimetry for a Philips SL75/10 linear accelerator.

Both small and irregular fields are frequently the treatment of choice in many clinical applications of electron therapy. The fields are often shaped by lead or low melting point alloy placed at the end of the cone or on the patient's surface. The dosimetry for electrons of energies of 4, 6, 8, and 10 MeV is examined with particular emphasis on very small fields for treatment such as the lip, nose, and eye and irregular fields of various area/perimeter ratios. The paper discusses the dosimetry correction due to field shaping as a function of the location of the shield.

Humans↗