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Biomedical subjects

C G Orton

Publications and source records attributed to C G Orton.

12 recordsLinked to original sources
PubMed1991

Comparison of high and low dose rate remote afterloading for cervix cancer and the importance of fractionation.

Analysis of the data obtained from a survey of 56 institutions treating a total of over 17,000 cervix cancer patients with high dose rate (HDR) remote afterloading, shows that the average fractionation regimen is about 5 fractions of 7.5 Gy each to Point A, regardless of stage of disease. Comparison with historical controls treated by the same clinicians at low dose rate (LDR), showed that 5-year survival was statistically significantly better for HDR versus LDR for Stage III patients (47.2% compared to 42.6%, P = 0.005) and for all patients pooled together (60.8% vs. 59.0% P = 0.045). Morbidity rates were considerably lower for HDR versus LDR for both severe (2.23% vs. 5.34%, P less than 0.001) and moderate plus severe complications (9.05% vs. 20.66%, P less than 0.001). There is an apparent geometrical advantage of HDR intracavitary therapy in that there is a reduction in the "hot-spot" rectal and bladder doses relative to Point A of, on average, (13 +/- 4)% for the HDR compared to the LDR treatments. Fractionation of the HDR treatments significantly influenced toxicity: morbidity rates were highly significantly lower for Point A doses/fraction less than or equal to 7 Gy compared with greater than 7 Gy for both severe injuries (1.28% vs. 3.44%, P less than 0.001) and moderate plus severe (7.58% vs. 10.51%, P less than 0.001). The effect of dose/fraction on cure rates was equivocal. Finally, the data showed that for conversion from LDR to HDR the total dose to Point A was reduced on average by a factor 0.54 +/- 0.06.

Brachytherapy↗
PubMed1991

Recent developments in time-dose modelling.

Two recent innovations in time-dose models are reviewed: the linear-quadratic (L-Q) and the variable-exponent Time-Dose Factor (TDF) models. The basic L-Q equations for fractionated and continuous (brachytherapy) regimes are presented as well as those for incomplete repair and short half life radionuclides. None of these equations has provision for a repopulation factor, so a "wasted ERD" parameter is introduced, which is a linear function of overall treatment time, with incorporation of a lag time if desired. For low dose rate therapy, an effective treatment time is defined, at which the ERD reaches its maximum value when the rate of increase due to irradiation equals the rate of decrease due to repopulation. The variable-exponent TDF model has a volume-effect parameter and scaling factors which make TDFs of 100 correspond to tolerance for all volumes of tissue treated, for both fractionated and continuous therapy. These, as well as the exponents, are all tissue-specific. Volume-effect and scaling factors are also appropriate for the L-Q equations. With these it is possible to apply the TDF and L-Q models to problems which involve inhomogeneous dose distributions. Several examples of the use of these models are presented.

Animals↗
PubMed1979

Contrast enhancement of high-energy radiotherapy films.

An order-of-magnitude improvment in the contrast of high-energy localization and verification films has been achieved through the application of a simple, inexpensive, contrast enhancement technique. The method involves making reversal contact "prints" of the original film onto ordinary X-ray fi-m with equipment commonly available in any radiotherapy department. This results in "gamma multiplication". The theory as well as several applications of this effect are presented.

Humans↗
PubMed1975

Errors in applying the NSD concept.

An analysis of selected papers in which the Nominal Standard Dose (NSD) concept is used reveals that about 50% of them contain errors. These mistakes are both conceptual and mathematical in nature and average plus or minus 7%. Typical errors and methods to eliminate them are discussed. A table is provided for interconversion of NSDs, partial tolerances, and time, dose and fractionation (TDF) factors.

Humans↗