Radiocirurgia estereotáxica / Estereotactic radiosurgery

A radiocirurgia é uma tecnica de irradiaçäo que nos ultimos anos vem se tornando mais frequentemente utilizada. De inicio realizada apenas em poucos e superespecializados centros, devido à extremamente sofisticada e cara aparelhagem. A introduçäo das tecnicas radiocirurgicas com o acelerador linear fez com que esse procedimento pudesse ser agora realizado na maioria dos grandescentros de radioterapia. Alguns dos requerimentos essenciais para a radiocirurgia incluem a localizaçäo acurada da lesäo a ser tratada, o calculo tridimensional da dose, a precisäo da irradiaçäo no alvo predeterminado e um acentuado gradiente de dose fora do volume-alvo. Nesse trabalho, os princípios, as indicaçöes, uma descriçäo sucinta das principais tecnicas e os resultados terapeuticos iniciais da radiocirurgia, numa variedade de patologias, säo discutidos.

Extracorporeal irradiation of dog blood: the effects of a radiostrontium irradiator on blood stem cells (CFU-C).

The radiation sensitivity of dog blood stem cells was measured in vitro and in an extracorporeal circulation passing through a radiation field. It was established that the calculated D0 was as low as 0.45 Gy. Investigating the cell killing rate in our equipment (Buchler type 90Sr device for extracorporeal irradiation), we found an overkill situation; the dose delivered was in excess of that which would be required for the total eradication of all stem cells in the peripheral blood passing through the radiation field. Various other types of devices used for extracorporeal irradiation of blood are also reviewed.

The basis of a suggested instrumental approach to the surveying of neutron fields and the measurement of personal dose from neutrons.

The basis of a two-component neutron monitoring system that could be applied to both survey instruments and personal dosemeters is considered. Neutrons with energies below 10 keV are detected by a thermal neutron detector which, in the survey instrument, is located inside a small moderating sphere, whereas in the personal dosemeter it is positioned behind a thermal neutron shield located on an individual's body. Neutrons above 10 keV are detected by counting pulses produced by protons ejected from a thin hydrogenous foil. By judicious choice of the characteristics of the detection elements, it is possible to ensure that the sum of the sensitivities of the elements of both survey instrument and personal dosemeter vary with neutron energy in a way close to that required for radiological protection purposes throughout the range thermal-10 MeV. The realisation of the elements sensitive below 10 keV presents few fundamental problems and appropriate devices have been reported in the literature. Those sensitive above 10 keV have proved to be more difficult to realise in practice.

Dosimetry with a diamond operating as a resistor.

A very pure diamond with contacts of graphite has a linear current-voltage characteristic when subjected to irradiation. The resistivity is inversely proportional to the dose rate and the sensitivity is extremely high for gamma- and X-rays and electron beams. It is concluded that diamond resistors are suitable for clinical radiation dosimetry. This conclusion is also based on earlier work in which diamonds were used as pinpoint counters.

Glenn A. Fry Award Lecture--1977. The ocular effects of ultraviolet radiation.

The author reviews the previous known effects of UV radiation on the eye together with results obtained on human and animal eyes in his laboratory during the past 11 years. Damage to the cornea and lens is assessed, classified, and discussed. Methods of calculating safe UV exposures and establishing characteristics of protective devices are presented.

Measurement of kilovoltage by the penetrameter - theoretical aspects.

The penetrameter method makes use of the attenuation in copper of a heavily filtered X-ray beam to predict the generating kVp. This is derived from the matching step or copper reference number (CRN) of a film density matching process in which a fast and slow screen combination is employed. In the present work, theoretical spectra resulting from chosen representative kV and mA wave-forms have been derived by computer analysis, assuming Kramers' expression for the bremsstrahlung emission from a thick target. The CRN appropriate to each spectrum has been found and its relation to kVp recorded. The uncertainty in the use of the penetrameter is expressed in terms of the spread of the CRN as a function of kVp and waveform. The computer predictions agree well with experiment, provided a fall in the fast-slow screen ratio with energy is postulated - a fall verified by separate experimental work in screen ratios. Since Kramers' expression relates only to bremsstrahlung radiation, the theoretical analysis has been extended to include the effects of K characteristic and extrafocal radiation. An expression has also been derived for the sensitivity of the penetrameter.

Build-up region of megavoltage photon radiation sources.

Measurements of surface dose and build-up have been measured for photon radiation sources with maximum energy from 1.2 to 25 MeV. A variable volume ionization chamber was used and the results extrapolated to what would be obtained with a zero volume chamber. The results are found to depend systematically on the plate separation of a parallel plate ionization chamber and an empirical method was derived for correcting measurements made with a fixed volume chamber. The relationship of dose build-up curves with skin reactions in radiation therapy patients is discussed.