Volume 5, Issue 4, July 1978
Index of content:
5(1978); http://dx.doi.org/10.1118/1.594477View Description Hide Description
The development and techiques of radioimmunoassay are reviewed in the Nobel Prize lecture.(AIP)
5(1978); http://dx.doi.org/10.1118/1.594507View Description Hide Description
A method has been developed for calculating the fluence and dose perturbations which occur in the shadow of inhomogeneous structures exposed to beams of charged particles. It is shown that differences in scattering power in adjacent portions of irradiated material can give rise to fluence perturbations which, in turn, are responsible for dose perturbations. A quantitative analysis of this process is developed which permits calculation of both the perturbed primary fluence and dose distributions. Results of these calculations are given for a square‐faced edge discontinuity. The analytic technique, however, can be applied to more complicated interfaces and the general formulae are developed in this paper. They include provisions for the important modifying effects of beam divergence, of overlying or underlying homogeneous material, and of nonuniform beam profiles. In a companion paper, more complex geometries are analyzed and comparisons between calculations and experiments are presented.
5(1978); http://dx.doi.org/10.1118/1.594509View Description Hide Description
The predictions of an analytic technique for calculating fluence and dose distributions beneath thin inhomogeneities are presented for a number of structures, including a rectangular cavity or bar, a cylinder, a disk, and an angled or diffuse edge. Experiments with both electrons and protons for several geometries are presented and compared with predictions based on this technique. We offer some clinical guidelines for avoiding large perturbations due to scattering effects.
New method for exposing mammalian cells to intense laser radiation using the evanescent fields created in optical waveguides5(1978); http://dx.doi.org/10.1118/1.594517View Description Hide Description
A new method has been developed for exposing mammalian cells to intense laser radiation, using optical waveguides. Attached cells are exposed to the intense evanescent tail associated with the propagating waveguide modes. This technique allows a monolayer of attached cells covering a wide area on the waveguidesurface to be exposed to optical power densities in the 105–108 W/cm2 range. Waveguide modes containing power densities in this range are easily excited by moderate‐power continuous‐wave (CW) lasers. A monolayer consisting of an asynchronous population of 105 EMT‐6 cells was plated over a 2‐cm2 area on the top surface of an optical waveguide. This waveguide was fabricated by rf sputtering Ba−glass on a glass microscope slide used as a substrate. The area occupied by the cells was defined by a cell chamber constructed on top of the waveguide and filled with alpha‐MEM growth medium. TE0 and TE1waveguide modes were excited in the waveguide using a single mode (TEM00 and single longitudinal mode) CW Ar+‐ion laser at a wavelength of 5145 Å. Only 33.7% of the cells survived when the maximum power density and electric field strength within the waveguide reached 4×105 W/cm2 and 104 V/cm, respectively. No appreciable absorption of the laser radiation was detected due to the presence of the cells or nutrient growth medium and no significant temperature rise was noticed at the waveguide‐cell interface. It is strongly suggested that the cell‐killing mechanism is directly related to both the intense electric field at the cell‐waveguide interface and the penetration of the evanescent tail into the cell. Interactions which can only take place in the presence of intense electric field strengths at optical frequencies are presented as possible mechanisms involved in the cell‐killing process. Procedures are outlined for the design of waveguides capable of producing optical power densities and electric field strengths up to 108 W/cm2 and 105 V/cm, respectively.
5(1978); http://dx.doi.org/10.1118/1.594432View Description Hide Description
Attempts to increase the degree of blurring of nonfocused layers in tomography are inevitably associated with a worsening in the amount of artefactual detail introduced. A mathematical optimization technique has been employed to indicate how these conflicting characteristics may best be reconciled. The technique uses plausible definitions, based on the transfer function, of the effectiveness and the fidelity of the blurring, and generates a sequence of spread functions in which these two aspects are optimally combined.
5(1978); http://dx.doi.org/10.1118/1.594479View Description Hide Description
High‐energy x‐ray radiotherapy machines generate neutrons by photonuclear reactions in the target and the treatment head and expose the patient to a neutron flux. In order to evaluate the neutron exposure quantitatively, fast and thermal neutron profiles for 25‐MV x‐ray beams of the Sagittaire accelerator have been measured. An activation technique, using the reactions31P(n, γ)32P (thermal neutrons) and 31P(n, p)31Si (fast neutrons,E>0.7 MeV), has been developed to measure fast‐ and thermal‐neutron fluxes in an intense high‐energy photon flux. The sensitivity of this activation detector to high‐energy photons, which has plagued many previous neutron measurements, was carefully measured and found to be less than 4%. Neutron fluxes for various photonfield sizes ranging from 5×5 cm to 30×30 cm have been measured. The fast‐neutron profiles were observed to have rounded edges and the thermal fluxes were found to be relatively uniform. In the central part of the x‐ray beam, the ratio of neutrondose equivalent to photon absorbed dose was found to be between 0.2% and 0.5%. Outside of the photon field, the ratio of neutrondose equivalent to the central‐axis photon absorbed dose was 0.12%.
5(1978); http://dx.doi.org/10.1118/1.594433View Description Hide Description
This vignette recites significant steps leading to the formation of the AAPM and transpiring in the developments of the first decade, approximately. Persons involved, dates, and places are recognized. A table summarizes the progression of events. This recitation ends with the term of Kereiakes, the last President to be elected by the Board of Directors from its own membership, and with the move of the annual meeting time to mid‐summer.
5(1978); http://dx.doi.org/10.1118/1.594481View Description Hide Description
5(1978); http://dx.doi.org/10.1118/1.594482View Description Hide Description