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Radioimmunoassay: a probe for the fine structure of biologic systems

Rosalyn S. Yalow

Med. Phys. 5, 247 (1978); http://dx.doi.org/10.1118/1.594477 (11 pages) | Cited 1 time

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The development and techiques of radioimmunoassay are reviewed in the Nobel Prize lecture.(AIP)

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87.57.-s	Medical imaging
87.63.-d	Non-ionizing radiation equipment and techniques
87.85.Pq	Biomedical imaging
87.50.C-	Static and low-frequency electric and magnetic fields effects
87.15.-v	Biomolecules: structure and physical properties

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A technique for calculating the influence of thin inhomogeneities on charged particle beams

Michael Goitein

Med. Phys. 5, 258 (1978); http://dx.doi.org/10.1118/1.594507 (7 pages) | Cited 15 times

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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.

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87.53.Bn	Dosimetry/exposure assessment
87.55.-x	Treatment strategy

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Measurements and calculations of the influence of thin inhomogeneities on charged particle beams

Michael Goitein, G. T. Y. Chen, J. Y. Ting, R. J. Schneider, and J. M. Sisterson

Med. Phys. 5, 265 (1978); http://dx.doi.org/10.1118/1.594509 (9 pages) | Cited 15 times

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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.

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87.55.-x	Treatment strategy
87.53.-j	Effects of ionizing radiation on biological systems

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New method for exposing mammalian cells to intense laser radiation using the evanescent fields created in optical waveguides

Hollace L. Cox, Jr., William S. C. Chang, Karen L. Brandt, and Palmer G. Steward

Med. Phys. 5, 274 (1978); http://dx.doi.org/10.1118/1.594517 (6 pages)

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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 waveguide surface 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 TE₁ waveguide 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.

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87.50.S-	Radiofrequency/microwave fields effects
87.50.W-	Optical/infrared radiation effects
87.55.-x	Treatment strategy

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Towards optimum blurring in spiral tomography

G. Harding, U. Bertram, and H. Weiss

Med. Phys. 5, 280 (1978); http://dx.doi.org/10.1118/1.594432 (5 pages) | Cited 1 time

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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.

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87.57.-s	Medical imaging
87.63.-d	Non-ionizing radiation equipment and techniques
87.85.Pq	Biomedical imaging
87.50.C-	Static and low-frequency electric and magnetic fields effects

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Fast and thermal neutron profiles for a 25‐MV x‐ray beam

K. W. Price, Ravinder Nath, and G. R. Holeman

Med. Phys. 5, 285 (1978); http://dx.doi.org/10.1118/1.594479 (5 pages) | Cited 2 times

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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 reactions ³¹P(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 photon field 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 neutron dose equivalent to photon absorbed dose was found to be between 0.2% and 0.5%. Outside of the photon field, the ratio of neutron dose equivalent to the central‐axis photon absorbed dose was 0.12%.

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87.53.Bn	Dosimetry/exposure assessment
87.55.-x	Treatment strategy
07.85.-m	X- and γ-ray instruments

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Formation and early years of the AAPM

G. D. Adams

Med. Phys. 5, 290 (1978); http://dx.doi.org/10.1118/1.594433 (7 pages) | Cited 2 times

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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.

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