Modulated radiation

Clarification of the role of radiation dose escalation particularly using innovative techniques such as intensity modulated radiation therapy (IMRT) and either single dose or fractionated stereotactic radiation. 

Improvements in the physical selectivity, from orthovoltage x-ray to cobalt-60 and high-energy linear accelerators, combined with more powerful diagnostic tools and radiation delivery methods have continuously improved the results of photon therapy (3-D or inverse planning, conformal- and intensity-modulated radiation therapy, and stereotactic methods). The safety and the reliability of photon therapy are well established. 

From a technical point of view, intensity-modulated radiation therapy (IMRT) optimizes several parameters selection of multiple beams and, for each beam, optimization of dose, dose rate, size and shape, etc. Tomotherapy optimizes the dose distribution by IMRT in successive sections with immediate verification gamma knife, cyberknife, and radiosurgery concentrate high radiation doses in well-defined small volumes. 

Powerful irradiation techniques are now available or under development for photons intensity-modulated radiation therapy (IMRT), tomotherapy, gamma knife, cyberknife, radiosurgery, etc. These techniques make it possible to irradiate any volume of any complex shape with minimum irradiation of critical normal structures. 

Sy D, Savoye C, Begusova M, Michalik V, Charlier M, Spotheim-Maurizot M (1997) Sequence-depen-dent variations of DNA structure modulate radiation-induced strand breakage. Int J Radiat Biol 72 147-155... 

Mikkelsen, T Thykier-Nielsen, S., Astrup, P., Santabarbara, J.M., S0rensen, J.H., Rasmussen, A., Robertson, L., Ullerstig, A., Deme, S., Martens, R., Bartzis, J.G., and Pasler-Sauer, J. (1997) MET-RODOS A Comprehensive Atmospheric Dispersion Module, Radiat. Prot. Dosim. 73,45-56. 

Figure 26-F1 Instrument diagram for a basic FTIR spectrometer. Radiation of all frequencies from the IR source is reflected into the interferometer where it is modulated by the moving mirror on the left. The modulated radiation is then reflected from the two mirrors on the right through the sample in the compartment at the bottom. After passing through the sample, the radiation falls on the detector. A data acquisition system attached to the detector records the signal and stores it in the memory of a computer as an interferogram. (Courtesy of Thermo Electron Corp., Madison, WI. With permission).

Finally, the FT-IR system operates by coding the infrared source with an amplitude modulation which is unique to each infrared frequency. The detector is sensitive to the modulated radiation so that unmodulated stray radiation is eliminated from the experiment, permitting the use of the FT-IR as an in-situ detector in many experiments. For example, an FT-IR has been used to monitor the evolution of coal pyrolysis products within a drop tube furnace (24) and within an entrained flow reactor (25). The latter has been operated up to 1200 C. 

The noise equivalent power (NEP) and specific detectivity (D ) are figures of merit that express the sensitivity of infrared detectors. The NEP is the root-mean-square (rms) power in a sinusoidally modulated radiation signal incident on the detector that gives a response equal to the rms dark noise in a 1-Hz... 

Modulated radiation from a tunable IR laser falls onto a prism at the condition of attenuated total reflection. Arising evanescent radiation can excite SEW on a metal surface at a suitable distance from the prism base. SEW propagates along the metal surface and can be attenuated by a thin dielectric film deposited on this metal. By means of a similar prism placed at a certain distance from the first one the SEW is transformed into normal radiation and detected by a pyroelectric detector. 

Clinical Target Volumes in Conformal and Intensity Modulated Radiation Therapy... 

P. L. Marston, Shape oscillation and static deformation of drops and bubbles driven by modulated radiation stresses theory, J. Acoust. Soc. Am. 67, 15, 1980. 

It can readily be shown (e.g., see [2.80]) that the rate of change of temperature of a material having heat capacity C and thermal conductance to its surroundings K when modulated radiation falls upon it is described by... 

Infrared Photothermal Beam Deflection Spectroscopy Infrared photothermal beam deflection spectroscopy (IR-PDS) is better than PAS because it does not have a microphone near the sample. It involves two light sources. One is an interferometer that produces modulated radiations to illuminate the sample, and the other is a laser source that is placed so that its beam grazes the surface of the carbon sample. The absorption of the incident-modulated radiation beam by the sample produces heat, causing thermal gradients that deflect the laser beam. The deflected laser beam is detected by the detector, and the signal reproduced is a measure of the photothermal effect induced on the sample surface. The resulting... 

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