http://www.rosalindfranklin.edu/Portals/3/Documents/Clinical_Skills_Workbook_ONLINE_VERSION__Revised_10-23-12A%5B1%5D.pdf
Clinical training, etc.
Monday, April 29, 2013
Thursday, April 25, 2013
Thyratron replacement tonight
Thyratron is a switching tube and is essentially a gas filled triode. When the grid is charged positively, the electrons flow from the cathode to the anode. The gas within the tube ionizes and conducts larger currents than do other switching devices. At the end of the pulse, the grid voltage is removed, preventing further current flow while the pulse forming network recharges. This cycle is repeated between 50 and 500 times per second.
Notes: 4252013 Sh, WI Siemens Primus
Virtual source position for electrons
Today the concept of virtual source position for electrons came up.
I looked it up on my blog and had posted from an unknown reference a few years ago and never included the information.
8.1.3. Inverse square law (virtual source position)
In contrast to a photon beam, which has a distinct focus located at the
accelerator X ray target, an electron beam appears to originate from a point in
space that does not coincide with the scattering foil or the accelerator exit
window. The term ‘virtual source position’ was introduced to indicate the
virtual location of the electron source.
The effective source to surface distance (SSD) for electron beams
(SSDeff) is defined as the distance from the virtual source position to the point
of the nominal SSD (usually the isocentre of the linac). The inverse square law
may be used for small SSD differences from the nominal SSD to make
corrections to the absorbed dose for variations in air gaps between the patient
surface and the applicator.
There are various methods to determine the SSDeff. One commonly used
method consists of measuring the dose at various distances from the electron
applicator by varying the gap between the phantom surface and the applicator
(with gaps ranging from 0 to 15 cm). In this method, doses are measured in a
phantom at the depth of maximum dose zmax, with the phantom first in contact
with the applicator (zero gap) and then at various distances g from the
applicator. Suppose I0 is the dose with zero gap (g = 0) and Ig is the dose with
gap distance g. It follows then from the inverse square law that:
I looked it up on my blog and had posted from an unknown reference a few years ago and never included the information.
8.1.3. Inverse square law (virtual source position)
In contrast to a photon beam, which has a distinct focus located at the
accelerator X ray target, an electron beam appears to originate from a point in
space that does not coincide with the scattering foil or the accelerator exit
window. The term ‘virtual source position’ was introduced to indicate the
virtual location of the electron source.
The effective source to surface distance (SSD) for electron beams
(SSDeff) is defined as the distance from the virtual source position to the point
of the nominal SSD (usually the isocentre of the linac). The inverse square law
may be used for small SSD differences from the nominal SSD to make
corrections to the absorbed dose for variations in air gaps between the patient
surface and the applicator.
There are various methods to determine the SSDeff. One commonly used
method consists of measuring the dose at various distances from the electron
applicator by varying the gap between the phantom surface and the applicator
(with gaps ranging from 0 to 15 cm). In this method, doses are measured in a
phantom at the depth of maximum dose zmax, with the phantom first in contact
with the applicator (zero gap) and then at various distances g from the
applicator. Suppose I0 is the dose with zero gap (g = 0) and Ig is the dose with
gap distance g. It follows then from the inverse square law that:
Swiss Society of Radiobiology and Medical Physics
Swiss Society of Radiobiology and Medical Physics Member of the European Federation of Organisations for Medical Physics (EFOMP) and the International Organization for Medical Physics (IOMP) Quality Control of Medical Electron Accelerators
http://www.sgsmp.ch/r11qca-e.pdf
http://www.sgsmp.ch/r11qca-e.pdf
Book in the works
I haven't posted much to this blog in a few years, it was originally hosted at medicalphysicsinfo.blogspot.com I have recently migrated it to my personal blog.
Last year I discussed with the friend the idea of writing an interesting book related to my career and some of the pioneers responsible for the equipment. It is in the research stage, but I hope to publish some excerpts from it as they become available. I am still very busy clinically so work on this project, is accomplished sporadically. While much of this blog may discuss my career, it is certain to also feature my other interests including music and exercise. As you can see I already posted one of my favorite training methods for running your best mile.
Last year I discussed with the friend the idea of writing an interesting book related to my career and some of the pioneers responsible for the equipment. It is in the research stage, but I hope to publish some excerpts from it as they become available. I am still very busy clinically so work on this project, is accomplished sporadically. While much of this blog may discuss my career, it is certain to also feature my other interests including music and exercise. As you can see I already posted one of my favorite training methods for running your best mile.
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