Wednesday, August 4, 2010
Wednesday, April 14, 2010
Prostate IMRT
RMH
Rectum
Dose Vol%
75 Gy 7
70 Gy 12
65 Gy 17
60 Gy 25
50 Gy 35
Bladder
Dose Vol%
80 Gy 7
75 Gy 12
70 Gy 17
65 Gy 25
Rectum
Dose Vol%
75 Gy 7
70 Gy 12
65 Gy 17
60 Gy 25
50 Gy 35
Bladder
Dose Vol%
80 Gy 7
75 Gy 12
70 Gy 17
65 Gy 25
Sunday, March 28, 2010
Wednesday, January 27, 2010
Desirable chamber characteristics
D. Desirable Chamber Characteristics
A practical ion chamber for exposure measurement should have the following characteristics:
1)
There should be minimal variation in sensitivity or exposure calibration factor over a wide range of photon energies.
2)
There should be suitable volume to allow measurements for the expected range of exposures. The sensitivity (charge measured per roentgen) is directly proportional to the chamber-sensitive volume. For example, the reading obtained for a given exposure with a 30-cm3 chamber will be approximately 50 times higher than that obtained with a 0.6-cm3 chamber. However, the ratio may not be exactly 50, because a chamber response also depends on the chamber design, as discussed previously.
3)
There should be minimal variation in sensitivity with the direction of incident radiation. Although this kind of variation can be minimized in the design of the chamber, care is taken to use the chamber in the same configuration with respect to the beam as specified under chamber calibration conditions.
4)
There should be minimal stem “leakage.” A chamber is known to have stem leakage if it records ionization produced anywhere other than its sensitive volume. The problem of stem leakage is discussed later in this chapter.
5)
The chamber should have been calibrated for exposure against a standard instrument for all radiation qualities of interest.
6)
There should be minimal ion recombination losses. If the chamber voltage is not high enough or regions of low electric field strength occur inside the chamber, such as in the vicinity of sharply concave surfaces or corners, ions may recombine before contributing to the measured charge. The problem becomes severe with high-intensity or pulsed beams.
Khan 4th ed
A practical ion chamber for exposure measurement should have the following characteristics:
1)
There should be minimal variation in sensitivity or exposure calibration factor over a wide range of photon energies.
2)
There should be suitable volume to allow measurements for the expected range of exposures. The sensitivity (charge measured per roentgen) is directly proportional to the chamber-sensitive volume. For example, the reading obtained for a given exposure with a 30-cm3 chamber will be approximately 50 times higher than that obtained with a 0.6-cm3 chamber. However, the ratio may not be exactly 50, because a chamber response also depends on the chamber design, as discussed previously.
3)
There should be minimal variation in sensitivity with the direction of incident radiation. Although this kind of variation can be minimized in the design of the chamber, care is taken to use the chamber in the same configuration with respect to the beam as specified under chamber calibration conditions.
4)
There should be minimal stem “leakage.” A chamber is known to have stem leakage if it records ionization produced anywhere other than its sensitive volume. The problem of stem leakage is discussed later in this chapter.
5)
The chamber should have been calibrated for exposure against a standard instrument for all radiation qualities of interest.
6)
There should be minimal ion recombination losses. If the chamber voltage is not high enough or regions of low electric field strength occur inside the chamber, such as in the vicinity of sharply concave surfaces or corners, ions may recombine before contributing to the measured charge. The problem becomes severe with high-intensity or pulsed beams.
Khan 4th ed
Tuesday, January 26, 2010
Wednesday, January 20, 2010
Tuesday, December 29, 2009
Radiation Safety list server
radlab.nl/radsafe/archives/9802/msg00510.html
This looks like a radiation safety list server.
This looks like a radiation safety list server.
Wednesday, August 5, 2009
Magnetron current
Reference: Elekta manual
If the current of the magnetron magnet is reduced, the magnetron impedance will also be reduced, the HT current will increase, but the RF power will go down because the effective voltage is reduced.
V=IR
I decreases, V decreases
P=IV
if V decreases Power decreases
If the current of the magnetron magnet is reduced, the magnetron impedance will also be reduced, the HT current will increase, but the RF power will go down because the effective voltage is reduced.
V=IR
I decreases, V decreases
P=IV
if V decreases Power decreases
Monday, March 23, 2009
Procedures
TSET- Stanford Technique
TBI- With different lung blocking protocols
HDR ring and tandem
HDR vaginal cylinder
HDR Mammosite
LDR Tandem and Ovoid
LDR Ir-192 interstitial (shoulder, neck, other locations)
LDR Eye plaque (ocular melanoma)
LDR Brain lesions with I-125
Stereotactic Radiosurgery with cones, MMLC
Stereotactic Radiosurgery for AVM
TBI- With different lung blocking protocols
HDR ring and tandem
HDR vaginal cylinder
HDR Mammosite
LDR Tandem and Ovoid
LDR Ir-192 interstitial (shoulder, neck, other locations)
LDR Eye plaque (ocular melanoma)
LDR Brain lesions with I-125
Stereotactic Radiosurgery with cones, MMLC
Stereotactic Radiosurgery for AVM
Monday, December 29, 2008
Varian OBI (kV)
Specs on kV imaging system
Varian G242 tube
14 degree anode
.4 and .8 mm focal spot
kvD amorphous silicon detector
Layer is 1.8 cm below the scatter grid
40x30 cm panel at isocenter
the kV arms are defined by anatomy, shoulder, arm etc
Defaults for the arms are 100 cm source to isocenter, 50 for the panel
kVp maxes out at 140, says it goes up to 150 but really 140.
OUT is out of the way, retract is fully retracted. But to access cabinets has to be OUT but not fully retracted (back).
Varian G242 tube
14 degree anode
.4 and .8 mm focal spot
kvD amorphous silicon detector
Layer is 1.8 cm below the scatter grid
40x30 cm panel at isocenter
the kV arms are defined by anatomy, shoulder, arm etc
Defaults for the arms are 100 cm source to isocenter, 50 for the panel
kVp maxes out at 140, says it goes up to 150 but really 140.
OUT is out of the way, retract is fully retracted. But to access cabinets has to be OUT but not fully retracted (back).
Tuesday, September 16, 2008
Question and answer site
http://www.hps.org/publicinformation/ate/cat1.html
Lots of questions and answers from health physicists.
Lots of questions and answers from health physicists.
Monday, September 15, 2008
Bowtie filter
The field of view in the half-fan mode is 45 cm in
diameter with a 14 cm in the cranial caudal extent when SID
is 150 cm. An accessory, called a bowtie filter, is placed in
front of the kV beam to attenuate the edges of the kV beam.
The bowtie filter reduces skin dose, allows larger x-ray tech-
niques to be employed without saturating the detector, reduces
x-ray scatter, and reduces the effects of charge trapping
in the detector.
Source (Nov 2006 Medical Physics "A quality assurance program for the on board imager")
diameter with a 14 cm in the cranial caudal extent when SID
is 150 cm. An accessory, called a bowtie filter, is placed in
front of the kV beam to attenuate the edges of the kV beam.
The bowtie filter reduces skin dose, allows larger x-ray tech-
niques to be employed without saturating the detector, reduces
x-ray scatter, and reduces the effects of charge trapping
in the detector.
Source (Nov 2006 Medical Physics "A quality assurance program for the on board imager")
Tuesday, July 22, 2008
Thursday, July 17, 2008
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