Collimator scatter provides...

Collimator scatter factor Sc(r), provides the

a) Output factor measured in air
b) influence of head scatter on beam outpu with increasing collimator field size.

TMR Data are generally obtained from...

TMR Data are generally obtained from
1) measurements
2) PDD data

TMR Depends on...

TMR Depends on the following...

Depth
Field Size
Beam quality

But not SSD.

SOURCE
2007 Therapy Part II (attached)
Related to Tg-51

Simple question 11
11. TG51: What's the upper limit for Pion?

DRR answer: Per pg 1853 of TG51, I get 1.05, or 5% would be the answer. Above this it states that if the correction for the chamber is larger than this it is unacceptable.

Question 12 TG51. Where is the cylindrical chambers center placed for photon beam calibration?

DRR answer: On central axis of the chamber and placed at the reference dpeth when measuring dose at an individual point.

Question 13. To cross calibrate a parallel plate chamber what should one us?

DRR answer: Since Co-60 cal factors for plane parallel chambersare sensitive to their construction, they should be calibrated against already calibrated cylindrical chambers in a high energy electron beam.

NOTE
Questions 14, 15, 16 aren't as well formulated, or in some cases the choices listed aren't complete so we'll have to come up with a better worded question for these.

Enjoy,
Dave

Pitch and patient dose.

OBJECTIVE. With single-slice helical CT, an increased pitch can decrease the radiation dose to the patient if all other parameters are constant. The purpose of this study was to determine whether the same relationship holds for a particular multislice helical CT system (Somatom Plus 4 VZ multislice helical CT scanner, version A11A) in our department.
CONCLUSION. The measured radiation dose to the phantom was identical for all pitch selections on the multislice helical CT system we tested. This unexpected result was because of an automatic proportionate increase in the tube current when the pitch selection was increased. Radiologists and physicists should exercise caution when extrapolating dose reduction strategies from single-slice to multislice helical CT systems, and they must acquire a detailed understanding of the multislice helical CT scanner of their chosen manufacturer.

For multislice helical CT scanners, manufacturers use different definitions of pitch, which has resulted in much confusion [9]. For the multislice CT scanner we described, the manufacturer defines "pitch" as the ratio of table movement per 360° rotation to single section thickness (P). We chose to use the definition of pitch [9] as table increment per 360° rotation divided by the total beam width (P'). This definition is applicable to both single- and multislice helical CT scanners, as shown in Table 1. Using slice combinations of 4 x 1 mm and 4 x 2.5 mm, the test volume was scanned on the multislice helical CT scanner at the manufacturer's defined pitch selections of 2, 4, and 8 (P' = 0.5, 1, 2). At a slice width of 3 mm, the same volume was scanned at pitch selections of 0.5, 1, and 2, respectively, on the single-slice helical CT system for comparison. Three dose measurements were recorded and averaged for each pitch setting we tested.

http://www.ajronline.org/cgi/content/full/177/6/1273

Gamma emissions

Emission of gamma does not change the identity of the radionuclide.

Gamma emissions take the nuclides only from excited states to the ground state.

Beta Decay

Neutron rich radionuclides are responsible for beta decay.

Output factor

Output factor is the ratio of the dose rate of a given field size to the dose rate of the reference field size.

the output fator is usually normalized or referenced to a 10x10cm field size, so there it will be 1.0

For fields sizes smaller than 10x10, the output factor is <1.0 because of a decrease in scatter as the collimator setting is decreased.

For field sizes >10x10 the output factor is >1.0 because of an increase in scatter as the collimator setting is increased.