Transcript d max (cm)

Dosimetry of Therapeutic Beams
Annette Wygoda, PhD
Radiotherapy
Water Phantom
Detectors
Percentage Depth Dose (%DD or PDD)
PDD = ratio of absorbed dose at any depth d /
to absorbed dose at a fixed reference depth (d0)
x100
along the central axis of the beam
PDD 
Dd
Dd0
. 100
Percentage Depth Dose (%DD or PDD)
Percentage Depth Dose (%DD or PDD)
Depth of Maximum Dose (dmax) in water
for various photon energies
Energy (MeV)
Cs-137 (0.662)
Co-60 (1.25)
4
6
10
18
24
dmax (cm)
0.1
0.5
1.0
1.5
2.0
3.3
4.0
Isodose Distributions
Central Axis Depth Dose Distribution: not sufficient to
characterize a dose distribution in a 3D volume
→ depicted by Isodose Curves:
. 2D dose variation
. Lines of equal absorbed dose
→ Isodose Chart:
. a family of isodose curves at equal increment of percent depth dose
. representing the variation in dose as a function of depth and
transverse distance from the CAX
Isodose Distributions
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Photon Beam
Energy : 6 MV
Field Size: 10x10 cm
SSD: 100cm
Isodose Distributions
6 MV
10x10cm
SSD=100cm