Basic principles of dosimetry Eirik Malinen • Radiation field striking a small sphere: • Fluence: • Energy Fluence: Ionizing radiation field dN da Φ= (da is the great circle area) dA dE = Ψ • A photon field with total energy R in,u enters a volume, while R out,u-rl is the energy leaving the volume: • Energy transferred: • KERMA (kinetic energy release per mass): KERMA R in,u R out,u-rl V Q R R rl u , out u , in tr Σ + - = ε - ρ μ Ψ = ε = tr tr dm d K • Kerma includes all kinetic energy given to secondary electrons, and this energy may be lost by: – Collisions – Radiative losses • Kerma may be divided into two components: • K=K c +K r • K c : collision Kerma; provides a measure of the energy loss per unit mass from photons resulting in collisional losses for secondary electrons! Components of KERMA
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Basic principles of dosimetry - Forsiden principles of dosimetry Eirik Malinen • Radiation field striking a small sphere: • Fluence: • Energy Fluence: Ionizing radiation field
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Basic principles of dosimetry
Eirik Malinen
• Radiation field striking a small sphere:
• Fluence:
• Energy Fluence:
Ionizing radiation field
dN
daΦ = (da is the great circle area)
dA
dE=Ψ
• A photon field with total energy Rin,u enters a volume, while
Rout,u-rl is the energy leaving the volume:
• Energy transferred:
• KERMA (kinetic energy release per mass):
KERMA
Rin,u Rout,u-rl
V
QRR rlu,outu,intr Σ+−=ε −
ρ
µΨ=
ε= trtr
dm
dK
• Kerma includes all kinetic energy given to secondary
electrons, and this energy may be lost by:
– Collisions
– Radiative losses
• Kerma may be divided into two components:
• K=Kc+Kr
• Kc: collision Kerma; provides a measure of the energy loss per
unit mass from photons resulting in collisional losses for
secondary electrons!
Components of KERMA
• Is defined by:
• Net energy transfer : total kinetic energy of secondary
electrons which is not lost as brehmsstrahlung
• May take radiative losses into account by defining the qantity
g; the fraction of kinetic energi lost as brehmsstrahlung
• Definition:
• µen/ρ: mass energy absorption coefficient
Collision Kerma
n
trc
dK
dm
ε=
trcK K(1 g) (1 g)
µ= − = Ψ −
ρ
en tr (1 g)µ µ
≡ −ρ ρ
n
trε
• Look at all energy transport (both charged and uncharged
particles) through the volume of interest:
• Absorbed dose:
Absorbed dose
Rin,u+Rin,c
in ,u in ,c out ,u out ,cR R R R Qε = + − − + Σ
Rout,u+Rout,c
dD
dm
ε= unit: [Gy] = [J/kg]
• If charged particle equilibrium (CPE) is present, Rin,c = Rout,c
• Energy imparted:
• In this case, absorbed dose equals collision Kerma:
Dose from photons, CPE
v
CPE:
n
in,u in ,c out ,u out,c in ,u out,u trR R R R R Rε = + − − = − = ε