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TG-51 and Clinical Monitor Unit Calculations
1. Treatment
Machine
Calibra0on
(TG51)
and
Monitor
Unit
Calcula0ons
By
Vibha
Chaswal,
PhD
Mentors:
Dr.
Alfredo
R
Siochi,
Edward
Pennington
2. ObjecBves
• Nuances
of
Clinical
MU
calculaBons
• TG-‐51
protocol:
clinical
reference
dosimetry
procedures
for
high
energy
photons
and
electron
beams
3. Part
1:
MU
CalculaBons
• Hand-‐calculaBons
performed
over
number
of
cases
• Performed
using
TPR
technique
• MU
equaBons:
MUTPR =
MU PDD =
Dose / fx * beam weight
K * TPR@ calc depth for fs@ calc * Sp fs@ calc * Sc coll fs * ISF * OAR@ calc depth for off -axis distance * TF *WF
Dose / fx * beam weight
K * PDD@ calc depth for fs @ surface, SSD * Sp fs@ surface * Sc coll fs * ISF * OAR@ calc depth for off -axis distance * TF *WF
5. Hand
Calcula0ons
are
a
stepwise
transla0on
Dose
to
the
Water
Phantom
at
reference
condi0ons
=>
Dose
at
any
point
in
the
pa0ent
Source
Source
100
cm
Reference
calibraBon
point
Dose
CalculaBon
point
6. Hand
MU
calculaBons
i. Iso-‐centric
calculaBons
ii. Point
off
Isocenter
in
the
iso-‐centric
plane
(AP/
PA)
iii. Point
off
isocenter
off
the
iso-‐centric
plane
(AP/
PA)
iv. Whole
brain
v. TangenBal
asymmetric
fields
–
Breast
plan
vi. 4
field
breast
–
PAB
/super-‐calv
and
tangenBal
fields
8. Rearrange
MLCs
to
get
simpler
shapes….
….Or
use
%
esBmaBon
for
blocked
area
9. Error
elimina0on:
calc
point
depth
Either
measure
physical
depth
from
pinnacle,
or
use
effec0ve
depth
reported
by
Pinnacle
TPS
10. Other
lessons
Account
for
missing
Bssue
Use
correct
ISF,
big
difference
MU
calculaBons
in
dmax
region
have
more
uncertainty
11. TangenBal
breast/chest
wall
tx
and
4-‐field
breast
tx
Involves:
-‐
Constantly
changing
breast
contour
and
volume
in
the
field
-‐
Oblique
surface
contour
-‐
Asymmetric
Jaw
-‐
Off-‐axis
calculaBon
point
12. TG-‐51
CalibraBon
• TG-‐51
calibraBon
for
6X
photon
beam
–
Elekta
• TG-‐51
calibraBon
for
all
Photon
and
Electron
Energies
on
Oncor
A
Lessons:
-‐ EffecBve
point
of
measurement
and
point
of
measurement
depths
-‐ What
is
real
dmax
