1. Rota%on
13:
Shielding
Design
(Mentors:
Edward
C
Pennington,
Sarah
McGuire)
By
Vibha
Chaswal,
Ph.D.
2. The
Problem
40I
x
125I
area
design
layout
and
shielding:
•
A
Dual
energy
Linear
Accelerator
room:
6
MV
low-‐energy
and
18
MV
high-‐energy
facility.
(IMRT
and
TBI
capable)
•
A
High
Dose
rate
Brachytherapy
Suite:
Ir-‐192
• A
PET/CT
Area
4. Assump%ons:
Linac
room
Overes%ma%ons
in
workload
8
h
day,
5
d
week–1,
50
pa%ents
per
week
Average
absorbed
dose
of
3
Gy
delivered
at
isocenter
per
pa%ent
40
%
pa%ents
18
MV
beam,
60
%
treated
using
6
MV
beam
Maximum
absorbed
dose
output
rate
at
1
m
of
15
Gy/min,
and
the
normal
rate
used
is
5
Gy/
min
• The
isocenter
is
at
1
m
from
the
radia%on
source
for
this
facility.
• IMRT
WorkLoad:
•
•
•
•
– 80
%
of
6MV
pa%ents
–
24
pa%ents
per
day
treated
as
IMRT
– 40
%
of
18
MV
pa%ents
–
8
pa%ents
per
day
treated
as
IMRT
• 6
MV
TBI
beam
• Future
increase
of
18
MV
beam
to
60%
usage
Use
factor
of
walls:
• Lateral
walls:
0.3
as
opposed
to
0.25
(IMRT
usage)
Sca`er
and
Leakage
angle
of
incidence:
All
sca`er
and
leakage
taken
at
the
minimum
angle
of
incidence
6. Tedious
calcula%ons:
watch
out
for
errors!
• The
wall
adjacent
to
the
HDR
vault
is
calculated
for
design
dose
of
0.02
mSv/week,
i.e.,
that
of
an
uncontrolled
area.
• This
is
DEFINITELY
a
control
area
in
a
Radia%on
Oncology
department.
The
primary
wall
thickness
for
the
control
area
design
dose
is
173
cm
as
opposed
to
202
cm
calculated
in
the
report.
• However,
this
error
lead
to
an
overes%ma%on.
An
error
of
the
opposite
kind
will
lead
to
an
underes%ma%on
of
shielding.
• Since
this
wall
is
also
TBI
wall,
overes%ma%on
is
good.
7. Linac
room
roof
design
R
Q
6.44 m
2.22
m
2.12
m
1.83
m
2.1
m
4.8
m
2.7
m
3.3 m
0.72 m
1.3m
8. Assump%ons:
HDR
and
PET/CT
HDR
• HDR
Pa%ents
per
week
=
25
• Dose
per
pa%ent
=
10
Gy
at
1
cm
from
the
source.
PET/CT
• PET/CT
pa%ents:
15
pa%ents/week
• F-‐18
FDG
dose
is
555
MBq
(15
mCi)
with
an
uptake
%me
of
60
min
