Brachytherapy Physics

Brachytherapy Physics
Yoichi Watanabe, Ph.D.
Office: Masonic Cancer Center M10-M
Telephone: (612)626-6708
E-mail: [email protected]
http://www.tc.umn.edu/~watan016/Teaching.htm
Spring semester
Prostate implant equipment
Brachytherapy
“Brachy” means short in Greek.
 The first radium implant was performed in
1901 by Dr. M. Danlos et al. at St.Louis
Hospital in Paris. A few cases of lupus (a
skin disease ) were successfully treated.
 Brachytherapy is a major modality in
radiation therapy.
 Brachytherapy is effective for treatment of
localized tumors.

http://www.americanbrachytherapy.org/
Type of Brachytherapy
LDR, MDR, or HDR ( ≥ 20 cGy/min)
 Permanent or temporary
 Direct “hot” loading, afterloading, or
remote afterloading
 Interstitial, intracavitary, and surface
 Photons, electrons, or neutrons

Outline
1.
2.
3.
4.
5.
6.
7.
Radioactive Sources
Dose Calculation
Implant dosimetry systems
LDR Interstitial and Intracavitary
HDR/PDR
New Techniques
QA and radiation safety
Major Radionuclides
Radionuclide
Ra-226
Rn-222
Au-198
Ir-192
Cs-137
I-125
Pd-103
Co-60
Half-Life
1600 yr
3.83 days
2.697 days
73.7 days
30.0 yr
59.4 days
17.0 days
5.26 yr
Photon Energy [MeV]
0.047-2.45 (0.83 avg)
0.047-2.45 (0.83 avg)
0.412
0.136-1.06 (0.38 avg)
0.662
0.028 avg
0.021 avg
1.17, 1.33 (1.25 avg)
Production of Radioisotopes
Radioisotope
Method
Ra-226
Au-198
Natural
Neutron (N)–
induced
N-induced
By-product
N-induced
N-induced
N-induced
Ir-192
Cs-137
Pd-103
I-125
Co-60
Source
nuclide
Decay
mode
NA
Au-197
α
β-
Ir-191
NA
Pd-102
Xe-124
Co-59
β-, EC
βEC
EC
β-
Radium-226

Radium is the 6th member of uranium
series. It decays through α-decay process
and its half-life is about 1600 years.
226
88
222
86
a → Rn + He + 4.78 MeV
Ra 1622
222
86
4
2

→ Po+ He + 5.49 MeV
Rn 
3.83d
218
84
4
2
Radium Source




Radium is the first radioactive material used for brachytherapy.
Radium source is no longer used in USA.
Radium source emits 49 photons with energies varying from 0.184
to 2.45 MeV.
The average energy of radium source filtered with 0.5 mm of
platinum is 0.83 MeV. High energy beta and alpha particles are
emitted; but those are stopped by the encapsulation material.
http://www.orau.org/ptp/collection/brachytherapy/needlestubescase.htm
Cesium-137
Cs-137 is a γ ray-emitting radioisotope.
 The energy of γ rays is 0.662 MeV.
 It requires less shielding than Radium
source.
 The half-life is 30 years.
 Cesium source is supplied in the form of
insoluble powders or microspheres.
 β-particles and characteristic x-rays are
absorbed by the stainless-steel container.

Cs-137 Source Schematic
Iridium-192





Ir-192 has a complicated γ ray spectrum with an
average energy of 0.38 MeV.
The half-life is 73.8 day.
Ir-192 is used in temporary implants.
Ir-192 sources are available in the form of thin
flexible wire and a series of tiny seeds contained
in Nylon ribbon. The seeds are 3 mm long and
0.5 mm in diameter.
Ir-192 is used as the radioactive source for high
dose rate brachytherapy.
Ir-192 LDR Source Schematic
Iodine-125




I-125 emits 35.5 keV γ-rays.
Characteristic x-rays (27 to 35 keV) are
produced due to electron capture and internal
conversion.
The half-life is 59.4 days.
I-125 sources are used for permanent prostate
implants. There are many designs of seeds.
Most seeds are less than 5 mm long and 1 mm
in diameter. Radioactive source is contained in a
metal (titanium etc.) container.
I-125 Seed Models
Amersham OncoSeed
Model 6702
Model 6711
Palladium-103
Pd-103 seeds were developed for
permanent prostate implants.
 Pd-103 decays by electron capture with
the emission of characteristic x-rays in the
energy range of 20 to 23 keV (average
20.9 keV) and Auger electrons.
 The half-life is 17 day.

Pd-103 Seed
Theragenics TheraSeed Model 200
Source Strength
Activity [Ci] or [Bq]
 Specific activity [Ci/kg] or [Ci/g]
 mgRa-equivalent [mgRaeq]
 Apparent activity [Ci]
 Air kerma strength [µGy m2/hr] or [cGy
cm2/hr]

Note: 1 Ci = the decay rate of 1 g Radium
Exposure Rate Constant


Exposure is the total charge of the ions of one sign
produced in air when all electrons liberated by
photons in air of mass are completely stopped in
air. The unit is R and 1R=2.58x10-4 C/kg of air.
Exposure rate at distance d from a point
radioactive source of activity A is
A

X = Γδ 2
d
Γδ
[
R⋅cm 2
mCi⋅hr
]
[ R hr ]
is the exposure rate constant.
The subscript δ indicates we consider photon with
energy greater than δ.
Exposure Rate Constants (cont)
Source
Ra-226, Pt-filtered
Exposure rate constant
[R cm2/mCi h]
8.25 R cm2/mgRa h
Co-60
13.07
Au-198
2.35
Ir-192
4.69
Cs-137
3.26
I-125
1.46
mgRa-equivalent



The exposure rate at 1 cm from 1 mg of Radium
source (filtered with 0.5 mm platinum wall) is 8.25
R.
The exposure rate constant of the Radium source
(0.5 mm Pt filtered) is 8.25 R cm2mg Ra-1h-1.
The activity of any radioisotope is defined as 1
mgRa-equivalent (not mgRa), when it produces
the same exposure rate as 1 mg Radium source
(0.5mm Pt filtered)
Example: mgRa-equivalent

What is a 50 mCi Cs-137 source in the unit of
mgRa-equivalent?
The exposure rate constant of Cs-137 source is 3.26
R cm2/mCi h.
50
A
3.26 2 = 8.25 2
d
d
A = 19.76 mgRaeq
Apparent Activity


Apparent activity is a unit of the activity of a
contained radioactive source in Ci.
Apparent activity is smaller than the contained
activity to take into account the attenuation of
radiation by the container.
(ΓX )withcontainer
Aapp
Areal
(
)
=
Γ
X
bare point
2
2
d
d
Air-kerma Strength
Air-kerma strength is a unit for the strength
of a radioactive source.
 The unit is µGy m2/h or cGy cm2/h.
 A radioactive source of 1 cGy cm2/h
produce dose rate of 1 cGy/h at 1 cm from
the source in air.
 The unit is denoted by U.

Source Strength Standards





Primary standard is obtained at NIST from calorimeters,
an extrapolation chamber, standard chambers with
precisely known volumes for high energies, or from free
air ionization chambers at low energies.
NIST uses Cs-137 and 250 kVp x-ray unit for calibration
of Ir-192 sources.
NIST uses wide-angle-free-air chamber (WAFAC) with
actual sources for lower energy sources (since 1999).
The standards at NIST are transferred to ADCL and
source manufactures.
The source calibrated at the ADCL or manufacturer is
called “to have secondary traceability”.
Accredited Dosimetry Calibration
Laboratory (ADCL)

Services: to provide ionization chamber
calibration of ionization chambers used
with radioactive sources.
 University of Wisconsin, Madison, Wisconsin
 MD Anderson Cancer Center, Houston, Texas
 K&S Associates, Inc., Nashville, Tennessee
Source Calibration



To determine the strength of a radioactive
source (or seed), measure the air-kerma in air at
a distance between 10 cm to 1 m from the
source.
An cylindrical ionization chamber can be used
for this measurement. The ionization chamber
response to the source is calibrated by an ADCL
using a source traceable to NIST.
An easier way is to use a well-type ionization
chamber.
Well-type ionization chamber


The response of well-type “reentrant” ionization chamber
depends on the energy
spectrum, which in turn
depends on the energy of
emitted photons and the
structure of the source
container.
A well-type ionization
chamber must be calibrated
for every source (radioisotope
and design).
Well-type ionization chamber (cont)
Standard Imaging HDR1000Plus
Model CRC-10
Outline
1.
2.
3.
4.
5.
6.
7.
Radioactive Sources
Dose Calculation
Implant dosimetry systems
LDR Interstitial and Intracavitary
HDR/PDR
New Techniques
QA and radiation safety
AAPM TG-43 Report



AAPM Task Group 43 report (1994) proposed a
standardized dose calculation formula for LDR
interstitial sources: Ir-192, I-127, and Pd-103.
The report was updated in 2004 to implement
new calibration standards and many new
sources.
The formulas specifically take account of
anisotropic dose distributions around single
source.
TG-43 formula for point source
g
r
(
)
D (r ) = ΛS K 2 φan
r
 The anisotropy factor φan ( r) is the ratio
of 4π averaged dose rate at a given
radial distance divided by the dose rate
at the same distance along the
transverse axis. Anisotropy constant is
the average of the anisotropy factor over
the radial distance.
 For calculation the source is anisotropic,
but the dose rate is weighted for the
anisotropy.
Source
φan
Pd103 200
0.90
I125 6711
0.93
I125 6702
0.95
Ir192 s.s. clad
0.98
TG-43 Dose Formula (General)
Assumes cylindrical symmetry about source axis
(
)
θ
G
r
,
D (r ,θ ) = ΛS K
F (r , θ ) g (r )
G (1, π 2 )
Transverse axis
r
θ
Source axis
L
TG-43 Dose Formula (cont)
Λ = dose rate constant [cGy/U/hr]
 G = geometry factor
 F = anisotropy function
 g = radial dose function
 SK = air-kerma strength [U]

P
θ2− θ1
θ 2 − θ1
G (r , θ ) =
Lr sin (θ )
1
G (r ,θ ) = 2
r
for point source
Geometry factor
r
θ
L

ρ (r ')
′
d
V


∫v r − r '
G (r , θ ) =

∫ ρ (r ')dV ′
V
For line source,
θ 2 − θ1
G (r , θ ) =
Lr sin (θ )
For point source,
1
G (r ,θ ) = 2
r
r ⋅ sin (θ )

(
)
tan
=
θ
1

r ⋅ cos(θ ) + L

2

r ⋅ sin (θ )
tan (θ 2 ) =

r ⋅ cos(θ ) − L
2

Dose rate constant Λ
D (1, π 2 )
Λ=
SK
 cGy / hr 
 U 
 The dose rate constant can be
measured by measuring dose at 1 cm
on the plane transverse to the source
cylindrical axis for a known air-kerma
strength.
Dose Rate Constant Λ
cGy hr-1 U-1
Seed
Pd-103 (Model 200)
0.686
I-125 (6702)
1.036
I-125 (6711)
0.965
Cs-137 (3M)
0.968
Ir-192 (stainless steel clad)
1.11
TG43 Update (2004) and L.Liu et al, MP31:477 (2004)
Radial dose function g(r)
D (r , π 2)G (1, π 2 )
g (r ) =
D (1, π 2 )G (r , π 2 )
 The radial dose function indicates the
dose variation along the transverse
axis when the 1/r2 effect is removed or
the effects of photon absorption and
scatter in the medium.
Radial Dose Function g(r) (cont)
1.6
Pd-103 (200)
1.4
I-125 (6711)
1.2
Ir-192 (ss clad)
g)
1.0
0.8
0.6
0.4
0.2
0.0
0
1
2
3
4
5
6
7
Distance r [cm]
8
9 10
Anisotropy function F(r,θ)
D (r , θ )G (r , π 2 )
F (r , θ ) =
D (r , π 2 )G (r , θ )
 F(r,π/2)=1.0
 The anisotropy function accounts
for the angular dependence of
photon attenuation in the
encapsulation and medium.
Anisotropy Function F(r,θ)
I-125 (model 6711)
1.0
F
0.8
0.6
0.4
r = 1 cm
r = 5 cm
0.2
0.0
0 10 20 30 40 50 60 70 80 90
Polar angle
Dose Distribution of LDR Sources
TG43 (1994)
Outline
1.
2.
3.
4.
5.
6.
7.
Radioactive Sources
Dose Calculation
Implant dosimetry systems
LDR Interstitial and Intracavitary
HDR/PDR
New Techniques
QA and radiation safety
Implant dosimetry systems
Manchester (or Paterson-Parker) system
(1934-1938)
 Quimby system (1935-1941)
 Paris system (1960s)
 Computer aided system (1970s?-)
 Plan evaluation tool – DVH etc.

Ref: Brachytherapy Physics, AAPM Summer School 1994 and 2005
Common assumptions for
Manchester and Quimby systems




Both systems were originally developed for
Radium sources, which were unfiltered line or
point sources. There are tables for 0.5 mm and
1.0 mm Platinum filtered sources.
Oblique filtration was not taken into account.
Photon scattering and attenuation in tissue were
ignored.
Should be used for radioactive sources emitting
photons of energy greater than 200 keV.
Manchester System
(Patterson-Parker)



An implant planning system designed to deliver
uniform dose within ±10% to a plane or volume.
Crossing needles are used. The system gives the
total activity in mgRa-equivalent*hr required to
deliver 1000 R at the prescription point.
Planar implant: the uniform dose is achieved in
parallel planes at 0.5 cm from the implant plane
and within the area projection of the peripheral
needles on that plane. The stated dose is 10%
higher than the minimum dose.
Volume implant: Needles (or sources) are
implanted to cover a volume. The prescribed
dose is 10% higher than the minimum dose within
the implanted volume.
Manchester:
Planar Implant Table
Johns and Cunningham, Physics of Radiology 4th ed. (1983) Table 13-4.
Example:
Single plane implant - Manchester
•
4 cm
•
•
•
3 cm
•
a b
c d e
•
•
Source plane
The activities of a and e are 3 mgRa-eq.
The activities of b, c and d are 1 mgRa-eq.
The area of implant, A = 3 x 4 = 12 cm2.
No crossing source at both ends. Hence, the
area of implant must be reduced by 20 %. A =
12x0.8 = 9.6 cm2.
To give 1000 R at 0.5 cm from the source
plane, the total mgRa*hour = 244 mgRa*h.
Total loading time is 244/9 = 27.1 hours.
The exposure rate is 1000 /27.1 = 36.9 R/h.
Rule of Patterson-Parker system:
Treatment area
0.5 cm
Area
Peripheral
< 25 cm2
2/3
25 to 100 cm2
1/2
> 100 cm2
1/3
Quimby System





The system assumes a uniform distribution of
sources of equal linear activity.
This implant leads to a non-uniform dose
distribution.
The Quimby tables give the mgRa-equivalent*hr
to produce 1000 R (or 1000 cGy).
Planar implant: The stated dose is given in the
center of the treatment plane up to 3 cm from
the plane. The stated dose is the maximum dose
in the plane of treatment.
Volume implant: the stated dose is the minimum
in the implanted volume.
Quimby-like Implant

Ir-192 seeds with
equal activity were
implanted on a
plane. The figure
shows the dose
distribution
calculated by
computer.
Computer aided systems
Brachytherapy treatment planning
software
Varian BrachyVision
 Varian VariSeed (for prostate implant)
 Philips Medical Systems Pinnacle
 CMS Interplant (for prostate implant)
 Nucletron PLATO Brachytherapy
 Prowess Panther 3D Brachy Pro
 Rosses Medical Systems Strata Suite

Brachytherapy Treatment Planning
1)
2)
3)
4)
5)
Simulation – takes films or CT images.
Define spatial coordinates of potential
source locations.
Specify points-of-interest.
Determine the source locations and their
source strength to meet the treatment
prescription.
Prepare treatment report for loading.
Source Localization
Two films (orthogonal, arbitrary angle,
stereo-shift)
 Three films
 Ultrasound
 CT (kVp)
 MVCT
 No-film

Two film localization technique
Orthogonal films
 Simple and
accurate.
 Sensitive to the
patient
movement.
 May misidentify
source locations
(2 circles in fig.)
Orthogonal Films: Interstitial
Plan Evaluation
Dose volume histogram (DVH)
 Differential dose volume histogram (DDVH)
 Natural dose volume histogram (NDVH)
 Coverage quantifier – V100 or D100
 Homogeneity index
 Conformity index
 Tumor control probability

Dose Volume Histogram
Prostate
Volume
V ( D)
y = 100
V ( 0)
Rectum
Urethra
Dose [Gy]
W.S.Bice, Brachytherapy Physics, pp.604-640 (2005)
Outline
1.
2.
3.
4.
5.
6.
7.
Radioactive Sources
Dose Calculation
Implant dosimetry systems
LDR Interstitial and Intracavitary
HDR/PDR
New Techniques
QA and radiation safety
Interstitial Implants
Temporary or permanent
 Cs-137 needle, Ir-192, I-125, and Pd-103
 Templates

Treatment sites:
 Brain, eye
 Head and neck: nasopharynx, base-oftongue, floor of mouth, etc.
 Sarcoma: thigh, extremities (legs or arms)
 Breast
 Prostate or Cervix
Catheter implant technique
a) A hollow steel needle is inserted through the target.
b) The thin header end of a nylon catheter is threaded through the needle. The
catheter is then pulled through the target together with the steel needle.
c) Both ends of the catheter is sealed with buttons and fixed to the treatment site.
d) Source ribbons (Ir-192) are afterloaded by inserting the ribbons through the
catheters.
Non-looping technique
for base of tongue implant
Permanent prostate implant




A radiation therapy option for treatment of prostate
cancer in Stage I-III.
Prostate implants were performed using retropubic
technique in 1970 and 80’s. An introduction of
transperineal technique lead to an explosion of the
implant practices. The procedure gained wide
acceptance in mid 1990s.
I-125 or Pd-103 seeds are implanted permanently
in the prostate grand.
Dose is 100 Gy to 150 Gy to the periphery of the
treatment volume.
Prostate anatomy
Prescription dose
Primary
Boost
I-125
145 Gy
115 Gy
Pd-103
135 Gy
105 Gy
Typical source strength: I-125 (0.4-1U), Pd-103 (1.4-3.5U)
Intracavitary Implant


An applicator or mold made of tissue-like
material is placed in a cavity around which tumor
is expected.
Radioactive source(s) is placed inside the
applicator for temporary irradiation.
Treatment sites:
 Brain
 Head and neck - nasopharynx
 Cervix/vagina
 Breast – MammoSite
Gynecological malignancies
Cancer of cervix




Wickman treated cervical cancer with radium as
early as 1906 and reported results for 1000
patients by 1913.
Intracavitary brachytherapy with MV external
beam therapy is a standard treatment.
Five-year disease free survival: 70%-90% for
FIGO stages I&II, 25% to 48% for stage III, and
5% to 34% for stage IV.
In the 1970s, Cs-137 was widely adopted as a
radium substitute.
Uterine Cervix Anatomy
Fundus
Uterine
cavity
Endometrium
Uterus
Corpus
Myometrium
Cervix
External
cervical os
Fornices
Vagina
Applicators for Cervix Implants
Fletcher-Suit Delclos
 Henschke
 Variations of those

Manchester System - Cervix

8000 R to point A in two sessions of about
72 hours each with a 4-to-7 day interval
between. (a dose rate of 55 R/h).

Point A : 2 cm lateral to the uterine canal and 2
cm from the mucous membrane of the superior
fornix of the vagina in the plane of the uterus.
Point B : 5 cm from the midline and 2 cm up
from the mucus membrane of the lateral fornix. It
represents the dose to the vicinity of pelvic wall
near the obturator nodes and a good measure of
the lateral spread of the effective dose.

Dose Specification of Cervix Implant
Manchester
Original point A and B
U3
U2
U1
Modified point A and B
Manchester: Dose Rate
 For U1=10 mg, U2=10 mg, U3=15 mg, and two 20 mg medium ovoids with
spacer => Point A dose rate=35+19=54cGy/h.
Source loading
Point A
[cGy/h]
Point B
[cGy/h]
1)
U1=10 mg, U2=10 mg, U3=15 mg
35
8.0
2)
U1=15 mg, U2=10 mg
35
7.0
3)
Large ovoids with spacer: 2x22.5 mg
19
9.0
4)
Medium ovoids with spacer: 2x20 mg
19
8.2
5)
Small ovoids with space: 2x17.5 mg
19
7.4
6)
Special loading: U1=20 mg
28
5.7
Johns and Cunningham Table 13-10
Reference Points: example
Dose distribution of Cervix implant
Outline
1.
2.
3.
4.
5.
6.
7.
Radioactive Sources
Dose Calculation
Implant dosimetry systems
LDR Interstitial and Intracavitary
HDR/PDR
New Techniques
QA and radiation safety
High Dose Rate (HDR)
High dose rate is greater than 20 cGy/min.
 HDR device can deliver 100 cGy/min or
higher at a treatment distance (~2 cm),
compared with LDR of 1 cGy/min.
 Higher dose rate demands fractionation to
minimize normal tissue damage.
 High activity source requires remote
handling/delivery (or remote afterloading).

HDR Brachytherapy

HDR brachytherapy covers a subset of
LDR brachytherapy in terms of application
sties.
Gynecological
Prostate
Intraluminal-eshophagus and endobronchial
Interaoperative- head/neck, liver, pancreas, etc.
Partial breast
HDR Device






Ir-192 source of approximately 10 Ci.
The dose rate at 1 cm from the source is in the
order of 100 cGy/min.
The source is typically a 5-mm long and 0.6-mm
diameter cylinder.
The source is welded to a steel wire.
The wire is extended through a plastic catheter
to the treatment position by motor-driven
mechanism.
The source stops at many positions in a catheter
and in many catheters (or channels) to deliver
dose conforming the target volume.
HDR remote afterloaders
Neucletron
Varisource
Gammamed Plus
HDR device comparison
MicroSelectron
Varisource
Gammamed
Company
Nucletron
Varian
Varian
Channels
Up to 18
Up to 20
Up to 24
Treatment
planning
PLATO
Oncentra
BrachyVision
Abacus
BrachyVision
Source
size
0.9 mm diameter 0.59 mm OD
3.5 mm long
5 mm long
0.9 mm OD
4.5 mm long
HDR Device Design
Nucletron
HDR Source (Varisource)
Dose Profile : VariSource
Λ=1.101 cGy/h/U (Note:1.12 for LDR Fe cladded)
Ref:A.Angelopoulos, Med Phys 27:2521-2527 (2000)
Outline
1.
2.
3.
4.
5.
6.
7.
Radioactive Sources
Dose Calculation
Implant dosimetry systems
LDR Interstitial and Intracavitary
HDR/PDR
Special Techniques
QA and radiation safety
Xoft AXXENT
Outline
1.
2.
3.
4.
5.
6.
7.
Radioactive Sources
Dose Calculation
Implant dosimetry systems
LDR Interstitial and Intracavitary
HDR/PDR
New Techniques
QA and radiation safety
Regulations on Use of Radioactive
Sources
Code of Federal Regulations (CFR) title 10
Part 35 (Nuclear Regulatory Commission,
NRC) documents regulatory requirements
on the use of by-product materials (or
radioactive sources).
 It describes the requirements for users
(i.e., authorized users and license),
equipment, QA program, and reporting (of
medical events).

http://www.nrc.gov/reading-rm/doc-collections/cfr/part035/
Quality control tests of LDR sources
Long-lived:
T1/2>120 days
*Cs-137
*Co-60
*Sr-90
Short-lived:
T1/2≤120 days
decay-in-storage
*Ir-192
*I-125
*Pd-103
G.A.Ezzel, Brachytherapy Physics, page 52 (2005)
HDR Quality Management Program
(QMP)
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
Written directive
Patient identification
Treatment plan verification
Pre-treatment safety checks
Treatment delivery
Post-treatment safety checks
Source replacement and calibration
Recording
Supervision
Medical events
Periodic review
HDR Safety

Pre-treatment safety check and QA:
- door interlock
- radiation monitor
- TV monitor
- emergency tool
- radiation survey (room, RAU, and patient)
- HDR unit QA (source stopping position, catheter integrity, emergency stop, etc.)

Operating procedures (treatment delivery)
- pre-treatment QA
- Both radiation oncologist and medical physicist present during treatment
- post-treatment radiation survey

Emergency procedures
- improper source retraction
- electrical power loss (The battery takes over the treatment operation.)
- applicator dislodging
- timer failure
Radiation Monitor Equipment
GM
 Ionization chamber
 Film badges and rings
 Treatment room radiation monitor

Half-value Layer of
Brachytherapy Sources
Radionucli Half-value Layer
de
[mmPb]
Ra-226
12.0
/Rn-222
Co-60
11.0
Cs-137
5.5
Ir-192
2.5
Au-198
2.5
I-125
0.025
Pd-103
0.008
Tenth-value Layer
[cm of concrete]
~ 25.0
~ 20.0
~ 15.0
14.7
~14.0
~ 2.0
< 1.0
Room shielding
Shielding requirements
 Public: 0.1 rem (1 mSv) in 1 year (new).
 Occupational: 5 rem (50 mSv) in 1 year.
 Less than 2 mrem (20 mSv) in any 1 hour
in any unrestricted area.
LDR Treatment Room
A common hospital room without special
shielding can be used LDR brachytherapy.
 The room may be large enough to
accommodate afterloader carts, portable
bedside shields, and positioning visitor’s
chair far from the patient.
 Rooms adjacent to the treatment room
may be low occupancy.

Portable radiation shielding devices
http://www.rpdinc.com/
HDR Treatment Room Design
HDR RAU dedicated
Shielded operating theater
Unit storage area
Summary
Type of Brachytherapy
LDR, MDR, or HDR ( ≥ 20 cGy/min)
 Permanent or temporary
 Direct “hot” loading, afterloading, or
remote afterloading
 Interstitial, intracavitary, and surface
 Photons, electrons, or neutrons
