Intravascular Brachytherapy
Dosimetry Techniques for Gamma systems
Shirish K. Jani, Ph.D., FACR
Scripps Clinic
La Jolla, California
Physics Parameters-1: IVBT Gamma or X ray Isotopes
Iridium-192
Iodine-125
Palladium-103
Samarium-145
Ytterbinm-169
Cadmium-109
Gadolinium-153
Energy [ keV ]
Average
Maximum
370
612
28
35
20
23
41
61
93
340
22
88
41
103
Half Life
[ days ]
74
60
17
340
32
462
241
Physics Parameters-2: IVBT Gamma or X ray Isotopes
The utility of an isotope depends on a
variety of factors. Two main factors
are:
1.
Specific Activity [ Ci/gm ] which varies
as the inverse of half life and atomic
mass.
2.
Exposure rate in R/mCi.Hr at 1 cm.
S. K. Jani- SCRIPPS CLINIC
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Physics Parameters-3: IVBT Gamma or X ray Isotopes
Ir-192
I-125
Pd-103
Sm-145
Yb-169
Cd-109
Gd-153
Specific Activity
[ Ci / g ]
9,200
17,400
74,600
2,650
24,150
2,600
3,540
Exp Rate const
[ R/mCi*hr ]
4.6
1.45
1.48
0.88
1.8
Physical dosimetry: IVBT Gamma or X ray Isotopes
Computation
Monte Carlo ; TG-43 & TG-60 ( Jeff Williamson,
Zuofeng Li and Ravi Nath )
Measurements
Scintillation Detectors – Ulrich Quast
Film dosimetry- Rosanna Chan, Ravi Nath ,
Shirish Jani
RDF of the Gamma or X ray emitting isotopes
Radial Dose Function **
Distance [ mm ]
Ir-192
I-125
Pd-103
0.5
0.94
1.09
1.06
1.0
1.00
1.01
1.02
2.0
1.00
1.01
0.99
3.0
0.99
0.97
0.96
4.0
0.98
0.99
0.93
5.0
1.00
0.99
0.90
10.0
1.01
0.97
0.70
** Un-encapsulated isotopes. Computed by Ravi Nath, TG-60 : Figure 11.
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Attenuation of gamma or x rays by high Z material
Material [ mm ]
Shielding Correction Factors **
Ir-192
I-125
Pd-103
0.1 - Titanium
1.00
0.7
0.5
0.1 – Stainless Steel
1.00
0.4
0.1
2 - Hypaque
1.00
0.6
0.3
2 - Omnipaque
1.00
0.5
0.2
1 – Calcified Plaque
1.00
0.8
0.6
** Computed with point source geometry (Nath, R. & Yue, N., CRM 2:93,2001).
Dose Response of films for brachytherapy dosimetry
Optical Density
0.5
1.0
1.5
2.0
2.5
3.0
EDR-2 Film
100
190
280
380
490
~700
Dose Required [ cGy ]
Ga F Chromic Film
4,000
9,000
15,000
22,000
27,000
-----
Commercial Gamma Systems for IVBT
Isotope
Company
Activity (mCi)
IVBT
Ir-192
Ir-192
I-125
Pd-103
Cordis/Best
Nucletron
Amersham
Theragenics
≤ 35 mCi
≤ 10 Ci
≤ 40 mCi
≤ 5 mCi
Yes (coronary)
Yes (Peripheral)
No
No
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The Cordis Checkmate System
Radioactive Source
- Ir-192 seeds/ nylon ribbon
- 3 ribbon configurations:
6, 10, 14 seeds
- 33 mCi per seed activity (max)
- Average 20 minute
treatment times
Delivery Device
- Pig (lead containment device)
- Hand fed system
The Checkmate Source Ribbon
10-Seed Ribbon
The Dummy Ribbon
facilitates proper catheter
positioning across the lesion
and the selection of an
appropriate source ribbon.
6-Seed Ribbon
14-Seed Ribbon
Dummy Ribbon
ÝContains non-radioactive
seeds
ÝRadiopaque marker seeds
delineate source ribbon
treatment length
configurations
6 Seeds
10 Seeds
14 Seeds
PARIS
Peripheral Arteries Radiation Investigational Study
CENTERING CATHETER
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Clinical Dosimetry with Gamma-based IVBT
SCRIPPS I (Coronary) : single site, 60 patients, initiated 3/9 5
WRIST (Coronary)
: single site, 130 patients, initiated 2 /97
GAMMA I ( Coronary) : 12 sites, 252 patients, initiated 12/97
PARIS (Peripheral)
: sites, 300 patients, initiated 1997
Ir- 192 Trials- Dosimetry parameters
SCRIPPS
GAMMA-I
Dist-to- point A
1.3 mm
1.47 mm
Dist-to-point B
3.34 mm
3.19 mm
Ave dose to A
24.08 Gy
20.32 Gy
Ave dose to B
7.8 Gy
7.97 Gy
Dose at 2 mm
13.96 Gy
13.53 Gy
Fixed point vs. IVUS-based Dosimetry
Distances
( mm )
IVUS based
doses (Gy)
14 Gy @ 2 mm
Small
vessel
R1 = 1.2
R2 = 2.4
17.8
8
25.3 (42%⇑
⇑)
11.4 (42%⇑
⇑)
Large
vessel
R1 = 1.4
R2 = 3.8
26.6
8
21.4 (20%⇓
⇓)
6.4 (20%⇓
⇓)
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Native Coronary Arteries [No New Stent]
(Scripps, Wrist and Gamma-I)
80
70
P=0.0001
50
66.7%
60.8%
65.0%
65.7%
40
76.0%
30
20
31/51
7/48
In-Stent
Restenosis
34/51
11/48
In-Lesion
Restenosis
Placebo
Radiation
24.5%
22.9%
14.6%
10
0
P=0.0001
70.0%
60
%
P=0.0001
42/60
13/53
MACE
PARIS
Peripheral Arteries Radiation Investigational Study
Delivery System : the microSelectron-HDR afterloader
(Nucletron Corporation)
The source : Iridium-192 (< 10 Ci, 3.5-mm length,
0.6 mm diameter)
The dose : 14 Gy at reference radius + 2 mm
The target length : Total dilated area + 10 mm
PARIS
Peripheral Arteries Radiation Investigational Study
Lesion Length
Target Length
Vessel Diameter
Target Distance
Treatment time
S. K. Jani- SCRIPPS CLINIC
9.8+ 3.0 cm
12.4 + 3.1 cm
5.2 + 0.5 cm
6.6 + 0.9 cm
253.7 + 57.8 Sec
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REFERENCES
1.
1. Jani SK: Handbook of Dosimetry Data for Radiotherapy. Boca Raton, FL: CRC Press, 1993, 137-167.
2.
2.
Nath R: Physical properties and clinical uses of brachytherapy radionuclide. In Williamson JF,
Thomadsen BR, Nath R eds):
(
Brachytherapy Physics. Madison, WI: Medical Physics
Publishing Co., 1995, 7-38.
3.
3. Jani SK: Physics of vascular brachytherapy. J Invas Cardiol 11:517-523, 1999.
4.
4. Kline RW, Gillin MT, Grimm DF, et al: Computer dosimetry of
1985.
192Ir
wire. Med Phys 12:634-638,
5.
5. Jani SK: Gamma vs. Bets irradiation: which is superior? J. Cardiovascular Radiation Medicine 1:102106,1999.
6.
6. Jani SK: Basic Physics of Gamma Isotopes, Vascular Brachytherapy , 2nd Ed., Waksman
R (Ed). Futura Publishing Co., Armonk, NY (1999) pp. 167-176.
7.
7. JANI SK, Massullo VM, Teirstein PS, Huppe GB : BEST – Medical Hand Delivered Ir-192 Ribbon,
Vascular Brachytherapy, 2nd Edition, Waksman R (Ed). Futura Publishing Co., Armonk, NY
(1999) pp. 485-488.
S. K. Jani- SCRIPPS CLINIC
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