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 Energy [ kev ] Half Life Average Maximum [ days ] Iridium-192 370 612 74 Iodine -125 28 35 60 Palladium-103 20 23 17 Samarium-145 41 61 340 Ytterbinm-169 93 340 32 Cadmium-109 22 88 462 Gadolinium-153 41 103 241 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 1
Physics Parameters-3: IVBT Gamma or X ray Isotopes Specific Activity [ Ci / g ] Exp Rate const [ R/mCi*hr ] Ir-192 9,200 4.6 I-125 17,400 1.45 Pd-103 74,600 1.48 Sm-145 2,650 0.88 Yb-169 24,150 1.8 Cd-109 2,600 Gd-153 3,540 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. S. K. Jani- SCRIPPS CLINIC 2
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 Dose Required [ cgy ] EDR-2 Film Ga F Chromic Film 0.5 100 4,000 1.0 190 9,000 1.5 280 15,000 2.0 380 22,000 2.5 490 27,000 3.0 ~700 ----- Commercial Gamma Systems for IVBT Isotope Company Activity (mci) IVBT Ir-192 Cordis/Best 35 mci Yes (coronary) Ir-192 Nucletron 10 Ci Yes (Peripheral) I-125 Amersham 40 mci No Pd-103 Theragenics 5 mci No S. K. Jani- SCRIPPS CLINIC 3
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 The Dummy Ribbon facilitates proper catheter positioning across the lesion and the selection of an appropriate source ribbon. 10-Seed Ribbon 6-Seed Ribbon 14-Seed Ribbon Dummy Ribbon 6 Seeds 10 Seeds 14 Seeds Contains non-radioactive seeds Radiopaque marker seeds delineate source ribbon treatment length configurations P A R I S Peripheral Arteries Radiation Investigational Study CENTERING CATHETER S. K. Jani- SCRIPPS CLINIC 4
Clinical Dosimetry with Gamma-based IVBT SCRIPPS I (Coronary) : single site, 60 patients, initiated 3/95 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 Dist-to- point A Dist-to-point B Ave dose to A Ave dose to B Dose at 2 mm SCRIPPS 1.3 mm 3.34 mm 24.08 Gy 7.8 Gy 13.96 Gy GAMMA-I 1.47 mm 3.19 mm 20.32 Gy 7.97 Gy 13.53 Gy Fixed point vs. IVUS-based Dosimetry Distances ( mm ) IVUS based doses (Gy) 14 Gy @ 2 mm Small vessel R 1 = 1.2 R 2 = 2.4 17.8 8 25.3 (42% ) 11.4 (42% ) Large vessel R 1 = 1.4 R 2 = 3.8 26.6 8 21.4 (20% ) 6.4 (20% ) S. K. Jani- SCRIPPS CLINIC 5
Native Coronary Arteries [No New Stent] (Scripps, Wrist and Gamma-I) % 80 70 60 50 40 30 20 10 P=0.0001 60.8% 76.0% 14.6% P=0.0001 66.7% 65.7% 22.9% P=0.0001 70.0% 65.0% 24.5% Placebo Radiation 0 31/51 7/48 34/51 11/48 42/60 13/53 In-Stent Restenosis In-Lesion Restenosis MACE P A R I S 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 P A R I S Peripheral Arteries Radiation Investigational Study Lesion Length Target Length Vessel Diameter Target Distance Treatment time 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 S. K. Jani- SCRIPPS CLINIC 6
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 192 Ir wire. Med Phys 12:634-638, 1985. 5. 5. Jani SK: Gamma vs. Bets irradiation: which is superior? J. Cardiovascular Radiation Medicine 1:102-106,1999. 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, 2 nd Edition, Waksman R (Ed). Futura Publishing Co., Armonk, NY (1999) pp. 485-488. S. K. Jani- SCRIPPS CLINIC 7