Intravascular Brachytherapy Dosimetry Techniques for Gamma systems

Transcription

1 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 Iodine Palladium Samarium Ytterbinm Cadmium Gadolinium 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

2 Physics Parameters-3: IVBT Gamma or X ray Isotopes Specific Activity [ Ci / g ] Exp Rate const [ R/mCi*hr ] Ir-192 9, I , Pd , Sm-145 2, Yb , 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 ** Un-encapsulated isotopes. Computed by Ravi Nath, TG-60 : Figure 11. S. K. Jani- SCRIPPS CLINIC 2

3 Attenuation of gamma or x rays by high Z material Material [ mm ] Shielding Correction Factors ** Ir-192 I -125 Pd Titanium Stainless Steel Hypaque Omnipaque Calcified Plaque ** 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 , , , , , ~ 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

4 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

5 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 Gy 7.8 Gy Gy GAMMA-I 1.47 mm 3.19 mm Gy 7.97 Gy Gy Fixed point vs. IVUS-based Dosimetry Distances ( mm ) IVUS based doses (Gy) 14 2 mm Small vessel R 1 = 1.2 R 2 = (42% ) 11.4 (42% ) Large vessel R 1 = 1.4 R 2 = (20% ) 6.4 (20% ) S. K. Jani- SCRIPPS CLINIC 5

6 Native Coronary Arteries [No New Stent] (Scripps, Wrist and Gamma-I) % P= % 76.0% 14.6% P= % 65.7% 22.9% P= % 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 cm cm cm cm Sec S. K. Jani- SCRIPPS CLINIC 6

7 REFERENCES Jani SK: Handbook of Dosimetry Data for Radiotherapy. Boca Raton, FL: CRC Press, 1993, 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, Jani SK: Physics of vascular brachytherapy. J Invas Cardiol 11: , Kline RW, Gillin MT, Grimm DF, et al: Computer dosimetry of 192 Ir wire. Med Phys 12: , Jani SK: Gamma vs. Bets irradiation: which is superior? J. Cardiovascular Radiation Medicine 1: , Jani SK: Basic Physics of Gamma Isotopes, Vascular Brachytherapy, 2nd Ed., Waksman R (Ed). Futura Publishing Co., Armonk, NY (1999) pp 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 S. K. Jani- SCRIPPS CLINIC 7