1. MONTE CARLO RADIATION DOSE SIMULATIONS AND DOSIMETRY COMPARISON OF THE MODEL 6711 AND 9011 125 I BRACHYTHERAPY SOURCES Mark J. Rivard Department of Radiation Oncology, Tufts Medical Center, Boston, Massachusetts 02111 Med. Phys. 36 (2), February 2009

2. BACKGROUND 6711 125 I seed model Smaller sources allows smaller diameter needles Lower incidence of healthy-tissue complications

3. INTRODUCTION TRUS guided prostate implantation 125 I seed (6711 Model) Sources placed with needles into prostate Results in swelling Minimized by small diameter needles New model 9011 125 I seed –Oncura GE Healthcare (Arlington Heights, IL)

4. PURPOSE OF THE STUDY Study and determine dosimetry parameters of the new 125 I 9011 model Treatment planning Clinical implementation

5. MATERIALS AND METHOD A. Source Characteristics

6. B. Radiation Transport code 125 I spectrum from TG43U

7. MCNP 5 with EPDL97 (LLNL report) 20 cm radius liquid water phantom Coordinate system origin located at the center of the capsule Photon transport MODE P Tallies Track length estimator (F6) Cell energy fluence (*f4) 1 keV energy cutoff 2 x 10 9 photon histories B. Radiation Transport code

8. Coordinates system in MCNP

9. TG 43U Dose Calculation Formalism According to TG 43, the dose distribution around a cylindrical symmetric brachytherapy source is defined by the following equation.

10. C. UNCERTAINITY ANALYIS

11. III. RESULTS AND DISCUSSION III. A. Dose rate constant **Recommended value 0.965 cGy h−1 U−1

12. III. B. Dose rate constant

13. III. C. Anisotropy function

15. IV. D. DOSE RATE TABLE

16. CONCLUSION Monte Carlo simulations of dose rate distributions Model 6711 and 9011 125I sources Similar trends and dose falloff characteristics Determine the TG-43 brachytherapy dosimetry parameters Needed for clinical brachytherapy treatment planning Two source models dose rate difference are 2% Require separate data entry into treatment planning systems