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

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

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 I seed –Oncura GE Healthcare (Arlington Heights, IL)

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

MATERIALS AND METHOD A. Source Characteristics

B. Radiation Transport code 125 I spectrum from TG43U

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

Coordinates system in MCNP

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

C. UNCERTAINITY ANALYIS

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

III. B. Dose rate constant

III. C. Anisotropy function

IV. D. DOSE RATE TABLE

CONCLUSION Monte Carlo simulations of dose rate distributions Model 6711 and I 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