MONTE CARLO RADIATION DOSE SIMULATIONS AND DOSIMETRY

COMPARISON OF THE MODEL 6711 AND 9011 125I BRACHYTHERAPY SOURCES

Mark J. Rivard

Department of Radiation Oncology, Tufts Medical Center, Boston, Massachusetts 02111

Med. Phys. 36 (2), February 2009

BACKGROUND

• 6711125I seed model

• Smaller sources allows smaller diameter needles

• Lower incidence of healthy-tissue complications

INTRODUCTION

• TRUS guided prostate implantation

• 125I seed (6711 Model)

• Sources placed with needles into prostate

• Results in swelling

• Minimized by small diameter needles

• New model 9011 125I seed – Oncura GE Healthcare (Arlington Heights, IL)

PURPOSE OF THE STUDY

• Study and determine dosimetry parameters of the new 125I 9011 model

• Treatment planning

• Clinical implementation

MATERIALS AND METHOD

A. Source Characteristics

B. Radiation Transport code

125I 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 109 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 0.965 cGy h−1 U−1

III. B. Dose rate constant

III. C. Anisotropy function

III. C. Anisotropy function

IV. D. DOSE RATE TABLE

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