MONTE CARLO RADIATION DOSE SIMULATIONS AND DOSIMETRY COMPARISON OF THE MODEL 6711 AND 9011 125I BRACHYTHERAPY SOURCES

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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
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BACKGROUND

• 6711125I seed model
• Smaller sources allows smaller diameter needles
• Lower incidence of healthy-tissue complications

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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)

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PURPOSE OF THE STUDY

• Study and determine dosimetry parameters of the
  new 125I 9011 model
• Treatment planning
• Clinical implementation

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MATERIALS AND METHOD
A. Source Characteristics
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B. Radiation Transport code

• 125I spectrum from TG43U

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B. Radiation Transport code

• 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

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Coordinates system in MCNP
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TG 43U Dose Calculation Formalism
According to TG 43, the dose distribution around
a cylindrical symmetric brachytherapy source is
defined by the following equation.
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C. UNCERTAINITY ANALYIS
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III. RESULTS AND DISCUSSION
III. A. Dose rate constant
Recommended value 0.965 cGy h-1 U-1
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III. B. Dose rate constant
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III. C. Anisotropy function
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III. C. Anisotropy function
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IV. D. DOSE RATE TABLE
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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

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