A comprehensive dosimetric comparison between 131Cs and 125I brachytherapy sources for COMS eye plaque implant
Received 7 January 2009; received in revised form 23 June 2009; accepted 28 July 2009. published online 29 January 2010. Corrected Proof
Abstract
Purpose
To verify the dosimetric characteristics of 131Cs source in the Collaborative Ocular Melanoma Study (COMS) eye plaque brachytherapy, to compare 131Cs with 125I in a sample implant, and to examine the accuracy of treatment planning system in dose calculation.
Methods and Materials
Monte Carlo (MC) technique was used to generate three-dimensional dose distributions of a 16-mm COMS eye plaque loaded with 131Cs and 125I brachytherapy sources separately. A spherical eyeball, 24.6mm in diameter, and an ellipsoidal tumor, 6mm in height and 12mm in diameter, were used to evaluate the doses delivered. The simulations were carried out both with and without the gold and gold alloy plaque. A water-equivalent seed carrier was used instead of the silastic insert designed for the traditional COMS eye plaque. The 13 sources involved were also individually simulated to evaluate the intersource effect. In addition, a treatment planning system was used to calculate the doses at the central axis for comparison with MC data.
Results
The gold plaque had significantly reduced the dose in the tumor volume; at the prescription point of this study, that is, 6mm from the edge of inner sclera, the gold plaque reduced the dose by about 7% for both types of 131Cs and 125I sources, but the gold alloy plaque reduced the dose only by 4% for both types of sources. The intersource effect reduced the dose by 2% for both types of sources. At the same prescription dose, the treatment with the gold plaque applicator tended to create more hot regions for either type of sources than were seen with the homogeneous water phantom. The doses of TPS agree with the MC.
Conclusion
The 131Cs source is comparable to the 125I source in the eye plaque brachytherapy. The TPS can provide accurate dose calculations for eye plaque implants with either type of sources.
3Department of Radiation Medicine, North Shore University—LIJ Health System, Manhasset, NY
4Department of Medical Physics, University of Wisconsin, Madison, WI
5Department of Human Oncology, University of Wisconsin, Madison, WI
6Department of Engineering Physics and Biomedical Engineering, University of Wisconsin, Madison, WI
Corresponding author. Department of Radiation Oncology, The Ohio State University, 300 West 10th Avenue, Columbus, OH 43210-1228. Tel.: +614-559-2343; fax: +614-293-4044.
Financial disclosure/conflict of interest notification: This study does not have any actual and potential conflicts of interest.
ABSTRACT
mm in diameter, and an ellipsoidal tumor, 6