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M.D. Anderson Prostate Seed Implant Dose Calculator

A Anand

A Anand1*, W Du1, H Chung2, S Frank1, T Pugh1, R Kudchadker1, (1) University of Texas, M. D. Anderson Cancer Center, Houston, TX, (2) University of Maryland School of Medicine, BALTIMORE, MD,

SU-E-T-46 Sunday 3:00:00 PM - 6:00:00 PM Room: Exhibit Hall

To develop a prostate seed implant dose calculator for conducting independent verification of Variseed (Varian Medical, Palo Alto, CA) brachytherapy treatment planning system (TPS).
AAPM TG 43 based formalism was used in our method to compute point doses for prostate implant seeds commissioned in Variseed 8.0®. We have investigated four different isotope seeds, I¹²⁵ (Model 6711, 9011), Cs¹³¹ (Model Cs-1) and Pd¹⁰³ (Model 200) in this work. Three distinct Methods: point source model using anisotropy factors, line source model using anisotropy factors, and line source model using anisotropy functions were used to develop in-house dose calculator software. The dose calculator accounts for source strength, geometric dose fall off, attenuation, scatter and time, but does not consider any heterogeneous corrections. Source data parameters obtained from customer technical bulletins were input into both the Variseed TPS and our calculator. Spline and non oscillatory, seed specific fit functions to parameterize dose distribution for these seeds was evaluated for our software. These functions were then imported into the dose calculator to compute point doses as a function of radial distance from various seeds. The functions developed for our modeling were selectively chosen to account for self absorption from the seed's housing. The doses obtained by our secondary dose verification software were then compared against Variseed8.0® computed doses to clinically relevant radial distances. The dose calculator software has been packaged into a GUI module and is currently being tested for its robustness.
A good agreement (within 3% for 5 cm radial distance) for the isotopes studied is observed between the TPS and our calculator.
We have validated Variseed computed point doses by using our dose calculator. Within all uncertainties as described within TG-43, our results have been found to be in good agreement between our system and TPS.

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