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Producing a Look-Up Table for Mesh Brachytherapy Dosimetry with I-125, Pd-103, and Cs-131

Z Grelewicz

Z Grelewicz*, D Cutright , V Sathiaseelan , H Zhang , Northwestern Memorial Hospital, Chicago, IL


SU-I-GPD-T-48 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: To provide look-up tables for predetermining the source strength of mesh brachytherapy of three types of brachytherapy sources for a given treatment area, to help arrange source spacing with available source activities.

Methods: Three types of commonly used brachytherapy sources (Amersham 6711 ¹²⁵I, Theragenics model-200 ¹⁰³Pd, and Isoray ¹³¹Cs) were used in the calculations, the TG-43 source data for line and point source approximations were entered in an in-house dose calculation engine in MATLAB, and the calculation results were verified by Variseed Planning system ( VariSeed 8, Varian, California). 100 Gy of prescription dose was administered 0.5 cm above the center of the source plane. The look-up tables of appropriate activities for a list of sizes of treatment areas were generated. This study investigated 12 different geometric arrangements of sources, ranging from 4 to 6 strands, with 0.8 to 1.5 cm strand spacing.

Results: Point source models demonstrated higher required activities. Required source strength is closely tied to strand spacing. For 100 Gy prescription, required activity per seed is approximately 0.52 U/cm for ¹²⁵I, 3.91 U/cm for ¹⁰³Pd, and 3.25 U/cm for ¹³¹Cs for a point source model for the arrangements studied. MATLAB dose calculation agrees with VariSeed within 1%. These averages are within 10% of the individual values for different coverage areas. For 4x9 cm², 0.8, 1.0, 1.3 cm and 1.5 cm spacing will require 0.41. 0.49, 0.68 and 0.79 U for ¹²⁵I source, 2.51. 2.97, 4.34 and 5.18 U for ¹⁰³Pd source, 2.11, 2.54, 3.49 and 3.99 U for ¹³¹Cs, respectively,

Conclusion: Our in-house software is able to quickly produce reliable look up tables for mesh brachytherapy. The look up tables will assist clinicians to order sources and prepare treatment thus it is very useful. This data helps provide assistance in source parameter selection for mesh brachytherapy.

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