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Purpose: In clinical practice, specific air kerma strength (S-K) value is used in treatment planning system (TPS) permanent brachytherapy implant calculations with I-125 and Pd-103 sources; in fact, commercial TPS provide only one S-K input value for all implanted sources and the certified shipment average is typically used. However, the value for S-K is dispersed: this dispersion is not only due to the manufacturing process and variation between different source batches but also due to the classification of sources into different classes according to their S-K values. The purpose of this work is to examine the impact of S-K dispersion on typical implant parameters that are used to evaluate the dose volume histogram (DVH) for both planning target volume (PTV) and organs at risk (OARs). Methods: The authors have developed a new algorithm to compute dose distributions with different S-K values for each source. Three different prostate volumes (20, 30, and 40 cm(3)) were considered and two typical commercial sources of different radionuclides were used. Using a conventional TPS, clinically accepted calculations were made for I-125 sources; for the palladium, typical implants were simulated. To assess the many different possible S-K values for each source belonging to a class, the authors assigned an S-K value to each source in a randomized process 1000 times for each source and volume. All the dose distributions generated for each set of simulations were assessed through the DVH distributions comparing with dose distributions obtained using a uniform S-K value for all the implanted sources. The authors analyzed several dose coverage (V-100 and D-90) and overdosage parameters for prostate and PTV and also the limiting and overdosage parameters for OARs, urethra and rectum. Results: The parameters analyzed followed a Gaussian distribution for the entire set of computed dosimetries. PTV and prostate V-100 and D-90 variations ranged between 0.2% and 1.78% for both sources. Variations for the overdosage parameters V-150 and V-200 compared to dose coverage parameters were observed and, in general, variations were larger for parameters related to I-125 sources than Pd-103 sources. For OAR dosimetry, variations with respect to the reference D-0.1cm3 were observed for rectum values, ranging from 2% to 3%, compared with urethra values, which ranged from 1% to 2%. Conclusions: Dose coverage for prostate and PTV was practically unaffected by S-K dispersion, as was the maximum dose deposited in the urethra due to the implant technique geometry. However, the authors observed larger variations for the PTV V-150, rectum V-100, and rectum D-0.1cm3 values. The variations in rectum parameters were caused by the specific location of sources with S-K value that differed from the average in the vicinity. Finally, on comparing the two sources, variations were larger for I-125 than for Pd-103. This is because for 103Pd, a greater number of sources were used to obtain a valid dose distribution than for I-125, resulting in a lower variation for each S-K value for each source (because the variations become averaged out statistically speaking). (C) 2015 American Association of Physicists in Medicine.