SU‐E‐T‐527: A Fast Novel Analytical Model Accounting for Interseed Attenuation Effect in Low Energy Brachytherapy Sources

Purpose: Currently, treatment planning systems make two assumptions that can affect dose calculation; Homogenous media and Radio‐transparency of surrounding seeds. In this project a fast novel analytical model to correct the inter‐seed attenuation (ISA) in multiseed implants for TG‐43U1 LDR brachytherapy have developed. Model sensitivity of the results to examined for multiple seeds of I‐125 and Ir‐192 in different distanc and angles in water phantom. Methods: In this model, dose perturbation (P‐value) and inter‐seed attenuation (ISA‐value) in a multi‐source brachytherapy implant is based on pre Monte Carlo simulated 3D kernels of perturbation and ISA data for single active and single dummy configuration, arranged at different distances and angles relative to each other. The final model results have been examined by a compared for the calculated Perturbation and ISA‐values with full Monte Carlo water simulations (FMCWS). Finally by multiply the model values in TG‐43U1 dose rate for any interest point, the ISA deficiency will be modified. Results: The results show that the perturbation model values at interest point or voxel are equal to multiply perturbation factor of single active‐inactive sources which are placed in straight line from active source to interest point of implant. The accuracy of the model for parallel multi‐source implants was 3.5% and 5% for Ir‐192 and I‐125, respectively. Sensitivity of the results for non‐parallel multi‐source implants was up to 5%. Conclusion: Base on this novel fast approach, one could expedite the processes of dose ISA corrections with the minimum increase of the planning time for standard and loos brachytherapy implants as compared to the FMCWS in TG‐43U1 brachytherapy treatment planning systems. This model is applicable for energy of I‐125 to Ir‐192 sources.