SU‐E‐T‐455: A Treatment Planning Feasibility Study for Prostate LDR Brachytherapy Treatments Using the New 103‐Pd CivaString Source. Comparison with Clinical Cases Using the TheraSeed Model 200 103‐Pd Source

Abstract

Purpose: This is a comparative dosimetric study using a new 103Pd CivaString source for prostate brachytherapy seed implants. Clinical plans using TheraSeed Model 200 103Pd seeds were used as the standard. The aims were to explore the feasibility and planning advantages with, and define guidelines for optimization and clinical implementation of, CivaString linear sources. Methods: Treatment plans from twelve patients implanted with Model 200 seeds were re‐planned using the CivaString source. Prostate volumes ranged from 23 to 61 cm3. CivaString dosimetric characterization was based on TG‐43 parameters derived from Monte Carlo simulations. Two CivaString plans were generated for each patient, first with a uniform source strength, then using higher‐strength sources peripherally and lower‐strength sources interiorly. The planning objective was matching the prostate D90 of the analogous Model 200‐based plan and was achieved by scaling CivaString source strength for a fixed but patient‐specific needle placement. Dosimetric quality was assessed in reference to prostate D90, V100, and V150, rectum V100, and urethra V150. Results: For virtually the same prostate D90, CivaString plans matched all dosimetric parameters yet provided a slight reduction in prostate V150. CivaString plans permitted reduction in the number of needles required to deliver implants, ranging from 55% to 68% compared with Model 200 plans. This allowed large prostate 103Pd source implants with 12–14 needles. In large‐volume prostate implants, use of two source strengths appeared beneficial to reduce V150 for prostate and urethra. Conclusion: Based on clinical scenarios, planning with the CivaString source significantly reduced the number of required needles while delivering similar dose distributions to the prostate, urethra, and rectum. Planning was dramatically simplified, and optimization was replaced by simple guidelines that allowed creation of high‐quality treatment plans within minutes.