Dosimetric comparison of interactive planned and dynamic dose calculated prostate seed brachytherapy

PurposeTo compare the dosimetrical results of an interactive planning procedure and a procedure based on dynamic dose calculation for permanent prostate brachytherapy.Materials and methodsBetween 6/2000 and 11/2005, 510 patients underwent 125I implants for T1–T2 prostate cancer. Before 4/2003, 187 patients were treated using an interactive technique that included needle updating. After that period, 323 patients were treated with a more refined dynamic technique that included constant updating of the deposited seed position. The comparison is based on postimplant dose–volume parameters such as the V100 and d90 for the target, V100r for the rectum and d10u for the urethra. Furthermore, the target volume ratios (TVR≡V100body/V100), and the homogeneity indices (HI ≡ [V100 − V150]/V100) were calculated as additional quality parameters.ResultsThe dose outside the target volume was significantly reduced, the V100r decreased from 1.4 cm3 for the interactive technique to 0.6 cm3 for the dynamic technique. Similarly the mean TVR reduced from 1.66 to 1.44. In addition, the mean V100 increased from 92% for the interactive procedure to 95% for the dynamic procedure. More importantly, the percentage of patients with a V100 < 80% reduced from 5% to 1%. A slight decline was observed with regard to the d10u (136% vs. 140%) and the HI (0.58 vs. 0.51).ConclusionThe dynamic implant procedure resulted in improved implants. Almost ideal dose coverage was achieved, while minimizing the dose outside the prostate.