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

Abstract

Purpose To compare the dosimetrical results of an interactive planning procedure and a procedure based on dynamic dose calculation for permanent prostate brachytherapy. Materials and methods Between 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 V 100 and d 90 for the target, V 100 r for the rectum and d 10 u for the urethra. Furthermore, the target volume ratios ( TVR ≡ V 100 body / V 100 ) , and the homogeneity indices (HI ≡ [ V 100 − V 150]/ V 100) were calculated as additional quality parameters. Results The dose outside the target volume was significantly reduced, the V 100 r decreased from 1.4 cm 3 for the interactive technique to 0.6 cm 3 for the dynamic technique. Similarly the mean TVR reduced from 1.66 to 1.44. In addition, the mean V 100 increased from 92% for the interactive procedure to 95% for the dynamic procedure. More importantly, the percentage of patients with a V 100 < 80% reduced from 5% to 1%. A slight decline was observed with regard to the d 10 u (136% vs. 140%) and the HI (0.58 vs. 0.51). Conclusion The dynamic implant procedure resulted in improved implants. Almost ideal dose coverage was achieved, while minimizing the dose outside the prostate.