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Dosimetric comparison of interactive planned and dynamic dose calculated prostate seed brachytherapy
Gert J Meijer1, Hetty A van den Berg, Coen W Hurkmans
1Radiotherapy Department, Catharina Hospital, Eindhoven, The Netherlands. gert.meijer@cze.nl
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 (125)I 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 identical with V(100)(body)/V(100)), and the homogeneity indices (HI identical with [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.
