A comparison of different three-dimensional treatment planning techniques for localized radiotherapy of prostate cancer

Purpose: Four different three-dimensional planning techniques for localized radiotherapy of prostate cancer were compared with regard to dose homogene ity within the target volume and dose to organs at risk, dependent upon tum or stage. Patients and Methods: Six patients with stage T1, 7 patients with stage T2 and 4 patients with stage T3 were included in this study. Four different 3D treatment plans (rotation, 4-field, 5-field and 6-field technique) were ca lculated for each patient. Dose was calculated with the reference point at the isocenter (100%). The planning target volume was encompassed within the 95% isodose surface. All the techniques used different shaped portal for e ach beam. Dose volume histograms were created and compared for the planning target volume and the organs at risk (33%, 50%, 66% volume level) in all t echniques. Results: The 4 different three-dimensional planning techniques revealed no differences concerning dose homogeneity within the planning target volume. The dose volume distribution at organs at risk show differences between the calculated techniques. In our study the best protection for bladder and re ctum in stage T1 and T2 was achieved by the 6-field technique. A significan t difference was achieved between B-field and 4-field technique only in the 50% volume of the bladder (p = 0.034), between the 6-field and rotation te chnique (all volume levels) and between 5-field and rotation technique (all volume levels). In stage T1, T2 6-field and 4-field technique in 50% (p = 0.033) and 66% (p = 0.011) of the rectum volume. Ln stage T3 a significant difference was not observed between the 4 techniques. The best protection o f head of the femur was achieved by the rotation technique. Conclusion: In the localized radiotherapy of prostate cancer in stage T1 or T2 the best protection for bladder and rectum was achieved by a 3D-planned conformal 6-field technique. If the seminal vesicles have been included in the target volume and in the case of large planning target volume other te chniques should be taken for a better protection for organs at risk e. g. a 3D-planned 4-field technique box technique.