3-DIMENSIONAL COMPARISON OF BLOCKED ARCS VS 4-FIELD AND 6-FIELD CONFORMAL TREATMENT OF THE PROSTATE

Purpose: The purpose of this study is to compare five different techni ques for treatment the prostate without seminal vesicles. Dose volume histograms and a time survey are the tools that were used for this ana lysis. Methods and materials: For this study we compared 3D techniques using four and six field conformal treatments, to open and blocked 8 x 8 cm(2) 120 degrees bilateral area. All the plans were normalized to deliver 100% to the central axis, and full 3D calculations were perfo rmed. Blocked arcs were created using the 'average beam's eye view' (A -BEV) technique [11]. Results: Analysis of the dose volume histograms revealed: (1) Arcs with blocks result in an improved dose distribution compared to standard arcs and four field 3DCRT techniques, (2) The DV H associated with blocked arcs, using block margins of 1.3 cm, resulte d in a somewhat lower dose to the rectum but a 'tighter' margin around the prostate compared to the DVH generated using the six field 3DCRT technique. Conclusion: This technique is for treatment of the prostate only, when treatment of the seminal vesicle is not required. The use of blocked arcs significantly improved the dose distribution compared to using standard arcs and 4-field conformal techniques. The DVHs asso ciated with using blocked arcs is comparable to the SFC technique. It is likely to be less expensive, faster to set-up and may allow for saf e dose escalation when only the prostate is receiving treatment.