Advantages of CT and beam's eye view display to confirm the accuracy of pelvic lymph node irradiation in carcinoma of the prostate.

Possible advantages of computed tomography (CT) and beam's eye view (BEV) display in the design of pelvic irradiation fields were studied in 20 consecutive patients with localized adenocarcinoma of the prostate. Pelvic fields were designed with standard four-field techniques. Then, CT and BEV display were done to define the reduced prostate tumor volumes. With treatment-planning CT, the location of the pelvic vascular structures (internal and external iliac artery and vein) was outlined. These were used as an approximation of the location of the lymph nodes. A BEV display of these lymph node volumes was then compared with the pelvic fields designed without CT and BEV display. Nineteen of the 20 patients had part of the CT-defined lymph node volume (a portion of the internal iliac lymph node volume) excluded from the original field design. Thirteen patients also had part of the external iliac nodal volume excluded. Dose-volume histograms showed that up to 30% of the lymph node volume received only 56% of the prescribed dose.