ENHANCEMENT OF PROSTATE TUMOR VOLUME DEFINITION WITH INTRAVESICAL CONTRAST - A 3-DIMENSIONAL DOSIMETRIC EVALUATION

Purpose: To assess the impact of intravesical contrast during computed tomography (CT) simulation on prostate tumor volume definition and do se distribution.Methods and Materials: Sixteen patients with localized adenocarcinoma of the prostate underwent CT-based virtual simulation in preparation for definitive radiotherapy, Patients were immobilized with a foam cradle and an initial CT was performed after oral but with out intravesical contrast (noncontrast scan), A second scan was perfor med following administration of intravesical contrast (contrast scan), Beam apertures were designed on the noncontrast scans and digitized i nto the contrast scan file, Beam apertures were also designed on the c ontrast scans, Isodose plans were generated for several beam apertures and arrangements. Results: There was enhanced visualization of the pr ostate at the cephalad portion of the field for 15 of the 16 cases, Th e mean differences between the noncontrast and contrast volumes was si gnificant (p = 0.0001), The mean percent underdosage to the prostate r anged from 3.9% to 18.6%, depending upon the target volume and beam ar rangement. Conclusion: This study demonstrates the necessity of using intravesical contrast for defining the location of the prostate during CT simulation, The underestimation of the extent of the prostate when omitting intravesical contrast leads to significant underdosage, The value of intravesical contrast is most evident when small (prostate on ly) conformal fields are used. (C) 1997 Elsevier Science Inc.