A customized non-axial external beam technique for treatment of prostate carcinomas

A nonaxial four-field technique for primary and boost treatment of prostate carcinoma has been developed in an effort to minimize dose to rectum and bladder. Using a treatment planning CT scan, prostate, rectal and bladder volumes are outlined and corresponding three-dimensional structures are created. An oblique CT image, which bisects the prostate volume and excludes rectum and bladder, is reconstructed. Four beams, consisting of direct laterals and two anterior, inferior obliques, are designed, which lie in the plane of the generated image. Utilizing a beam's-eye-view display and multilevel dose calculations, blocks are designed for each port, which encompass the target volume within a minimum isodose surface. These customized angles result in oblique ports with rectal and bladder sparing that can be comparable to that of direct lateral ports. Dose-volume histogram analysis is used to evaluate the merits of this nonaxial method with other approaches.