Use of multiplanar reformatted radiographic and digitally reconstructed radiographic images for planning conformal radiation therapy.

A three-dimensional treatment planning system capable of gantry, collimator, and table rotations is required for a noncoplanar conformal therapy. Unfortunately, such a system is not widely available. A method in which multiplanar reformatted radiographic (MPR) and digitally reconstructed radiographic (DRR) images are used is presented for conformal treatment of brain tumors. A head phantom containing a target volume was scanned on a computed tomographic (CT) simulator. The coronal MPR images were digitized on a treatment planning system to create a conformal block of the planned treatment field. The DRR images were generated on the CT simulator with the setup parameters calculated from the treatment planning system. A second set of conformal blocks was generated based on DRR images of the fields. The accuracy of the MPR- and DRR-generated blocks was verified on the vertex field. The differences between the actual planning target volume and the field edges of the MPR and DRR blocks were within +/- 4 mm and +/- 2 mm, respectively. The authors conclude that the MPR and DRR images could be successfully used to generate conformal blocks and for treatment planning of noncoplanar beams in radiation therapy.