EFFICIENT CT-SIMULATION OF THE 4-FIELD TECHNIQUE FOR CONFORMAL RADIOTHERAPY OF PROSTATE-CARCINOMA

Purpose: Conformal radiotherapy of prostate carcinoma relies on contou ring of individual CT slices for target and normal tissue localization , This process can be very time consuming, In the present report, we d escribe a method to more efficiently localize pelvic anatomy directly from digital reconstructed radiographs (DRRs), Materials and Methods: Ten patients with prostate carcinoma underwent CT simulation (the spir al mode at 3 mm separation) for conformal four-field ''box'' radiother apy, The bulbous urethra and bladder were opacified with iodinated con trast media, On lateral and anteroposterior DRRs, the volume of intere st (VOI) was restricted to 1.0-1.5 cm tissue thickness to optimize dig ital radiograph reconstruction of the prostate and seminal vesicles, B y removing unessential voxel elements, this method provided direct vis ualization of those structures, For comparison, the targets of each pa tient were also obtained by contouring CT axial slices, Results: The m ethod was successfully performed if the target structures were readily visualized and geometrically corresponded to those generated by conto uring axial images, The targets in 9 of 10 patients were reliable repr esentations of the CT-contoured volumes, One patient had 18 mm variati on due to the lack of bladder opacification, Using VOIs to generate th in tissue DRRs, the time required for target and normal tissue localiz ation was on the average less than 5 min, Conclusion: In CT simulation of the four-field irradiation technique for prostate carcinoma, thin- tissue DRRs allowed for efficient and accurate target localization wit hout requiring individual axial image contouring, This method may faci litate positioning of the beam isocenter and provide reliable conforma l radiotherapy, (C) 1997 Elsevier Science Inc.