A technique for optimization of digitally reconstructed radiographs of thechest in virtual simulation

Introduction: Virtual simulation (VS) of radiotherapy uses CT data. Digital ly reconstructed radiographs (DRRs) are a critical element of this process, and the quality of these images is frequently suboptimal. We present techn iques to improve DRR quality for clinical purposes. The results of two appr oaches to DRR optimization are presented. Methods and Materials: One approach to DRR optimization is to use tradition al radiographs as a guide and to adjust the algorithm parameters based on i mage and objective contrast to produce images that more closely resemble tr aditional radiographs (Method 1). Another approach is to focus on the visib ility of specific anatomic structures. Using this method, two DRR images ar e optimized manually by interactively adjusting reconstruction parameters, then they are combined into a single composite image (Method 2). DRRs for t he chest region, generated using both methods, were evaluated by clinical s taff based on usability for treatment verification and held definition. Results: Using Method 1, the resulting DRRs more closely resembled traditio nal radiographs. This technique allows DRR quality to be improved with litt le user interaction. These DRRs are generally adequate for clinical use, bu t not optimal for sites such as the chest. Images generated using Method 2 were considered clinically superior in terms of visibility of specific anat omic structures. These images also compare well with traditional radiograph s, although they show an increased contrast level between bone and lower de nsity structures. Conclusion: Both Methods 1 and 2 can be used to improve DRR quality for cli nical purposes. For the chest region, the additional effort required by Met hod 2 to achieve a more detailed image appears justified. (C) 2001 Elsevier Science Inc.