Computed tomogram prior to prostatectomy. Advantage in defining planning target volumes for postoperative adjuvant radiotherapy in patients with stage C prostate cancer?

Purpose: To evaluate the influence of a preoperative computed tomogram (CT) on delineation of the planning target volume (PTV) for adjuvant radiation therapy of pT3 pNO prostate cancer. Patients and Methods: PTVs of ten patients who had an additional preoperative CT examination were contoured by three independent radiation oncologists. PTV included the former prostatic bed and seminal vesicles with a safety margin. First PTVs were drawn without knowledge of the preoperative CTs and in a second attempt, this procedure was repeated with these CTs available for visual comparison. Changes in PTV dimensions for every patient were analyzed. Results: In 93% of all PTVs there was a decision to increase the PTV after viewing the preoperative CT images. Mean PTV length increased from 7.3 to 8.4 cm and PTV volumes expanded 26% from 244 to 308 cm3. These differences were statistically significant for all three participating radiation oncologists. Conclusion: Planning target volume definition probably is a critical factor in adjuvant radiation therapy after radical prostatectomy. As there is a considerable incertaincy in PTV definition a preoperative CT is helpful and therefore may have beneficial influence on results. (orig.)