Comparison of prostate cancer treatment in two institutions: A quality control study

Purpose: To minimize differences in the treatment planning procedure between two institutions within the context of a radiotherapy prostate cancer trial. Patients and Methods: Twenty-two patients with NO MO prostate cancer underwent a computed tomography (CT) scan for radiotherapy treatment planning, For all patients, the tumor and organs at risk were delineated, and a treatment plan was generated for a three-field technique giving a dose of 78 Gy to the target volume. Ten of the 22 cases were delineated and planned in the other institution as well, The delineated volumes and dose distributions were compared. Results: All treatments fulfilled the trial criteria. The mean volume ratio of the gross tumor volumes (GTVs) in both institutions was 1.01, while the mean volume ratio of the planning target volumes (PTVs) was 0.88. The three-dimensional (3D) PTV difference was 3 mm at the prostate apex and 6-8 mm at the seminal vesicles. This PTV difference was mainly caused by a difference in the method of 3D expansion, and disappeared when applying an improved algorithm in one institution. The treated volume (dose greater than or equal to 95% of isocenter dose) reflects the size of the PTV and the conformity of the treatment technique. This volume was on average 66 cm(3) smaller in institution A than in institution B; the effect of the PTV difference was 31 cm(3) and the difference in technique accounted for 36 cm(3). The mean delineated rectal volume including filling was 112 cm(3) and 125 cm(3) for institution A and B, respectively. This difference had a significant impact on the relative dose volume histogram (DVH) of the rectum, Conclusion: Differences in GTV delineation were small and comparable to earlier quantified differences between observers in one institution. Different expansion methods for generation of the PTV significantly influenced the amount of irradiated tissue, Strict definitions of target and normal structures are mandatory for reliable trial results. (C) 1999 Elsevier Science Inc.