Abstract
Purpose: To quantitatively assess the differences between supine and prone positions on normal tissue dose in different clinical target volumes (CTVs) in irradiation of prostate cancer.
Materials and Method: Eighteen patients with prostate cancer underwent treatment planning CT scans in the supine and prone positions. The prostate only (PO) and prostate plus seminal vesicles (PS) were delineated as CTVs. A six-field plan was generated and compared concerning the rectum and bladder dose-volume histogram in both treatment positions in each of the respective CTVs. The distance between the PS and rectum in both treatment positions was also measured.
Results: In some cases, the distance between the seminal vesicles and rectum changed by more than 20 mm in the transition from supine to prone, although the change in distance was about 5 mm in many cases. Significant differences in rectal V90 were observed only in PS between the supine and prone positions (p=0.0015). However, significant differences in bladder V90 were not observed in both CTVs between the supine and prone positions.
Conclusion: The effect of rectal dose reduction using the prone position in irradiation of prostate cancer depends on the range of CTV.
