A comparison of ventilatory prostate movement in four treatment positions

Purpose: To ensure target coverage during radiotherapy, all sources of geom etric uncertainty in target position must be considered. Movement of the pr ostate due to breathing has not traditionally been considered in prostate r adiotherapy. The purpose of this study is to report the influence of patien t orientation and immobilization on prostate movement due to breathing. Methods and Materials: Four patients had radiopaque markers implanted in th e prostate. Fluoroscopy was performed in four different positions: prone in alpha cradle, prone with an aquaplast mold, supine on a flat table, and su pine with a false table under the buttocks. Fluoroscopic movies were videot aped and digitized, Frames were analyzed using 2D-alignment software to det ermine the extent of movement of the prostate markers and the skeleton for each position during normal and deep breathing. Results: During normal breathing, maximal movement of the prostate markers was seen in the prone position (cranial-caudal [CC] range: 0.9-5.1 mm; ante rior-posterior [AP] range: up to 3.5 mm), In the supine position, prostate movement during normal breathing was less than 1 mm in all directions. Deep breathing resulted in CC movements of 3.8-10.5 mm in the prone position (w ith and without an aquaplast mold). This range was reduced to 2.0-7.3 mm in the supine position and 0.5-2.1 mm with the use of the false table top. De ep breathing resulted in AP skeletal movements of 2.7-13.1 mm in the prone position, whereas AP skeletal movements in the supine position were negligi ble. Conclusion: Ventilatory movement of the prostate is substantial in the pron e position and is reduced in the supine position. The potential for breathi ng to influence prostate movement, and thus the dose delivered to the prost ate and normal tissues, should be considered when positioning and planning patients for conformal irradiation. (C) 2000 Elsevier Science Inc.