ULTRASOUND IMAGE FUSION FOR EXTERNAL-BEAM RADIOTHERAPY FOR PROSTATE-CANCER

Purpose: To determine whether real-time ultrasound imaging and targeti ng system for the treatment of prostate cancer was feasible, The initi al phase of this project included a study to develop and determine (a) software for the fusion of ultrasound images to standard x-rays obtai ned during simulation, and (b) the potential reduction in field size w ith real-time imaging. Methods and Materials: During 13 patient simula tions a transrectal ultrasound image was obtained, Orthogonal x-ray fi lms were acquired with the rectal probe in place, Both the x-ray and u ltrasound images were digitized and a fusion image was created of the prostate position in relation to the probe, bladder, and rectum, The t wo-dimensional area of the rectum, bladder, and prostate was determine d in the lateral projection, Potential conformal blocks were designed for the lateral portals in a four-field treatment technique. Results: The transrectal ultrasound probe enabled real-time prostate imaging, T he lateral field size can be reduced to 6.08 x 5.68 cm(2) +/- 0.62 x 0 .48 cm(2) from the standard 8 x 8 cm(2) field, The posterior rectal wa ll was physically displaced out of the lateral field, The area of the rectum included in the lateral field is 1.75 cm(2) +/- 0.85 cm(2). Con clusion: The prostate position can be determined with certainty on a r egular basis with transrectal ultrasonography, The amount of normal ti ssue in the high dose volume can be reduced, This approach may reduce acute and chronic morbidity and allow further dose escalation.