Ultrasound-based stereotactic guidance of precision conformal external beam radiation therapy in clinically localized prostate cancer

Objectives. Use of external beam radiation fields that conform to the shape of the target improves biochemical control in prostate cancer by facilitat ing dose escalation through increased sparing of normal tissue. By correcti ng potential organ motion and setup errors, ultrasound-directed stereotacti c localization is a method that may improve the accuracy and effectiveness of current conformal technology. The purpose of this study was to quantify the precision of the transabdominal ultrasound-based approach using compute d tomography (CT) as a standard. Methods. Thirty-five consecutive men participated in a prospective comparis on of daily CT and ultrasound-guided localization at Fox Chase Cancer Cente r. Daily CT prostate localization was completed before the delivery of each final boost field. In the CT simulation suite, transabdominal ultrasound-b ased stereotactic localization was also performed. The main outcome measure was a three-dimensional comparison of prostate position as determined by C T versus ultrasound. Results. Sixty-nine daily CT and ultrasound prostate position shifts were r ecorded for 35 patients. The magnitude of difference between the CT and ult rasound localization ranged from 0 to 7.0 mm in the anterior/posterior, 0 t o 6.4 mm in the lateral, and 0 to 6.7 mm in the superior/inferior dimension . The corresponding directed average disagreements were extremely small: an terior/posterior, -0.09 +/- 2.8 mm SD; lateral, -0.16 +/- 2.4 mm SD; and su perior/inferior, -0.03 +/- 2.3 mm SD). Analysis of the paired CT-ultrasound shifts revealed a high correlation between the two modalities in all three dimensions (anterior/ posterior r = 0.88; lateral r = 0.91; and superior/i nferior r = 0.87). Conclusions. Ultrasound-directed stereotactic localization is safe and as a ccurate as CT scanning in targeting the prostate for conformal external bea m radiation therapy. The application of this technology to current conforma l techniques will allow the reduction of treatment margins in all dimension s. This should diminish treatment-related morbidity and facilitate further dose escalation, resulting in improved cancer control. (C) 2000, Elsevier S cience Inc.