Patient positioning using detailed three-dimensional surface data for patients undergoing conformal radiation therapy for carcinoma of the prostate: a feasibility study.

Abstract

PURPOSE: The increasing complexity of radiotherapy highlights the need for accurate setup. This paper assesses the potential of position corrections, derived from the three-dimensional (3D) surface of the patient, in reducing positioning errors in patients undergoing conformal radiation therapy of the prostate. METHODS AND MATERIALS: Twenty patients undergoing conformal radiation therapy for prostate cancer had planning computed tomography (CT) scans and then weekly treatment CT scans over the course of their treatment. Patients were positioned on the CT table using three coplanar tattoo marks used for patient setup on the accelerator. Surfaces were computed from the planning CT (planning surface), and the treatment CT (treatment surfaces). Using a surface matching utility, the planning and treatment 3D surfaces were compared. The prostate was implicitly localized based on surface matching of the external contour and by matching the bony anatomy. The resultant prostate displacement after correction was assessed for the two localization methods. RESULTS: Correcting patient position via the surface comparisons reduced the standard deviation of prostate displacement with respect to the patient isocenter in the lateral and anterior/posterior directions. In the lateral direction, prostate and surface motion was highly correlated (r = 0.96). In the anterior/posterior direction the corrections from the surface data were as effective as those derived from the bony anatomy. CONCLUSION: Detailed surface data can aid the positioning of patients receiving conformal radiation therapy to the prostate by reducing the displacement of the target from the intended treatment position. This study shows that surface corrections can be as effective as those derived from bony anatomy, and may be exploited where definition of bony anatomy is difficult.