Fiducial-based image-guided radiotherapy for whole breast irradiation

Abstract

Objectives: Image-guided radiation therapy (IGRT) improves setup accuracy and reduces treatment margins, potentially improving efficacy while decreasing long-term toxicity of whole breast irradiation (WBI). This study quantifies intraparenchyma fiducial motion and utility during the course of WBI. Methods: On a prospective IRB-approved protocol, textured gold fiducials were placed intraoperatively at the periphery of the surgical bed in 25 patients who then received 3D conformal conventional WBI. Free breathing and 4D CT image sets were obtained at pre-treatment simulation and at 6 weeks of treatment. Respiration-induced motion was assessed by comparing fiducials' position between inspiration and expiration. Fiducial migration and setup variation were determined by comparing the relative positions of each marker from the pre- and post-treatment megavoltage and 4D CT image sets. Results: Average intrafraction respiratory motion on 4D CT image sets was 0.1 mm. Variation in separation between fiducial pairs compared to simulation CT was on average 0.7 mm. The position of the seroma center was stable with respect to the center of mass (COM) of the fiducials throughout treatment. Based on daily megavoltage portal images, the average variation in the fiducial COM relative to the vertebral body landmark was 9.4 mm. The average variation of the seroma relative to fiducial COM from the 4D CT data was 6.2 mm. Conclusions: Fiducial position was stable during treatment, and there was minimal respiration-induced motion. Using IGRT may improve the accuracy of daily setup and reduce PTV margins in WBI. Better tumor bed localization and reduced margin size will decrease the volume of normal tissue treated, which may translate into improved outcomes and lower toxicity. © 2013 Springer-Verlag Berlin Heidelberg.