Evaluation of Fiducial Marker Migration and Respiratory-Induced Motion for Image Guided Radiotherapy in Whole Breast Irradiation.

Abstract

Abstract Purpose: Image guided radiation therapy (IGRT) may be beneficial to improve set up accuracy and reduce treatment margins, therefore improving efficacy while decreasing long term toxicity of whole breast irradiation (WBI). In order to assess if intraparenchymal fiducials can facilitate the use of IGRT, this study quantifies fiducial motion over the normal course of whole breast irradiation.Materials and Methods: On a prospective IRB-approved protocol, fiducials were placed in fourteen patients who were then treated with 3D conformal WBI. Three or four intraparenchymal gold fiducial markers were placed in each patient at the periphery of the surgical bed intraoperatively. Free breathing 4D CT image sets were obtained at pre-treatment simulation and then every two weeks over a six week course of treatment. Each fiducial marker was contoured at end-inspiration and end-expiration on all 4D CT image sets. The effects of respiration induced motion were assessed by comparing the positions of the fiducials between inspiration and expiration. Overall fiducial migration was determined by comparing the relative positions of each marker to one another from the pre-treatment and post-treatment 4D CT image sets.Results: The 4D CT image sets were acquired over a period of 55±4 days with a range of 49 to 60 days. The respiration induced fiducial motion, as measured by the average change in the fiducials' center of mass, was 0.8±0.6 mm with a range of 0 to 2.2 mm. The average fiducial displacement over the course of treatment as determined from relative seed position from the image sets was 1.5±1.2 mm with a range of 0.1 to 3.3 mm for all individual fiducials with 71% of the fiducials moving closer to each other and 29% away from each other.Conclusions: The preliminary results of using gold fiducials for breast IGRT are promising. Fiducial position was very stable during treatment, and there was very little respiration induced motion. Using IGRT, there is the potential to improve the accuracy of daily set-up and to reduce margins in WBI. Better tumor bed localization and reduced margin size will decrease the volume of normal tissue treated, which may translate into improved local control by ensuring accurate coverage of the target volumes throughout the treatment course and improvement in cosmesis and other long term toxicities. Citation Information: Cancer Res 2009;69(24 Suppl):Abstract nr 4113.