Impact of the Body-Mass Factors on Set-up Displacement in Patients Treated with Pelvic Irradiation for Gynecological Cancer with Daily On-Line Image Guidance

Abstract

Purpose: This study was to determine the impact of the body-mass factors on magnitude of setup displacements in patients treated with pelvic intensity modulated radiotherapy (IMRT) for gynecological cancer.Methods: Using the alignment data of daily on-line On Board Imaging (OBI) from image-guided radiotherapy (IGRT), the clinical data of 22 patients treated with pelvic IMRT for cervical or endometrial cancer was analyzed. Body-mass factors included body weight, body height, body mass index (BMI), waist circumference, waist thickness, hip circumference and hip thickness. Setup displacements for each patient were assessed by four components: namely systemic error (SE), and random error (RE), through three translational directions and couch rotation (CR). The median values for the body-mass factors were used as cutoff points to divide the groups. The Mann-Whitney U test was conducted to assess the predictive role of these factors for the set-up errors.Results: Population SE and RE were 2.8 mm, 2.6 mm, 2.4 mm and 1.7 mm, 1.4 mm, 1.3 mm in the superior-inferior (SI), anterior-posterior (AP) and medial-lateral (ML) directions, respectively. The SE and RE for rotation (CR) was 0.33 and 0.25 degree. Larger waist circumference (WC) was significantly correlated with greater SI-SE (p = 0.02), and CR-RE (p = 0.013), whereas larger hip circumference (HC) with greater SI-RE (p = 0.045), and CR-RE (p = 0.018). Higher BMI was associated with greater, CR-RE (p = 0.006). Body height correlated with AP-SE (p = 0.036).Conclusions: To reduce setup displacements in women with gynecological cancer requiring pelvic IMRT, the use of on-line IGRT should be recommended for those who have a WC ＞ 80.5 cm or a HC ＞ 88.8 cm, or a BMI ＞22.1 Kg/m^2.