Impact of Body Mass Index and Abdominal Subcutaneous Fat Thickness of Setup Errors in Postoperative Cervical Cancer Patients Underwent Daily Image-Guided Radiation Therapy

Abstract

The purpose of this study was to investigate the relationship between body mass index (BMI) and abdominal subcutaneous fat thickness (SFT) and setup errors for postoperative cervical cancer patients treated with adjuvant radiotherapy, aiming to provide reference for precise individual radiotherapy.Ninety-two postoperative cervical cancer patients underwent volumetric-modulated arc therapy (VMAT) in Peking Union Medical College Hospital between August 2019 and August 2020 were enrolled. The BMI and SFT were measured before treatment. The daily shifts, systematic errors, and random errors in the anterior-posterior (AP), superior-inferior (SI), and left-right (LR) directions were recorded. Planning target volume (PTV) margins were calculated based on the equation of MPTV = 2.5Σ + 0.7δ among each BMI and SFT categories. Receiver operating characteristics (ROC) curve, linear regression, spearman rank correlation coefficient, and Kolmogorov-Smirnov test were employed.The median BMI for all patients was 22.1 kg/m2 (range, 15.2-29.7 kg/m2). Of the 92 patients, 9.8% (n = 9) were underweight; 67.4% (n = 62) were normal weight; 22.8% (n = 21) were excess weight. There was a strong correlation between BMI and SFT (P < 0.001). SFT level of underweight < 21.3 mm and SFT level of excess weight ≥ 26.3 mm were observed in 31 and 37 patients, respectively. On linear regression, mean absolute SI shifts were moderately correlated with BMI (P = 0.044) and SFT (P = 0.046). Mean absolute AP and LR shifts did not significantly correlate with BMI and SFT. The margin of AP direction was reduced to 4 mm to significantly diminish the inclusion of rectum in the PTV.For postoperative cervical cancer patients with excess weight or heavy abdominal SFT, a PTV margin of 10 mm in SI direction may be insufficient in the absence of image-guided radiation therapy (IGRT). A PTV margin of AP direction should be moderately reduced while internal target volume (ITV) is considered.D. Wang: None. K. Hu: None. F. Zhang: None.