Analysis of CBCT Shift Data from Head-and-Neck Cancer Patients

• Activity Number: 615
• Type: Contributed
• Date/Time: Thursday, August 2, 2012 : 8:30 AM to 10:20 AM
• Sponsor: Biometrics Section
• Author(s): Yijiang Pan*+ and Yi Zhang and Xiaoli Tang
• Companies: INC Research and The University of North Carolina at Chapel Hill and The University of North Carolina at Chapel Hill
• Keywords: treatment margin ; CTV-to-PTV margin ; CBCT shift data

Abstract

Prior to the radiation therapy, CT images are obtained to locate the tumor and design an optimal treatment plan for the patient. To ensure the accurate targeting of the tumor, physician design the treatment plan to treat tumor plus a margin so that the daily positioning variation won't miss partial or the whole tumor. The goal of this paper is to help physicians to select treatment margin adaptively for individual patients instead of using the "rule of thumb" 0.3 cm margin. We analyze the daily CBCT shift data collected by UNC Radiation Oncology investigators for head and neck cancer patients. The magnitudes of shifts are derived from shifts along the medial-lateral (ML), superoinferior (SI), and anteroposterior (AP) directions respectively. The clinical target volume (CTV) to planning target volume (PTV) margin expansions are calculated and compared with isotropic 0.3 cm margin around the CTV. Additional analyses are conducted to compare shifts at different directions, explore the longitudinal effect, and evaluate the influence of other patient characteristics such as age, gender, etc.. Our results suggest using the average shifts during the baseline (Week 1) as treatment margin.