SU‐E‐T‐306: Study of the Reduction Technique for the Secondary Cancer Risk Due to Cone Beam CT in Image Guided Radiotherapy

Abstract

Purpose:This study evaluated the effectiveness of a thin lead sheet based simple shielding method for imaging doses from cone beam computed tomography (CBCT) in image‐guided radiotherapy (IGRT).Methods:The entire body, except for the region scanned by CBCT, was shielded by wrapping in a 2 mm lead sheet. Reduction of secondary doses from CBCT was measured using a radio‐photoluminescence glass dosimeter (RPLGD) placed inside an anthropomorphic phantom and changes in secondary cancer risk due to the shielding effect were estimated using BEIR VII model.Results:Doses to out‐of‐field organs for head‐and‐neck, chest, and pelvis scans were decreased 15∼100 %, 23∼90 %, and 23∼98 %, respectively, and the average reductions in lifetime secondary cancer risk due to the 2 mm lead shielding were 1.61, 10.4, and 12.8 persons per 100,000, respectively.Conclusion:This study suggests that a simple thin lead sheet based shielding method results in a non‐negligible reduction of secondary doses to out‐of‐field regions for CBCT.