Reducing radiation exposure to patients from kV-CBCT imaging

Background and purpose: This study explores methods to reduce dose due to kV-CBCT imaging for patients undergoing radiation therapy. Material and methods: Doses resulting from kV-CBCT scans were calculated using Monte Carlo techniques and were analyzed using dose-volume histograms. Patients were modeled as were CBCT acquisitions using both 360 and 200 gantry rotations. The effects of using the half fan bow-tie and the full fan bow-tie filters were examined. Results: Doses for OBI 1.3 are 15 times (head), 5 times (thorax) and 2 times (Pelvis) larger than the current OBI 1.4. When using 200 scans, the doses to eyes and cord are 0.2 (or 0.65) cGy and 0.35 (or 0.2) cGy when rotating the X-ray source underneath (or above) the patient, respectively. The 360 Pelvis scan dose is 1-2 cGy. The rectum dose is 1.1 (or 2.8) cGy when rotating the source above (or below) the patient with the 200 Pelvis scan. The dose increases up to two times as the patient size decreases. Conclusions: The dose can be minimized by reducing the scan length, the exposure settings, by selecting the gantry rotation angles, and by using the full fan bow-tie whenever possible. (C) 2010 Elsevier Ireland Ltd. All rights reserved. Radiotherapy and Oncology 97 (2010) 585-592