Equivalent doses for gynecological patients undergoing IMRT or RapidArc with kilovoltage cone beam CT

PurposeTo investigate in-field and peripheral kilovoltage cone beam CT (CBCT) doses in gynecological patients in comparison with IMRT or RapidArc scatter and linac leakage doses.Materials and methodsMonte Carlo codes BEAMnrc/DOSXYZnrc were used to simulate dose for daily use of kV CBCT in patients undergoing adjuvant pelvic radiotherapy for uterine or ovarian malignancies. Biological effectiveness was accounted for using a lineal energy based quality factor. Organ equivalent doses (OED) within the treatment field were modeled with linear-exponential, plateau and linear dose response curves. CBCT doses in peripheral regions were compared with IMRT and RapidArc scatter doses as well as linac leakage doses.ResultsCBCT doses in peripheral regions were on the order of linac leakage doses and one order of magnitude lower than IMRT or RapidArc scatter doses. OEDs increased slightly, leveled off or even decreased within the treatment field with the addition of CBCT doses according to different dose response models.ConclusionThe results of this study indicate that patients undergoing IMRT or RapidArc treatments with daily use of kV CBCT imaging are not subjected to additional risk due to CBCT imaging doses.