Patient dose evaluation for kilovoltage cone beam CT in image-guided radiotherapy

Objective To evaluate patient dose from linac-integrated kilovolt cone beam CT (CBCT) imaging in image-guided radiotherapy. Methods Air CT dose index (CTDI air ) and weighted CT dose index (CTDI w ) were measured with PTW TM30009 CT ion chamber in the air, in T40017 head phan-tom and T40016 body phantom, respectively. During the measurement, different combinations of tube volt-age, current, exposure time per frame, collimator, and gantry rotation range of ⅩⅥ CBCT were used. Dose length products (DLP) were subsequently calculated. Normalized CTDI was then compared to ACQSim sim-ulator CT. Results Both CTDI air and CTDI w depended quadratically on the voltage, while linearly on mAs. CTDI w and DLP had close relation with the collimator and the gantry rotation range. Normalized CTDI w for ⅩⅥ CBCT under routine clinical condition was lower than that of ACQSim simulator CT . Conclusions CTDI w , being convenient and reliable for measurement, can be used to assess the patient dose during CBCT imaging, Regular measurement should be performed in QA & QC program. Optimal image parameters should be chosen to reduce the scanning range and patient dose. Key words: Radiotherapy;  image-guided; Tomograph;  X-ray computed;  cone beam; Tomograph;  X-ray computed; dose index; Dose length product