Comparison of verification accuracy and radiation dose between megavoltage CT and kilovoltage cone-beam CT

Purpose: This study evaluated the difference in verification performance and organ doses between megavoltage computed tomography (MVCT) and kilovoltage cone-beam computed tomography (kV CBCT). Methods: Anthropomorphic phantoms of head-and-neck (H&N) and pelvic regions were scanned by the computed tomography-simulator. A common reference standard setup position for each phantom was determined. Markings of known deviations from the standard position in the lateral, longitudinal and yaw displacements were made on the phantoms. The verifications by kV CBCT and MVCT were conducted in the linear accelerator and helical tomotherapy treatment unit respectively. The phantoms were then shifted in steps according to the assigned different degree of positional deviations. The discrepancy between the detected data and the known data (δD) indicated the detection error of the verification system. Thermoluminescent dosimeters were used for dose measurements of kV CBCT and MVCT. Results: δD of the lateral translations and yaw rotation in kV CBCT of the H&N region were lower than MVCT. There were no differences in the error detection along longitudinal direction between the two verification methods. For H&N, the mean doses of the various organs were significantly lower in kV CBCT except the skin. For the pelvis, MVCT delivered significantly higher mean dose to the prostate and femoral heads.