ABSTRACT
Objective:
To evaluate the
dose calculation accuracy of
cone-beam CT (CBCT) image by actual measurement
method.
Methods:
CBCT images of 60
patients in the Second Affiliated
Hospital of Soochow
University from September, 2021 to May, 2022 were retrospectively analyzed. CBCT images of full-fan and half-fan scanning of the
head, half-fan scanning of the
chest and
pelvis were obtained by the Varian OBI system. Hounsfield unit -
electron density (HU-ED) curves corresponding to the scanning conditions were established with CIRS
electron density phantom. The
radiotherapy plans were designed on the CBCT images, and the
dose calculation results of the
detection point were compared with the ionization chamber measurement results to analyze the
dose error. Then, three-dimensional
dose verification system was adopted to detect the accuracy of the CBCT image
radiotherapy plans implementation process in 60
patients, and the accuracy of
dose calculation was verified according to the D 99%, D mean, D 1% of target volume, D mean and D 1% of
organs at risk (OAR), and the γ pass rate.
Results:
In point
dose detection in phantom, the
dose calculation errors of CBCT images in the above four scanning patterns were -1.06%±0.87%、-1.67%±0.86%, 0.91%±0.73%, -1.54%±0.90%, respectively. In dosimetric verification based on
patients' CBCT image
treatment plan, the mean difference of D mean, D 99%, and D 1% of
planning target volume (PTV) in all scanning modes were not higher than 2%, and the D mean and D 1% differences of other OAR were not higher than 3%, except for the lens of
patients in the
head. The average γ values of target volume and OAR were less than 0.5 under the criteria of 3%/2 mm.
Conclusions:
Under the condition of correctly establishing HU-ED curves, intensity-modulated
radiation therapy (IMRT) /
volumetric-modulated arc therapy (VMAT)
planning based on CBCT images can be employed to estimate and monitor the actual
dose to target volume and OAR in adaptive
radiotherapy. Full-fan scanning patterns can further improve the accuracy of
dose calculation for the
head of
patients.