SU-E-I-09: Patient Organ Doses from KV-CBCT Acquisitions as Function of Patient Size and Scan Protocols

To investigate the organ dose dependence on patient size and position resulting from an image guidance procedures. Depending upon the degree of variability between patients, the feasibility tabulating the organ dose based upon patient size and imaging acquisition procedure. Such tables could be useful in estimating and accounting for organ dose resulting from imaging procedures.

Monte-Carlo methods were used to calculate radiation dose to the patient resulting from a kV CBCT imaging scan based upon CT image data. A Python program was created to generate DVHs using the calculated 3D dose matrix and the DICOM-RT Structure Set for the patient. A number of head and pelvic CT scans were used in the study, and the resulting DVHs were analyzed to determine the variation of organ dose as a function of patient size.

For the head scans in supine position, the average of the mean doses for some organs, along with the standard deviation in those mean doses, are as follows:Brainstem: 0.25cGy +/- 0.02cGyBrain: 0.26cGy +/- 0.01cGyOptic Chiasm: 0.22 +/- 0.03cGyBone: 0.55 +/- 0.04cGyAnterior Skin: 0.13 +/- 0.05cGyPosterior Skin: 0.23 +/- 0.06cGyEye: 0.11cGy +/- 0.05cGyFor Pelvic scans, dose to organs such as rectum, have likewise been shown to have some variation between patients of different sizes.

The results show that it is possible to express organ dose as a function of imaging procedure, imaging device, scan location, body size, and orientation. For example, using a standard head scan on an OBI 1.4 system, the dose to the eye ranged from 0.05-0.20cGy, depending upon the patient size. Considering the amount of imaging dose compared to the therapeutic dose, this study indicates that organ dose could be estimated by using tabulated values based upon the scan procedure and patient size.