MO‐F‐BRB‐05: Dose Calculation of KV Cone‐Beam CT by Use of Pinnacle

Abstract

Purpose: For dose calculation of kV Cone Beam CT (CBCT), Monte‐Carlo simulation method is the best for accuracy. However, Monte‐Carlo method is very time‐consuming. Therefore it is not practical to be used in daily clinical work. The CTDI has been a useful tool to estimate dose for human bodies, however, this index is not intended to calculate the dose distribution in our bodies. Clearly, we need a reasonably fast and accurate calculation method. We propose a new calculation method by use of super position algorithm in Pinnacle. We calculated low‐energy kernels in the range of 10– 100 keV and implemented them in Pinnacle3 and estimated the dose from CBCT. Methods: We used a user code of EGSnrc to make low energy kernels. To implement a cross section of low energy photons in the kernels, a cross section table on NIST XCOM was used. Then we implemented these kernels for 10–100 keV in Pinnacle3 and the modeling of the kV cone beam was performed. In order to validate the accuracy of them, we calculated a PDD and beam profiles in a water phantom and compared them to the measured values. To simulate the dose distribution in a human body, we used a RANDO phantom and measured the dose with glass dosimeters. Results: The comparison of the results shows good agreement of the calculated beam profiles and measured values. Estimated maximum dose in the body from the RANDO phantom measurement was about 2 cGy that is about 1 % of the clinical dose. The discrepancy between glass dose and calculated dose by Pinnacle is within 20–30 %. Conclusions: A fast and reasonably accurate dose calculation method by use of Pinnacle3 was proposed and validated. This is the first step toward a total treatment planning involving CBCT dose in clinical use.