A table top suited for CT and radiotherapy

A radiotherapy table top was to be designed and manufactured, suitable for computer tomography in the same room. The aim was a distortion of the dose distribution by the table top of not more than 4% in small subunits of the target volume (TV) and less than 2% for the mean dose in the TV. Only negligible artifacts in the CT slices should occur in order to assure the exact relocalization of the TV. The table top manufactured of carbon fiber reinforced plastic was constructed by means of finite-element-algorithms. The trapezoidal shaped sandwich plate is supported with tapered beams. The small side of the table can penetrate a 60 cm CT-gantry. When turned, the table top allows large ap-pa opposed fields without irradiating through the beams. Transmission measurements were performed with an ionization chamber under different irradiation angles to determine the influence of the beams and the covering plate. Additionally, a portal imaging device (PID) was used for comparison. It was found that the deflection and torsion of the carbon fiber table top was smaller than for the original. The transmission of the sandwich plate was 97.5% (18 MV) and 96.5% (6 MV photons) respectively. If the irradiation of the beam walls can not be avoided the transmission is not in a critical range. The CT-slices show only minor artifacts along the side walls of the beams. The localization of the tumor or the TV is not restricted.