Analysis of uncertainties in dose distribution due to geometrical deviation of target from isocenter in serial tomotherapy

The tomotherapy system in radiation therapy department of “V. Fazzi” hospital in Lecce (Italy) is a serial device. It means that the coverage of the target is obtained by moving the couch in and out the gantry position. It has been shown that the choice of target positioning respect to the isocenter reflects on dose distribution in terms of heterogeneities. The entity of the heterogeneities can reach 10% in abutment regions nearby the isocenter. Moreover, by using gantry rotations less than 300 degrees, hot and cold spots can be seen above and over the isocenter. Aim of the present work is to characterize the performance of the serial tomotherapy device in order to avoid, as more as possible, heterogeneities in the abutment regions.