On the verification of the incident energy fluence in tomotherapy IMRT

For any radiotherapy verification technique, it is desirable that issues with the accelerator, multileaf collimator and patient position be detected. In previous works, an effective method for this level of verification was presented. This paper identifies second-order issues affecting the part of the process in which the incident energy fluence is verified. These problems will affect any rotational intensity-modulated radiotherapy delivery that divides each rotation or arc into projections; however the solutions offered in this paper are specific to the method previously developed. The issues affecting the energy fluence verification method include leaf bouncing, delivery implementation and leaf latency. All three matters were found to introduce small errors in the verified energy fluence values for a small fraction of leaf states. The overall effect on the deposited dose over the course of a rotational delivery involving thousands of beam pulses per rotation is negligible. Regardless, effective correction strategies are presented; these are utilized in order to characterize both the delivered energy fluence and deposited dose as accurately as possible.