AbstractID: 7766 Title: Computer verification of stereotactic radiotherapy and intensity modulated arc
therapy plans
Rotational arc therapy, such as micro-MLC stereotactic radiotherapy, MLC-based
conformal arc therapy and intensity modulated arc therapy, is a technique that delivers a
dose distribution by moving the MLC leaves while rotating the gantry. Because of the
inherent complexity of the modality, an efficient and robust treatment plan validation
becomes important. We present a method to use computer simulation for second check of
the monitor unit calculations. The software program reads in the MLC/micro-MLC based
arc delivery file and re-calculates the dose at the isocenter based on the MU setting from
the treatment planning system and on the TMR and OAR tables. When static MLC fields
are used, individual SSD and depth are used. While for dynamic arc treatments, the
effective depth is used, with the monitor unit divided among the total arc degrees for the
individual arc. The QA tool was tested on a head phantom and several clinical cranial
cases using the BrainLab radiosurgery system. The BrainLab calculated dose was
compared with the measured dose, and the dose calculated by our MU calculator. The
program was also used for 3D conformal arc prostate cases, and results were compared
with those calculated by the FOCUS treatment planning system. The monitor unit
calculation results agree within 3%, with the majority of the calculations agree within
1%, with the Focus treatment planning system. Comparison of our measurements and
calculations with the theoretical predictions indicated that the system is robust and
suitable for routine plan validation in rotational arc therapy.