Various methods of measuring the RFO have been discussed, and may be dependent upon the delivery method (static or dynamic modulation), and physical size of the leaves.
These methods include: (1) measuring the distance between the nominal and radiation field edge with a MLCdefined field size, (2) optimizing flatness of dose profiles obtained from sweeping leaves with a narrow band of aperture,(3) matching calculated gap width (or slit) profiles with measured profiles, or (4) adjusting the parameter in order to optimize accuracy in treatment delivery.
Within these methods,the analysis of the RFO becomes more complex. As shown in Fig.2, when leaves are moved from left to right with identical start and stop positions, exposure through the leaf gaps (if any) leads to an extra darkening of the film at the abutment of fields