AbstractID: 8083 Title: IMRT QA using Superimposed Film/MOSFET Technique
Ion chambers and films are often used in IMRT QA. Due to the complexity of IMRT
dose distribution, the ion chamber size can easily cause variations and uncertainties in
dose measurement. Film is helpful to verify dose distribution pattern. But many steps are
required to obtain accurate quantitative dose information. A superimposed film/MOSFET
phantom was developed for routine IMRT QA to obtain multiple quantitative point doses
and relative dose distribution pattern verifications. The phantom contains multiple
MOSFET detectors situated on two orthogonal planes. One of the two planes containing
five detectors is the dividing plane of two sub-phantoms where the film is housed. An
IMRT plan is applied to the phantom and the phantom is then exposed per IMRT plan
with a film placed between the two sub-phantoms. As such, the five detectors are in
direct contact with the film. All point doses are accessed through the MOSFET reader
and compared to the computed data. The isodose curves generated from the RTP
computer are then superimposed on the film aligned by the five detectors. The dose
distribution pattern is visually compared with the film density pattern. This assures the
orientation of the dose distribution, while the five detector points superimposed on the
film and the other detectors distributed on the orthogonal plane are used for direct dose
verifications. Since the dose level of each isodose line is quantitatively obtained through
MOSFET detector, the HD curve is not needed during the film analysis.