Verification of single beam treatment planning using a ferrous dosimeter gel and MRI (FeMRI)

A method for analysing and comparing treatment planning system (TPS) data a nd ferrous dosimeter gel measurements evaluated with MRI (FeMRI) was develo ped, including image processing to final absorbed dose images. Measurements were analysed according to this method and FeMRI data were thereby compare d with the TPS-calculated dose distribution. For photons, differences betwe en FeMRI- and TPS dose data were mainly within +/- 2%. Minor shortcomings f ound in both the FeMRI system and the TPS are explained and discussed. For electron beams, there was an overall good agreement. It was found that the TPS underestimates the lateral scattering dose outside the primary beam, bu t the reported dose difference corresponds to a small spatial deviation (le ss than 2 mm). It is important to consider this single beam data comparison when the method is extended to more complicated situations, for example wh en using several beams.