Berechnung und messung der spezifischen dosis bei irregulärer feldformung durch lamellenblende und individualblende

Output factors of irregularly shaped beams created by multileaf collimator (MLC) or individually moulded blocks were measured and compared with the results of a commercial treatment planning system. Rhombs and triangles of various sizes were created by blocking half of the area of the corresponding open fields. Taking into account the tray factor, the measured output factors using individually moulded blocks were between 2% and 5% higher than the corresponding values for the MLC. In most cases deviations less than 2% were found when comparing output factors calculated by the treatment planning system with the measured values. However, rhomb-shaped fields with diagonals of 7 cm or 5 cm showed deviations of 3% or 8%, respectively.