Dosimetric evaluation of a beam matching procedure

Objective:The dosimetric characteristics for linear accelerators with the same model, and nominal energy are known to be very similar, as long as the machines are unaltered from the manufacturer’s original specifications. In this pre-liminary study, a quantitative investigation of the similarity in the basic photon and electron dosimetry data from the Siemens Oncor linear accelerators at our hospital (Children’s Cancer Hospital, Cairo, Egypt) was reported. Methods:The output factor (OF), wedge factors (WF), percentage depth dose (PDD), and beam profile for the 6 and 10 MV photon beams were measured. Results:The measured output factors varied by less than about 1%for each field size. The dif erence between the maximum and minimum PDD values at each depth was less than about 1%. The dif erence between the beam flattnes and symetry was no more than 1%at al of-axis distances. For electron the results showed that the PDD, OF, and the beam profiles were matched within 1%dif erences. Conclusion:These results strongly suggest that it is feasible to establish one reference photon and electron dosimetry data set for the two machines and nominal energies.