Qclin;Qmsr for several small detectors and for two linear accelerators using Monte Carlo simulations

clin;fmsr Qclin;Qmsr was evaluated. Moreover, a MC analysis of the parameters that influence the change of k f clin;fmsr Qclin;Qmsr as a function of field dimension was performed. A detailed analysis of uncertainties related to the measurements of the field specific output factor and to the Monte Carlo calculation of k f clin;fmsr Qclin;Qmsr was done. Results: The simulations demonstrated that the correction factor k f clin;fmsr Qclin;Qmsr can be considered inde- pendent from the quality beam factor Q in the range 0.68 60.01 for all the detectors analyzed. The k f clin;fmsr Qclin;Qmsr of PTW 60012 and EDGE diodes can be assumed dependent only on the field size, for fields down to 0.5 � 0.5 cm 2 . The microLion, and the microchambers, instead, must be used with some caution because they exhibit a slight dependence on the radial FWHM of the electron source, and therefore, a correction factor only dependent on field size can be used for fields � 0.75 � 0.75 and � 1.0 � 1.0 cm 2 , respectively. The analysis of uncertainties gave an estimate of uncertainty for the 0.5 � 0.5 cm 2 field of about 0.7% (1r )f ork f clin;fmsr Qclin;Qmsr factor and of about 1.0% (1r) for the field output factor, X f clin;f msr Qclin;Qmsr , of diodes, microchambers, and microLion. Conclusions: Stereotactic diodes with the appropriate k f clin;fmsr Qclin;Qmsr are recommended for determining X f clin;f msr Qclin;Qmsr of small photon beams. V C 2011 American Association of Physicists in Medicine.