Purpose: Macro electron Monte Carlo(eMC version 13) was validated in small beam output factors as well as depth dose.
Methods: eMC calculation was done on five electron beam energies with standard cones and 3cm x 3cm insert of each cone on Varian Truebeam linac using <2.5mm calculation grid and 3D Gaussian smoothing with a low level. Ion chamber measurement was performed at the depth of dose maximum near the central axis for each field and along the depth for the insert within the cone of 10cm x 10cm and the 10cm x 10cm cone(depth dose for 6, 9, 12MV only). eMC calculated dose of the insert was compared with ion chamber dose after normalization at the dose maximum of 20cm x 20cm. The ion chamber dose was all acquired after conversion from ionization charges using stopping power ratios between each measurement depth(dose maximum of 3cm x 3cm and that of each standard cone for each energy). For the depth dose, the pin-point chamber(2.9mm diameter, Sun Nuclear) was used. For the output, a standard scanning chamber(4.75mm diameter) was used.
Results: The output factor of 3cm x 3cm agreed with ion chamber within a maximum 2.3% difference that occurred for 6MV and 9MV both under the 10cm cone. Depth dose by eMC agreed with ion chamber dose within 2 mm maximum at the 50% range, occurred for the insert under the 10cm cone, limited by both calculation and measurement uncertainties.
Conclusion: eMC was found to produce accurate small beam output factors and reasonable depth doses for all energies. More study will be done using smaller beams than 3cm x 3cm.