Conclusion
In this study the photoneutron contamination arising from the 18 MV Varian Clinac 2100C and Elekta Precise has been estimated using TLD600 and TLD700 pairs and the MCNPX code. The results represent the larger photoneutron production in Varian linac compared to Elekta due to the differences in the linac head configuration as well as the accelerating potential of the incident electrons impinging the target. According to the results, TLD600 and TLD700 pairs do not seem to be a reliable tool in the study of doses to patients from emitted photoneutrons in central axis, while the comparison of the MCNPX code results with other published data showed a coherent agreement, confirming the MCNPX code to be a valuable tool for studying photoneutron production along the beam axis.