Dosimetric measurements are often required in radiation fields containing a mixture of high and low LET components such as the secondary dose from photons and neutrons to patients treated with photon beams with energy > 10 MV, and in passively scattered proton and carbon beams. The concern is the potential induction of secondary cancers due to the high relative biological effect of neutrons related to its high LET. Absorbed dose measurements in these mixed radiation fields is challenging because most detectors have different sensitivities to both types of radiation. Using the sensitivity difference between the two main temperature peaks at 210 and 280 0C to LET radiation in LiF thermoluminescent dosimeters (TLDs), the high and low LET dose components can be determined. By measuring the area under the two peaks the different dose components can be extracted. Also, the QF can be obtained using TLD600 and 700 in a 10 inch Bonner sphere exposed to secondary radiation. Measurements of the out-of-field photon and neutron doses in 15 and 18 MV photon beams and 160 and 250 MeV proton beams were obtained. From the QF and LET measurements information on the relative biological effectiveness of the secondary radiation can be inferred.