The effects of thermal treatments at 400 °C in oxygen or helium atmospheres at 180 bar on the radiation hardness of amorphous SiO2 are studied. The generation efficiency of several point defects under c irradiation is compared to that of the untreated material. All the effects on point defects generation here observed can be explained in terms of changes in the precursor sites. In particular it has been observed that the thermal treatments can change the precursors sites of point defects both through temperature and pressure related processes, not depending on the atmosphere, and through oxygen related processes creating oxygen excess sites. The presence of dissolved oxygen also inhibits some hydrogen related processes, as the generation of H(I) centers, probably by activating different reactions paths for hydrogen.