"you mentioned 0.1 - is that a "magic" mark? or could the psa find a level even later at i dont know 0.3 or 0.6?"
The magic mark is 0.2 although once you get to 0.1 and keep rising it is reasonable to assume that you are going to reach 0.2 sooner or later. The reason is that very small amounts of PSA are produced in other parts of the body (e.g prostate specific antigen is not prostate specific!) but only in amounts smaller than 0.1 Even women can produce PSA; it can be present in breast milk, for example.
The complex bit is that the magic mark means different things in different circumstances. For a man who has had his prostate removed, 0.2 (or 3 rises above 0.1) is the point at which he is said to have biochemical recurrence. The same would be said of a man who has had his prostate removed and then had salvage RT. However, in the second case, although BCR may be confirmed at 0.2 the onco may delay restarting treatment until the PSA is 5 or 10 or the doubling time reaches less than 6 months. For a man who has had RP and reaches BCR, many oncos want to start treatment as soon as it is confirmed.
For a man who still has his prostate and has had radiotherapy / brachytherapy, BCR would be 2.0 plus his lowest ever reading