Your state of anxiety over the ultrasensitive test results is the reason why some doctors, including mine at JH, recommend not using the test. They claim that there is a lot of statistical noise in the results. As a consequence I started out with the regular test but asked for the ultrasensitive at 6 months after surgery because I wanted more detail to decide whether to do radiation. As my PSA was 0.08 I decided to go for it, if it had been lower I might have decided against it.
As you say if you were getting the regular test you would be considered undetectable at this point. So in your case, as you already had radiation you might want to ask your doctor whether a PSA rise below 0.1 would have any effect on your immediate treatment. If they say no then I can see why you might want to go to the regular test.
Age 60, Dx 11/2013, PSA 5.0, Biopsy 4 cores: 3+3, 4+3, 4+4, second opinion found some 4+5.
RRP 1/2014, G9(4+5), negative margins, pT3a, EPE:yes, Seminal ves.: no, Lymph nodes: 14 negative. PSA (3/2014) < 0.1 (6/2014) 0.08. Adjuvant radiation started 8/2014, PSA = 0.06 (10/2014), 0.05 (1/2015)