Two effects here.
The hormone therapy will temporarily stop you from producing semen, and it will take some months after recovery of Testosterone for this to reverse. It also does some permanent damage to the sperm production in the Testicles, so your sperm count would be lower.
The radiotherapy will permanently impact your ability to produce semen. The healing cycle after radiation induces widespread fibrosis of the prostate which prevents contraction and blocks the fine tubes, and parts of it where the cancer was will have lost their PSA generating cells. On average, prostates are only about 5% effective after radiotherapy, although that's skewed to most men not being able to produce any semen, and to a small number of men who might recover up to about half their semen. It's likely this effect is more pronounced the higher power (and fewer) radiotherapy doses you had, which is known to produce more fibrosis.
The other thing is semen has several components. 50% (thick white) comes from the seminal vesicles, 40% from the prostate (clear fluid which is mainly PSA), a tiny amount from the testicles carrying sperm, and an amount from Cowpers glands (precum). All except the last pass through and are mixed in the prostate. Even if you do have some semen after treatment, it's very likely some of the components will be completely missing so it will look different. This also means the semen is unlikely to be viable from a fertility perspective, but not so unlikely that you can rely on it as a contraceptive. Precum from Cowpers glands is less likely to be impacted by radiotherapy.