Maximum prostate contains zinc, selenium, cholesterol and isoflavones. It is intended for an enlarged prostate and maintaining prostate health. Since you have had cancer and radiation therapy you may not see a benefit and it is unlikely to help with burning urination.
Have you seen a urologist since your RT? What other urinary symptoms are you having (urgency, frequency, blood in urine?) RT therapy can cause burning on urination, but this comes on with the therapy and usually dissipates within three weeks. However, a long-term complication of RT to the prostate is urethral stricture, which persists and can cause burning on urination. A urologist can determine whether or not you have a stricture.