I never had any issues with it when I did five rounds of SBRT last spring at 59 years old. In fact, both my RO and my urologist encouraged sexual activity whenever possible during the entire treatment process, since the penis can be a "use it or lose it" organ. My urologist explained to me and my GF/partner that the penis can atrophy over time as we age and may experience ED. And hormone (ADT) therapy can accelerate that process, so "regular exercise" was recommended. And the GF was more than happy to help out. 😉