Erectile Dysfunction (ED) refers to the inability to have an erection that gets firm enough or stays firm enough to have satisfactory sexual relations (e.g., intercourse).
Prevalence: Some change to the hardness of your erection and/or how long the erection lasts occur in most men after a radical prostatectomy, radiation therapy or androgen deprivation therapy (i.e. hormonal therapy). 
With a radical prostatectomy, erections are at their lowest point right after surgery (sometimes this takes up to 4 months after surgery) and can improve over the first 18-24 months. Predictors of poor erectile function recovery after radical prostatectomy include: older age at time of the operations, poor preoperative erections, lower grade nerve sparing, and having other medical problems associated with erectile dysfunction (e.g., high blood pressure, high cholesterol, diabetes, cardiovascular system, cigarette smoking, obstructive sleep apnea, low testosterone).
Following radiation therapy, the effects are usually not seen immediately (unless hormonal therapy was employed in conjunction with radiation therapy), but over time erectile function may start to decline, with the low-point in erectile function after the third year. Predictors of poor erectile function recovery after radiation therapy include: older age at time of the radiation therapy, poor pre-treatment erections, higher dose of radiation therapy, inclusion of hormonal therapy in the treatment plan and having the medical problems listed above.
By 3 years after treatment, the rates of erectile dysfunction are similar between (nerve-sparing) radical prostatectomy and radiation therapy (without hormonal therapy) patients. Given the profound effects that having no testosterone has on erectile tissue health, it is usual for even a short course of hormonal therapy to have some negative effect on erectile function.
It is difficult to determine the exact rates of erectile dysfunction after prostate cancer treatments given different ways of assessing erectile dysfunction, different definitions used, and different time points after treatments when erections are assessed. One review paper showed that after a robotic-assisted laparoscopic prostatectomy where both nerves were spared, that 44-93% of men had functional erections. If only one nerve was spared, 29-80% had functional erections.1 Another review looked at research papers that asked men if they had erections that lasted long enough for successful intercourse. The rate of men who said yes to this question ranged from 10-67% after radical prostatectomy.2
With regards to radiation therapy, a review paper identified a broad range of 17-90% of men with erectile dysfunction after radiation therapy.3 There is also a broad range for reported erectile dysfunction rates for ablative therapies, such as cryotherapy or high-intensity focused ultrasound (HIFU). A meta-analysis demonstrated ED in 4-49% of men after cryotherapy and 5-58% of men after HIFU.4
High rates of erectile dysfunction are often seen in men receiving hormonal therapy (androgen deprivation therapy). Some studies show after 1 year of hormonal therapy, 80-91% of men have erectile dysfunction.5 Higher rates of erectile dysfunction have been reported in patients after combination or multi-modal therapy (e.g., radical prostatectomy followed by radiation therapy and hormonal therapy). For example, one study compared men with local prostate cancer compared to men of the same age without prostate cancer. Men who had an radical prostatectomy had 2.3 times more risk of erectile dysfunction compared to controls. Men with radical prostatectomy and radiation therapy had 3.5 times more risk and men with radical prostatectomy, radiation therapy and hormonal therapy had 3.7 times higher risk of erectile dysfunction.6
Impact: Erectile dysfunction can make it difficult for either partner to have satisfactory intercourse. Many couples find it helpful to explore other ways to express their sexuality or have intimacy.
Treatment: A typical penile rehab program is designed to protect the erectile tissue in your penis. This involves using oral medication, penile injections, and/or a vacuum erection device (VED) to maximize oxygen delivery to the erectile tissue. Getting regular erections will keep the muscle and blood vessels in the penis healthy while the nerves recover after the trauma of the surgery or radiation. These treatments can be continued after penile rehab if erectile dysfunction persists. In men who don’t achieve adequate erections with these therapies, surgical management with a penile implant is an option as well.
References
[1] Lima TFN, Bitran J, Frech FS, Ramasamy R. Prevalence of post-prostatectomy erectile dysfunction and a review of the recommended therapeutic modalities. Int J Impot Res. 2021;33: 401-09.
[2] Schauer I, Keller E, Muller A, Madersbacher S. Have rates of erectile dysfunction improved within the past 17 years after radical prostatectomy? A systematic analysis of the control arms of prospective randomized trials on penile rehabilitation. Andrology. 2015;3: 661-5.
[3] Nukala V, Incrocci L, Hunt AA, Ballas L, Koontz BF. Challenges in Reporting the Effect of Radiotherapy on Erectile Function. J Sex Med. 2020;17: 1053-59.
[4] Ramsay CR, Adewuyi TE, Gray J, et al. Ablative therapy for people with localised prostate cancer: a systematic review and economic evaluation. Health Technol Assess. 2015;19: 1-490.
[5] Katz A. What happened? Sexual consequences of prostate cancer and its treatment. Can Fam Physician. 2005;51: 977-82.
[6] Carlsson S, Drevin L, Loeb S, et al. Population-based study of long-term functional outcomes after prostate cancer treatment. BJU international. 2016;117: E36-45.