SBRT is an effective and convenient treatment for localized prostate cancer, delivering a full course of radiation in as few as five sessions, unlike conventional radiation therapy which requires many weeks. This accelerated approach uses highly focused beams to deliver a large radiation dose directly to the prostate tumor, maximizing cancer cell destruction while minimizing exposure to surrounding healthy tissues. Although SBRT is generally well-tolerated, the high-dose delivery can lead to side effects that persist or appear long after treatment. Understanding these lasting effects, known as late toxicities, is important for men considering this option. These long-term changes primarily affect the urinary, gastrointestinal, and sexual systems, which are located near the prostate.
Defining SBRT and the Timeline of Late Effects
Stereotactic Body Radiation Therapy is a form of external beam radiation that delivers high-dose radiation in a limited number of fractions. This concentrated method leverages the understanding that prostate cancer cells are highly sensitive to larger doses of radiation per session. However, the proximity of the prostate to the bladder and rectum means these adjacent organs receive a radiation dose that can lead to tissue changes over time. Side effects are categorized as acute, occurring during or shortly after treatment, or late, appearing or persisting well after the acute phase. Late effects are defined as those beginning three to six months following treatment and continuing for years, though the incidence of severe late toxicity (Grade 3 or higher) is generally low.
Genitourinary System Effects
The genitourinary system, encompassing the bladder and urethra, is highly susceptible to long-term radiation effects due to the prostate’s location directly beneath the bladder. Persistent urinary symptoms are the most common long-term complaint, often presenting as increased frequency and urgency. This occurs because radiation causes inflammation and scarring (fibrosis) in the bladder wall and prostatic urethra. Patients may experience nocturia, which impacts sleep quality, or, in rare cases, chronic radiation cystitis, damaging the bladder lining and sometimes causing hematuria. Less commonly, scar tissue can accumulate in the urethra, leading to a stricture that restricts urine flow.
Gastrointestinal System Effects
The rectum sits directly behind the prostate, making it the primary organ at risk for long-term gastrointestinal side effects from SBRT. The most frequent late effect is chronic radiation proctitis, an inflammation of the rectal lining that often manifests as intermittent or persistent rectal bleeding. This bleeding occurs because the radiation damages the small blood vessels within the rectal wall, causing them to become fragile. Other persistent bowel symptoms include increased urgency, more frequent bowel movements, or minor fecal leakage. Using rectal spacers, such as hydrogel, helps push the rectum away from the prostate to reduce the radiation dose and lower the risk of these late effects.
Impact on Sexual Function
A significant long-term concern is the impact of SBRT on sexual health, with the development or worsening of erectile dysfunction (ED) being the primary issue. Unlike urinary and bowel effects, radiation-induced ED tends to be a slow, progressive process that develops over months to years. This progressive decline is attributed to damage to the neurovascular bundles—networks of nerves and blood vessels surrounding the prostate responsible for maintaining an erection. Factors like older age, lower baseline sexual function, and pre-existing health conditions influence the risk and severity of ED following SBRT. Less common effects include a reduction in ejaculate volume or changes in penile length, but ED remains the most prominent sexual side effect.
Strategies for Symptom Management
Long-term side effects are generally manageable and require strategies to maintain a good quality of life.
Managing Urinary Symptoms
For persistent urinary issues like urgency and frequency, management often begins with lifestyle modifications, such as limiting fluid intake before bed and reducing consumption of bladder irritants like caffeine and alcohol. Medications, such as alpha-blockers or anticholinergics, can be prescribed to relax bladder muscles or decrease spasms.
Managing Gastrointestinal Symptoms
Gastrointestinal symptoms, especially chronic rectal bleeding from proctitis, are often managed through dietary adjustments, including increasing fiber intake and avoiding irritating foods. If bleeding is significant, a minimally invasive procedure like argon plasma coagulation (APC) can be performed to cauterize the damaged blood vessels in the rectal lining.
Managing Sexual Dysfunction
For erectile dysfunction, the first line of treatment is typically oral medications, specifically phosphodiesterase type 5 (PDE5) inhibitors, which increase blood flow to the penis. Other effective options include vacuum erection devices or penile injection therapy. Regular follow-up care and open communication with the oncology and urology teams are important to address these persistent issues effectively.