Radiation Effects on the Prostate and Surrounding Normal Tissues

The prostate is relatively resistant to radiation. Pelvic irradiation of the prostate in the absence of prostate cancer to doses of 45 to 65 Gy reduces the serum prostate-specific antigen (PSA) level to a median value of 0.5 ng/mL. Pathologic response to irradiation includes atrophy of glandular tissue, fibrosis, and typical radiation-induced vascular changes. Significant prostate shrinkage in response to high-dose radiation is seen in roughly 50% of patients. The prostate also may become firmer because of fibrosis. These changes are usually not accompanied by significant changes in urinary function over the long term, although improvement or worsening (possibly requiring a transurethral resection of the prostate [TURP]) may occur. Stricture of the urethra is uncommon and appears mostly in patients who have undergone TURP before radiation therapy. TURP after radiation therapy should be used with caution because it has been associated with increased rates of incontinence.

 

Side effects from high-dose radiation therapy for prostate cancer are primarily related to the bladder and rectum, although the dose to the femoral heads also should be considered in treatment planning. Acute bladder side effects during treatment and for 1 to 6 months afterward include increased nocturia, urinary frequency, dysuria, hematuria, urgency, bladder spasm, and urinary incontinence. Acute rectal side effects include increased bowel movement frequency, pain on defecation, hematochezia, spasm, and fecal incontinence. Ejaculation during the latter half of radiation therapy is painful. Symptoms lessen considerably by 1 month after external beam radiation therapy (EBRT), but chronic symptoms may persist. Urinary symptoms persist for longer periods after brachytherapy, sometimes for more than a year. Acute and late morbidities are traditionally graded on a scale of 0 to 5 using Radiation Therapy Oncology Group (RTOG) criteria or modifications thereof (Table 28-1).

 

TABLE 28-1 Acute and Delayed Radiation Toxicity Grading Scales