Radiation Effects on the Bowel
A study from Texas published in the June 2006 issue of the journal, Cancer, shows that lower gastrointestinal (GI) toxicity after radiation therapy for prostate cancer continues for at least five years and may be more common than previously reported.
The prostate gland is located just below the bladder at the base of the penis. According to the Canadian Cancer Society, prostate cancer is the most common cancer among men in Canada. Due to its usually slow-growing nature, 99% of men diagnosed with prostate cancer survive at least five years, and 92% survive ten years.
External beam radiation, which targets higher doses of radiation at the tumour site while minimizing damage to healthy adjacent tissues, is an effective therapy for prostate cancer. However, this treatment can affect the nearby rectum, sigmoid colon, and bowel. The most common toxicity is rectosigmoid radiation proctitis, which often manifests as rectal bleeding or hemorrhaging. Studies have shown that higher doses of radiation may improve survival – but at the cost of increased lower GI toxicity.
Researchers in Texas gathered information through the Surveillance, Epidemiology, and End Results Medicare (SEEM) database, which houses medical information on the American population. The study gathered information on 57,955 men, aged 66 or older diagnosed with localized or regional stage prostate cancer, from 1992 to 1999. They included those who had undergone external beam radiation (41.5%), surgery (20.5%), or neither treatment (38%).
Starting approximately six months after diagnosis for prostate cancer, and continuing for up to five years, data shows a 19% increase in number of GI diagnoses among those patients treated with radiation, compared with patients treated with surgery or those whom had neither procedure. The most common diagnosis was hemorrhage, which affected 40% of the irradiated patients, compared with only 21% of those who had undergone neither surgery nor radiation.
Diagnostic procedures, such as colonoscopy, were more common among irradiated men, but the percentage of patients requiring major GI surgery or resections did not differ significantly between the irradiated group and the group who did not receive therapy. Of the 24,130 men treated with radiation, over half had outpatient visits suggestive of lower GI toxicity, however, the toxicity appears to have been mild, since only 4.4% of patients required hospitalization.
A higher proportion of older men developed GI diagnoses over the five years following radiation therapy, although the severity of the GI disease appeared low. In addition, patients who also had diabetes, hemorrhoids, or peripheral vascular disease, and patients treated with hormonal therapy, were at increased risk of lower GI toxicity than were those patients without these conditions.
Knowing these risk factors allows doctors and patients to make informed decisions when choosing between radiation therapy and surgery as potential treatments for prostate cancer. As the researchers pointed out, while radiation treatment may affect quality of life in prostate cancer survivors, its side effects are rarely as serious as the consequences of a cancer left untreated.