Because the anterior wall of the rectum is so close to the posterior lobe of the prostate, there is a small risk of the radiation causing damage to the rectal wall resulting in short term diarrhea or irritation and long term in rectal bleeding or even an ulcer or fistula. (see risk of fistula).     As noted the risk is quite small.

Approximately 2–10% of prostate cancer patients treated with 125I or 103 Pd brachytherapy will develop radiation proctitis, which generally manifests within the first 2 years after therapy and is related to the rectal dose . Because transperineal brachytherapy is rapidly replacing radical prostatectomy for the treatment of early-stage prostate cancer, increasing numbers of patients present with brachytherapy-related proctitis. The optimum management of the persistent bleeding is unclear from the paucity of available data—Hu and Wallner   reported that no medical intervention was more effective than simply waiting for spontaneous resolution of the implant-related bleeding. There are two schools of thought regarding invasive therapy. Some brachytherapists warn that any interventional procedure may predispose to more severe complications, including fistula formation. Other investigators have reported that therapeutic modalities such as the neodymium:yttrium-aluminum-garnet (Nd:YAG) laser, bipolar electrocoagulation coagulation, argon plasma coagulation (APC), and topical formalin are safe and effective, but no author has addressed prostate brachytherapy-related proctitis specifically

Hu and Wallner  reported that most prostate brachytherapy-related rectal bleeding resolves spontaneously with time and that large volume bleeding is rare. Nonetheless, persistent minor bleeding can be distressing and inconvenient, adversely affecting patients' quality of life. Various medical treatments, including aminosalicylic acid derivatives, sucralfate enemas, or rectal corticosteroids, are inconsistently effective, probably because they act through anti-inflammatory mechanisms and do not address the underlying pathologic features—connective tissue fibrosis and obliterative endarteritis . In fact, radiation ''proctitis'' should more appropriately be referred to as radiation proctopathy, because biopsies taken from the lesions generally lack a significant inflammatory component.

Although medical therapies are inconsistently effective, more invasive treatments have generally been reported to attain higher degrees of success. Viggiano and colleagues have documented the effectiveness of Nd:YAG laser therapy for the treatment of proctopathy after various forms of radiation. Of 47 patients with medically refractory radiation-related hematochezia, 41 (87%) reported marked decreases in their bleeding and 37 (79%) had complete resolution with treatment . Three complications were noted, with one rectovaginal fistula directly attributed to the Nd:YAG laser. Others have confirmed the efficacy and safety of the Nd:YAG laser to treat radiation proctopathy. Although effective, the Nd:YAG laser has the disadvantages of high cost and an inability to control the depth of coagulation.

Thermal coagulation with a heater probe or bipolar electrocoagulation has also proved effective.. The disadvantages to thermal coagulation devices include the potential to exacerbate bleeding, adhesion of the probe to tissue, and difficulty assessing the depth of the thermal effect.

Endoscopically placed topical formalin has also been shown to be a highly effective treatment for radiation proctopathy. Mathai and colleagues  reported that 17 of 29 patients had complete cessation of bleeding after 1 treatment and 5 more had complete cessation after a second treatment. The only complication was a worsening of a radiation-induced stricture . The disadvantages of formalin include a relatively high incidence of posttreatment anal pain in some series and the need for spinal or general anesthesia.

Although a variety of invasive therapies have proved effective for radiation proctopathy, enthusiasm is growing for APC, a newer electrocoagulation method in which high-frequency alternating current is delivered by a no-touch technique through ionized argon gas, coagulating tissue to a depth of 1–3 mm and blood vessels [le] 1.5 mm in diameter.. APC is a well-established treatment for persistent rectal bleeding (oozing) from angiodysplastic lesions or polypectomy sites, and its effectiveness in the management of hemorrhagic radiation proctopathy has been well documented. Kaassis and colleagues described 16 patients treated with APC for bleeding from radiation proctopathy. All patients improved, with a mean number of 3.7 sessions necessary to relieve symptoms . Patient tolerance was good, with no long-term treatment-related complications; the authors considered APC to be first-line therapy for radiation proctopathy.
To better define the efficacy and safety of argon plasma coagulation (APC), specifically for brachytherapy-related proctitis, we reviewed the clinical course of 7 patients treated for persistent rectal bleeding. Approximately 2–10% of prostate cancer patients treated with 125I or 103 Pd brachytherapy will develop radiation proctitis. The optimum treatment for patients with persistent bleeding is unclear from the paucity of available data. Prior reports lack specific dosimetric information, and patients with widely divergent forms of radiation were grouped together in the analyses.

Methods and Materials: Seven patients were treated with APC at the Veterans Affairs Puget Sound Health Care System and the University of Washington from 1997 to 1999 for persistent rectal bleeding due to prostate brachytherapy-related proctitis. Four patients received supplemental external beam radiation, delivered by a four-field technique. A single gastroenterologist at the Veterans Affairs Puget Sound Health Care System treated 6 of the 7 patients. If the degree of proctitis was limited, all sites of active bleeding were coagulated in symptomatic patients. An argon plasma coagulator electrosurgical system was used to administer treatments every 4–8 weeks as needed. The argon gas flow was set at 1.6 L/min, with an electrical power setting of 40–45 W.

Results: The rectal V100 (the total rectal volume, including the lumen, receiving the prescription dose or greater) for the 7 patients ranged from 0.13 to 4.61 cc. Rectal bleeding was first noticed 3–18 months after implantation. APC (range 1–3 sessions) was performed 9–22 months after implantation. Five patients had complete resolution of their bleeding, usually within days of completing APC. Two patients had only partial relief from bleeding, but declined additional APC therapy. No patient developed clinically evident progressive rectal wall abnormalities after APC, (post-APC follow-up range 4–13 months).

Conclusions: Most patients benefited from APC, and no cases of clinically evident progressive tissue destruction were noted. Although APC appears to be efficacious and safe in the setting of the rectal doses described here, caution is in order when contemplating APC for brachytherapy patients.