Radiation Bowel Injury

DEFINITION
Complications from therapeutic ionizing radiation, encompassing short term and long term effects.
 

D E A B M I M


EPIDEMIOLOGY

Post radiation exposure.
D E A B M I M
 

AETIOLOGY

Radiation injury


D E A B M I M
 

BIOLOGICAL BEHAVIOUR

Pathophysiology

Radiation injury is biphasic.
Terminal ileum often at risk as may be fixed in pelvis due to adhesions.

Acute injury
Occurs during administration of radiation therapy
- damage to dividing cells at the base of cryps
- flattening of villi, alteration of absorptive and resorptive functions
--> diarrhoea, cramping, bleeding, anismus (failure of pelvic floor relaxation during defecation).
These effects begun almost as soon as radiation therapy starts.

Chronic injury
Progressive obliteration end-arteritis
- leads to submucosal and transmural fibrosis and ischaemia.
Can occur years after treatment
- understanding risk factors is valuable in minimizing this problem
Lead to non-compliance of the bowel wall, fibrosis, strictures, fistulization and haemorrhage.

Risk Factors for Chronic Injury

1. Dose of radiation delivered
- total dose and rate of administration.
- 1-5% of pts receiving 4500 cGY
- 50% of pts with 6500 cGY within 5 years
- higher doses over shorter time frame.
- larger fields as more bowel included.

2. Concommitant chemo administration
Increases tissue susceptability.

3. Other factors impairing tissue oxygenation
- diabetes, atheroclerosis, vasculitis, smoking

D E A B M I M
 

MANIFESTATIONS

Early
As above

Chronic

Diarrhoea and fecal incontinence if gut becomes noncompliant.
Fibrosis can lead to malabsorption and malnutrition.
Strictures can cause intermittent, or worsening obstructions
Fistulae can occur to bowel, bladder, vagina or previous surgical sites.
D E A B M I M


INVESTIGATIONS

1. Thorough workup reqd before surgical intervention considered.

2. Consider prognosis of original tumour and if metastatic disease the cause of symptoms.
- CT, MRI and PET as indicated
- biopsies of rectal fistulae

3. Fistulography if indicated

4. Colonoscopy if indicated
- avoid capsule endoscopy or it may get stuck in a stricture.
D E A B M I M


MANAGEMENT

Symptom Relief


Early

Antimotiliy agents, occasionally anti-inflammatories
Mesalamine and steroid enema use has been reported effective.
Low-residue or elemental diets - improved absorption
- IV hydration and TPN if seriously deilitated.

Fractioning radiation dose or delaying tx allows most patients to resolve early toxicity.

Chronic
Management tailored to problem.

Radiation Proctitis

Bleeding usually secondary to this.
Acutely, rectum appears swollen, red, with areas of mucosal sloughing.
- usually resolve at cessation of rads
- avoid deep biopsies; may not heal.
Chronically, mucosa paler with telangiectasis.

Mild

Sucralfate enemas, steroids
No evidence for routine short-chain fatty acids
Hyperbaric oxygen if available may help.
Telangiectasia Rx with endoscopic ablation.  Nd:YAG lasers, argon-beam.
- may need repeatedly
- small risk of ulceration and perforation
Chemical cauterization by topical formalin is another option
- put into packed off rectum and left for 2-3 min
- 60-90% success with 4% irrigation; minimal relapse.
- current experience is quite limited but promising.

Radiation Enteritis

1. May lead to malabsorption
- resection of involved bowel will not alter function; remaining bowel may not maintain nutrition and hydration.

2. If TI involved --> chronic diarrhoea and electrolyte imbalance, bowel unable to resorb bile salts.
- symptomatic Rx with cholestyramine and anti-motility agents may minimize diarrhoea symptoms.

3. Low residue or elemental diets, occasionally TPN

4. Surgery reserved for patients with severe symptoms related to tight strictures.
- then can eithe resect or bypass.
- bypass used to be widely practiced, however can lead to bacterial overgrowth, or even disease progression and perforation.
--> high reoperation rate.
--> still has a role in pts with dense pelvic adhesions.  Bypass anastomosis shd be between two loops of healthy, nonirradiated bowel.
- resection with anastomosis preferred where possible.
--> use non-irradiated bowel for one end if possible; may be necessary to put TI onto transverse colon.
- if ansatomosing colon, consider proximal diverting stoma cover, as high risk joins.

5. Stricturoplasty in stricturing chronic disease = alternative to resection.
- usually for Crohns; studies limited in radiation.

6. Fistulizing complications = as conservatively as possible.
- will not heal spontaneously or with bowel rest; TPN may improve nutrition but conservative resolution is rare.
- ultimately, resect and anastomose if necesssary
- similar for genitourinary or vaginal fistulae; alternatively can leave fistula intact but exclude bowel still attached to bladder or vagina.
- enterocutaneous fistulae are challenging; better to hold off surgery, wait for hydration, nutrition, draining, sepsis, maturing; can go back 3-6m with inflammation settled.
- rad induced rectovaginal or rectourethral fistulae may represent technical mistakes made during surgery, e.g portion of vaginal cuff in staple line.
- must do biopsies of fistula tracts to exclude cancer
Resection preferred for upper rectal fistulae, using nonirradiated proximal colon to low rectum or anal canal.
- goal = closefistula, preserve sphincter fx; avoid pelvic dissection and can use perineal approach.
- can make coloanal anastomosis or J pouch; temporary diversion.

Strategies for Prevention

1. Specific and localized rad delivery.
- multiplanar delivery systems.
- 3D conformal radiation and intensity modulaiton.

2. Filling bladder prior to treatment may help displace small bowel from pelvis.
- at surgery, wise to pack pelvis with omentum, close retroperitoneal tissue inlets.
- minimise pelvic adhesions, e.g. seprafilm

3. Pre-op rads for rectal tumours
- reduces injury to bowel fixed in pelvis; majority or radiated bowel removed.
- but raises risk of non-healing; divert the stream.

4. Natural history is progressive disease
- manage nutrition and hydration, relieve sepsis.
- optimize quality of life, minimize morbidity of interventions.

5. Surgical exploration should be meticulous and operative time alloted accordingly.
- limited adhesiolysis, repair serosal injuries.
- bypass if no other approach.
Many will have further problems.

D E A B M I M


REFERENCES
Cameron 10th