Radiation-Induced Injury to the Small and Large Bowel Flashcards
What is the most common method of delivering radiation therapy?
External beam radiation therapy (EBRT), which uses a linear accelerator to produce ionizing radiation
How does EBRT damage DNA within cells?
By interacting with water and releasing free radicals, leading to direct or indirect DNA damage
What are the potential cellular outcomes of DNA damage from EBRT?
Mitotic inhibition or cellular apoptosis.
What is brachytherapy
A method of radiation delivery involving the placement of a radiation source within the body, often as pellets or beads
What is the “target cell” theory of radiation-induced bowel injury?
It describes acute effects targeting bowel epithelium cells and chronic effects targeting cells with slower turnover, such as endothelial cells and fibroblasts.
Which cells are most susceptible to radiation injury and why?
Rapidly dividing cells, such as those in the gastrointestinal (GI) tract, because they are the first to be affected
What is a characteristic chronic effect of radiation injury on the bowel?
Ischemic injury and fibrosis due to fibroblast reaction to cytokines, growth factors, and chemokines
What pathological changes can chronic radiation injury cause in the bowel?
Intestinal atrophy, malabsorption, stricture formation, and vascular damage including telangiectasias and arteriolar constriction.
What are histopathologic features of acute radiation injury to the bowel?
Extensive mucosal inflammation
crypt atrophy/abscesses
nuclear atypia with bizarre mitoses
and eosinophilic submucosal infiltration.
What characterizes chronic radiation injury histopathologically?
Obliterative enteritis
small-vessel vasculopathy
ulceration
fibrous induration
and superimposed ischemic changes
What can result from arteriolar constriction due to chronic radiation injury?
Bowel ischemia and necrosis.
What are common patient-related risk factors for radiation-induced bowel injury?
Smoking
diabetes mellitus
hypertension
vascular and collagen disorders
atherosclerosis
coronary artery disease
inflammatory bowel disease
prior intestinal surgery
How can chemotherapy affect the risk of radiation-induced bowel injury?
Chemotherapy agents such as
fluoropyrimidines
taxanes
platinum agents
mitomycin C
gemcitabine
methotrexate
actinomycin D
topotecan
doxorubici
can act as radiosensitizers and potentiate radiation effects.
How does body mass index (BMI) influence the risk of radiation-induced bowel injury?
Low BMI is associated with a higher risk due to an increased rate of radiation toxicity.
What radiation treatment-related factors increase the risk of radiation-induced bowel injury?
Higher radiation dose
longer length of bowel irradiated
fewer dose fractionation
and larger radiation field size.
Why are patients with vascular and collagen disorders at higher risk for radiation-induced bowel injury
Because these conditions can impair the vascular supply and structural integrity of the bowel, making it more susceptible to radiation damage.
When can acute radiation-induced bowel injury occur?
From the time of radiation treatment up to 6 months after treatment completion.
What is one of the most common symptoms of acute radiation-induced bowel injury?
Diarrhea due to mucosal inflammation and damage.
What complication can arise from damage to the mucosal barrier during acute radiation injury?
Increased risk for bacterial translocation, leading to bacteremia and sepsis
What are other symptoms of acute radiation-induced bowel injury?
Nausea
bloating
cramping
abdominal pain
and GI dysmotility.
What additional symptoms can acute radiation colitis and proctitis present with?
Bleeding, mucus discharge, urgency, and tenesmus
When do symptoms of chronic radiation-induced bowel injury typically present?
8 to 12 months after treatment, though symptoms can appear up to 30 years later.
What is one of the most common symptoms of chronic radiation-induced bowel injury?
Diarrhea, similar to acute radiation injury.
What symptom is common in chronic radiation proctitis?
Rectal bleeding due to telangiectasias
What complications can chronic radiation-induced bowel injury lead to?
Ulcerations from ischemia, abscesses, fistula formation, stricture formation, and bowel obstruction.
What severe outcomes can result from chronic ischemic changes in the bowel?
Full thickness necrosis, fistulae, or free perforation.
How is acute radiation-induced injury to the small intestine, colon, and rectum generally diagnosed?
Based on the patient’s presenting symptoms and history.
What diagnostic methods are used for chronic radiation-induced bowel injury?
Imaging such as CT scans or MR enterography to evaluate anatomy and assess for strictures, fistulae, or bowel wall thickness abnormalities
What can barium and water-soluble contrast enemas reveal in patients with suspected radiation colitis or proctitis?
Shortening, narrowing, lack of distensibility, and absent haustral/mucosal folds of the bowel.
Which imaging methods can be used for further evaluation of fistulae in radiation-induced bowel injury?
MRI, fistulograms, cystograms, and pelvic examinations
How is a definitive diagnosis of radiation-induced bowel injury confirmed?
Endoscopically with biopsies demonstrating specific histologic features
What type of endoscopy is used for suspected radiation injury to the duodenum?
Upper endoscopy
When should capsule endoscopy be considered in evaluating radiation-induced bowel injury?
Only if intestinal strictures have been excluded
What is the benefit of lower endoscopy (colonoscopy or sigmoidoscopy) in diagnosing radiation colitis and proctitis?
It helps visualize neovascularization with fragile vessels and other signs like pallor and friability
What precaution should be taken when performing rectal biopsies in patients with radiation-induced bowel injury?
They should be performed judiciously due to the increased risk of rectal fistula formation.
How are symptoms of acute radiation-induced bowel injury typically managed?
Medically, as they are often self-limited
What medications and dietary modifications are used to manage diarrhea in acute radiation-induced bowel injury?
Antidiarrheal medications like loperamide
fiber supplements
dietary changes (e.g., lactose-free, low-fat, low-residue, or elemental diet)
What medication can be used if first-line antidiarrheals are ineffective in managing diarrhea from radiation-induced bowel injury?
Octreotide.
What treatment options are available for nausea associated with radiation-induced bowel injury?
Antiemetics.
What additional agents can be used to manage symptoms of radiation-induced bowel injury?
Anticholinergics, antispasmodics, bile acid–binding agents like cholestyramine, and antisecretory agents.
How can acute radiation proctitis be managed with butyrate enemas?
They provide short-chain fatty acids as nutrients for colonocytes, though results for chronic proctitis have been mixed
What do the MASCC guidelines recommend for managing chronic proctitis with rectal bleeding?
Sucralfate enemas for their protective barrier and epithelial healing properties
What are other types of enemas that have been used for radiation proctitis, and what are their outcomes?
Mesalamine (5-ASA) enemas
short-chain fatty acid enemas
and steroid enemas
have shown mixed results and require more investigation.
What is formalin therapy used for in radiation-induced bowel injury?
As a topical treatment for chronic radiation proctitis to chemically cauterize telangiectasias and ulcers
How is formalin therapy administered for chronic radiation proctitis?
Via irrigation with 4%–10% formalin or direct application using formalin-soaked gauze, followed by formaldehyde washout.
What are potential complications of formalin therapy for radiation proctitis?
Anal/pelvic pain
stricture
rectal wall necrosis
and fistula formation
What are some additional medical treatments that can be considered for radiation-induced bowel injury?
Antioxidants (vitamins E and C), probiotics, hyperbaric oxygen, and oral metronidazole
What effect has oral metronidazole shown in treating radiation proctitis?
It may be associated with decreased bleeding, ulceration, and diarrhea over a 4-week course
What endoscopic therapy is the treatment of choice for bleeding in chronic radiation-induced bowel injury?
Argon plasma coagulation (APC).
What is the success rate of argon plasma coagulation (APC) in stopping bleeding in radiation-induced bowel injury?
80% to 90% of cases.
Why is APC considered a safe approach for treating bleeding?
Because it coagulates tissue at a superficial depth.
What improvement, besides stopping bleeding, has been demonstrated after APC treatment?
Improvement of bowel function.
What precaution should be taken when performing APC in patients with chronic radiation-induced bowel injury?
Avoiding the dentate line to prevent anorectal pain
What are potential complications of APC?
Anorectal pain and abdominal cramping
What other endoscopic treatments are alternatives to APC but are rarely performed?
Neodymium-doped yttrium aluminum garnet
(Nd;Yag) laser therapy, radiofrequency ablation, and cryotherapy
What is a similarity between APC and formalin therapy in the treatment of chronic radiation-induced bowel injury?
Both may require multiple treatment sessions.
What percentage of patients with chronic radiation-induced bowel injury will require surgical intervention?
More than 30%
What are indications for surgery in patients with chronic radiation-induced bowel injury?
Symptoms not manageable medically or endoscopically, complications such as perforations, fistulae, strictures, obstruction, intractable pain, and incontinence.
What is the range of morbidity and mortality rates after surgical intervention for radiation-induced bowel injury?
Morbidity: 30% to 65%, Mortality: 6.7% to 25%.
Why is surgery in radiation-induced bowel injury considered challenging?
Due to a hostile operative environment with friable tissue, extensive adhesions, high risk for bowel injury, and poor healing.
What should be included in preoperative planning for patients with radiation-induced bowel injury?
Correcting electrolyte derangements, providing enteral nutrition for malnourished patients, and considering individual patient factors in a multidisciplinary setting
What surgical options are available for managing radiation-induced bowel injury?
Limited bowel resection, bypass/exclusion procedures, stricturoplasty, and fecal diversion
What considerations should be made when choosing a surgical incision for patients with chronic radiation injury?
Consider impaired wound healing; options include low transverse incisions, lower midline incisions, or a Pfannenstiel incision for thin female patients
What is the role of minimally invasive surgery for radiation-induced bowel injury?
It is controversial and depends on individual assessment, with diagnostic laparoscopy via open Hasson technique determining feasibility.
What are contraindications for a minimally invasive approach in radiation-induced bowel injury surgery?
Dense adhesions or pelvic fibrosis.
Where should dissection begin in surgery for radiation-induced bowel injury?
Proximally, where radiation damage is less severe, moving distally
What type of dissection is recommended to prevent bowel injury during surgery for radiation-induced bowel injury?
Sharp dissection using Metzenbaum scissors
Why should blunt dissection be avoided during surgery for radiation-induced bowel injury?
It is associated with a high risk of enterotomy
What should be done for patients with extensive, dense adhesions during surgery for radiation-induced bowel injury?
Limited adhesiolysis should be performed only in the area of interest and only if the bowel is resectable to reduce the risk of fistula formation and bowel injury
What is the surgical challenge associated with pelvic adhesions in radiation-induced bowel injury?
Small bowel segments may be adherent in the pelvis, and careful dissection is needed to avoid damaging the presacral veins and managing potential hemorrhage
What should a surgeon do if a bowel segment is fibrosed to the sacrum?
It may be safer to leave the segment attached and apply diathermy to the mucosal surface.
What technique can prevent serosal injuries during the dissection of dense interloop adhesions?
Hydrodissection via saline injection.
Why is limited bowel resection preferred over bypass/exclusion in surgical management?
It is associated with decreased rates of reoperation and increased survival.
What should be considered when selecting bowel segments for anastomosis in radiation-induced bowel surgery?
Use nonirradiated bowel for anastomosis when possible, as anastomotic leak rates can be as high as 50% between irradiated segments.
What are the visual characteristics of grossly irradiated bowel?
It can appear pale, mottled, yellowish/gray, or telangiectatic with features of vascular insufficiency, but may sometimes look indistinguishable from normal bowel.
Which bowel segments should be avoided for anastomosis in radiation-induced bowel surgery?
The cecum and terminal ileum due to their common exposure to severe radiation injury
What type of anastomosis is preferred in radiation-induced bowel surgery to avoid staple-line ischemia?
Hand-sewn anastomosis.
What is the recommended technique for managing the mesentery in radiation-induced bowel surgery?
Over-sewing the mesentery with an interlocking heavy #1 chromic suture between clamps, rather than using vessel sealers or the clamp, cut, tie technique
When might bypass/exclusion be considered instead of bowel resection in radiation-induced bowel injury?
When extensive adhesions and/or pelvic fixation make resection impossible
What are the benefits and drawbacks of bypass/exclusion compared to bowel resection?
It has a lower risk of bowel or mesenteric injury and lower anastomotic leak rate but increases the risk of blind loop syndrome and fistula formation.
What surgical alternative may be used to preserve intestine and avoid TPN dependence in radiation-induced bowel injury?
Stricturoplasty.
What is a common approach for managing postradiation enteric and pelvic fistulae?
Sepsis management, nutritional optimization, and fistula maturation/output optimization.
How are higher pelvic fistulae (e.g., rectovaginal, rectourethral) treated surgically?
With proctectomy and anastomosis of the colon to the distal nonradiated rectum or anus.
When is hand-sewn coloanal anastomosis recommended in radiation-induced bowel injury?
Only in younger patients with intact sensation, function, and control
What type of tissue is recommended for interposition between the affected organ and anastomosis?
Well-vascularized tissue such as omentum or rectus pedicle flap
How can lower pelvic fistulae be managed surgically?
Through perineal (Kraske) or transsphincteric (York-Mason) approaches.
What types of flaps may be used for reconstruction to promote better healing in pelvic fistulae?
Gracilis, omentum, rectus, bulbocavernosus, or Martius flaps
What is a severe surgical option for cases where pelvic fistulae are extensive?
Pelvic exenteration
What is the role of fecal diversion in managing radiation-induced bowel injury?
It helps manage pain, tenesmus, incontinence, obstruction, and sepsis, especially in non-optimal surgical candidates.
Why might loop ileostomies and transverse/descending colostomies be safer than sigmoid colostomies in irradiated pelvis?
Due to the difficulty of dissection and higher risk of bowel injury in an irradiated pelvis.
What is 3D conformal radiation therapy (3DCRT)?
A technique using 3D planning via CT and computer technology to deliver radiation that matches the tumor’s shape, allowing higher doses to the tumor with less impact on normal tissue.
What is intensity-modulated radiation therapy (IMRT)?
A radiation technology that delivers varying intensities of radiation in a planned field with clear differentiation between malignant and normal tissue.
How does brachytherapy help minimize radiation-induced bowel injury?
By delivering radiation directly to the tumor or as an adjunct to EBRT to reduce normal tissue exposure.
What is proton therapy, and how does it benefit radiation delivery?
A new technology used in certain tertiary centers to minimize radiation exposure to surrounding organs and structures
What are some positioning and procedural strategies to reduce radiation injury?
Prone positioning, use of protective belly boards, and ensuring a full bladder during radiation delivery.
What is amifostine, and how is it used in radiation therapy?
A prodrug metabolized into a thiol metabolite that acts as a free radical scavenger, potentially preventing symptoms of acute radiation proctitis
What operative maneuvers can be considered to minimize radiation injury if radiation is given postoperatively?
The use of omental slings and tissue expanders to fill the pelvis
