Epidemiology:
Incidence is equal among men and women.¹
Etiology:
Enviornmental factors and dietary factors are assumed to be the cause for colorectal cancer. Diets high in animal fats and meats and also low intake of fiber and calcium also have a clear association with colorectal cancer.2
Signs & Symptoms:
Presenting symptoms include abdominal pain, change in bowel habit, nausea, vomiting, anemia, or abdominal mass.³
Diagnostic Procedures:
Detailed H&P, endoscopic, radiographic, and laboratory studies. Radiographic examinations include barium enema, chest radiograph, CT, MRI (if indicated), and intrarectal ultrasound. Laboratory examinations include CBC, biological markers, carcinoembryonic antigen, and blood chemistry.
Histology:
Most common histology is adenocarcinoma consisting of 90-95% of cases. The rest of the histology types include mucinous adenocarcinoma, signet-ring cell carcinoma, and squamous cell carcinoma.
Lymph Node Drainage:
"The right colon follows the mesenteric vessels. The right colon follows the superior mesenteric vessels and includes the ileocolic and right colic nodes." The left colon drains into the midcolic, inferior mesenteric, and left colic. The sigmoid colon drains into superior rectal, sigmoidal, and sigmoidal mesenteric vessels.
Metastatic Spread:
Risk of metastatic disease correlates with the depth of bowel wall invasion by the tumor and it occurs in 10-20% of tumors confined to the wall.⁶ Low-grade tumors have a 30% chance of metastatic spread through lymph nodes and high-grade tumors have an 80% chance of spread through the lymph nodes to distant sites.⁷ Metastatic disease can also be spread through the blood stream with the main distant site being the liver.⁸ Disease can occur in the peritoneum due to seeding of cancer cells from surgical procedures.⁹Another major metastatic site is the lungs.¹⁰Local extension in the colon is fairly circumscribed; however, in metastatic nodal disease, the disease can "skip" to other sites without continually disseminating. "Skip" metastases are thought to be caused by blockages in the lymph system.¹¹
Grading:
General grading system recommended by the American Joint Committee on Cancer and the International Union Against Cancer is based on the degree of cell differentiation:
Grade 1: low grade, cells well-differentiated.
Grade 2: moderate grade, cells moderately differentiated.
Grade 3: high grade, cells undifferentiated.
There is also a classification of that the grade can't be assessed.¹²

Staging:
According to Chao, et. al. there are 4 possible staging systems for colon cancer: Dukes, Astler-Coller, Modified Astler-Coller and the American Joint Committee on Cancer TNM system. Chao, et. al. advise that the first 3 staging systems can only be used postoperatively and the TNM system can be used either before or after surgery.¹³:

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Radiation Side Effects:
  • skin irritation at the site where radiation beams were aimed
  • nausea
  • rectal irritation, which can cause diarrhea, painful bowel movements, or blood in the stool
  • bowel incontinence
  • bladder irritation, which can cause frequent urination, burning sensations while urinating, or blood in the urine
  • fatigue
  • sexual problems (impotence in men and vaginal irritation in women)¹⁴
Prognosis:
Tumor penetration of the bowel wall and lymph ode involvement is important prognostic factors; both are associated with increased risk of local recurrence. Absolute and proportion of involved lymph nodes are important predictors of outcome.
Stage 1 disease and stage II disease with 5-year survival rates approaching 90%. Stage III disease denotes lymph node involvement, and studies indicate that the number of lymph nodes involved affects prognosis. (National Cancer Institute). Patients with 1 to 3 involved nodes have a significantly better prognosis than those with 4 or more involved nodes.
Stage 4 colon cancer (metastatic) clearly has the worst prognosis. However, not all stage IV cancers are the same. For example, the NCI reports that patients with 3 or less hepatic (liver) metastases have a five-year survival rate of 20 to 30%.¹⁴
Treatments:
Shrinking fields should be used with initial irradiation fields designed to treat the primary tumor volume and regional lymph nodes. Smaller fields can be used to treat the primary tumor bed to higher doses as clinically indicated. The width of PA portals should cover the pelvic inlet with a 2cm margin; the superior margin is usually 1.5cm above the level of the sacral promontory. In patients who have had anterior resection, the usual inferior margin is below the obturator foramina. If the pelvis is treated, lateral fields should be used for a portion of the treatment to avoid as much small bowel as possible. Bladder distention and prone position hrinking field technique are useful techniques for displacing the small bowel out of the pelvis. The posterior field margin for lateral fields is critical because the rectum and perirectal tissues lie just anterior to the sacrum and coccyx; the posterior field margin should be at least 1.5 to 2.0 cm behind the anterior bony sacral margin. The entire sacral canal should be included for locally advanced disease to avoid sacral recurrence form tumor spread along nerve roots included in the initial irradiation volume treated to 45 GY. External iliac nodes are not a primary lymph node drainage site and are not included unless pelvic organs wit external iliac drainage (prostate, upper vagina, bladder, uterus) are involved by direct extension.
Temporary acute and moderate to moderately severe perinea discomfort can be mitigated with use of three field technique (PA, and lateral s with wedges on lateral fields)
Bolus applied to the perineal scar during PA treatment ensures adequate dose to the site
Dose to the large fields including tumor bed and regional lymph nodes, should be 45 Gy in 5 weeks. After this a boost to the primary tumor bed and immediately adjacent lymph nodes should be considered. Doses greater than 50.4 Gy generally should not be administered unless there is complete shift of the small bowel out of the final boost fields. If irradiation is used for locally advanced extra pelvic colon cancer, the tumor bed should be covered with a 3-5 cm margin.¹⁴

TD5/5:
Organ (1/3 of organ), (2/3), (3/3)
Colon 55 Gy, xx, 45 Gy
Rectum 75 Gy, 65 Gy, 60 Gy
Small bowel 50 Gy, xx, 40 Gy¹⁵







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Figure 1: IMRT Colon with DRR from Eclipse¹⁶


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Figure 2: Field diagram for conventional colon and rectum treatment¹⁵


References
1. Philip Rubin, Clinical Oncology-A Multidisciplinary Approach for Physicians and Students. 7th edition, Philadelphia, PA: W. B. Saunders Co.; 1993.
2. Nishele Lenards, www.uwlax/edu, D2L - Clinical Oncology for Medical Dosimetrist: Colon and Rectum, accessed 1/19/2010
3. Chao KS, Perez CA., Brady LW. Radiation Oncology - Management Decisions. 2nd ed. Philadelphia, PA: Lippincott, Williams & Wilkins; 2002

4. Chao KS, Perez CA., Brady LW. Radiation Oncology - Management Decisions. 2nd ed. Philadelphia, PA: Lippincott, Williams & Wilkins. 2002.
5. Washington CM, Leaver D. Principles and Practice of Radiation Therapy. 2nd ed. St. Louis, MO: Mosby. 2004
6.Gunderson LL, Haddock MG, Goldberg, R, et. al. Alimentary Cancer. In: Rubin P, ed. Clinical Oncology: A Multidisciplinary Approach for Physicians and Students. 8th ed.Philadelphia, PA: W.B. Saunders Company; 2001:724.

7.Gunderson LL, Haddock MG, Goldberg, R, et. al. Alimentary Cancer. In: Rubin P, ed. Clinical Oncology: A Multidisciplinary Approach for Physicians and Students. 8th ed.Philadelphia, PA: W.B. Saunders Company; 2001:724.
8.Gunderson LL, Haddock MG, Goldberg, R, et. al. Alimentary Cancer. In: Rubin P, ed. Clinical Oncology: A Multidisciplinary Approach for Physicians and Students. 8th ed.Philadelphia, PA: W.B. Saunders Company; 2001:725.
9. Chao KS, Perez CA., Brady LW. Radiation Oncology - Management Decisions. 2nd ed. Philadelphia, PA: Lippincott, Williams & Wilkins; 2002:395.
10. Chao KS, Perez CA., Brady LW. Radiation Oncology - Management Decisions. 2nd ed. Philadelphia, PA: Lippincott, Williams & Wilkins; 2002:400.
11. Chao KS, Perez CA., Brady LW. Radiation Oncology - Management Decisions. 2nd ed. Philadelphia, PA: Lippincott, Williams & Wilkins; 2002:396.
12. Spitalnik PF, di Sant'agnese PA. The Pathology of cancer. In: Rubin P, ed. Clinical Oncology: A Multidisciplinary Approach for Physicians and Students. 8th ed.Philadelphia, PA: W.B. Saunders Company; 2001:54.
13. Chao KS, Perez CA., Brady LW. Radiation Oncology - Management Decisions. 2nd ed. Philadelphia, PA: Lippincott, Williams & Wilkins; 2002:398.

14. Chao KS, Perez CA, Brady LW. Radiation Oncology- Management Decisions. 2nd ed.
Philadelphia, PA: Lippincott, Williams & Wilkins; 2002

15. Chao KS, Perez CA., Brady LW. Radiation Oncology - Management Decisions. 2nd ed. Philadelphia, PA: Lippincott, Williams & Wilkins. 2002.
16. United Hospital. Eclipse planning system. Accessed January 21, 2010.