Rectum


 * **Epidemiolgy:** || The third most common cancer in both men and women. Risk of development increases with age, but no gender difference has been demonstrated.[1] ||
 * **Etiology:** || Dietary factors, especially diets high in animal fats and meat and low in fiber and calcium, chronic ulcerative colitis, familial adenomatous polyposis. An increased risk is demonstrated in patients with a first degree family member diagnosed with colorectal cancer before the age of 60.[1,2] ||
 * **Signs & Symptoms:** || Most common sign of lower sigmoid colon and rectal cancer is hematochezia (blood in stool). Abdominal pain is a common complaint with colon cancer. Other indicators include change in bowel habits, nausea and vomiting, abdominal mass and anemia.[2] ||
 * **Diagnostic Procedures:** || The diagnosis of rectal cancer involves an extensive work up including a history and physical examination, laboratory values, colonoscopy and medical imaging studies. A computed tomography (CT) is used as a primary imaging study to assess the extent of the primary tumor. Also, magnetic resonance imaging (MRI), and transrectal ultrasound can be used as diagnostic imaging studies. A Positron emission tomography (PET) can be used to determine distant metastasis. [2] ||
 * **Histology:** || The most common histologic type of rectal cancer is adenocarcinoma. It accounts for more than ninety percent of all rectal cancers. It is further classified by the cellular differentiation. A Colloid or mucinous adenocarcinoma accounts for 17 percent of colon tumors.These tumors are defined by the amounts of extracellular mucin retained within the tumor. Also, a rare type of tumor of colon and rectum, known as signet-ring cell carcinoma, isknown to have a poor prognosis. [2,3] ||
 * **Lymph node drainage:** || The major lymphatic drainage of the rectum follows the superior hemorrhoidal arterial trunk toward the inferior mesenteric artery. The superior half of the rectum drains to the para rectal, sacral, sigmoid, and inferior mesenteric lymph nodes. The inferior half of the rectum drains to the internal iliac lymph nodes. Tumors extending to the anal canal may drain into the superficial inguinal lymph nodes. [3] ||
 * **Metastatic spread:** || Most common site of metastasis is the liver. May also spread to perirectal, internal iliac and/or inguinal lymph nodes. ||
 * **Grading:** || Tumor Grading for Large Bowel Cancer.

G1: Well differentiated (low grade). G2: Moderately differentiated (intermediate grade). G3: Undifferentiated (high grade). || Tis No extension through muscularis mucosa T1 Invades submucosa T2 Invades muscularis propria T3 Invades through the muscularis propria into perirectal fat T4 Perforates the visceral peritoneum or invades other organs or structures N0 No involved nodes N1 1-3 involved nodes N2 >4 involved nodes M0 No distant metastatic disease M1 Distant metastatic disease
 * **Staging:** || __TNM Staging System for Large Bowel Cancer__ [2]

Stage Groupings I = T1-2, N0, M0 II = T3-4, N0, M0  III = any T, N1-2, M0  IV = any T, N, M1 ||
 * **Radiation side effects:** || Constipation is the most common acute toxicity during pelvic irradiation. Patients may experience consistently worse bowel function when receiving irradiation and chemotherapy. Other side effects include minor rectal bleeding and rectal urgency. Ulcers may also develop in patients with intracavitary radiation therapy.[2] ||
 * **Prognosis:** || Many factors affect a person's rectal cancer prognosis. One of the most important factors is the rectal cancer stage, which is the extent to which the cancer has metastasized.Other factors that may also affect the rectal cancer prognosis include the person's:
 * Age
 * General health
 * Response to treatment [2]

Tumor penetration of the bowel wall and lymph node involvement are important prognostic factors. * They are associated with the increased risk of local recurrence. • Absolute number and proportion of lymph nodes involved are also important predictors of outcome. * Presence of both lymph node involvement and extension of disease beyond the bowel wall is more ominous than the presence of either alone. • In patients with low rectal cancer who are being considered for sphincter sparing treatment: * clinical mobility, size, and morphology of the lesion are predictors of outcome.[2] || Advanced stages of tumor will be treated with higher dose (45-46Gy, 1.8 to 2.0 fractions) combined with chemotherapy, and surgery 4 to 6 weeks later. [2]
 * **Treatments:** || Surgical resection is the treatment of choice for most patients.Preoperative irradiation is usually for lesions larger than 2 cm (20-25Gy in 5 fractions)

Figure 2. A conformal 3-dimenstional radiation treatment plan with sagittal, coronal and axial views through the treatment isocenter along with a view of a posterior-anterior (PA) treatment portal for a patient with stage III rectal cancer undergoing neoadjuvant combined modality therapy. Isodose lines representing radiation dose to the “at-risk” regional lymph nodes and pelvic tissues along with higher doses to the areas of gross disease are demonstrated.[4]

Figure 3. An intensity-modulated radiation therapy (IMRT) treatment plan with sagittal, coronal and axial views through the treatment isocenter for a patient with stage III rectal cancer undergoing neoadjuvant combined modality therapy. Isodose lines representing radiation dose to the “at-risk” regional lymph nodes and pelvic tissues along with higher doses to the areas of gross disease are demonstrated.[4] || Rectum 60 Gy Femoral Head 52Gy Spinal cord 47 Gy(20 cm) 50 Gy(10 cm) 50(5 cm).[2] || [2] Chao KS, Perez CA, Brady LW. //Radiation Oncology Management Decisions//. 2nd ed. Lippincott Williams & Wilkins; 2002. [3] Hoppe TR, Phillips LT, Roach M. Leibel and Phillips Textbook of Radiation Oncology. 3rd Edition. Philadelphia: Saunders, Elsevier. 2010 [4] J Gastrointest Oncol. //Management of stage II/III rectal cancer.// [|__http://www.thejgo.org/article/view/3/html_2__] Accessed, June 9, 2012. || Figure 1. Lymphatic Drainage of Rectum. [2] Back to Week 3
 * **TD 5/5:** || __ ORGAN WHOLE ⅓ __ Bladder 65 Gy 80 Gy
 * **References:** || [1] Washington CM, Leaver D. //Principles and Practice of Radiation Therapy//. 2nd ed. Mosby; 2004.