# Radiation Oncology/Small intestine

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## Epidemiology

Account for only 2% of malignant tumors of the GI tract in spite of the small bowel accounting for 75% of the length and 90% of the surface area of the gut.
5,000 cases/year. 1,200 deaths.

## Presentation

Small bowel neoplasms generally present with pain, obstruction, bleeding, anorexia, weight loss and sometimes jaundice. Small bowel neoplasms are more common in the proximal small bowel (duodenum > jejunum > ileum). Most occur in the 1st or 2nd portion of the duodenum. Adenocarcinomas of the duodenum tend to lead to small bowel obstruction.

## Anatomy

Duodenum is 25 cm (0.82 ft) in length. Jejunum is 8 ft (2.4 m) in length. Ileum is 12 ft (3.7 m) in length. There is no abrupt division between the jejunum and ileum. The duodenum is retroperitoneal, whereas the remainder of the bowel is encased in mesentery. The duodenum is divided into four portions. The first portion of the duodenum is defined as the portion sitting underneath the gall bladder and quadrate lobe of the liver. The second portion of the duodenum is the concave portion. The third portion of the duodenum is portion that lies horizontally at the level of the 3rd lumbar vertebral body. The fourth portion of the duodenum ascends to the 2nd lumbar vertebral body.

## Lymphatics

Lymph nodes are located along the mesenteric vessels to the root of the mesentery.
Regional nodes include: For duodenum: duodenal, hepatic, pancreaticoduodenal, infrapyloric, gastroduodenal, pyloric, superior mesenteric, pericholedochal For ileum and jejunum: posterior cecal, ileocolic, superior mesenteric, mesenteric NOS
Distant mets: celiac axis

## Pathology

45% of small bowel malignancies are adenocarcinomas. Other histologies include carcinoid, lymphoma, sarcoma and GIST. Carcinoid is the most common histology of the distal small bowel.

## Staging

Does not include lymphomas, carcinoid tumors, or GISTs. Does not include tumors arising from the ileocecal valve or from Meckel's diverticula. Tumors from the ampulla of vater have their own staging system.
AJCC 7th Edition (2009) Is similar to that for colon/rectum but has only N1 and no subdivisions of overall stage
Tumor
* T1a - invades lamina propria
* T1b - invades submucosa
* T2 - invades muscularis propria
* T3 - invades through muscularis propria into the subserosa or into the nonperitonealized perimuscular tissue (mesentery or retroperitoneum) with extension 2 cm or less
* T4 - perforates the visceral peritoneum or directly invades other organs or structures (includes other loops of small bowel, mesentery, or retroperitoneum more than 2 cm, and abdominal wall by way of serosa; for duodenum only, invasion of pancreas or bile duct)
Nodes
* N0 - no regional lymph node metastasis
* N1 - metastasis in 1-3 lymph nodes
* N2 - metastasis in 4 or more lymph nodes
    regional nodes: celiac nodes are considered M1. Regional nodes include: (duodenum) - duodenal, hepatic, pancreaticoduodenal, infrapyloric, gastroduodenal, pyloric, superior mesenteric, pericholedochal; (ileum and jejunum) - cecal, ileocolic, superior mesenteric, mesenteric
Metastasis
* M0 - no
* M1 - yes
Stage grouping
* I - T1-T2 N0
* IIA - T3 N0 M0
* IIB - T4 N0 M0
* IIIA - N1
* IIIB - N2
* IV - M1
Changes from 6th edition:
* Subdivided T1 into T1a/b
* T3 and T4 are similar but modified slightly
* N category changed from N0-1 to N0-2
* Stage II subdivided into IIA and IIB, Stage III subdivided into IIIA and IIIB

### Older staging systems

AJCC 6th Edition (2002)
* T1 - invades lamina propria or submucosa
* T2 - invades muscularis propria
* T3 - invades into subserosa or into non-peritonealized pericoloic or perirectal tissues
* T4 - invades other organs or structures or perforates visceral peritoneum
* N1 - regional lymph node metastases
Stage grouping:
* I - T1-2 N0 M0
* II - T3-4 N0 M0
* III - N1
* IV - M1
Changes in AJCC staging:
* No changes from the 5th edition

## Treatment

Treatment depends on the portion of the small bowel affected. Adenocarcinomas of the 2nd or 3rd portion of the duodenum are treated with pylorus-sparing pancreaticoduodenectomy. Adenocarcinomas of other regions of the small bowel may be treated with segmental resection plus regional lymphadenectomy.
The role for adjuvant chemotherapy remains undefined, but 5FU is considered to be the agent of choice.
Indications for adjuvant radiation may include close or positive margins. Adjuvant radiation is generally given concurrently with chemotherapy.
Duodenum
* Duke; 2007 (1975-2005) PMID 17689032 -- "Duodenal adenocarcinoma: patterns of failure after resection and the role of chemoradiotherapy." (Kelsey CR, Int J Radiat Oncol Biol Phys. 2007 Dec 1;69(5):1436-41. Epub 2007 Aug 6.)
** Retrospective. 32 patients. Surgery alone (n=16), neoadjuvant chemo-RT (n=11), adjuvant chemo-RT (n=5). Median RT dose 50.4 Gy, concurrent 5-FU based chemo.
** Outcome: 5-year OS 48%, DFS 47%, LC 55%. No difference if surgery alone or surgery with chemo-RT
** Conclusion: Local failure after surgery high, chemo-RT should be considered