Unresectable Nonmetastatic Colon Cancer

• Neoadjuvant RT with concurrent fluoropyrimidine-based chemotherapy may be considered for initially unresectable or medically inoperable non-metastatic T4 colon cancer to aid resectability
• Intraoperative radiotherapy (IORT) may be considered for patients with T4 tumors or recurrent cancers
• Recommended dose: 45-50 Gy in 25-28; additional 10-20 Gy external beam radiation therapy (EBRT) and/or brachytherapy could be considered if IORT is not available

Resectable Nonmetastatic Rectal Cancer

• Associated with decreased rates of local recurrence for rectal cancer
• Administration should include the tumor bed with 2 to 5-cm margin, mesorectum, internal iliac nodes and presacral nodes
  • External iliac nodes are included in T4 tumors involving anterior structures 
• Risks include increased hematologic toxicities, radiation-induced injury

Preoperative versus Postoperative Radiation Therapy (RT)

• Preoperative RT (along with chemotherapy) is recommended for those with stage II and III rectal cancer
  • Short-course RT may be an option for patients with T3N0 or T1-3N1-2 rectal CA
  • Recommended dose: 45-50 Gy in 25-28 fractions to the pelvis; consider a tumor bed boost of 5.4 Gy in 3 fractions with a 2-cm margin after 45 Gy
• Advantages of preoperative RT include:
  • Increased rate of sphincter preservation
  • Increased sensitivity to radiation therapy of surgically-naive tissues
  • Avoiding radiation-induced injury that can arise from post-surgical adhesions
  • Increases the likelihood that an anastomosis with a healthy colon can be done

• Disadvantage of preoperative RT is the possibility of overtreating early-stage tumors that do not require RT
• Postoperative RT is recommended when stage I rectal cancer has been upstaged to stage II or III after pathologic review of the surgical specimen
  • Recommended dose: 5.4-9.0 Gy in 3-5 fractions

Intraoperative Radiotherapy (IORT)

• For patients with T4 tumors or recurrent cancers, or if margins are positive or very close
• Involves direct exposures of tumors to RT intraoperatively while normal structures are removed from the field of treatment
• Considered as an additional boost to facilitate surgery
• If unavailable, brachytherapy and/or 10-20 Gy EBRT may be considered soon after resection, prior to adjuvant chemotherapy

Metastatic Colorectal Cancer

Arterial Radioembolization

• While toxicity is relatively low, evidence supporting its use is still lacking
• Alternative for highly-selected patients with predominantly hepatic metastases and with chemotherapy-resistant or refractory disease

External Beam Radiation Therapy (EBRT)

• May be considered in highly selected cases where patients have limited number of liver or lung metastases or in symptomatic patients or in the setting of a clinical trial
• Intensity-modulated radiation therapy (IMRT) should be reserved for special situations (eg reirradiation of previously irradiated patients with recurrent disease) or unique anatomical sites where tissue dose-volume constraints are necessary; stereotactic body radiation therapy (SBRT) should be considered for patients with oligometastatic disease 
• Should not replace surgical resection