Radiation Therapy Guidelines for Rectal Cancer

Introduction to Radiation Dose Guidelines

The American Cancer Society recommends that radiation therapy for rectal cancer should include the primary tumor with a 2-5 cm safety margin, presacral lymph nodes, internal iliac lymph nodes, and obturator lymph nodes, with a standard dose of 45.0-50.4 Gy delivered in 1.8-2.0 Gy fractions 1

The minimum recommended preoperative dose is 45 Gy delivered in conventional fractionation, as suggested by the British Journal of Cancer 2, 3
For long-course chemoradiotherapy, a total pelvic dose of 45.0-50.4 Gy over 25-28 fractions (1.8-2.0 Gy per fraction) is standard, according to the Annals of Oncology 1, 4
After delivering 45 Gy, an additional boost of 4-6 Gy in 2-4 fractions to the primary tumor is often recommended, as per the Annals of Oncology 5, 6
Short-course radiotherapy (25 Gy in 5 fractions) followed by surgery within 1 week is an alternative option for T3 rectal cancers without need for sphincter preservation, as stated in Cancer Communications 1
For unresectable tumors, dose escalation to 54-56 Gy may be considered if technically feasible, according to Cancer Communications 1

The primary tumor (or tumor bed) with a safety margin of 2-5 cm should be included in the clinical target volume (CTV), as recommended by Cancer Communications 1
The entire mesorectum, except for very early tumors, should be included in the CTV, as suggested by the Annals of Oncology 5, 6
Presacral nodes along aa rectalis superior up to the level of S1-2 should be included in the CTV, according to the Annals of Oncology 5, 6
Internal iliac lymph nodes up to below the bifurcation or to the level of about S1-2 should be included in the CTV, as recommended by the Annals of Oncology 5, 6
Obturator lymph nodes should be included in the CTV, as stated in Cancer Communications 1

A three- or four-field technique is recommended, as suggested by the British Journal of Cancer 2, 3
Three-dimensional precision radiotherapy such as 3D-CRT, VMAT, or IMRT should be used, according to Cancer Communications 1
The dose to the small intestine should be limited to within 50 Gy, as recommended by Cancer Communications 1
Specific dose constraints, such as small bowel loops V15 <120 mL and abdominal cavity V45 <195 mL, should be followed, as per QUANTEC recommendations 1

For T1 N0 M0 tumors, postoperative radiotherapy is indicated only if histology shows incomplete clearance, metastatic nodes, or invasion of perirectal fat, as suggested by the British Journal of Cancer 3, 7
For T2 N0 M0 tumors, preoperative radiotherapy is optional, according to the British Journal of Cancer 2, 3
For T3 and T4 tumors, preoperative radiotherapy is standard, as recommended by the British Journal of Cancer 2, 3
For locally recurrent disease, preoperative radiotherapy (50 Gy for 5-6 weeks) with concurrent chemotherapy is recommended if not previously irradiated, according to the Annals of Oncology 5, 4

Capecitabine 825 mg/m² twice daily, 5 days per week during radiotherapy, is a recommended regimen, as stated in Cancer Communications 1
5-FU continuous infusion at 225 mg/m²/day during radiotherapy is another recommended regimen, according to Cancer Communications 1
Irinotecan combined with Capecitabine (doses based on UGT1A1 genotype) is also a recommended regimen, as suggested by Cancer Communications 1

The National Comprehensive Cancer Network (NCCN) recommends capecitabine 825 mg/m² twice daily as an acceptable alternative to infusional 5-FU for patients with locally advanced rectal cancer who can manage self-administered oral chemotherapy, with equivalent survival outcomes and a favorable toxicity profile 8, 9

The NCCN explicitly lists capecitabine given concurrently with RT as an acceptable alternative to infusional 5-FU for patients who can manage self-administered oral chemotherapy, based on non-inferiority to 5-FU for 5-year overall survival (75.7% vs 66.6%, P=0.0004) in a phase III trial of 401 patients with stage II or III rectal cancer 8, 9, 10, 11, 12
Capecitabine 825 mg/m² twice daily showed superior 3-year disease-free survival (75.2% vs 66.6%, P=0.034) compared to 5-FU-based chemoradiotherapy 8, 9, 10, 11, 12
No differences in locoregional events, complete pathologic response, sphincter-saving surgery, or surgical downstaging were observed in the NSABP R-04 trial of 1,608 patients 8, 9, 10, 11

Capecitabine is appropriate for patients with stage II or III (T3-T4 and/or N+) rectal cancer who can reliably manage self-administered oral chemotherapy and are not candidates for or cannot tolerate infusional 5-FU 8, 9, 10, 11
Bolus 5-FU/leucovorin with RT is reserved only for patients unable to tolerate either capecitabine or infusional 5-FU 8, 9, 10, 11

Adding oxaliplatin to capecitabine/RT is NOT recommended based on multiple phase III trials, including NSABP R-04, which showed no improvement in locoregional events, DFS, OS, or pCR with oxaliplatin addition 8, 9, 10, 11, 12
The ACCORD 12 trial also showed similar pCR rates (19.2% vs 13.9%, P=0.09) but no improvement in local recurrence, DFS, or OS at 3 years, with significantly increased toxicity (grade 3/4 adverse events 24% vs 8%, P<0.001) 8, 9, 10, 11, 12

Chronological age alone should not exclude standard treatment with capecitabine/RT, and fit elderly patients should receive standard guideline-based therapy, with treatment decisions based on comprehensive geriatric assessment rather than age cutoffs 13