What is the role of radiotherapy in the treatment of rectal cancer?

From the Guidelines

Radiotherapy plays a crucial role in the treatment of rectal cancer, particularly in reducing the risk of local failure and downsizing tumors to allow for radical surgery 1.

Key Principles of Radiotherapy in Rectal Cancer

• The primary tumor, mesorectum, and lymph nodes outside the mesorectum should be irradiated, with a boost of 4-6 Gy in 2-4 fractions to the primary tumor often given 1.
• The entire mesorectum should be included in the clinical target volume (CTV) for all tumors except the very earliest (T1 sm1), and high tumors are an exception where only 4-5 cm distal to the tumor needs to be included 1.
• Besides mesorectal nodes, pre-sacral nodes along the superior rectal arteries and nodes along the internal iliac arteries should always be included in the CTV 1.
• The appropriate dose for subclinical disease is not precisely known, but with 5-FU chemotherapy, it should be at least 45-46 Gy in 1.8-2 Gy fractions 1.

Considerations for Treatment Planning

• The lateral nodes along the rectal arteries and internal iliac nodes should be included in tumors below the peritoneal reflection 1.
• External iliac nodes should only be included if there is a risk of involvement of these lymph node stations, such as in cases of anterior organ involvement 1.
• The medial inguinal nodes need to be prophylactically included only when the tumor grows at or below the dentate line 1.
• Individualization of treatment is essential based on the stage and location of the tumor, as well as the patient's overall health and performance status.

From the Research

Role of Radiotherapy in Rectal Cancer Treatment

• Radiotherapy is a crucial component in the treatment of rectal cancer, particularly for locally advanced and unresectable cases 2, 3, 4.
• Neoadjuvant radiotherapy is recommended for patients with stage II-III rectal cancer, with either conventional fractionation with concurrent 5-FU or capecitabine or short-course radiotherapy 4.
• The addition of chemotherapy before or after chemoradiation or after short-course radiotherapy is conditionally recommended 4.
• Radiotherapy can be used as an alternative to surgery in elderly and frail patients who are clinically inoperable or refuse surgery, with promising response rates 5.

Types of Radiotherapy

• External beam radiotherapy (EBRT) is a common type of radiotherapy used in rectal cancer treatment, with a recommended dose of 45-50.4 Gy 3, 4.
• Intraoperative radiotherapy (IORT) can be used as an immediate adjuvant treatment for rectal cancer, particularly in cases where access to EBRT is limited 6.
• High-dose-rate brachytherapy (HDR-BT) can be used in combination with EBRT for definitive treatment of rectal cancer, with promising response rates 5.

Treatment Outcomes

• The overall resectability rate for rectal cancer patients treated with radiotherapy is relatively low, with R0 resection achieved in 43% of patients in one study 2.
• Complete pathological response can be achieved in a subset of patients, with rates ranging from 7-11% in one study 2.
• Local progression-free survival and overall survival rates are comparable between patients treated with IORT alone and those treated with both neoadjuvant EBRT and IORT 6.