Radiation therapy (radiotherapy) uses high-energy rays or particles, similar to X-rays, to damage the DNA within cancer cells, stopping them from growing and dividing. While the term “colon cancer” is frequently searched, radiation therapy is far more common in the treatment of cancers located in the rectum, which is the last part of the large intestine. Understanding the total duration requires looking beyond the daily sessions to include the preparation phase and the specific treatment strategy chosen.
Treatment Strategy: When Radiation is Used
Radiation treatment duration for cancer in the lower digestive tract depends largely on when the therapy is administered relative to surgery. Radiation is used most often for locally advanced rectal cancer because these tumors are typically located in the pelvis, which is well-suited for targeted delivery. Conversely, radiation is less common for upper colon cancer, which is generally treated with surgery and chemotherapy.
The primary strategy is neoadjuvant therapy, given before surgery to shrink the tumor and make it easier to remove. Radiation can also be used as adjuvant therapy, given after surgery to kill any remaining microscopic cancer cells and reduce the risk of recurrence. Neoadjuvant radiation is generally preferred for advanced rectal cancer as it results in better local control and is often associated with less long-term toxicity than post-operative radiation.
The Pre-Treatment Planning Phase
The time commitment begins with the pre-treatment planning phase, well before the first dose of radiation is delivered. This process starts with a CT simulation, a specialized imaging session that precisely maps the tumor’s location and surrounding healthy organs. During the simulation, the patient is positioned exactly as they will be for treatment, sometimes requiring customized immobilization devices to ensure they do not move.
Following the simulation, a team including a radiation oncologist, physicist, and dosimetrist creates a personalized treatment plan. This planning uses computer software to calculate the optimal radiation dose and delivery angles to maximize tumor destruction while sparing normal tissue. This process, from the simulation scan to final plan approval, typically takes 1 to 2 weeks, or longer depending on the case complexity. Patients may also receive tiny, permanent skin markings to help therapists align the radiation beams accurately for each daily session.
Typical Daily and Weekly Treatment Duration
The total length of the active radiation treatment phase varies significantly based on the schedule chosen. For rectal cancer, two primary schedules are used, both delivered five days a week (Monday through Friday). While the time inside the treatment room is short (10 to 30 minutes), the total appointment time may be closer to an hour to account for setup and positioning.
The first approach is long-course chemoradiation, spanning five to six weeks. This schedule consists of 25 to 28 separate treatments (fractions) and is often delivered concurrently with chemotherapy to make the cancer cells more sensitive to the radiation. The extended duration allows the total radiation dose to be spread out, potentially reducing acute side effects.
The second approach is short-course radiation, a compressed schedule completed in five days. This method uses a higher dose per session but delivers a lower total dose overall, with five fractions given in a single week. Short-course therapy is often favored for convenience and allowing earlier systemic chemotherapy, but it may result in a different pathological response. The choice depends on factors like the tumor’s stage, location, patient health, and the intended time interval before surgery.