Radiation therapy follows a predictable sequence: a consultation, a planning session, and then daily treatments that typically last 15 to 30 minutes each. Most people receive treatment five days a week for several weeks, though shorter courses are increasingly common. The process is more involved than many patients expect before treatment begins, but the daily sessions themselves are quick and painless.
How Radiation Destroys Cancer Cells
Radiation works by damaging the DNA inside cancer cells. When that damage is severe enough, the cell can no longer divide and eventually dies. Healthy cells in the treatment area also take some damage, but they’re much better at repairing themselves. Cancer cells, which tend to have broken repair systems, are more vulnerable. They often attempt to divide with badly damaged DNA and fail, a process that leads to cell death over days or weeks after each session. This is why radiation’s effects build gradually rather than appearing all at once.
The Consultation Visit
Your first visit to the radiation oncology department is not a treatment session. It’s a consultation that typically takes two hours or more. The radiation oncologist will review your imaging (CT, MRI, or PET scans), examine you, go over your medical history and medications, and discuss whether radiation is appropriate for your situation. You’ll learn how many sessions to expect, what side effects are likely given the area being treated, and whether radiation will be combined with other therapies. This is the time to ask every question you have.
Simulation: Mapping Your Treatment
Before any radiation is delivered, you’ll have a simulation appointment that lasts about an hour. The purpose is to map the exact area that needs to be treated so every future session targets the same spot precisely.
During simulation, the team will position you on the treatment table and may create custom immobilization devices to help you hold that position. For head and neck cancers, this is often a mesh mask molded to your face. For other areas, it might be a foam mold for your legs or arms. You’ll then have a CT scan (sometimes with IV contrast) so the team can see the anatomy around your tumor in detail. Small dots of permanent ink, essentially tiny tattoos, are placed on your skin as reference points. These marks ensure you’re lined up identically for every session.
After simulation, there’s a gap of a few days to a few weeks before treatment starts. During this time, your radiation oncologist and a medical physicist design a plan tailored to your anatomy, choosing the radiation angles, doses, and number of sessions that will deliver the most radiation to the tumor while sparing as much healthy tissue as possible.
What a Daily Session Looks Like
You’ll be in the treatment room for about 15 to 30 minutes per session. Most of that time is spent on setup: positioning you on the table, aligning the machine using your skin marks and imaging, and verifying everything matches the plan. The actual radiation beam is on for only one to five minutes. You won’t feel anything while the beam is active. There’s no heat, no pain, no sensation at all. The machine may rotate around you and pause at different angles, but it never touches you.
A standard course of external beam radiation uses one session per day, five days a week. The total number of sessions varies widely depending on the cancer type, location, and treatment goals. A conventional course might run 25 to 35 sessions over five to seven weeks. Shorter courses, called hypofractionated schedules, deliver larger doses per session over fewer visits. For prostate cancer, for example, some patients now receive as few as five sessions total instead of the traditional 28 to 33. Your oncologist will explain which schedule fits your situation and why.
Internal Radiation Is Different
Not all radiation comes from an external machine. Brachytherapy places tiny radioactive sources directly inside or next to the tumor. The experience varies considerably depending on the approach used.
Temporary implants deliver radiation over a set period and are then removed. Low-dose-rate implants stay in place for one to seven days, during which you’ll remain in the hospital. High-dose-rate implants are placed for just 10 to 20 minutes per session and removed afterward, so you go home the same day. Permanent implants, by contrast, are left in the body. They release low levels of radiation over weeks or months, gradually becoming inactive on their own.
One important distinction: with external beam radiation, you are never radioactive. The beam passes through you and no radiation source remains in your body, so there are no restrictions on being around other people. With internal radiation, your body may emit small amounts of radiation for a limited time. Your treatment team will give you specific safety instructions based on the type and dose of your implant.
Side Effects During Treatment
Side effects from radiation are mostly local, meaning they occur in the area being treated. Someone receiving radiation to the chest will have different side effects than someone treated in the pelvis. Fatigue is the most common side effect across all treatment areas, and it tends to build as treatment progresses.
Most side effects start within the first few weeks. Some appear within days, while others don’t show up until several weeks into treatment or shortly after the course ends. Skin changes in the treated area are common with external beam therapy. The skin may become red, dry, or tender, similar to a sunburn. Keeping the area moisturized and protecting it from sun exposure helps. Some treatment centers use preventive measures like topical steroid creams or barrier films to reduce skin irritation.
Other side effects depend on location. Radiation to the head and neck can cause mouth sores, dry mouth, and difficulty swallowing. Pelvic radiation may cause bowel changes or bladder irritation. Chest radiation can lead to a sore throat or mild cough. Your care team will tell you which effects to expect based on your specific treatment plan.
Recovery After Treatment Ends
Side effects don’t stop the day your last session is over. They typically peak in the first week or two after treatment finishes, then gradually improve. Common effects like fatigue and skin irritation usually resolve within the first few months. Your body is still healing from the cumulative radiation exposure, so improvement is gradual rather than immediate.
Some effects can linger longer or become permanent, depending on the dose delivered and the tissues involved. In rarer cases, new side effects appear weeks, months, or even years later. These late effects vary by treatment site and are something your radiation oncologist will monitor during follow-up visits. You’ll be given a follow-up schedule when treatment ends, and your first post-treatment appointment is usually booked a few weeks out.
Practical Tips for Getting Through Treatment
Daily radiation requires a real time commitment. Even though each session is short, traveling to the treatment center five days a week for several weeks adds up. Many people continue working during treatment, scheduling sessions early in the morning or late in the afternoon. Plan for the possibility that fatigue will increase toward the end of your course, and give yourself more margin in those final weeks.
Wear comfortable, loose clothing to sessions, especially over the treated area. Avoid applying lotions, deodorants, or fragrances to the treatment area before sessions unless your team says otherwise. Stay hydrated, eat well when your appetite allows, and don’t hesitate to report new symptoms between appointments. Side effects that are caught early are almost always easier to manage.