Those tiny dots before radiation: what the marks are for

Before your first radiation treatment, you go through a session called simulation. NCI describes it as the appointment where a radiation oncologist and a radiation therapist determine the treatment area using imaging scans, while you stay still on the table.

At the end of that process, someone marks your skin. NCI's description: the radiation therapist will put small marks, either tattoos or dots of coloured ink, on your skin.

If they are tattoos, NCI says they are about the size of a freckle.

Radiation is planned on a scan, in three dimensions, before it is ever delivered. The plan says where the beam goes relative to your anatomy.

Getting your actual body back into the exact position the plan assumes, on a Tuesday morning three weeks later, is the problem the marks solve. They are fixed reference points that the therapists use to line you up. NCI's phrasing is that the marks help ensure identical positioning for every treatment.

Without them, every session would start with a fresh estimate. With them, every session starts from the same landmarks.

The dots are small. What they anchor is not.

This is the question that bothers people most, and NCI answers it directly.

Tattoos will remain on your skin for the rest of your life. Ink markings fade over time.

Whether you get one or the other depends on your treatment centre and your treatment. Some places use permanent tattoos as standard because they cannot fade or wash off. Others use ink and rely on you looking after them.

If it matters to you, ask before the planning session rather than afterwards. This is a reasonable thing to care about and staff are used to being asked.

NCI's instruction is that patients must preserve the marks and alert staff if they fade.

That second part is easy to forget. If a mark is washing away or is no longer clear, tell the therapists. They will redo it. What you should not do is quietly try to touch it up yourself with a pen, or assume it does not matter because they seem to know where to put you.

Ask your team specifically how to wash the area, because skin care during radiation comes with its own restrictions and the answer might not be what you would assume.

A freckle-sized dot is genuinely small. Most people who have them find that nobody notices, including themselves after a few months.

Where they sit depends on the treatment area, so they may or may not be visible in everyday clothes. If that matters to you, ask about placement at the planning appointment. Sometimes there is a little flexibility.

For people who have permanent tattoos, the dots stay long after the treatment is finished, and reactions to that vary a great deal.

Some people find them an unwelcome reminder of a period they would rather leave behind. Others come to see them as a record of something survived. Neither response is wrong, and you do not have to decide how you feel about them straight away.

If you want to explore removal later, that is a conversation for a dermatologist once treatment is well behind you. Bring it up when you are ready, not because anyone else thinks you should.