RECIST Criteria on Your Scan Report — How Treatment Response Is Measured

RECIST criteria are a standard set of rules radiologists use to describe whether a solid tumour has shrunk, grown or stayed the same between two scans. A few lesions are measured, their diameters are added into one number, and that number is compared with your earlier scan. The size of the change decides which of four labels goes on the report.

RECIST stands for Response Evaluation Criteria In Solid Tumours. The version in use worldwide is RECIST 1.1. Its whole purpose is consistency: the rules exist so that a response measured on a scanner in Hyderabad is described in exactly the same words as a response measured anywhere else. That is why guideline bodies including NCCN and ESMO reference it, and why almost every clinical trial in solid-tumour oncology reports its results through it.

What RECIST does not do is just as important. It does not measure how you feel. It does not weigh your blood work, your symptoms or your scan from two years ago. It does not tell anyone what happens next. It is a ruler with four bands drawn on it — nothing more, and nothing less.

The sections below take each label in turn, give the number behind it, and explain who applies these rules and when.

Notice the asymmetry that trips most people up. Shrinkage is measured against the baseline scan, the one taken before treatment. Growth is measured against the smallest sum recorded so far — the lowest point your measurements have reached, not the starting point. That is why a tumour can still be far smaller than it was at diagnosis and yet be labelled progressive disease if it has crept up 20% from its lowest reading.

Stable disease means the measurements changed too little to be called anything else. They did not fall by the 30% needed for a partial response. They did not rise by the 20% needed for progression. The word describes movement on a ruler between two scans. It is not a judgement about how well you are doing.

Families often read the word as a disappointment — as though the treatment merely held its ground. In practice, oncologists group complete response, partial response and stable disease together when they describe how many patients had their disease held in check by a treatment. For a slow-growing tumour, and especially for a site that has been treated with radiation, stable disease can be exactly the reading the team expected.

The radiation point matters here. Radiation damages the ability of tumour cells to keep dividing, but the visible mass can take weeks or months to shrink on a scan, and sometimes it never fully disappears. What is left behind may be scar tissue rather than active disease, and a ruler cannot tell the two apart. A scan taken soon after a radiation course can therefore read as stable disease while the treatment has done what it was intended to do. Our page on fibrosis or recurrence on a scan goes into exactly why this distinction is so hard to make from imaging alone.

If stable disease is the line on your own report, that is a direct question worth putting to your treating team — they will read it against your symptoms, your prior scans and the timing of your treatment.

Radiologists apply RECIST when they report a follow-up CT or MRI, and oncologists use the label it produces when they review the scan with you. Clinical trials rely on it most heavily of all, because a trial only means anything if every centre in it describes a response the same way.

RECIST covers solid tumours — lung, breast, colorectal, head and neck, gynaecological, sarcoma and others that form a measurable mass. It is not a universal system. Lymphoma is assessed on a PET-based five-point scale instead. Leukaemia and myeloma are followed through blood and bone-marrow tests, because there is often no mass to measure. Brain tumours use their own framework, since post-treatment changes on brain imaging make size alone unreliable. Prostate cancer is frequently followed through a blood marker and bone imaging rather than tumour diameters, which is why a PSA nadir after radiation is the number that matters there rather than a RECIST label.

One more thing worth knowing: outside a clinical trial, not every follow-up report uses RECIST at all. Many routine reports simply describe change in words — smaller, unchanged, larger. If your report has no RECIST label on it, nothing is missing. It is a reporting convention, not a required test.

Your CT, MRI or PET-CT is performed and reported at an NABH-accredited partner centre equipped for that scan. Your radiotherapy is delivered at an NABH-accredited partner centre; CION Cancer Clinics coordinates your treatment plan, your oncology team and your care throughout. CION does not itself own or operate imaging or radiotherapy equipment.

What that means in practice is that one team handles the appointment, receives the report and sits with you to explain it — you are not left refreshing a portal trying to decode a word on your own. If you are the family member coordinating from Bengaluru, Dubai or New Jersey, that conversation happens over a call, at a time that works across the time difference. Our page on coordinating radiation treatment remotely covers how families abroad usually set this up.

Any cost figure discussed for a follow-up scan is indicative only, as of August 2026, and depends on the scan type, the partner centre and your insurance or scheme cover. Your care team confirms the actual figure before anything is booked.

• Following prostate radiation and watching a blood value instead of tumour diameters? Understanding PSA Nadir After Radiation explains what the lowest reading means and why it is tracked.
• Your report quotes an uptake number rather than a size? SUV Values on a PET Scan: What Counts as High After Radiation? decodes the figure PERCIST is built around.
• Treated for thyroid cancer and following a blood marker at each review? Thyroglobulin Levels After Thyroid Cancer Treatment walks through what the trend is meant to show.
• Stuck on whether what is left on your scan is scar tissue or disease? Fibrosis or Recurrence? Why Scans Cannot Always Tell is the direct answer to the question RECIST cannot settle.
• For the full picture of radiation therapy at CION — how it is planned, delivered and coordinated with NABH-accredited partner centres — see our radiation therapy hub.

Still unsure what your own report says? Book a free consultation and a radiation oncologist will read it with you directly.