Response assessment
How Doctors Use PET-CT to Judge — Whether Treatment Is Working
When your PET-CT result arrives, it uses categories that your oncologist reads alongside your symptoms and clinical history. This page explains what those categories mean and what is being compared — not to interpret your result, but so you understand the conversation.
Medically reviewed by Dr. Bharati Devi Gorantla, Medical Oncologist, MBBS · MD · DM (Adyar, Chennai) · ECMO · MRCP SCE (UK) · Last reviewed September 2026
- Always compared to a baseline — A follow-up scan is only meaningful alongside the scan taken before treatment started.
- Different criteria for different cancers — Lymphoma uses Deauville scoring. Solid tumours more often use PERCIST.
- Complete response is not permanent clearance — No detectable disease on imaging does not mean no cancer cells remain anywhere in the body.
- The scan is one part of the picture — Your oncologist reads it alongside symptoms, blood tests, and clinical examination.
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Your oncologist compares your follow-up PET-CT against a baseline scan taken before treatment started. Using criteria from NCCN, ASCO, and ESMO — such as Deauville for lymphoma and PERCIST for solid tumours — they classify whether the cancer has responded, stayed the same, or progressed. No scan result is interpreted in isolation.
What do the terms in a PET-CT report actually mean?
- Baseline scan
- The PET-CT done before treatment begins. Every later scan is compared against this one. Without it, response cannot be measured.
- SUV (Standardized Uptake Value)
- A number showing how intensely a tissue has absorbed radioactive glucose. Higher SUV generally means more metabolically active tissue. Your report compares SUV at key sites to the baseline values.
- Complete metabolic response (CMR)
- No FDG uptake distinguishable from normal background. No metabolically active disease is detectable on the scan at this time. This does not mean no cancer cells remain anywhere in the body.
- Partial metabolic response (PMR)
- FDG uptake has decreased compared to the baseline scan, but some remains. The cancer is less active than before — treatment is having an effect.
- Stable metabolic disease (SMD)
- FDG uptake has not changed meaningfully in either direction. The cancer does not appear to be growing, but it is not responding either.
- Progressive metabolic disease (PMD)
- FDG uptake has increased, new lesions are visible, or existing ones are larger. The current treatment is not controlling the disease adequately.
- Deauville score
- A numbered scale used in lymphoma to grade residual FDG uptake against reference points in the body. Lower scores indicate a better response. Your oncologist interprets where your result sits on this scale.
- PERCIST
- PET Response Criteria in Solid Tumours. A standardised framework to categorise treatment response in solid cancers — lung, breast, colorectal, and others.
What to ask when your result comes back
- Ask which response criteria were used — Deauville, PERCIST, or something else — because interpretation differs by system.
- Ask what the SUV at the key site was on your baseline scan and what it is now.
- Ask whether the number of lesions has changed, not just the activity at the main site.
- Ask what the result means for your next step: continue the same treatment, change it, or scan again in a few months.
- Ask when the next response assessment will happen.
- If any term in the written report is unclear, ask your oncologist to explain it before you leave.
PET-CT Partner Centres
PET-CT Scan Centres in Hyderabad
CION offers PET-CT scans through 4 trusted partner PET-CT centres across Hyderabad, so you can choose the one closest to you. Call 18002028726 and we’ll guide you to the earliest available appointment.
PET-CT Centre — Punjagutta
PET-CT Centre — Himayatnagar
PET-CT Centre — Narayanaguda
These are partner diagnostic centres within the CION network. Toll-free booking: 18002028726.
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What does 'complete response' actually mean?
A complete metabolic response means the scan cannot detect metabolically active disease. That is a meaningful result — your team will use it to decide the next phase of treatment.
It does not mean the disease is gone permanently. Whether treatment continues, pauses, or moves to monitoring depends on your cancer type, stage, and clinical history. Your oncologist will explain what it means specifically for you.
Questions patients ask about response assessment
Why does my report say 'partial response' when I feel so much better?
How you feel and what a scan shows often move at different speeds, and both carry weight. A partial response means measurable improvement on imaging even if some residual activity remains. Feeling significantly better is real clinical information. Your oncologist considers symptoms, functional status, and the scan result together — not the scan alone.
What happens if the scan shows progressive disease?
Progressive disease means the current treatment is not controlling the cancer well enough. Your oncologist will discuss the next step — a different regimen, a clinical trial, or a reassessment of the overall plan. Ask what the alternatives are and the reasoning behind them. This is information that moves the plan forward, not the end of options.
Can a PET-CT be wrong?
PET-CT is sensitive for many cancers but has known limitations. Infection and inflammation can cause FDG uptake that resembles cancer. Very small deposits may fall below what the scan can detect. If the result does not match the clinical picture, your oncologist may request a repeat scan, a biopsy, or a second radiologist's opinion. It is reasonable to raise any concern.
If I get a complete response, do I still need more treatment?
In most situations, yes. The planned course of treatment was established through clinical trials that include the full duration. Stopping early based on a scan result alone risks allowing residual disease to recover. The scan is one checkpoint within the plan — not the plan itself.
How is PERCIST different from RECIST?
RECIST measures physical tumour size on CT or MRI — whether a lump got bigger or smaller. PERCIST measures metabolic activity on PET — whether cancer cells are using more or less glucose. A tumour can lose metabolic activity before it visibly shrinks, or shrink without losing metabolic activity. Many oncologists use both together to get a fuller picture.
Can the Deauville score be used for cancers other than lymphoma?
The Deauville score was developed and validated for lymphoma. PERCIST is the more widely accepted standard for solid tumours. The Deauville scale is most reliable where it was designed. If you are unsure which criteria apply to your cancer, ask your oncologist directly — the answer shapes how your result is read.
A whole-body PET-CT at CION is Rs 10,499 — among the lowest published prices in Hyderabad — with a free Rs 950 oncologist consultation to talk through your report. Indicative price, as of September 2026.
Explore 94 more Understanding Your PET-CT Report topics
Response Assessment Scores & Criteria
- Complete Metabolic Response: What It Means
- Deauville Score 1 to 5: The Lymphoma Scale Explained
- End-of-Treatment PET Scan: What It Decides
- How Doctors Judge Whether Treatment Is Working on PET-CT
- Interim PET Scan During Chemotherapy: Why It Is Done
- Metabolic Response vs Size Response: Why They Differ
- PERCIST Criteria: How Metabolic Response Is Measured
- Partial Metabolic Response: Is That Good Enough?
- Progressive Metabolic Disease: What Happens Next
- RECIST vs PERCIST: Size vs Activity
- Stable Metabolic Disease: Good News or Bad?
- Tumour Flare and Pseudoprogression on PET
- What Is a Deauville 3 and Why Is It Ambiguous?
- Why the Scan Says One Thing and You Feel Another
False Positives, False Negatives & Pitfalls
- Bladder, Kidney and Ureter Activity on PET
- Bone Marrow Uptake After Growth Factor Injections
- Bowel Uptake: Normal, Inflammation or Something Else?
- Brown Fat Uptake: A Common Cause of Confusing Findings
- Does a Suspicious PET Finding Always Need a Biopsy?
- Getting a Second Read of Your PET-CT Images
- How Often Is a PET-CT Scan Wrong?
- Muscle Uptake After Exercise or Injections
- Thymic and Rebound Uptake in Younger Patients
- Uptake After Radiotherapy: Inflammation or Disease?
- Uptake at a Biopsy or Surgery Site
- What Causes a False Negative on a PET Scan?
- What Causes a False Positive on a PET Scan?
- What Happens If Two Scans Disagree?
- Which Cancers Do Not Show Well on PET-CT?
- Why the Brain Always Lights Up on PET
Incidental Findings
- A Second Unrelated Cancer Found on PET-CT
- An Incidental Bone Finding on PET-CT
- An Incidental Breast Finding on PET-CT
- An Incidental Kidney or Adrenal Finding
- An Incidental Liver Lesion on PET-CT
- An Incidental Lung Nodule Found on PET-CT
- An Incidental Prostate Finding on PET-CT
- An Incidental Thyroid Nodule on Your PET Scan
- Do All Incidental Findings Need Investigation?
- Focal Bowel Uptake: Could It Be a Polyp?
- Incidental Findings on a PET-CT Scan: What They Are
- Incidental Heart Findings on a Cancer PET Scan
- The Cost of Chasing an Incidental Finding
- What to Ask Your Doctor About an Incidental Finding
Infection, TB & Inflammation on PET
- Can Tuberculosis Look Like Cancer on a PET Scan?
- Dental Infection and Jaw Uptake on PET
- Fungal Infection and Abscess on PET-CT
- How Long Should You Wait After an Infection Before a PET Scan?
- If It Might Be Infection, What Test Comes Next?
- Inflammation After Injections, Vaccines and Cannulas
- Old Healed TB and Calcified Nodes on PET-CT
- PET-CT for Fever of Unknown Origin
- PET-CT for Suspected Infection in Implants and Prostheses
- PET-CT for Vasculitis and Inflammatory Conditions
- Pneumonia and Recent Chest Infection on PET
- Sarcoidosis on PET-CT: The Great Mimic
- TB or Cancer? How Doctors Tell Them Apart
- Thyroid Uptake on PET: Diffuse vs Focal
Reading Your Report: Core Terms
- 'Cannot Be Excluded' and Other Cautious Phrases
- 'Deauville Score' on a Lymphoma PET Report
- 'FDG Avid': What It Means on Your Report
- 'Hypermetabolic': What the Word Actually Means
- 'Hypometabolic' and 'Photopenic' Findings
- 'Impression' vs 'Findings': Which Section Should You Read?
- 'Interval Change' and 'Stable Since Previous Study'
- 'Krenning Score' on a DOTANOC or DOTATATE Report
- 'Lymphadenopathy' on Your PET Report
- 'Metabolically Active Disease': What It Tells You
- 'Metastasis' and 'Distant Spread' on Your Report
- 'Mildly FDG Avid' vs 'Intensely FDG Avid'
- 'No Abnormal FDG Uptake': Is That a Clear Scan?
- 'Physiological Uptake': Normal Areas That Always Light Up
- 'Residual Disease' vs 'Complete Metabolic Response'
- 'Sub-Centimetre Node' and Why Size Matters on PET
- 'Suspicious for Malignancy': How Certain Is That?
- How Long Does a PET-CT Report Take?
- How to Read Your PET-CT Report: A Section-by-Section Guide
- Should You Read Your Own PET-CT Report Before the Consult?
- TNM Staging on a PET-CT Report
- Why Your Report Mentions the Liver and Blood Pool
SUV Values Explained
- Comparing SUV Between Two Scans: Is It Meaningful?
- Does a Higher SUV Mean a More Aggressive Cancer?
- Factors That Change Your SUV Reading
- High SUV but Not Cancer: When the Number Misleads
- Is My SUVmax of 4 High? Reading Your Specific Number
- Low SUV but Still Cancer: The PET-Negative Cancers
- SUV in Non-Cancer Conditions
- SUVmax, SUVmean and SUVpeak: What Is the Difference?
- What Is SUV on a PET Scan?
- What Is a Normal SUV Value?
- What SUV Value Indicates Cancer?
- Why Blood Sugar Changes Your SUV Result
- Why Did My SUV Go Down but Not to Zero?
- Why Did My SUV Go Up After Treatment?
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Common questions
Frequently asked questions
What is being compared on a follow-up PET-CT?
Your follow-up scan is compared against the baseline PET-CT taken before treatment began. The radiologist records where FDG is being absorbed, how intensely, and at how many sites. The key questions are: has uptake changed since the baseline, and are there new areas of activity that were not there before?
Which response criteria will my oncologist use?
That depends on your cancer type. Lymphoma is assessed using the Deauville score. Solid tumours are typically assessed using PERCIST or RECIST. Your report will often name the criteria. It matters because the same finding can carry different weight depending on which standard is applied.
What does 'no evidence of disease' mean on a scan?
No evidence of disease on PET-CT means the scan cannot detect metabolically active cancer at the time of imaging. What it means for ongoing treatment, monitoring, and follow-up frequency depends on your cancer type and how the response was achieved. Your oncologist will explain what it means specifically for you.
Can I read my own PET-CT report?
You have the right to request and read your report. Some phrases — such as 'cannot exclude' or 'correlate clinically' — carry specific meaning in radiology that is easy to misread. Ask your oncologist to walk through the key findings with you so you understand what the report is and is not saying.
How often will I need a PET-CT scan?
Frequency depends on your cancer type, stage, treatment, and what the previous scan showed. ASCO and ESMO guidance for most cancers does not recommend scanning more often than clinically necessary, as each scan involves radiation exposure. Your oncologist sets the interval. If something changes between scheduled scans, call rather than wait.
Can CION arrange my PET-CT?
Yes. CION coordinates PET-CT through partner imaging centres across its network. Your oncologist will arrange the referral and confirm the right protocol for your cancer type. Results come back to your treating team for review and discussion at your next appointment.