Reading your PET scan report
Why Did My SUV Go Down — but Not to Zero?
A lower SUV after treatment is the most common result on a post-treatment PET scan. It does not mean treatment has failed. The question your oncologist is asking is how much it has changed, and what the remaining uptake is most likely to be.
Medically reviewed by Dr. Bharati Devi Gorantla, Medical Oncologist, MBBS · MD · DM (Adyar, Chennai) · ECMO · MRCP SCE (UK) · Last reviewed September 2026
- The most common result — Most people do not reach an SUV of zero after their first course of treatment.
- Lower is not the same as failed — A clear drop in SUV is generally a sign that treatment is having an effect.
- Residual uptake has multiple causes — Remaining uptake can come from inflammation, healing tissue, or dying cells — not only active cancer.
- SUV alone does not diagnose — Your oncologist interprets the number in context, never in isolation.
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A drop in SUV after treatment nearly always means the treatment is working. Residual uptake — a number above zero on your post-treatment scan — does not automatically mean active cancer remains. Your oncologist interprets the figure alongside the scan images, your clinical response, and your cancer type before deciding what it means for you.
What do different SUV patterns after treatment suggest?
| SUV higher than before | SUV lower, still above zero | SUV at or near zero | |
|---|---|---|---|
| Common description | Progressive metabolic disease | Partial metabolic response | Complete metabolic response |
| What it may suggest | Treatment may not be controlling the disease | Treatment is having an effect — the most common result | No detectable tracer activity at the treated site |
| Does this confirm active cancer? | Not alone — imaging and clinical assessment decide | Not necessarily — residual uptake has several causes beyond active cancer | Cannot confirm cancer is absent — only that no tracer activity is detectable |
| Typical next step | Oncologist reassesses the treatment plan | Oncologist reviews the full picture before any decision | Monitoring continues — one scan does not end follow-up |
What should you ask your oncologist about this result?
- Ask what your SUV was on the baseline scan and what it is now — the change matters more than a single number.
- Ask whether both scans were done on the same scanner, since values can differ between machines.
- Ask what the residual uptake is most likely to represent for your specific cancer type.
- Ask what happens next — whether that is a repeat scan, a biopsy, or continuing current treatment.
- Do not compare your number with another patient's. The same SUV can mean different things in different cancers.
- Bring your baseline scan report to the appointment so both results can be reviewed side by side.
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PET-CT Centre — Punjagutta
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What can cause uptake to remain above zero after treatment?
Residual uptake does not always mean living cancer cells are present. The FDG tracer used in PET scans is absorbed by any tissue with high glucose use — and treatment itself creates that.
Inflammation from radiotherapy, chemotherapy, or surgery can produce uptake that persists for weeks or months after treatment ends. The scan cannot always separate this from tumour activity.
Dying or recently dead cancer cells can also retain tracer activity briefly. A scan done too soon after treatment can look more alarming than the clinical picture justifies.
Your oncologist considers the scan images, not just the number, alongside your symptoms, your blood results, and the expected behaviour of your cancer — before drawing any conclusion.
What do the terms in your scan report mean?
- SUV (Standardised Uptake Value)
- A number on your PET report measuring how much tracer a tissue absorbed. Higher uptake produces a higher SUV. It measures metabolic activity, not cancer directly.
- Residual uptake
- Tracer activity remaining at a site after treatment. It may represent active cancer, inflammation, or healing tissue. The report records it; your oncologist determines which is most likely.
- Complete metabolic response (CMR)
- The treated site shows no tracer activity above the surrounding normal tissue. A goal of treatment, but not proof that every cancer cell is gone.
- Partial metabolic response (PMR)
- Uptake at the treated site has decreased since the baseline scan but remains detectable. This is the most common post-treatment PET result.
- FDG (fluorodeoxyglucose)
- The radioactive tracer injected before a PET scan. It behaves like glucose, so any tissue using high energy — cancer, but also inflammation and healing tissue — absorbs more of it.
Did you know?
Inflammatory tissue after radiotherapy can produce FDG uptake that looks similar to tumour activity on a PET scan.
This is why professional bodies including EANM and SNMMI recommend a waiting period between finishing radiotherapy and the follow-up scan — scanning too soon may overestimate the amount of residual disease.
Source: EANM/SNMMI Procedure Guidelines for Tumour Imaging with FDG-PET
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Explore 94 more Understanding Your PET-CT Report topics
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?
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
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
Your next step
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Common questions
Frequently asked questions
Does a lower SUV always mean the treatment is working?
A clear decrease in SUV between the baseline and post-treatment scan is generally a positive sign — it means the treated tissue is using less energy, which is what treatment aims to achieve. It does not guarantee a complete response or mean every cancer cell is gone. Your oncologist reads it alongside your symptoms, blood results, and the visual appearance of the scan, because those together tell a more complete story than the number alone.
Why didn't my SUV reach zero if the treatment worked?
Reaching zero is not the expected result for most patients after one course of treatment, and it is not required for treatment to be considered effective. Residual uptake can come from inflammation, scar tissue, slowly clearing cells, or normal activity in nearby tissue. Whether it is a concern depends on how much the SUV has fallen and what the scan images show — not on whether it has reached zero.
Can residual uptake be from inflammation rather than cancer?
Yes, and this is one of the most important things to understand. The FDG tracer does not distinguish between cancer and inflammation. Radiotherapy causes an inflammatory response that can produce uptake for weeks after treatment ends. Surgery and immunotherapy can do the same. In some situations, a repeat scan after more time passes gives a clearer picture than acting on the first post-treatment result.
What will happen next if my SUV went down but not to zero?
That depends on your cancer type, how much the SUV has changed, and what the rest of the scan shows. Common next steps include continuing treatment and rescanning at the next planned point, waiting before a further scan to allow inflammation to settle, or — in some cases — a biopsy to sample the area of remaining uptake directly. Your oncologist will explain which approach suits your situation.
Can I compare my SUV with another patient's result?
Not in any useful way. SUV values are affected by the scanner used, how long the tracer circulated before imaging, your body composition, and your blood sugar at the time of the scan. Two people scanned under slightly different conditions can have different numbers even with identical tumour activity. What matters is the change in your own scans — baseline compared to post-treatment, on the same or comparable equipment.
Where does CION arrange PET scans?
CION coordinates PET-CT scanning through partner imaging centres rather than operating its own scanners. Your care team will arrange the referral and try to ensure the post-treatment scan uses the same centre as your baseline, because scanner consistency matters for a reliable comparison. Staff at any of the 35-plus CION centres can advise you on logistics and how to prepare.