Mid-treatment response
Interim PET Scan — Why It Is Done Mid-Treatment
An interim PET scan is done partway through your chemotherapy to check whether the lymphoma is responding — before your treatment plan is locked in for the rest of the course. The result can prompt a change in your treatment, and that is exactly what it is designed to do.
Medically reviewed by Dr. C. Raghavendra Reddy, Medical Oncologist, MBBS (Gold Medal) · DNB · DM (Medical Oncology, Gold Medal) · Last reviewed September 2026
- Done mid-treatment on purpose — The scan is timed to give your team a chance to change your treatment if it is not working, while that change can still make a difference.
- Most established in lymphoma — Response-adapted therapy is best supported in Hodgkin lymphoma and some large B-cell lymphomas, where evidence from clinical trials guides its use.
- Scored on the Deauville scale — The result is a number from 1 to 5 that compares remaining lymphoma activity against reference tissues, not a simple positive or negative.
- Only your oncologist interprets it — The score feeds into a clinical decision that also weighs your cancer type, stage, and overall health — not the number alone.
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An interim PET scan is done partway through chemotherapy to check if your lymphoma is responding before treatment ends. The result is reported as a Deauville score, a five-point scale endorsed by NCCN, ESMO, and the Lugano classification. Your oncologist uses the score to decide whether to continue, intensify, or change your treatment.
What do the terms on your interim PET report mean?
- Interim PET scan (iPET)
- A PET scan done partway through your chemotherapy — usually after the second or third cycle — to measure whether the lymphoma is responding while treatment is still ongoing. It is not the same as the end-of-treatment scan.
- FDG
- Fluorodeoxyglucose, a slightly radioactive form of glucose injected before the scan. Active cancer cells absorb more of it than normal tissue, which is how the scanner identifies areas of remaining disease activity.
- Deauville score
- A five-point international scoring system used to report PET results in lymphoma. The score compares FDG uptake remaining in the tumour to uptake in two reference areas of the body. It is endorsed by ESMO, NCCN, and the Lugano classification.
- Metabolic response
- A fall in the amount of FDG being absorbed by the lymphoma compared to the staging scan. A metabolic response is the sign the interim PET is looking for — that the tumour cells are becoming less active.
- Response-adapted therapy
- A treatment strategy in which the interim PET result is used to change the original plan — intensifying treatment if the response is poor, or potentially reducing its intensity if the response is strong. ESMO and NCCN guidance for Hodgkin lymphoma endorses this approach.
- Residual uptake
- FDG activity remaining in an area of previous disease at the time of the interim scan. Whether residual uptake is significant depends on how it compares to the reference organs on the Deauville scale, not on how it looks to the eye alone.
Why is a scan done before your chemotherapy is finished?
An interim scan exists because the result can change your treatment while there is still time for that change to matter. Waiting until all cycles are done means finding out too late if the current regimen is not working.
If the response is good, treatment continues with confidence. If the response is poor, your oncologist has the information needed to switch to a different or more intensive regimen before more cycles of an ineffective treatment are given.
This is most established in Hodgkin lymphoma, where large clinical trials have shown that adapting treatment to the interim PET result — rather than treating everyone the same way to the end — improves outcomes, according to ESMO and NCCN guidance.
What can the result actually change?
A result showing a strong response may allow treatment to continue as planned, and in some protocols it opens a discussion about whether the intensity of later cycles needs to stay as high.
A result showing inadequate response may prompt a switch to a different or more intensive regimen. Neither of these decisions follows automatically from the score — your oncologist weighs it alongside your cancer type, stage, and how you have responded clinically.
If the result is equivocal — not clearly in either direction — your oncologist will explain what that means for your specific situation. Sometimes a further scan or biopsy is needed before a decision is made.
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What should you ask when your interim result is discussed?
- What was my Deauville score, and what does it mean for my type of lymphoma?
- Has the treatment plan changed, or will the same chemotherapy continue?
- If the plan is changing, what is the new regimen and what is it expected to achieve?
- If the result is equivocal, what needs to happen before a decision is made?
- When is my next scan, and what will that one be assessing?
- Is there anything to do or avoid before the next scan?
How is the interim scan different from the end-of-treatment scan?
| Interim PET scan | End-of-treatment PET scan | |
|---|---|---|
| When it is done | Partway through chemotherapy, usually after the second or third cycle | After all planned cycles of chemotherapy are complete |
| What question it answers | Is the lymphoma responding to this regimen? | Is there any detectable lymphoma remaining after treatment? |
| How the result is used | To decide whether to continue, change, or intensify the current treatment | To guide whether further treatment or monitoring is needed |
| What a clear negative means | The lymphoma appears to be responding well at this point in treatment | No active lymphoma is detectable at the end of treatment |
| Who it is most commonly done in | Patients with Hodgkin lymphoma and some large B-cell lymphomas | Most patients with lymphoma completing a planned treatment course |
The questions families ask most about the interim scan
Why did I not have an interim scan during my previous cancer treatment?
Interim PET scanning is most established in lymphoma, particularly Hodgkin lymphoma and some diffuse large B-cell lymphomas, where clinical evidence shows that adapting treatment to the interim result improves outcomes. For most other cancer types and treatment regimens, interim PET scanning has not been validated in the same way and is not part of the standard approach. Your previous treatment may have had a different monitoring protocol that was appropriate for that cancer type.
Can the scan pick up something unrelated to my lymphoma?
Yes. A PET scan covers the whole body, so it can occasionally show FDG activity in an area unrelated to your lymphoma — caused by infection, inflammation, or another incidental finding. Your oncologist will explain what was seen and whether further investigation is needed before drawing any conclusions. An unexpected finding does not automatically mean the cancer has spread; all findings are interpreted in clinical context.
Can the Deauville score be wrong?
No test is perfect. A PET result can be influenced by factors unrelated to the cancer, including recent infection, inflammation, or the timing of the scan relative to your last chemotherapy cycle. This is one reason your oncologist interprets the score in context rather than acting on the number alone. If there is genuine doubt about whether the result reflects the cancer or something else, your team may recommend further assessment before making a treatment decision.
My result was a Deauville 3. What does that mean?
A Deauville score of 3 falls in the middle of the scale and is sometimes described as equivocal — neither clearly negative nor clearly positive. How your oncologist responds to it depends on your specific cancer type, the treatment protocol being used, and the clinical picture overall. In some settings a score of 3 is treated as a good response; in others it prompts closer review. This is a question to put directly to your oncologist, who can explain what it means in the context of your own situation and the guidelines they are following.
Do I need to do anything special to prepare for the scan?
Yes. PET scans using FDG require preparation because the scanner measures glucose uptake, and anything that changes how your body uses glucose can affect the result. Instructions typically include fasting for several hours before the scan, avoiding strenuous exercise in the day or two before, and resting quietly after the tracer injection. Follow the instructions your imaging centre gives you exactly — arriving unprepared may mean the scan needs to be rescheduled, which can delay your treatment decision.
How does CION arrange the interim PET scan?
PET-CT imaging is coordinated by CION with partner imaging centres rather than performed at CION's own facilities. Your oncology team will arrange the referral, tell you where to go and what preparation is required, and receive the report when it is ready. Your CION oncologist will then discuss the result and its implications with you, either at your next scheduled appointment or sooner if the result affects an upcoming treatment decision.
PET-CT at CION starts from Rs 10,499 — among the lowest published prices in Hyderabad — across 4 partner centres in Banjara Hills, Punjagutta, Himayatnagar and Narayanaguda. 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
When during chemotherapy is the interim PET scan usually done?
In Hodgkin lymphoma it is most often done after the second cycle of chemotherapy, and is sometimes called iPET-2. The timing varies depending on your treatment protocol and cancer type. Your oncologist will tell you at which point in your course of treatment the scan is planned and what it is designed to assess at that stage. If your scan is at a different point — after the third or fourth cycle, for example — ask your team why, because the timing is usually chosen deliberately for your specific protocol.
Is the scan uncomfortable?
The scan itself is not painful. You will receive an injection of FDG and then be asked to rest quietly for about an hour before scanning begins. The machine is open rather than fully enclosed, and the scan takes roughly twenty to forty minutes during which you need to lie still. If you have concerns about the injection, the waiting period, or lying still for that long, tell the imaging team before the scan — they can often make adjustments to help.
What is the Lugano classification?
The Lugano classification is an international framework for staging lymphoma and for reporting PET scan results, including the Deauville scoring system. It was agreed by a group of lymphoma experts and is referenced in guidelines from ESMO, NCCN, and ASCO. When your report mentions the Lugano classification, it means the scan has been reported according to this agreed international standard rather than a local or informal method.
If my treatment changes after the interim scan, does that mean things are not going well?
Not necessarily. A change in treatment after an interim scan means your team caught something in time to act on it — which is the entire point of doing the scan mid-treatment. Response-adapted therapy exists because identifying an inadequate response early gives you a better chance than staying on the same plan to the end. A change may mean a more intensive regimen or a different approach, and your oncologist will explain what the new plan is intended to achieve. The important thing is that the information arrived when it could still be used.
How long does it take to get the result?
Usually a few days to a week, depending on the imaging centre and how quickly the report reaches your oncologist. If the result is needed before your next cycle of chemotherapy, your team will try to have it available in time. Ask at the time of the scan when to expect the result and who will contact you — you should not be left waiting without a timeline, and if you have not heard within the expected period, it is reasonable to call and ask.
Is interim PET scanning available through CION?
Yes. CION coordinates PET-CT scanning through partner imaging centres, and your oncology team will arrange the referral, preparation instructions, and result review as part of your treatment plan. The scan report is discussed with you by your CION oncologist, who will explain the result and what it means for the rest of your treatment course.