PET Scan in Cancer: When Do We Really Need It?

 


Understanding the correct role of PET-CT in oncology to avoid unnecessary tests

Positron Emission Tomography–Computed Tomography (PET-CT) has become one of the most valuable imaging tools in cancer care. It helps detect cancer spread, guides treatment, and monitors response. However, many patients today are advised PET scans even when they’re not truly required. Overuse of PET not only increases cost but can also mislead treatment decisions.

Let’s clearly understand where PET-CT is essential and where it is NOT needed in oncology.

☑️ When PET-CT is Required in Cancer Care

1. Staging of Certain Cancers Before Treatment

PET helps identify cancer spread and decide treatment intensity. It is essential for:

  • Lung cancer

  • Lymphomas (Hodgkin & Non-Hodgkin)

  • Head & neck cancers (except early oral cancers)

  • Esophageal cancer

  • Melanoma

  • Carcinoma of unknown primary (CUP)

2. Detecting Recurrence or Residual Disease

After treatment, PET-CT is helpful when:

  • Tumor markers rise (e.g., CEA in colorectal cancer).

  • CT or MRI shows unclear findings.

  • Symptoms suggest recurrence but routine tests are normal.

3. Evaluating Response to Treatment

Especially in:

  • Lymphomas (Deauville scoring)

  • Lung cancers on targeted/immunotherapies

  • Soft tissue sarcomas in some cases

4. Radiation Treatment Planning

For accurate target delineation, PET-CT is useful in:

  • Head & neck cancers

  • Lung cancers

  • Esophageal cancer

🚫 Where PET-CT is NOT Essential or Overused

❌ Early-Stage Cancers With Low Risk

PET-CT adds little value in:

  • Early-stage breast cancer

  • Early oral cavity cancers

  • Early-stage cervical cancer (IA, IB)

  • Early prostate cancer (low-risk)

In these situations, ultrasound/MRI/CT are adequate and cheaper.

❌ PET Cannot Replace Biopsy

  • PET may show false positives (infections, TB, inflammation).

  • Never start treatment based only on PET results.

  • Biopsy confirmation is mandatory before cancer diagnosis.

❌ Routine Follow-Up Without Symptoms

Many patients are asked to repeat PET every 3–6 months after treatment.
This is usually wrong and unnecessary.

Follow-up should be based on symptoms, clinical examination, ultrasound or CT — not PET every time.

❌ Screening Healthy Individuals

  • PET is not a screening tool for cancer.

  • It must NOT be used for health checkups without symptoms.

❌ Not Useful in Certain Tumors

Some cancers don’t show well in PET:

  • Prostate cancer (FDG PET is poor; PSMA PET is better)

  • Low-grade lymphomas

  • Renal cancers

  • Mucinous tumors

  • Some brain tumors (requires MRI as best scan)

⚠️ Risks and Limitations of Overusing PET-CT

  • High cost burden to patients.

  • Can show false positives, leading to unnecessary biopsies or aggressive treatment.

  • Exposure to radiation (though low, repeated scans add up).

  • Mental stress due to overdiagnosis.

🩺 How Oncologists Should Decide

The decision to use PET-CT must be based on:

  • Cancer type

  • Stage

  • Symptoms

  • Tumor markers

  • Whether the result will change treatment decision

If a scan does not change the treatment plan, it should not be done.

🔍 Quick Summary Table

SituationPET Needed?
Staging lung cancer, lymphoma, melanoma, esophagus, H&N✔️ Yes
Early breast/oral/prostate/cervical cancer❌ No
Suspected recurrence with markers/symptoms✔️ Yes
Routine follow-up without complaints❌ No
Before biopsy to diagnose cancer❌ No
For radiotherapy planning in lung, H&N, esophagus✔️ Yes
Screening healthy people❌ No

🏁 Final Takeaway

PET-CT is a powerful tool — but like any tool, it should be used wisely. Unnecessary scans increase financial burden and can lead to wrong decisions. Both doctors and patients must understand its appropriate use to ensure accurate, ethical, and cost-effective cancer care. Dr M G Giriyappagoudar a senior radiation oncologist of Hubli suggest that PET CT scan only if it's necessary and recommended by expert oncologist.

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