What is the frequency of Positron Emission Tomography (PET) scans for monitoring cancer?

Frequency of PET Scans for Cancer Monitoring

PET scans should not be used for routine cancer surveillance as they are not recommended outside of clinical trials for most cancer types.

General Guidelines for PET Scan Use in Cancer Monitoring

The American Society of Clinical Oncology (ASCO) and other major oncology organizations have clear positions on PET scan use for cancer surveillance:

• PET scans are not recommended for routine surveillance of cancer patients after treatment 1
• PET should only be used for surveillance within clinical trial settings 1
• When clinically indicated, PET scans should be used selectively based on specific suspicion of recurrence, not as a standard monitoring tool

Cancer-Specific Recommendations

Colorectal Cancer

• ASCO explicitly states that "PET scans should not be used for surveillance outside of the setting of a clinical trial" 1
• Standard surveillance includes:
  • Physical examinations every 3-6 months for first 2-3 years
  • CEA testing every 3-6 months
  • CT scans of chest/abdomen/pelvis annually for 3 years
  • Colonoscopy at 1 year post-surgery

Hodgkin Lymphoma

• "Surveillance PET should not be performed routinely because of risk for false-positives" 1
• Management decisions should not be based on PET scan alone; clinical or pathologic correlation is needed
• PET is indicated when there is clinical suspicion of recurrence while routine imaging is negative

Breast Cancer

• "FDG-PET scanning is not recommended for routine breast cancer surveillance" 1
• Standard surveillance includes:
  • History and physical exam every 3-6 months for first 3 years
  • Annual mammography
  • No routine blood tests or other imaging recommended

Neuroblastoma

• For MIBG-avid tumors, 123I-MIBG scan with SPECT is recommended:
  • Every 3-6 months in year 1
  • Every 6 months in year 2
  • Annually in year 3
  • Then as clinically indicated 1
• For non-MIBG avid tumors, FDG-PET follows the same schedule

Prostate Cancer

• For metastatic castration-resistant prostate cancer (mCRPC) without PSA progression or new symptoms, imaging should be performed at least annually 1
• PSMA PET imaging is recommended for patients considering 177Lu-PSMA-617 therapy who have previously received docetaxel and androgen pathway inhibitors

Factors Influencing PET Scan Use

Despite guidelines recommending against routine PET scans for surveillance, several factors drive their use:

• Information seeking from non-medical sources is associated with higher odds of PET use for surveillance (OR 3.7; 95% CI 1.1-12.1) 2
• PET use continues to grow rapidly (18% annual increase from 2004-2008) without evidence of replacing other imaging modalities like CT 3
• Approximately half of PET scans occur shortly after body CT, suggesting an additive rather than replacement role 3

Appropriate Indications for PET in Cancer Management

PET scans are appropriate in specific scenarios:

1. Initial staging of certain cancers
2. Treatment response assessment during therapy (not routine surveillance)
3. Suspected recurrence based on clinical symptoms or rising tumor markers when conventional imaging is negative
4. Prior to major therapeutic decisions where detection of additional disease sites would alter management

Conclusion

The evidence clearly shows that PET scans should not be used for routine cancer surveillance. Instead, cancer monitoring should follow evidence-based guidelines specific to each cancer type, with PET reserved for situations where there is clinical suspicion of recurrence or specific indications where it would change management.