Is a PET/CT scan medically necessary for a patient with Non-Small Cell Lung Cancer (NSCLC) post-radiation and post-chemotherapy, currently being treated with durvalumab (durvalumab is a brand name, the generic name is not needed here as it is the same)?

Medical Necessity Letter for PET/CT Scan Appeal

Clinical Justification

PET/CT imaging is medically necessary and appropriate for this patient with NSCLC post-chemoradiation currently on durvalumab maintenance therapy, specifically when there are equivocal CT findings or clinical suspicion of disease recurrence that requires definitive characterization to guide critical treatment decisions.

Evidence-Based Rationale

Current Clinical Context

This patient represents a complex post-treatment surveillance scenario where accurate disease assessment directly impacts survival outcomes:

• Post-radiation inflammatory changes create significant diagnostic uncertainty on standard CT imaging, as radiation-induced fibrosis, atelectasis, and inflammatory responses can mimic malignant recurrence 1
• Durvalumab maintenance therapy (consolidation immunotherapy following chemoradiation) requires ongoing assessment to detect progression that may necessitate treatment modification 2, 3
• Critical treatment window: Early detection of salvageable locoregional or oligometastatic recurrence can enable curative-intent interventions that prolong overall survival 1

Guideline-Supported Indications

The ACR Appropriateness Criteria (2025) explicitly state that PET/CT is appropriate for assessing CT findings concerning for malignancy that may alternatively represent radiation fibrosis, atelectasis, or other benign conditions 1. This is precisely the clinical scenario where PET/CT provides critical diagnostic value that CT alone cannot deliver.

Key guideline recommendations:

• PET/CT should not be performed within 3 months post-radiation to avoid false-positives from therapy-related FDG uptake 1
• PET/CT is specifically indicated when CT findings are equivocal or concerning for recurrence versus post-treatment changes 1
• In the post-stereotactic ablative radiotherapy setting, recurrent disease should be suspected if high-risk CT changes are seen with SUVmax ≥5 on PET 1

Superior Diagnostic Performance

PET/CT provides critical functional-metabolic information that anatomic CT imaging cannot:

• Differentiates hypermetabolic tumor from normometabolic post-radiation changes, including fibrosis and atelectasis 1
• Detects occult distant metastases that would alter management from local to systemic therapy 1
• Identifies oligometastatic disease (≤3 metastases) amenable to local ablative therapies that can prolong survival 1
• High sensitivity (94.4%) and specificity (97.6%) for detecting recurrence in asymptomatic NSCLC patients post-treatment 1

Impact on Patient Outcomes

Early detection of recurrence through PET/CT enables interventions that directly improve morbidity, mortality, and quality of life:

• Asymptomatic patients with recurrences detected by surveillance imaging have better prognosis than those presenting with symptomatic disease 1
• 3% of asymptomatic patients post-radical radiotherapy had progression amenable to curative treatment identified by PET/CT at 3 months 1
• Early identification of progression allows timely transition to second-line therapies, all of which were feasible in real-world durvalumab maintenance cohorts 3
• Prevents futile continuation of immunotherapy in patients with undetected progression, avoiding unnecessary toxicity and cost 3

Clinical Context for This Patient

In patients on durvalumab maintenance after chemoradiation:

• Median treatment duration is 6.4 months with 14 cycles before discontinuation or completion 3
• 31% develop relapse during maintenance after median 4.8 months, requiring prompt detection for salvage therapy 3
• Grade 3 pneumonitis occurs in 15% of patients, making differentiation between immune-related toxicity, radiation pneumonitis, and disease progression critical 3, 4
• No cases of hyperprogression were documented with appropriate surveillance 3

Addressing Common Pitfalls

Critical timing considerations:

• PET/CT should be performed >3 months post-radiation to minimize false-positives from inflammatory changes 1, 5
• False-positive findings from post-radiation inflammation and fibrosis are well-recognized limitations that must be interpreted in clinical context 1
• Correlation with clinical symptoms, tumor markers, and serial CT changes enhances diagnostic accuracy 6, 5

Important caveats:

• PET/CT is not recommended for routine asymptomatic surveillance without concerning CT findings or clinical suspicion 1
• Ground-glass lesions and small adenocarcinomas may be missed by PET and require CT correlation 1
• Brain metastases are better detected by MRI than PET/CT 1

Conclusion Statement

This PET/CT scan is medically necessary to definitively characterize equivocal post-treatment findings and guide critical management decisions that directly impact this patient's survival and quality of life. The superior diagnostic performance of PET/CT in distinguishing post-radiation changes from recurrent malignancy, combined with the potential for curative-intent salvage therapy if recurrence is detected early, provides clear medical justification supported by current ACR guidelines and clinical evidence 1.