“Post-Therapeutic Inflammatory Changes/Scarring” in Lung Cancer Cases
In lung cancer patients treated with chemotherapy and/or radiation, the PET/CT radiologist is asked to determine whether a shrinking lung tumor represents fully treated scar tissue or whether residual underlying active malignancy remains.
Unfortunately, within the first few months of even successful treatment, many of these masses are at least partially masked within large regions of FDG-avid parenchymal radiation changes. The original mass will frequently appear ill-defined and may be impossible to distinguish from the surrounding pneumonitis.
In these cases, it may be impossible to accurately conclude whether residual active malignancy remains.
Common Presentations After Initial Treatment:
- If the mass is fully obscured by acute FDG-avid radiation changes, the radiologist cannot offer much diagnostic assistance:
“Prominent, ill-defined and intensely avid soft tissue density is now noted within the medial right upper lobe, obscuring the region previously noted to contain the patient’s FDG-avid lung mass. Unfortunately, persistent active malignancy cannot be excluded within this area of acute radiation pneumonitis. Follow-up is recommended.”
- If the mass is partially obscured by FDG avid radiation changes, but we can still determine that the mass has decreased in size and metabolic activity since the prior exam, we should suggest interval improvement:
“The patient’s pulmonary mass has decreased in size and metabolic activity, now only moderately avid. While the remaining activity can reflect superimposed post-therapeutic inflammatory changes, residual underlying malignancy cannot be excluded and follow up is recommended.”
- If the mass has significantly decreased in size and is now non-avid, we report:
“Its decrease in size and lack of metabolic activity on today’s exam are most consistent with post-therapeutic scarring/fibrosis.”
Case 1
Case 1 (Image 2)
1-year post radiation treatment of the right lung cancer. MIP is now unremarkable. Axial images demonstrate prominent, ill-defined soft tissue density in the right paramediastinal region, not significantly FDG-avid. This is a typical appearance of radiation fibrosis (“post-therapeutic scarring”), the late/chronic sequela of radiation therapy. Note the linear lateral margin of these changes (box), corresponding to the margin of the radiation field.
Case 1 (Image 3)
Pre & post-therapy axial fused images demonstrate the evolution of hypermetabolic mass to ill-defined post-therapeutic scarring, not significantly avid (its metabolic activity is not greater than mediastinal blood pool uptake).
Case 1 (Image 4)
MIP images are a useful tool for assessing metabolic activity relative to liver or blood pool uptake. Here, the post-treatment MIP illustrates that any residual soft tissue in the region of the prior mass does not demonstrate activity above mediastinal blood pool uptake.
Case 2
Case 2 (Image 2)
Axial images confirm the hypermetabolic primary lung cancer and an adjacent FDG avid metastatic prevascular lymph node (arrow).
Case 2 (Image 3)
4-months after treatment. The mass and adjacent node have coalesced into prominent, ill-defined soft tissue density. The metabolic activity of these findings has markedly improved. Some residual metabolic activity, however, remains (greater than mediastinal blood pool uptake; equivalent to liver uptake).
Case 2 (Image 4)
Axial comparison of the pre and post therapy scans demonstrates marked improvement, yet residual metabolic activity.
Case 2 (Image 5)
Although comparison MIP images demonstrate marked interval improvement, the residual metabolic activity is still equivalent to liver uptake. So while this may now represent post-therapeutic scarring, residual active malignancy cannot be excluded. Follow up is recommended.
Case 3
Case 3 (Image 2)
2-months post chemoradiation: MIP image now demonstrates a very large region of intense metabolic activity in the location of the patient’s lung cancer – a dramatic increase from the initial study.
Case 3 (Image 3)
2-months post chemoradiation: The large PET abnormality noted on Image 2 corresponds to prominent, ill-defined and intensely avid soft tissue density, which has the appearance of a consolidation. The findings are most consistent with acute radiation pneumonitis, which now obscures the patient’s lung cancer. Persistent underlying active malignancy cannot be excluded within these FDG-avid radiation changes. Follow up is required.
Case 3 (Image 4)
6-months post chemoradiation: The acute radiation inflammatory changes have mildly decreased in size and no longer demonstrate significant metabolic activity (uptake ≤ mediastinal blood pool activity). Consequently, we now consider this to represent post-therapeutic scarring (the FDG avid precarinal node was presumed to reflect the patient’s known history of sarcoidosis).
Case 4
Case 4 (Image 2)
Fused axial image confirms the location of this hypermetabolic primary lung cancer.
Case 4 (Image 3)
2-months post chemoradiation. The mass is now smaller and more ill-defined. Its metabolic activity has also decreased. Surrounding post-radiation inflammatory changes are present (acute radiation pneumonitis). It is not possible to determine whether the remaining avidity of the mass reflects active malignancy or post-radiation inflammation. Follow up is required.
Case 4 (Image 4)
4-months post chemoradiation. Although residual post-radiation inflammatory changes of the pulmonary parenchyma remain, the patient’s primary lung mass is now non-avid, presumed to represent post-therapeutic scarring.
Case 4 (Image 5)
Comparison images of the original hypermetabolic malignancy and the resulting non-avid post-therapeutic scarring.
Case 5
Case 5 (Image 2)
2-months post chemoradiation. The mass is now partially obscured by post-radiation inflammatory changes (acute radiation pneumonitis). The primary lesion has decreased in metabolic activity. It is not possible to know whether the remaining avidity in the mass reflects active malignancy or post-radiation inflammatory changes. Follow up is required.
Case 5 (Image 3)
5-months post chemoradiation. The post-radiation inflammatory changes have improved. The mass is now smaller and demonstrates only minimal uptake.
Case 6
Case 6 (Image 2)
Fused axial image confirms the location of this hypermetabolic lung lesion (biopsy-proven lung cancer).
Case 6 (Image 3)
2-months post chemoradiation: MIP image now demonstrates a very large region of intense metabolic activity in the location of the patient’s lung cancer, markedly increased in size from the initial study.
Case 6 (Image 4)
2-months post chemoradiation: The large PET abnormality noted on Image 3 corresponds to prominent, ill-defined and intensely avid soft tissue density, containing air bronchograms, which has the appearance of a consolidation. The findings are most consistent with acute radiation pneumonitis, which now obscures the patient’s lung cancer. Persistent underlying active malignancy cannot be excluded within these FDG-avid radiation changes. Follow up is required.
Case 6 (Image 5)
6-months post chemoradiation: The post-radiation inflammatory changes have significantly improved. A nodular FDG-avid density, however, remains, corresponding to the location of the patient’s original mass. As its metabolic activity is greater than mediastinal blood pool uptake (it is actually greater than liver uptake), this is highly suspicious for residual/recurrent active malignancy.
Case 6 (Image 6)
MIP’s: Initial mass, acute radiation pneumonitis, and residual/recurrent active malignancy.
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