Location
Suwanee, GA
Start Date
17-4-2026 12:00 PM
End Date
17-4-2026 1:00 PM
Description
INTRODUCTION: Non–small cell lung cancer (NSCLC) represents the majority of lung cancer diagnoses and remains a leading cause of cancer-related mortality worldwide. Immune checkpoint inhibitors such as pembrolizumab are now commonly used as first-line systemic therapy in metastatic disease and have significantly improved patient outcomes. However, these therapies can produce atypical imaging findings due to inflammatory or immune-mediated processes. Distinguishing true tumor progression from infection, inflammation, or pseudoprogression on fluorodeoxyglucose (FDG) positron emission tomography–computed tomography (PET-CT) can therefore be challenging and may influence treatment decisions.
OBJECTIVES: To describe a case of apparent oligoprogression on PET imaging in a patient with metastatic NSCLC receiving pembrolizumab that was later determined to represent resolving pneumonia, and to highlight the implications of PET interpretation on stereotactic body radiotherapy (SBRT) planning.
METHODS: We present a single-patient case report describing clinical presentation, imaging findings, and radiation treatment planning considerations. Serial PET-CT imaging and CT simulation findings were reviewed to evaluate the suspected oligoprogressive lesion and its impact on SBRT planning.
RESULTS: A 70-year-old female with metastatic NSCLC receiving pembrolizumab presented with a newly identified hypermetabolic lesion in the left lower lobe (LLL) on surveillance PET-CT. The lesion was initially interpreted as possible oligoprogressive disease and the patient was referred for SBRT. However, CT simulation performed shortly afterward demonstrated near-complete resolution of the LLL lesion without a residual solid component, favoring a resolving infectious or inflammatory process consistent with pneumonia. As a result, SBRT to the LLL lesion was deferred. Treatment planning proceeded only for the persistent FDG-avid left upper lobe (LUL) primary tumor. Radiation planning required modification of standard lung SBRT immobilization because a symptomatic right upper-extremity abscess prevented bilateral arm elevation. The patient was positioned with only the left arm on the wingboard and the right arm maintained in an akimbo position. Left-sided partial beam arcs were used to achieve adequate target coverage while minimizing dose to the right upper extremity.
CONCLUSION: This case highlights the complexity of interpreting PET-avid lesions in patients receiving immunotherapy. Inflammatory or infectious processes may closely mimic tumor progression on PET imaging and can significantly alter management decisions. Short-interval imaging and careful clinical correlation are essential to avoid unnecessary local therapy. Additionally, unexpected clinical findings may require adaptive modifications in SBRT immobilization and beam design to safely deliver treatment.
Embargo Period
6-1-2026
Included in
Impact of PET-CT Interpretation on SBRT Planning: A Case of Pseudoprogression From Resolving Pneumonia During Pembrolizumab
Suwanee, GA
INTRODUCTION: Non–small cell lung cancer (NSCLC) represents the majority of lung cancer diagnoses and remains a leading cause of cancer-related mortality worldwide. Immune checkpoint inhibitors such as pembrolizumab are now commonly used as first-line systemic therapy in metastatic disease and have significantly improved patient outcomes. However, these therapies can produce atypical imaging findings due to inflammatory or immune-mediated processes. Distinguishing true tumor progression from infection, inflammation, or pseudoprogression on fluorodeoxyglucose (FDG) positron emission tomography–computed tomography (PET-CT) can therefore be challenging and may influence treatment decisions.
OBJECTIVES: To describe a case of apparent oligoprogression on PET imaging in a patient with metastatic NSCLC receiving pembrolizumab that was later determined to represent resolving pneumonia, and to highlight the implications of PET interpretation on stereotactic body radiotherapy (SBRT) planning.
METHODS: We present a single-patient case report describing clinical presentation, imaging findings, and radiation treatment planning considerations. Serial PET-CT imaging and CT simulation findings were reviewed to evaluate the suspected oligoprogressive lesion and its impact on SBRT planning.
RESULTS: A 70-year-old female with metastatic NSCLC receiving pembrolizumab presented with a newly identified hypermetabolic lesion in the left lower lobe (LLL) on surveillance PET-CT. The lesion was initially interpreted as possible oligoprogressive disease and the patient was referred for SBRT. However, CT simulation performed shortly afterward demonstrated near-complete resolution of the LLL lesion without a residual solid component, favoring a resolving infectious or inflammatory process consistent with pneumonia. As a result, SBRT to the LLL lesion was deferred. Treatment planning proceeded only for the persistent FDG-avid left upper lobe (LUL) primary tumor. Radiation planning required modification of standard lung SBRT immobilization because a symptomatic right upper-extremity abscess prevented bilateral arm elevation. The patient was positioned with only the left arm on the wingboard and the right arm maintained in an akimbo position. Left-sided partial beam arcs were used to achieve adequate target coverage while minimizing dose to the right upper extremity.
CONCLUSION: This case highlights the complexity of interpreting PET-avid lesions in patients receiving immunotherapy. Inflammatory or infectious processes may closely mimic tumor progression on PET imaging and can significantly alter management decisions. Short-interval imaging and careful clinical correlation are essential to avoid unnecessary local therapy. Additionally, unexpected clinical findings may require adaptive modifications in SBRT immobilization and beam design to safely deliver treatment.