What imaging modality should be ordered to evaluate the need for a further boost after completing radiation therapy (RT) to lung cancer?

From the Guidelines

Positron emission tomography-computed tomography (PET-CT) is the recommended imaging modality to evaluate the need for a radiation boost after completing initial radiation therapy for lung cancer. This recommendation is based on the latest evidence from the European Journal of Nuclear Medicine and Molecular Imaging, which suggests that 2-[18F]FDG PET/CT is a standard imaging modality for staging, selection for curative RT, defining and delineating the target volume in the RT planning phase, and detection of residual or recurrent disease 1.

After the planned course of radiation therapy, PET-CT should be performed approximately 3 months post-treatment to assess tumor response and identify any residual metabolically active disease that might benefit from additional targeted radiation 1. The timing allows for resolution of radiation-induced inflammation while still enabling early detection of persistent disease.

Key Benefits of PET-CT

• Provides both anatomical information and functional metabolic activity
• Helps distinguish between post-radiation changes and residual viable tumor
• The standardized uptake value (SUV) on PET can quantify metabolic activity, with persistent elevated values suggesting viable tumor cells that might require additional treatment

Considerations for PET-CT Interpretation

• Pattern recognition is important for detecting recurrence, with local recurrence tends to be more focal, whereas inflammation has a more diffuse appearance 1
• Software that allows fusion of radiation dose-volume contours as DICOM-object with PET images can be particularly helpful in differentiating between recurrent tumor and post-radiation fibrosis 1

If a boost is deemed necessary based on PET-CT findings, a typical dose would be 10-20 Gy delivered in 5-10 fractions to the residual disease volume with appropriate margins, though the specific dose should be individualized based on previous radiation exposure and normal tissue constraints.

From the FDA Drug Label

Fludeoxyglucose F 18 Injection, USP is indicated in positron emission tomography (PET) imaging for assessment of abnormal glucose metabolism to assist in the evaluation of malignancy in patients with known or suspected abnormalities found by other testing modalities, or in patients with an existing diagnoses of cancer To evaluate the need for a further boost after completing radiation therapy (RT) to lung cancer, a Positron Emission Tomography (PET) image should be ordered, specifically using Fluorodeoxyglucose (FDG) F 18 Injection 2. This imaging modality can help assess abnormal glucose metabolism associated with malignancy, which can inform the decision for additional treatment.

From the Research

Imaging Modalities for Evaluating the Need for a Further Boost after Completing Radiation Therapy to Lung Cancer

To assess if a further boost is needed after completing radiation therapy (RT) to lung cancer, the following imaging modalities can be considered:

• Positron Emission Tomography (PET) scanning, which has been shown to be valuable for the diagnosis, staging, prognosis, and restaging of lung cancer 3
• PET/CT imaging, which provides functional information and is attractive for evaluating tumor response after radiotherapy 4
• 18F-fluorodeoxyglucose (FDG) PET/CT, which has a well-established role in clinical routine after definitive chemo-radiotherapy for locally advanced head-and-neck cancers and is optional in many other circumstances 4

Advantages of PET/CT Imaging

The advantages of using PET/CT imaging in this context include:

• Improved accuracy in staging and restaging of lung cancer compared to conventional structural imaging alone 3, 5
• Ability to evaluate tumor response after radiotherapy and predict patient outcome 4, 6
• Greater diagnostic accuracy than other imaging modalities for the detection of tumor recurrence after definitive treatment 6

Clinical Applications of PET/CT Imaging

PET/CT imaging has various clinical applications in lung cancer, including:

• Initial staging and guiding surgical and radiotherapy planning 6
• Predicting tumor response and tailoring therapy after the initiation of chemoradiotherapy 6
• Detecting tumor recurrence after definitive treatment 6
• Evaluating different types of lung cancer, such as non-small-cell lung cancer (NSCLC), small-cell lung cancer (SCLC), and lung neuroendocrine tumors (NET) 7