Using Fluorodeoxyglucose Positron Emission Tomography to Assess Tumor Volume During Radiotherapy for Non–Small-Cell Lung Cancer and Its Potential Impact on Adaptive Dose Escalation and Normal Tissue Sparing

Abstract

Purpose Fluorodeoxyglucose–positron emission tomography (FDG-PET) has improved target definition in non-small cell lung cancer (NSCLC), but few data exist regarding changes during radiotherapy. The purpose of this study was to quantify changes in FDG-avid tumor volume and examine its potential use in adaptive radiotherapy for tumor dose escalation or normal tissue sparing. Methods and Materials As part of a pilot study, fourteen patients with stage I-III NSCLC underwent FDG-PET-CT prior to radiation (RT) and mid-RT (after 40–50 Gy). Gross tumor volumes (GTVs) were contoured on CT and PET scans obtained before and during RT. 3D conformal RT plans were generated for each patient first using only pre-treatment CT scans. Mid-RT PET volumes were then used to design boost fields. Results Fourteen patients with FDG-avid tumors were assessed. Two patients had a complete metabolic response, two patients had slightly increased FDG-uptake in the adjacent normal tissue. Mid-RT PET scans were useful in 10 remaining patients. Mean decreases in CT and PET tumor volumes were 26% (range: +15% to −75%) and 44% (range:+10% to −100%) respectively. Designing boosts based on mid-RT PET allowed for meaningful dose escalation of 30–102 Gy (mean 58 Gy), or normal tissue complication probability (NTCP) reduction of 0.4–3% (mean 2%) in 5 of 6 patients with smaller, yet residual, tumor volumes. Conclusions Tumor metabolic activity and volume can change significantly after 40–50 Gy of RT. Using mid-RT PET volumes, tumor dose can be significantly escalated or NTCP reduced. Clinical studies evaluating patient outcome after PET-based adaptive radiotherapy are ongoing.

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