Hyperpolarized Helium-3 Magnetic Resonance Imaging of Emphysema and Airway Function for Radiation Therapy Guidance in Non-Small Cell Lung Cancer
PURPOSE Survival rates for non-small cell lung cancer (NSCLC) are dismal, largely due to radiation dose restrictions to limit radiation-induced lung injury (RILI). Evidence suggests that chronic obstructive pulmonary disease (COPD) may be a predictor of RILI, although a direct relationship between RILI and COPD is yet to be determined. Our objective was to use hyperpolarized 3He magnetic resonance imaging (MRI) to evaluate patients with NSCLC before radiation therapy to provide evidence for the use of structure/function MR measurements to identify RILI risk and subjects suitable for dose-escalation. In this way, we hypothesize structure/function MRI can provide a way to guide radiation therapy treatment plans. METHOD AND MATERIALS Eleven subjects with stage 3 or 4 NSCLC scheduled for radical radiation therapy (>60Gy, 2Gy/fraction) provided written informed consent and underwent 3He MR static ventilation (SV) and diffusion-weighted (DW) imaging at 3T during a static breath-hold of a 1.0L 3He/N2 mixture. 3He MRI percent ventilated volume (PVV) and apparent diffusion coefficients (ADC) were generated for the contralateral lung prior to radiation therapy. Radiation treatment plans were generated blinded to the 3He MRI results and RILI was evaluated 3 months post-treatment using CT. RESULTS Two distinct classes of NSCLC subjects were identified based on 3He MRI ADC and PVV. Five of 11 subjects showed low ADC and high PVV values suggesting a lack of underlying COPD (left 2 panels) whereas six of 11 subjects showed both elevated ADC and decreased PVV (right 2 panels), both of which are related to emphysema and airway functional abnormalities that are the hallmarks of COPD. There was no relationship between FEV1 or smoking history and 3He MRI ADC or VDP. For both subject groups, there was no significant difference in survival or incidence of RILI, with radiological evidence of RILI present in two subjects in each group. CONCLUSION In this small pilot study of NSCLC patients undergoing radiation therapy, 5/11 subjects did not show 3He MRI evidence of underlying COPD; the presence of COPD was not related to the incidence of RILI or survival. CLINICAL RELEVANCE/APPLICATION In this pilot study, 3He MRI measurements of COPD in NSCLC showed no relationship to RILI incidence or survival, suggesting that for radiation therapy guidance, more information may be required.