Potential of 18F-FDG PET toward personalized radiotherapy or chemoradiotherapy in lung cancer.

Purpose: We investigated the metabolic response of lung cancer to radiotherapy or chemoradiotherapy by (18)F-FDG PET and its utility in guiding timely supplementary therapy.

Methods: Glucose metabolic rate (MRglc) was measured in primary lung cancers during the 3 weeks before, and 10-12 days (S2), 3 months (S3), 6 months (S4), and 12 months (S5) after radiotherapy or chemoradiotherapy. The association between the lowest residual MRglc representing the maximum metabolic response (MRglc-MMR) and tumor control probability (TCP) at 12 months was modeled using logistic regression.

Results: We accrued 106 patients, of whom 61 completed the serial (18)F-FDG PET scans. The median values of MRglc at S2, S3 and S4 determined using a simplified kinetic method (SKM) were, respectively, 0.05, 0.06 and 0.07 μmol/min/g for tumors with local control and 0.12, 0.16 and 0.19 μmol/min/g for tumors with local failure, and the maximum standard uptake values (SUVmax) were 1.16, 1.33 and 1.45 for tumors with local control and 2.74, 2.74 and 4.07 for tumors with local failure (p < 0.0001). MRglc-MMR was realized at S2 (MRglc-S2) and the values corresponding to TCP 95 %, 90 % and 50 % were 0.036, 0.050 and 0.134 μmol/min/g using the SKM and 0.70, 0.91 and 1.95 using SUVmax, respectively. Probability cut-off values were generated for a given level of MRglc-S2 based on its predicted TCP, sensitivity and specificity, and MRglc ≤0.071 μmol/min/g and SUVmax ≤1.45 were determined as the optimum cut-off values for predicted TCP 80 %, sensitivity 100 % and specificity 63 %.

Conclusion: The cut-off values (MRglc ≤0.071 μmol/min/g using the SKM and SUVmax ≤1.45) need to be tested for their utility in identifying patients with a high risk of residual cancer after standard dose radiotherapy or chemoradiotherapy and in guiding a timely supplementary dose of radiation or other means of salvage therapy.