Limonene for Pulmonary Nodule Chemoprevention

Inclusion Criteria: * Non-smokers (those who have smoked less than 100 cigarettes in their lifetime, including those who have never smoked in their lifetime). * Subjects must have positive nodules detected by high-resolution CT（HRCT）: longest diameter \> 6 mm and \< 20 mm; pure ground glass nodule; according to the judgment of the clinician, follow-up can be performed, and surgical excision is not recommended for the time being; the nodules did not disappear or were not significantly reduced by more than 2 mm after six months follow-up; subjects should have at least one positive nodule when had multiple nodules. * ECOG performance status 0-1. * Those who accept and are willing to sign the informed consent. Exclusion Criteria: * Subjects with the history of autoimmune diseases and severe gastrointestinal diseases; * Subjects suffering from malignant tumor, severe heart disease, severe liver or kidney disease currently or within the past 5 years; * Within 6 weeks since prior herbal supplements, non-steroidal anti-inflammatory drugs, or antibiotics * Subjects who are allergic to limonene capsules or citrus foods; * Use of any other investigational agents at time of enrollment in the study during the three months preceding study enrollment * Pregnant or lactating females, or those who disagreeing with contraception; * Subjects who have a history of mental illness and cannot cooperate with this project; * HIV-positive subjects should be excluded. * Subjects whose organ and bone marrow function indexes exceeded the following range of normal value were excluded: 1. Leukocytes: 3.5-9.5 109/L; 2. Absolute neutrophil count: 1.8-6.3 109/L; 3. Platelets: 125-350 109/L; 4. Total bilirubin: 5.0-21.0 µmol /L; 5. AST (SGOT)/ALT (SGPT): 0.8-1.5; 6. Serum creatinine: 41-81 μmol/L; * Other situations where the researcher thinks it is inappropriate to participate in this research.