Efficacy and Safety of Prophylactic Cranial Irradiation Versus MRI Surveillance in Patients With Limited-stage Small Cell Lung Cancer Who Achieved Remission After First-line Chemoradiotherapy

Inclusion Criteria:

1. Histological or cytological confirmation of LS-SCLC before first-linechemoradiotherapy (according to the staging system of the Veterans' Affairs Lung StudyGroup (VALSG), Appendix 2)；
2. Remission is achieved after first-line chemoradiotherapy (CR or PR determined byRECIST v1.1)；
3. Brain MRI examination should be performed to exclude metastatic lesions of brainparenchyma and meninges within four weeks before enrollment；
4. The ECOG PS score was 0~2；
5. The interval between the end of the last treatment cycle and the randomized groupingshould be no more than 8 weeks；
6. Estimated survival time ≥ 12 weeks；
7. Patients must agree to participate in the study, comply with the research plan andfollow-up process. Written informed consent must obtained.
8. Male or female aged≥18 and≤75 years old;
9. For fertile women and man: Subjects are required to agree to maintain abstinence (noheterosexual intercourse) or use contraception with an annual failure rate of lessthan 1% during the study treatment period and within at least 6 months after the endof the study treatment period.

≥75×109 /L,haemoglobin≥9.0g/dL, serum albumin≥3g/dL； 11. Liver function: serum total bilirubin level≤1.5 times normal upper limit (ULN),glutamic pyruvic transaminase, glutamic oxaloacetic transaminase and alkalinephosphatase≤2.5 times ULN； 12. Renal function: defined as serum creatinine ≤ 1.5 times ULN or calculated creatinineclearance ≥ 15ml/min (Cockcroft-Gault formula, Appendix 4); urinary protein negativeor less than 2g in routine urine examination, or 24-hour urinary protein < 1g； 13. Good clotting function, defined as international standardized ratio (INR) orprothrombin time (PT) ≤ 1.5x ULN;. If the subject is receiving anticoagulant therapy,as long as PT is within the range of anticoagulant use； 14. Women of childbearing age must undergo a urinary pregnancy test within 7 days beforethe start of treatment and the results are negative and are not breastfeeding.

Exclusion Criteria:

1. Patients with extensive SCLC (Appendix 2)；
2. The subjects are confirmed to have brain or meningeal metastasis before they arerandomly divided into groups；
3. During the 5 years before the start of the study, patients with malignant tumors otherthan SCLC, diseases with negligible risk of metastasis or death (such as expected 5-year OS > 90%) and malignant tumors expected to be cured (such as fully treatedcervical carcinoma in situ, basal or squamous cell skin cancer, localized prostatecancer treated by curable surgery, ductal carcinoma in situ treated by curablesurgery)；
4. Previous head and neck radiation fields overlapped with PCI field；
5. MRI examination contraindicated
6. There is evidence that significantly uncontrolled concomitant disease may affect thecompliance of the study program, including severe liver disease (such as livercirrhosis), uncontrollable major seizures or superior vena cava syndrome；
7. Major cardiovascular diseases, myocardial infarction or cerebrovascular events within 3 months before randomization, unstable arrhythmias, or unstable angina pectoris； --Patients with known coronary artery disease, congestive heart failure that do notmeet the above criteria, or left ventricular ejection fraction ((LVEF)) < 50% mustreceive a stable treatment plan and optimize it according to the advice of theattending physician, and consult a cardiologist if necessary。
8. Stroke (including hemorrhagic and ischemic) or transient ischemic attack occurredwithin 6 months before enrollment；
9. There were clinically significant bleeding symptoms or obvious bleeding tendencywithin 1 month before entering the group, such as gastrointestinal bleeding, gastriculcer bleeding, active hemoptysis or vasculitis；
10. Serious arteriovenous thrombosis events occurred within 3 months before enrollment,such as deep venous thrombosis, pulmonary embolism, etc. (except for implantablevenous infusion port, catheter-derived thrombosis or superficial venous thrombosis,these conditions are not considered "severe" thromboembolism);
11. Diabetic ketoacidosis or hyperglycemia and hyperosmosis occurred in the past 6 months;
12. There was a history of hypertensive crisis and hypertensive encephalopathy;
13. Any other disease, metabolic disorder, abnormal result of physical examination orlaboratory examination, and there is reason to suspect that it may affect thereliability of the results of the study or put the patient at high risk of treatmentcomplications；
14. The results of HIV test is positive --All patients must be tested for HIV; patients with positive results of HIV will beexcluded.
15. Major surgery has been performed within 28 days before the start of the studytreatment, or major surgery is expected to be performed during the study period (except those for diagnostic purposes)；
16. Severe infections occur at the beginning of the study, including, but not limited to,infectious complications requiring hospitalization, bacteremia, or severe pneumonia；
17. Pregnant or lactating women；
18. Previous history of severe neurological or mental disorders, including epilepsy,dementia or severe depression that interfere with assessment;
19. The researchers believe that some conditions of the patients may affect the evaluationof the efficacy of this study, as well as the compliance of patients with this study.