This is a prospective, randomized phase-II study observing the memory preservation and functional brain MRI changes with conformal avoidance of the hippocampal neural stem-cell compartment during prophylactic cranial irradiation for small cell lung cancer patients.

Brain metastasis is rather high in small cell lung cancer patients. Prophylactic cranial irradiation(PCI) is the standardized treatment. However, cognitive dysfunction like memory damage is observed in quite a number of patients after brain irradiation, which may due to the hippocampus being irradiated. Thus, the investigators conduct the study by reducing the dose to the hippocampal neural stem-cell compartment (HAZ) during PCI.

Patient Population: Age: 18-65y; small cell lung cancer undergoing PCI; Eastern Cooperative Oncology Group (ECOG) score: 0-1.

The patients are randomized to 2 arms:

Arm Routine PCI: PTV(planning target volume) 25Gy/10F. Arm Hippocampus avoidance PCI(HA-PCI): PTV 25Gray(Gy)/10Fraction(F), HAZ Dmin<9Gy Dmax<16Gy).

Measurements: Hopkins verbal learning test(HVLT) and functional brain magnetic resonance imaging.

Inclusion Criteria:

1. Histologically conformed small cell lung cancer;
2. Complete response (CR)/partial response (PR) after chemo-radiotherapy;
3. ECOG (Eastern Cooperative Oncology Group) : 0-1;
4. No imaging evidence of brain metastasis before PCI;
5. Normal hemodynamic indices before the recruitment (including white blood cell count>4.0×109/L, neutrophil count>1.5×109/L, platelet count >100×109/L, hemoglobin≥90g/l, normal liver/kidney function);
6. Able to understand this study and have signed informed consent.

Exclusion Criteria:

1. Unable to receive MRI;
2. Medical history of central nervous system, cognitive or psychological diseases;
3. The expectation of life is less than 6 months;
4. Female in pregnancy or lactating;
5. The researchers consider the patient not appropriate to be enrolled.