A dosimetric study of hippocampal-avoidance prophylactic cranial irradiation in intensity-modulated radiotherapy and volumetric modulated arc therapy for patients with localized small cell lung cancer achieving complete response after chemoradiotherapy / 中华放射肿瘤学杂志

ABSTRACT

Objective To investigate the dosimetric characteristics of hippocampal?avoidance prophylactic cranial irradiation ( HA?PCI ) in fixed?field intensity?modulated radiotherapy ( IMRT ) and volumetric modulated arc therapy ( VMAT) and the feasibility and risks of hippocampal avoidance. Methods Prophylactic cranial irradiation (PCI) was performed for 16 patients with localized small cell lung cancer ( SCLC) who were treated in our hospital from January to August, 2014, and achieved complete response ( CR) after chemoradiotherapy, with a prescribed dose of 25 Gy in 10 fractions. CT localization image was fused with brain MRI image to contour the hippocampus on the fused image, and the boundary of the hippocampus was extended 5 mm outward to form the area for reduced dose. IMRT and VMAT plans with hippocampal avoidance were developed separately, and the dose distribution in the whole brain, the hippocampus, and the 5?mm area outside the hippocampus was evaluated for these two plans. Independent?samples t test was applied to evaluate the difference between the two groups. Results The mean hippocampal volume in the 16 patients was 2. 76 cm3 ( range 2. 56 ?3. 01 cm3 ) . The mean radiation dose ( Dmean ) in the hippocampus during IMRT and VMAT was 9. 04± 0. 20 Gy and 10. 32± 0. 28 Gy, respectively, reduced by 66. 0% and 61. 2%, respectively, compared with the prescribed dose ( P=0. 55);Dmean in the area for reduced dose during IMRT and VMAT was 13. 57± 0. 90 Gy and 14. 86± 0. 60 Gy, respectively, reduced by 49. 0% and 44. 1%, respectively, compared with the prescribed dose (P=0. 88). Conclusions HA?PCI in IMRT and VMAT meets the clinical requirements, and can reduce the dose in the hippocampus while ensuring the whole?brain radiation dose, and therefore can be applied in PCI and provide a technical support to protect the patient’ s neurocognitive function.