ABSTRACT
At present,conventional whole brain radiotherapy is the standard treatment for brain metastases and prophylactic cranial irradiation,and it can improve patients' clinical symptoms and survival.However,whole brain radiotherapy may induce cognitive function impairment and affect patients' long-term quality of life.The newest radiotherapy technology can protect the hippocampal gyrus during whole brain radiotherapy and then protect cognitive function and improve quality of life.This article reviews the methods and clinical value of hippocampal gyrus protection in whole brain radiotherapy,as well as related advances.
ABSTRACT
Objective To preliminarily observe the clinical efficacy of hippocampal-sparing prophylactic cranial irradiation (HS-PCI) using helical tomotherapy (HT) in patients with limited-stage small-cell lung cancer (LS-SCLC) after chemoradiotherapy,and compare HT with intensity-modulated radiotherapy (IMRT) and volumetric modulated arc therapy (VMAT) in dose distribution.Methods From April to June,2014,six patients with LS-SCLC who had achieved a complete remission after chemoradiotherapy were assigned to HS-PCI using HT within a month after brain metastasis was ruled out using brain magnetic resonance imaging (MRI).After fusing CT images and MRI images,the hippocampus was contoured in the fusion images and hippocampal avoidance regions were created using a volumetric expansion of 3 mm around the hippocampus.A dose of 25 Gy in 10 fractions to 95％ of planning target volume (PTV) was prescribed in HT,IMRT,and VMAT.The clinical efficacy,adverse reactions,neurocognitive function,and brain metastasis were evaluated for HT.The dose distribution in PTV and hippocampus were compared between HT,IMRT,and VMAT.Results There were one patient with abdominal wall and abdominal lymph node metastases,one patient with local recurrence,and no patient with brain metastasis during the observation period.The numbers of patients with grade 1 and grade 2 headache,dizziness,and hair loss reactions were 3 and 1,3 and 1,and 4 and 2,respectively.There were no significant differences in the average score of the Mini-Mental State Examination before treatment and at 3 and 6 months after treatment (29.7,29.2,and 29.3 ; P =0.083,0.317,and 0.157).The mean dose to the hippocampus was 16.85 Gy for IMRT and 17.59 Gy for VMAT.For HT,the mean doses to the hippocampus and avoidance regions were reduced to 5.26 Gy and 6.21 Gy,respectively.The prescribed dose for HT was reduced by 79％ and 71％ compared with IMRT and VMAT,respectively.The average coverage rate of the prescribed dose was 94.48％ for HT.Conclusions HT achieves promising dose distribution and target coverage in sparing of the hippocampus.Moreover,HT dose not increase the incidence of adverse reactions.The change in neurocognitive function needs to be further studied with longterm observation and large-scale sampling.