Hypo-fractionated Adaptive Radiotherapy For Large Brain Metastasis:dosimetric And Clinical Analysis

ObjectiveThis study aimed to investigate the dosimetric and clinical analysis of hypo-fractionated adaptive radiotherapy in patients with large volume brain metastases,and analyze the related factors that affect the recent efficacy,so as to provide a reference for the clinical treatment of patients with large brain metastases.MethodsA total of 20 patients with large brain metastases who were initially treated with hypo-fractionated adaptive radiotherapy in our department of radiotherapy from October 2020 to September 2022 were collected.Large brain metastases with a lesion volume of 6 cm~3 to 20 cm~3 and the number of lesions 1 to 4 were selected for treatment observation and efficacy evaluation.All patients in this study underwent contrast-enhanced CT and MRI,had a slice thickness of 2 mm,and the images were fused to complete the plan design and treatment by Pinnacle planning system and Varian accelerator.The lesion was prescribed a dose of 52.5Gy/3.5Gy/15f,adducted 2 mm to form a boost zone,and pushed to 60Gy/4Gy/15f.Lesions in brainstem regions were treated with 50Gy/2.5Gy/20f.Patients were re-examined by MRI after 10 times treatment.The radiation field would be shrunk if the GTV was reduced,and complete the remaining dose of radiotherapy.Changes in dosimetric parameters of two segment planning brain and other organs at risk,rate of second segment planning tumor reduction,and recent efficacy(evaluation of recent efficacy 2 to 3 months after FSRT)were evaluated.Other end points included the rate of resolution of cerebral edema(to include bevacizumab with or without the use of bevacizumab in the factorial analysis of the rate of resolution of cerebral edema),adverse effects.The measurement data were described by mean±standard deviation.The parameters of DVH dose volume in brain and other organs at risk,such as obeying normal distribution,were tested by two paired samples t-test,and the rank sum test was performed if not conforming to normal distribution.Kruskal-Wallis H test analysis was used to analyze the relevant factors affecting the volume difference and edema regression rate of tumor contraction field.Results(1)The average rate of tumor reduction during second segment field reduction was 41.76%,the 3-month ORR was 90.5%,and the 3-month,6-month LCR was 100%.The mean regression of brain edema volume during second segment constriction field was 67.85%in the bevacizumab group and 81%in the bevacizumab group.(2)PTV of the two plans met the prescription dose requirements.Compared with Plan2,V29,V30,V36,V37,V43,V45 and Dmean of brain tissue of Plan2 were lower,and the difference was statistically significant(p<0.05);The brain tissue Dmean,brain stem Dmean,brain stem Dmax,optic nerve Dmean,optic nerve Dmax,optic chiasmatic Dmax,lens Dmean and lens Dmax of Plan2 were lower than those of Plan1,but the difference was not statistically significant.(3)The volume of the original focus has an impact on the tumor volume difference before and after two course constriction field radiotherapy.The larger the volume,the greater the tumor volume difference,the primary pathological type,whether EGFR-TKI drugs are used,whether BED is>70Gy,and whether bevacizumab is used,have no impact on the two stage planned tumor volume difference.The application of bevacizumab had an effect on the regression rate of brain edema,and the regression rate was more obvious in the bevacizumab edema group.(4)Patients were followed up for a median of 12.35 months.The occurrence of one adverse event was observed after radiotherapy,and one patient showed brain edema at 11.5 months after the start of radiotherapy and improved symptoms after hormonal therapy,with no evidence of recurrence at last follow-up,and was clinically diagnosed with RN.Two large lesions in 2 patients developed intracranial lesion progression at7.3 and 11.8 months after radiotherapy,and 1 patient developed a new lesion intracranially at 13.1 months after radiotherapy.ConclusionHypo-fractionated adaptive radiotherapy has a high rate of tumor reduction,can effectively reduce the value of dosimetric parameters of normal brain tissue,and has a good local control rate for large-volume lesions,and best short-term results.Bevacizumab is effective for peritumoral edema control with little toxic side effects.