Objective: The purpose of this study was to evaluate the early radiotherapy effect using 99Tcm-HL91 SPECT in patients with brain tumors. Methods: Twenty-one patients with brain tumors who were treated by radiotherapy were studied. KPS grade, tumor size on 99Tcm-HL91 SPECT , tumor size on MRI, and ratio of T/N (tumor counts/sec over normal brain tissue counts/sec) were investigated before ,during and after radiotherapy. Results: The average tumor size on 99Tcm-HL91 SPECT and MRI was 11.34±5.88 cm2, 9.46±5.66 cm2, respectively before radiotherapy. The tumor size on 99Tcm-HL91 SPECT was not in accordance with to that on MRI (P<0.05). KPS grade, tumor size on 99Tcm-HL91 SPECT and ratio of T/N had significance differences before, during and after radiotherapy (P<0.05), but the tumor size on MRI imaging had no significance differences before, during and after radiotherapy (P>0.05). The rate of symptom improvement was 80% during radiotherapy and 100% after radiotherapy. The rates of imaging remission based on the brain tumor size on 99Tcm-HL91 SPECT, MRI and T/N were 75%, 15%, and 80%, respectively during radiotherapy. The agreement rates between imaging remission diagnosed by those three methods and symptom improvement were 70%, 40%, and 60% respectively during radiotherapy. The rates of imaging remission based on the brain tumor sizes on 99Tcm-HL91 SPECT, MRI and T/N were 100%, 25%, and 95% respectively after radiotherapy. The agreement rates between imaging remission diagnosed by those three methods and symptoms improvement were 100%, 20%, and 95% respectively after radiotherapy. Conclusion: The tumor size on 99Tcm-HL91 SPECT is a valuable tool for evaluating early radiotherapy effect of brain tumor in process of radiotherapy. T/N is not a feasible method in evaluating radiotherapy effect of brain tumor because it may show elevation unrelated to the curative effect during radiotherapy. Objective: The purpose of this study was to evaluate the early radiotherapy effect using 99Tcm-HL91 SPECT in patients with brain tumors. Methods: Twenty-one patients with brain tumors who were treated by radiotherapy were studied. KPS grade, tumor size on 99Tcm- HL91 SPECT, tumor size on MRI, and ratio of T / N (tumor counts / sec over normal brain tissue counts / sec) were investigated before, during and after radiotherapy. Results: The average tumor size on 99Tcm-HL91 SPECT and MRI was 11.34 ± 5.88 cm2, 9.46 ± 5.66 cm2, respectively before radiotherapy. The tumor size on 99Tcm-HL91 SPECT was not in accordance to to that on MRI (P <0.05). KPS grade, tumor size on 99Tcm-HL91 SPECT and ratio of T / N had significance differences before, during and after radiotherapy (P <0.05), but the tumor size on MRI imaging had no significant differences before before, during and after radiotherapy (P> 0.05). The rate of symptom improvement was 80% during radiotherapy and 100% after radiotherapy. The rates of imaging remission based on the brain tumor size on 99Tcm-HL91 SPECT, MRI and T / N were 75%, 15%, and 80%, respectively during radiotherapy. The agreement rates between imaging remission diagnosed by those three methods and symptom improvement were 70% The rates of imaging remission based on the brain tumor sizes on 99Tcm-HL91 SPECT, MRI and T / N were 100%, 25%, and 95% respectively after radiotherapy. The agreement rates between imaging remission diagnosed by those three methods and symptoms improvement were 100%, 20%, and 95% respectively after radiotherapy. Conclusion: The tumor size on 99Tcm-HL91 SPECT is a valuable tool for evaluating early radiotherapy effect of brain tumor in process of radiotherapy. T / N is not a feasible method in evaluating radiotherapy effect of brain tumor because it may show elevation unrelated to the curative effect during radiotherapy.