Objective To observe the relationship between diffusion-weighted imaging ( DWI) characteristics and chemoradiotherapy response in recurrence patients with radical hysterectomy .Methods 26 recurrence patients with radical hysterectomy were included .All underwent conventional MRI and DWI before and after chemoradiotherapy . Baseline tumor characteristics including recurrence site ,gross tumor volume ,necrotic area and the ADC value were re-corded.Focal regions of restricted diffusion were delineated as a separate ROI and ADC value was determined .Ima-ging features were compared between complete response group and partial response group .Results 12 patients had complete response ( CR group ) ,14 patients had partial response ( PR group ) .ADC valueafter chemoradiotherapy was significantly higher than that before chemoradiotherapy in PR patients .Compared with CR group ,PR group had a grea-ter gross tumor volume ,higher ADC value and more focal regions of restricted diffusion .Recurrence type and necrotic areas was no significant differences .Conclusion ADC value and focal regions of restricted diffusion adquired by DWI help to determine chemoradiotherapy response in recurrence patients with radical hysterectomy ,which is helpful for clinicians to predic treatment effect early .It has great significance for developing reasonable programs and impro-ving the therapeutic effect .

Objective To measure the placing position error of different body position by analog positioning machine in patients with different body mass index (BMI) during radiotherapy for rectal cancer, then calculate the clinical target volume (CTV) to plan target volume (PTV) margins (Mptv). Methods Thirty-six patients with rectal cancer were selected, and the patients were divided into vacuum bag group (18 cases) and routine belly board group (18 cases) according to method of placing position. The BMI was calculated. Each patient was treated with positive and lateral position X-ray film before treatment and once a week during the radiotherapy. The data were contrasted with digitally rendered radiographs (DRR) of three-dimensional conformal radiotherapy plan system, then the placing position error on X, Y and Z axis was calculated, and the Mptv on X, Y and Z axis of patients with different BMI was calculated. Results The placing position error on X, Y and Z axis gradually increased with the increase of BMI in vacuum bag group and routine belly board group, and there were statistical differences (P<0.01 or <0.05). The Mptv on X, Y and Z axis in patients with normal BMI were 4.60, 5.51 and 5.29 mm respectively. The Mptv on X, Y and Z axis in patients with overweight were 5.48, 6.81 and 6.16 mm respectively. The Mptv on X, Y and Z axis in patients with obesity were 8.92, 8.59 and 7.02 mm respectively. Conclusions The rectal cancer patients with overweight and obesity have more placing position error. The influence of BMI should be considered when the patient's Mptv is determined.