Hi-ART螺旋断层放疗机MV螺旋CT剂量指数的测量

目的 探讨Hi-ART螺旋断层放疗机MV扇形束CT图像获取过程中患者接受的剂量。方法 用PTWTM30009CT电离室分别在T40017头部和T40016躯干模体中,选择扫描层厚2、4及6mm和改变扫描范围等参数,分别测量加权CT剂量指数,计算相应的剂量长度乘积,并与XVIkV锥形束CT、ACQSim模拟定位CT的结果进行比较。结果 Hi-ART螺旋断层治疗机的CT剂量指数与层厚成反比,剂量长度乘积与扫描范围成正比。临床应用条件下Hi-ART的CT剂量指数在头颈部比XVIkV锥形束CT大,但躯干较小。结论 CT剂量指数能反映患者成像过程中接受的剂量,可以作为治疗保证与控制的指标。图像引导过程中应该合理选择层厚,减少扫描范围,最大限度减少患者接受剂量。

Measurement of MV CT dose index for Hi-ART helical tomotherapy unit

Objective To evaluate the patient dose from Hi-ART MV helical CT imaging in image-guided radiotherapy. Methods Weighted CT dose index(CTDI_W) was measured with PTW TM30009 CT ion chamber in head and body phantoms, respectively, for slice thicknesses of 2, 4, 6 mm with scanned range of 5 cm and 15 cm. Dose length products (DLP) were subsequently calculated. The CTDI_W and DLP were compared with XVI kV CBCT and ACQSim simulator CT for routine clinical protocols. Results An inverse relationship between CTDI and the slice thickness was found. The dose distribution was inhomogeneous owing to the attenuation of the couch. CTDI and DLP had close relationship with the slice thickness and the scanned range. Patient dose from MVCT was lower than XVI CBCT for head, but larger for body scan. Results CTDI_W can be used to assess the patient dose in MV helical CT due to its simplicity for measurement and reproducibility. Regular measurement should be performed in QA & QC program. Appropriate slice thickness and scan range should be chosen to reduce the patient dose.