摘要目的 对MatriXX探头不同角度剂量响应进行刻度,从而以实际治疗角度对治疗计划进行剂量验证.方法 首先用指形电离室对直线加速器进行绝对剂量校准,使在最大剂量点深度处1 MU=1 cGy.将MatriXX放置在Mutlicbue模体里,并对电离室矩阵进行绝对剂量刻度之后,机架从0°开始每隔5°(在侧野方向间隔1°)对加速器出束测量,记录MatriXX电离室矩阵中心点的剂量.按相同的步骤用电离室测量固体水模体中相同深度处中心点的剂量.电离室测量的剂量和Matrixx测量中心点剂量的二者比值即是MatriXX对不同射野角度的剂量响应修正系数.结果 射野角度剂量响应修正因子随机架角度缓慢的变化,但在侧向角度变化的梯度比较大,从前后到后前方向时,最大变化达10%.治疗计划在侧野方向上的通过率相对其他角度射野要低.MatriXX矩阵经过角度修正后的测量结果的γ通过率相比修正前有较大提高,经过修正后的MatriXX测量结果与计划系统生成的结果在等剂量曲线上吻合很好.结论 如果用MatriXX在不治疗角度不归0位进行治疗计划验证的时候,必须要考虑到角度修正系数,同时将角度修正系数叠加到测量结果再与计划比较的方法也是可行的.

abstractsObjective To characterize angular dependency of MatfiXX and develop a method for its calibration in order to verify treatment plan with original gantry angles.Methods Absolute dose calibration was carried with thimble ionization chamber on the linear accelerator.so as to make sure 1 MU=1 cGy at the depth of maximum dose(dmax).A MatriXX was put into a Mutlicube phantom,and the ionization chamber matrix was calibrated with absolute dose.In order to determine a correction factor CF as a function of gantry angle θ.open beam fields of 10 cm×10 cm size were irradiated for gantry angles θ=0°-180°(every 5°)and every 1°for lateral angles θ in the range of 85°-95°.CF was defined as the ratio of the dose measured with ionization chamber and the dose from MatriXX.Results Relatively large discrepancies in response to posterior VS.anterior fields for MatriXX detectors(up to 10%)were found during the experiment and relatively large variability of response as a function of gantry angle.The pass rate of treatment plan in lateral beams was lower than that of other beams.The isodose distribution of corrected MatriXX matched well with the outcome from the treatment planning system. Conclusions The angular dose dependency of MatriXX must be considered when it is used to verify the treatment plan with original gantry angles.