Oncentra中异质性校正对绝对剂量验证的影响研究

Research on the Effects of Inhomogeneity Correction on Absolute Dose Verification in Oncentra

目的分析Oncentra中异质性校正对绝对剂量验证的影响。方法应用医科达Oncentra v4.1SP2计划系统设计36例计划,其中逆向调强计划18例,三维适形及简单调强计划(总子野数≤10)18例,对应每类计划,头颈部、胸部、腹部计划各6例。将以上计划移植到固体水上,分别在使用和不使用异质性校正的条件下,计算出电离室体积内的平均剂量,比较两者与电离室测量所得剂量的差异。结果对于所有病例,不使用均质性校准与同时使用均质校准且将电离室密度指定为水时TPS计算所得结果完全一致。除头颈部机架归零时6例调强病例在仅使用非均质较正时所得结果更接近实测结果外,其余病例,均是仅使用非均质校正时,TPS计算所得结果与实测值偏差较大。仅使用非均质校正时与实测值的差异与另外两种情况下TPS计算值与实测值的差异相比有统计学意义(P<0.05)。结论在利用Precise加速器及Oncentra v4.1SP2 CC算法进行精确放射治疗时,点剂量验证应在机架不归零的情况下测试,且TPS中计算时可在不使用均质修正或使用非均质修正且将电离室密度指定为水的情况下进行。

Objective To analyze the effect of inhomogeneity correction on absolute dose verification in oncentra. Methods Oncentra v4. 1SP2 was used to set up 36 plans,18 were reverse intensity-modulated plan,and 18 were three dimensional conformal and simple intensity modulated plan( whose sub-field smaller than 11). There were 6 patients each for head and neck,chest and abdomen in both plans. Transplanting all the plans to the Quality Assurance( QA) phantom and calculate the mean dose of the detector use the inhomogeneity correction or not,and the difference between mean dose and detector measured were compared. Results We obtained the same results for all the cases when we calculate the point dose and set the chamber density to water,whether use inhomogeneity correction or not. For all the dose difference between calculated by TPS and measured by chamber,the bigger difference were found when only use the inhomogeneity correction by TPS,except for 6 cases of head and neck whose gantry angle set to zero when make the dose validate. There were significant differences between the difference obtained when only use inhomogeneity correction and the difference obtained use inhomogeneity correction and set the chamber density to water( P < 0. 05). Conclusion The gantry angle must be set to original when we make the absolute dose validation for treatment planning calculated by CC in Oncentra v4. 1SP2 and Precise accelerator,at the same time use inhomogeneity correction and set the chamber density to water or not use inhomogeneity correction for the dose calculation.