基于患者解剖结构三维剂量重建进行容积调强弧形治疗剂量验证初探

Preliminary application of volumetric-modulated arc therapy dosimetry verification system based on three-dimensional dose reconstruction of patient anatomical structures

目的测试基于患者解剖结构三维剂量重建进行容积调强弧形治疗(VMAT)剂量验证系统(3DVH),并探索其临床应用。方法对ArcCheck行阵列校准后按10 cm×10 cm射野、源轴距100 cm、投照量200 MU标定其绝对量,标定时将FC65-G置于模体中心测量。根据实测剂量、3DVH重建中心点及百分深度剂量与对应计划值间差异,调整绝对量标定值或ArcCheck CT密度值,使上述差异最小。选择肺癌、宫颈癌VMAT病例各10例,使用TrueBeam投照并用ArcCheck、FC65-G测量,由验证后的3DVH重建各测试例三维剂量并与计划值及实测值比对。结果ArcCheck不同阵列校准文件对ArcCheck二维面剂量测量及3DVH三维剂量重建影响不同。使用自行阵列校准文件及249.96 cGy为标定值时得到最优结果。所有测试例重建与原计划剂量相比靶区D_(mean)、D_(95%)偏差<±4.2%,部分危及器官差异较大;点剂量差异平均值为负,重建值更接近实测值。各器官三维γ通过率中部分病例靶区通过率较低,50%处方剂量包绕区域稍高,其他器官大都较高。结论使用本研究方法能准确完成3DVH模型建立和测试,其能提供详实直观的信息用于剂量验证。

Objective To perform testing and clinical application of a volumetric-modulated arc therapy(VMAT)dosimetry verification system based on three-dimensional dose reconstruction of patient anatomical structures.Methods ArcCheck array calibration was performed.Then,200MU was delivered with a 10cm×10cm field when the source to center of ArcCheck was 100cm to calibrate the absolute dose and the dose was simultaneously measured by a FC65-G detector in the center of the ArcCheck.The absolute dose calibration value or the CT value of ArcCheck was adjusted to minimize the differences between the planning and measurement values of FC65-G,reconstructed value by 3DVH and reconstructed percent depth dose by 3DVH.10 lung and 10 cervical cancer VMAT cases were selected and measured by ArcCheck and FC65-G under the delivery of a TrueBeam LINAC.The three-dimensional doses of all cases were reconstructed by 3DVH and compared with the planning and measurement values.Results Different array calibration files of ArcCheck exerted different effect upon the two-dimensional dose measured by ArcCheck and three-dimensional dose reconstructed by 3DVH.The optimal reconstructed dose was obtained when self-calibration file was adopted and 249.96cGy was regarded as the absolute dose calibration value.The deviations of the mean dose(D_(mean))and D_(95%) of the target were within ±4.2% and parameters of some organs at risk significantly differed compared with the reconstructed and planning dose for all cases.A negative mean point dose difference was obtained and the reconstructed dose was closer to the measured value.The γ-passing rate of the target for some cases was low,the proportion of regions irradiated by 50% prescription dose was slightly higher and the proportion of other organs was relatively high.Conclusion The 3DVH model can be accurately established and tested with the acceptance test method in the present study,which can provide detailed information for dose verification.