ArcCHECK半导体探头特性及在容积调强弧形治疗剂量验证应用研究

目的 研究ArcCHECK半导体探头特性及在容积调强弧形治疗(VMAT)剂量验证应用。
方法 用PTWRW3型固体水模体对ArcCHECK探头测量固有敏感性、稳定性、剂量响应、剂量率响应、每脉冲剂量响应、射野大小依赖性、角度依赖性,并与PTW31010型0.125 cm³指形电离室测量值或VMAT计划系统计算值比较。随机选取211例已验证过的VMAT计划,分析计划与测量剂量分布的γ通过率差异,两两比较采用配对t检验。
结果 除角度依赖性外ArcCHECK探头其余特性均符合临床验证要求,当射束从探头底部入射时探头响应最小(180°时约为－3.9%),射束从两侧入射时响应最大(255°时约为 7.7%)。113例鼻咽癌、48例宫颈癌和50例直肠癌VMAT计划3 mm3%的γ平均通过率分别为93.5%、95.7%和97.5%,两两比较t=－12.69~－4.88,P均<0.01。
结论ArcCHECK半导体探头进行VMAT剂量验证前需精心校正,计划复杂度是影响VMAT计划验证通过率主要因素。

The characteristics and clinical application of the ArcCHECK diode array for volumetric-modulated arc therapy verification

Objective To evaluate the characteristics and clinical suitability of the ArcCHECK diode array for volumetric-modulated arc therapy (VMAT) verification. Methods The intrinsic sensitivity, short and long term reproducibility, dose and dose rate dependence, dose per pulsed dependence, field sizes dependence and directional response of the diodes were measured. The results of the diodes were compared with the measurement results of an ionization chamber and calculated results of treatment planning system. Gamma index was used to analyze the dose difference between the calculation and measurement for random selected 211 verified VMAT plans. Results The ArcCHECK performed well for all tests except directional dependence, which varies from a minimum of －3.9%(seen only when the beam was incident on the diode at 180°) to a maximum of 7.7%(approximately at 255°). Average gamma analysis passing rates with 3 mm/3% for 113 nasopharyngeal cancer, 48 cervical cancer and 50 rectal cancer patients VMAT plans were 93.5%,95.7% and 97.5%, respectively,statistical significance has been found between either two of the groups (t=－12.69—－4.88,all P<0.01). Conclusions With proposed calibration method, the ArcCHECK diode array is very suitable for VMAT pretreatment verification,the complexity of VMAT plan is the main factor affecting the passing rate.