CM治疗计划系统照射野剂量计算的验证

Verification by external beam calculation for CMS treatment planning system

目的 对美国CMS公司生产的肿瘤治疗计划系统 (TPS)计算结果值与实际测量值进行比较。方法 按照测量条件下的带有Farmer型电离室的固体水模在螺旋CT下进行扫描 ,图像通过网络数字传输系统传入TPS中 ,分别进行 10cm× 10cm规则野与不规则野、均匀组织与不均匀组织(分别含骨和肺 )、源轴距 10 0cm中心轴上深度 6和 10cm、野内任意点、机架角 30°、楔形板、MLC、铅挡、源皮距 90和 12 0cm条件下 6和 15MVX线计划设计并采用卷积和叠加两种算法计算 ,再与加速器治疗机上实际测量结果进行比较。结果 对于均匀组织和含骨的不均匀组织卷积和叠加算法的计算结果值具有良好的一致性 ,两种计算方法的结果偏差在 0 .5 %以内。多数实测值与计算值偏差在2 .5 %以内 ,个别计算与实测结果偏差在 3%以内 ,含肺的不均匀组织做不均匀组织校准后卷积算法与实测偏差较大 ,6MVX线为 7.8% ,15MVX线为 4 .5 % ,而叠加算法与实测偏差在 1.5 %以内。结论 除了卷积算法不能用于含肺组织或含气空腔剂量计算以外 ,卷积和叠加算法均可用于剂量计算 ,且偏差符合临床要求。

Objective To compare the actual measured value with the one provided by treatment planning system (TPS), CMS company, the United States. Methods A farmer ionization chamber water solid mold was scanned by spiral CT. The images were transferred to TPS by the network. All the values, including 10?cm×10?cm a regular field and an irregular field, symmetric and heterogeneitic organs (with either bone or lung), SAD=100?cm with the depth of 6 ?cm、10 ?cm in central axis, the arbitrary dots inside of a field, gantry 30 °, with wedges, MLC, with lead blocks, SSD=90?cm or SSD=120?cm under both 6 and 15 ?MV X-rays, were measured and compared with the actual value under the same condition. Results The values were consistent in the symmetric and asymmetric organs calculated by either converlution or superposition algorithms, giving a deviation within 0.5%. Most of the actual measured values and calculated results had deviations within 2.5%, some even within 3%. It was much larger for the asymmetric organ as corrected by asymmetric organs modification calculated by converlution algorithm under 6 ?MV X-Ray and 15 ?MV X-Ray namely 7.8% and 4.5%, whereas the deviation was 1.5% by superposition algorithms. Conclusions Both converlution and superposition algorithms can be used for dose calculation with deviation acceptable clinically except that converlution algorithm is not suitable for the asymmetric organ calculation.