螺旋断层放疗系统升级动态钨门技术的验收测试

目的 对螺旋断层放疗系统的动态钨门技术进行验收测试,评估其射野半影及治疗实施的准确性。方法 升级内容主要包括升级钨门的驱动系统和更新射野模型。升级钨门的驱动系统后行机械对准性测试。调试加速器输出,使其与新的射野模型吻合。分别用固定钨门和动态钨门技术设计螺旋断层调强计划,评估不同照射技术的射野半影。剂量验证分别用A1SL电离室和ArcCheck探测器矩阵测量点剂量和面剂量,并采用γ分析与计算结果进行比对。结果 系统的机械对准符合验收标准。不同射野宽度的百分深度剂量和离轴比与新的射野模型基本一致。IEC y轴向对称野和非对称野的射野宽度与参考值的偏差均<0.3%。采用动态钨门技术后,射野宽度为2.5 cm和5.0 cm时半影宽度比固定钨门技术分别减小了10.41 mm和26.76 mm,接近1.0 cm射野宽度的结果。对于临床病例计划,点剂量平均偏差为 0.33%±0.73%,剂量分布2%/2 mm、3%/3 mm和4%/4 mm的γ平均通过率分别为 97.9%±1.1%、99.8%±0.3%和 100.0%±0.06%。结论 动态钨门技术可大幅改善射野半影。验收测试结果均符合质控标准,表明其治疗实施是准确可靠的。

Commissioning of dynamic jaw delivery in tomotherapy

Objective To evaluate the dosimetric penumbra and delivery accuracy of dynamic jaw delivery in tomotherapy. Methods The jaw positioning hardware and the beam model were updated. Mechanical alignments were verified after the upgrade of the jaw positioning hardware. PDDs and beam profiles were measured by a two-dimensional water tank and compared with the new beam model. Dose penumbras in the longitudinal direction were compared between the dynamic and fixed jaw plans for different field width. Delivery accuracy was evaluated by point dose measurements with A1SL chamber and gamma analysis on the dose distribution measured by ArcCheck detector array. Results Mechanical alignments were in tolerance and beam characteristics were tuned to match the dynamic jaw beam model. Differences in the field width between the measured results and reference data were< 0.3% for both symmetric and asymmetric profiles in the longitudinal direction. The dose penumbra in dynamic jaw delivery was reduced from 17.92 mm to 7.51 mm for 2.5 cm jaw, and from 33.73 mm to 6.97 mm for 5.0 cm jaw, close to the penumbra of the traditional 1.0 cm jaw. IMRT verification of clinical cases was performed by A1SL ion chamber and ArcCheck detector array. The mean point dose difference was 0.33%±0.73% between the calculated and meassured data. Gamma analysis of dose distributions revealed that approximately 99.8% of the points satisfied the gamma criteria of 3% dose difference and 3 mm distance-to-agreement and the mean passing rates remained 97.9% even with tightest criteria of 2%/2 mm, and 100.0% with the criteria of 4%/4 mm, respectively. Conclusions Dosimetric penumbra in the longitudinal direction is significantly improved by the dynamic jaw delivery. Both the mechanical alignment and treatment delivery are qualified, suggesting that this new treatment is accurate and reliable.