全身照射中的“完全斜率法”肺屏蔽技术及其应用:附20例分析

Efficacy of "perfect gradient" lung shielding technique in total body irradiation:an analysis of 20 cases

目的:报道在20例全身照射患者中采用"完全斜率法"进行肺屏蔽技术,并对屏蔽效果进行验证。方法:根据每位患者的模拟定位片,在计算机控制下精确切割肺挡块,实现X射线光源投射方向、挡块斜率和肺部体表投影的基本一致。采用双点定位对肺挡块进行高精度摆位,并与手动制作和固定肺挡块的方法相比较。采用6 MV X射线对患者行前后对穿野分次照射,根据监测结果进行分段肺屏蔽和全身剂量均匀性计算。结果:全部患者的实测吸收剂量达到临床要求,"完全斜率法"的肺挡块在头足方向和左右方向上的摆位准确度和相对标准偏差均小于传统方法。结论:利用"完全斜率法"制作和定位肺挡块能有效提高全身照射肺屏蔽精度,限制肺挡块半影区的影响,降低摆位误差的影响,质量控制显著优于传统手动方法。

Objective To analyze the effect of the ＂perfect gradient＂ method for lung shielding in 20 patients receiving total body irradiation（TBI）.Methods For 20 patients scheduled for TBI,the lung block was precisely cut under the control by a computer according to the simulator image of each patient to ensure the consistency among the projection direction of Xray,the gradient of the lung block,and the skin projection of lungs.The lung block was positioned and fixed with a high precision using a two-point localization method,and the result was compared with that of manually prepared lung blocks.Fractionated TBI with 6 MV X-Ray of the anterior-posterior fields was administered in the 20 patients.Based on the monitoring results,the results of lung shielding and the dose uniformity were calculated.Results The measured absorbed doses in different regions of the body met the clinical requirements in all the 20 patients.The ＂perfect gradient＂ method resulted in a much higher positioning accuracy and a lower relative standard deviation than the conventional manual method both in the head-feet and the left-right orientations.Conclusion The ＂perfect gradient＂ method for preparing and positioning of the lung block can effectively improve the precision of lung shielding in TBI,obviously reduce the impact of the physical penumbra and positioning error on dose distribution,and allows better quality control than the conventional manual method.