摆位误差对乳腺癌患者放疗中心脏受量的影响

Effect of set-up error on cardiac dose during radiation therapy for patients with breast cancer

目的探讨摆位误差对乳腺癌患者放疗中心脏受量的影响。方法选取18例乳腺癌放疗患者制定放疗计划,保持原计划射野角度、射野剂量、射野权重等参数不变,移动射野中心,模拟3个方向(X、Y、Z轴)的线性摆位误差,重新计算移动射野中心后的心脏受量,并与原计划比较。其中X-、Y-分别代表患者身体相对于射野向患侧、头侧移动。结果新计划X-3、X-5、X-7、X-9、Y-5、Y-7、Y-9的30 Gy剂量线所包绕心脏的体积百分比(V30)较原计划增加(P<0.05),其中X-7、X-9、Y-9超过限量;X-9、Y-7、Y-9、Z7、Z9的V40较原计划增加(P<0.05);X-5、X-7、X-9、Y-5、Y-7、Y-9的心脏平均剂量较原计划增加(P<0.05),增加幅度分别为54 c Gy、80 c Gy、110 Gy、100 c Gy、142 c Gy、182 c Gy。结论对于接受放疗的乳腺癌患者,患侧方向和头方向均≥5 mm的摆位误差会使心脏平均剂量明显增加;患侧方向≥3 mm、头方向≥5 mm的摆位误差会使心脏V30明显增加。建议当患侧方向、头方向的摆位误差≥5 mm时,应校正误差。

Objective To explore the effect of set-up error on the cardiac dose during radiation therapy for patients with breast cancer. Methods Eighteen patients with breast cancer undergoing radiation therapy were selected. Firstly, parameters, including the angle, dose and weight of radiation field, of original plan remained unchanged, and then, the center of radiation field was removed, and the linear set-up errors in three directions （ including X, Y and Z axis ） were simulated. The cardiac dose was calculated again after removing the center of radiation field, and was compared with that of the original plan. And X- and Y- represented as movement to the normal side and affected side,respectively. Results The percentage of cardiac volume wrapped by irradiation with 30 Gy （ V30 ） at X-3, X-5, X-7, X-9 ,Y-5 ,Y-7 and Y-9 of new plan increased compared to those of original plan（P 〈0.05） ,and V30 of X-7 ,X-9 and Y-9 exceeded the limitation. V40 at X-9, Y-7, ZT, and Z9 of new plan increased compared to those of original plan （ P 〈 0.05 ）. The mean cardiac dose at X-5, X-7, X-9, Y-5, Y-7 and Y-9 of new plan increased compared to those of original plan （P 〈 0.05 ）, and the increase amplitudes at X-5, X-7,X-9,Y-5,Y-7 and Y-9 were 54 cGy,80 cGy, 110 cGy, 100 eGy, 142 cGy, and 182 cGy, respectively. Conclusion For the patients with breast cancer undergoing radiation therapy, the average cardiac dose might increase significantly with the set-up error no less than 5 mm to the normal side or affected side ,and the cardiac V30 might increase significantly with the set-up error no less than 3 mm to affected side or 5 mm to normal side. It is suggested that the set-up error should be corrected when it is more than 5 mm to the normal side or affected side.