头颈部肿瘤图像引导调强放疗中摆位误差对剂量学的影响研究

目的 通过头颈部肿瘤调强放疗中的平移和旋转摆位误差,分析摆位误差对肿瘤计划靶体积(PTV)及脑干受照剂量的影响,探讨头颈部肿瘤调强放疗中摆位误差在线校正的必要性.方法 30例头颈部肿瘤患者调强放疗中每周1次行治疗机下的锥形束CT扫描(共6次),其图像与计划CT图像融合配准获得x、y、z轴方向平移摆位误差和相应的旋转误差.将上述误差引入治疗计划系统中重新计算得到PTV、脑干等的剂量或体积参数并与原计划的行配对t检验.结果x、y、z轴方向平移摆位误差分别为1.06、0.95、1.31 mm,旋转误差分别为1.04°、1.06°、0.81°.6次摆位误差再计划的PTV 95％体积剂量(D95)和最小剂量明显小于原计划的(6526.6 cGy:6630.3 cGy,t =3.98,P =0.000和5632.6 cGy:5792.5 cGy,t=-2.89,P=0.007).6次摆位误差再计划的脑干接受45 Gy剂量体积(V45)和1％脑干体积剂量(D01)明显大于原计划的(3.54％:2.75％,t =3.84,P=0.001和5129.7 cGy:4919.3 cGy,=4.36,P=0.000).结论 平移和旋转摆位误差导致PTV D95明显不足,脑干V45、脑干D01均明显增加,因此头颈部肿瘤放疗过程中在线误差纠正是必要的.

The preliminary study of setup errors' impact on dose distribution of image guide radiation therapy for head and neck cancer

Objective To measure the set-up errors of patients with head and neck (H&N) cancer during the image guided intensity-modulated radiotherapy (IMRT) treatment and analyze the impact of setup errors on dose distribution ; then to further investigate the necessity of adjustment online for H&N cancer during IMRT treatment.Methods Cone-beam CT (CBCT) scanning of thirty patients with H&N cancer were acquired by once weekly with a total of 6 times during IMRT treatment.The CBCT images and the original planning CT images were matched by the bony structure and worked out the translational errors of the x,y,z axis,as well as rotational errors.The dose distributions were recalculated based on the data of each setup error.The dose of planning target volume (PTV) and organs at risk were calculated in the replanning,and than compared with the original plan by paired t-test.Results The mean value of x,y,z axis translational set-up errors were ( 1.06 ± 0.95 ) mm,( 0.95 ± 0.77 ) mm and ( 1.31 ± 1.07 ) mm,respectively.The rotational error of x,y,z axis were ( 1.04 ±0.791 ),( 1.06 ±0.89) and (0.81 ±0.61 ),respectively.PTV 95％ volume dose ( D95 ) and PTV minimal dose of replanning for 6 times set-up were lower than original plan (6526.6 cGy:6630.3 cGy,t =3.98,P =0.000 and 5632.6 cGy:5792.5 cGy,t =- 2.89,P =0.007).Brain stem received 45 Gydose volume ( V45 ) and 1％ brain stem volume dose ( D01 )were higher than original plan ( 3.54％:2.75％,t =3.84,P =0.001 and 5129.7 cGy:4919.3 cGy,t =4.36,P =0.000).Conclusions The set-up errors led to the dose of PTV D95 obviously insufficient and significantly increased V45,D01 of the brainstem.So,adjustment online is necessary for H&N cancer during IMRT treatment.