旋转误差对宫颈癌VMAT计划阳性淋巴结剂量影响及应对策略题录

目的研究旋转误差(绕前后轴)对晚期宫颈癌长靶区容积调强弧形治疗(VMAT)计划中不同位置淋巴结靶区剂量学参数的影响以及应对策略。方法简单随机抽样选取川北医学院附属医院的宫颈癌伴腹主动脉旁或腹股沟淋巴结转移患者资料进行回顾性分析, 按要求勾画出离计划中心不同距离的淋巴结靶区。根据每一病例CT图像设计VMAT计划后, 通过改变治疗床参数的方式引入旋转误差(绕前后轴), 其他参数不变的情况下重新计算剂量分布。然后, 按公式d=2πr(α/360)对原淋巴结靶区增加外放边界(r是淋巴结中心到计划中心的距离), 重新制作计划, 分析引入相应旋转误差后原淋巴结靶区剂量学参数的变化。结果当淋巴结靶区在与计划中心距离为6 cm误差为3°时、距离为9 cm和12 cm误差≥2.5°时、距离为15 cm误差≥2°时、距离为18 cm误差≥1.5°时, D_95%平均变化超过5%。旋转误差≤1°时淋巴结靶区D_95%的平均变化均小于5%, 淋巴结距离治疗计划中心18 cm时超过3%, 达到3.75%。以剂量参数V_100%评估, 旋转误差0.5°、...

Effect of rotational errors on dose of positive lymph nodes in cervical cancer VMAT plan and its coping strategies

Objective To evaluate the effect of rotational errors (antero-posterior) on dosimetric parameters of positive lymph nodes in the long target volumetric modulated arc therapy (VMAT) plan for advanced cervical cancer and investigate its coping strategies. Methods Clinical data of patients with cervical cancer complicated with para-aortic or inguinal lymph node metastasis admitted to Affiliated Hospital of North Sichuan Medical College were randomly selected and retrospectively analyzed. The target areas of the lymph nodes at different distances from the center of the plan were outlined according to the requirements. After designing the VMAT plan on the CT images of each case, the rotational errors (antero-posterior) were introduced by changing the parameters of the treatment couch, and the dose distribution was reconstructed by dose calculation with other parameters unchanged. Then, the external boundary of the original lymph node target was added according to d=2πr(α/360) (r is the distance from the center of the lymph node to the plan center), re-planned, and the changes of dosimetric parameters in the target area of the original lymph node were analyzed after the corresponding rotational errors were introduced. Results When the distance between the lymph node target area and the plan center was 6 cm with an error of 3°, the distance was 9 cm and 12 cm with an error of 2.5°, the distance was 15 cm with an error of 2°, and the distance was 18 cm with an error of 1.5°, the mean change of D_95% was more than 5%. When the rotational errors were ≤1°, the mean change of D_95% in lymph node target area was less than 5%, and when the lymph node was 18 cm away from the treatment plan center, the mean change was more than 3%, reaching 3.75%. When the rotational errors were 0.5° and the distance from the plan center was 18 cm (0.5°, 18 cm), the dose change of lymph node target was more than 5%, reaching 5.58%. At (1°, 15 cm), the V_100% change reached 8.96%, and at (1°, 18 cm), the V_100% change was 14.5%. The D_95% and V_100% parameters of the original lymph node target were changed by less than 1% after adding the external boundary of the original lymph node target and introducing corresponding rotational errors. Conclusions In the long target area radiotherapy of cervical cancer, the variation of dosimetric parameters of lymph node target was increased with the increase of rotational errors and with the increase of distance from the plan center. It is recommended to increase the efferent boundary of lymph nodes in different positions to avoid underdose by d=2πr(α/360).