调强放疗技术在射野衔接中的应用研究

Study on the Application of Intensity Modulated Radiotherapy in Field Juncti on

目的研究应用调强放疗技术进行射野衔接时的最佳优化参数。方法选择9例需射野衔接的患者,分别取1、2、4、8 cm作为射野衔接过渡区域,同时优化并模拟摆位误差,研究计划重叠长度对靶区实际受照剂量的影响。为了获得线性剂量过渡曲线,强制定义线性剂量过渡处方,利用Base Plan技术分段优化,研究计划优化次序和摆位误差对靶区剂量的影响。靶区剂量评价指标取计划重叠区域95%和1%体积所受到的照射剂量D_(95%)和D_(1%)。结果单从计划角度分析,射野衔接长度越短,计划衔接处的靶区剂量分布越差,差异有统计学意义(F=144.890&7.878,P<0.05);摆位误差越大,射野衔接长度越小,靶区的实际受照剂量偏差越大,差异有统计学意义(F=34.887&37.403,P<0.05);射野衔接长度接近时,在对抗摆位误差对靶区剂量的影响方面,分段优化比同时优化更有优势,差异有统计学意义(t=9.974&5.357,P<0.05)。结论利用调强放疗技术对长靶区进行射野衔接时,计划重叠长度≥4 cm,并采用线性剂量过渡处方分段优化的设计方式,可减少摆位误差对靶区实际受照剂量的影响。

Objective To explore the best optimization parameters of IMRT in feld junction. Methods Nine patients who need feld junction received 36 treatment plans, including 1, 2, 4, 8 cm overlying-feld region. Plan A and plan B were optimized together, and the isocenters moved 3, 5 and 10 mm at the directions of head and foot to simulate and analyze the in？uences of setup errors and overlying-feld lengths on the dose distribution of the target. In order to assure a ramp-like dose profle in the feld overlap region, the plan A was optimized frst, with dose prescription explicitly enforcing a ramp-like dose profle. The plan B was done afterwards, taking into account the dose contribution of the plan A. Results The shorter the overlying-feld length, the worse the dose distribution of the target, without considering the setup errors （F=144.890 and 7.878, P〈0.05）, which was the same when considering the setup errors （F=34.887 and 37.403, P〈0.05）. A linear ramp-like dose profle in treatment feld overlap regions could improve treatment plan robustness with respect to small shifts in patient position during the IMRT treatment （t=9.974 and 5.357, P〈0.05）. Conclusion The IMRT plans with the overlying-feld length ≥4 cm and ramp-like dose profle can minimize dosimetric dependence on minor positional errors in patient set-up.