腮腺癌术后不同放疗计划剂量学的比较

The dosimetric comparison of different treatment planning for postoperative radiaotherapy of parotid cancer

背景与目的:腮腺癌靶区位于头部的一侧,形状凹形,用何种照射方法可以更有效的使靶区剂量均匀及保护危及的器官,是目前讨论的热点。本研究通过比较采用二维常规、三维适形、正向和逆向调强放疗技术对腮腺癌术后靶区进行放疗计划设计,重点分析比较调强技术在保护正常器官和改善靶区适形度的作用,为临床治疗提供依据。方法:比较5种腮腺癌术后靶区照射技术,包括二野对穿照射(2F-2D)、二维电子线+X线混合照射(X+E)、三维适形放疗(3-dimensional conformal radiotherapy,3DCRT)、适形调强放疗(intensity-modulated radiotherapy, IMRT)正向多子野调强放疗(multi-segment radiotherapy, MSRT)照射。随机选择8例腮腺癌术后患者,为每位患者设计上述5种照射技术的治疗计划。处方剂量为60 Gy,2 Gy/次,共30次。分别比较这5种计划的剂量分布、剂量体积直方图(dose volume histogram,DVH)、靶区剂量均匀度以及正常器官受照剂量,同时比较2种调强技术放疗计划时间和实施治疗时间。结果:在靶区覆盖方面,3DCRT的V95%和适形指数(CI)(97.5%和0.78)明显优于二维照射(77.9%和0.45)(P<0.01),但劣于IMRT(99.1%和0.85)和MSRT(99.7%和0.81)(P<0.01);两调强技术相比差异无统计学意义(P均>0.05),但MSRT的实施时间(平均治疗时间5 min)明显短于IMRT(平均治疗时间15 min)。在正常器官保护方面,脑干、脊髓和对侧腮腺的受照剂量,IMRT(19.4、28.1和8.5 Gy)和MSRT(17.0、28.0和0.8 Gy)优于3DCRT(25.4、37.7和1.8 Gy)更优于二维(51.7、58.8和54.6 Gy),但同侧中耳、眼球、眼晶体和下颌骨的受照剂量5种计划差异无统计学意义(P值均>0.05)。结论:3DCRT、MSRT和IMRT技术无论从靶区覆盖还是对正常器官保护方面均优于二维照射技术,而调强计划(包括IMRT和MSRT)优于3DCRT计划,但MSRT在靶区覆盖、正常器官的保护上与IMRT之间差异无统计学意义,且计划的执行效率优于IMRT技术。

Background and purpose：Now 3-dimensional conformal radiotherapy （3DCRT） and intensitymodulated radiotherapy （IMRT） are widely used in the treatment of head and neck tumor.For the parotid,this target area is located on the side of the head and the tumor has a concave shape.What kind of radiation method can be used more effectively to achieve dose uniformity and protection organs at risk is the topic of much discussion.The postoperative irradiation of parotid tumor is varied in the techniques used.In this study,3-dimensional conformal radiotherapy （3DCRT）,intensity-modulated radiotherapy （IMRT） and simplified forward planned multi-segment radiotherapy （MSRT） were compared to conventional planning techniques in order to investigate the potential advantages of these new treatments.Methods：The conventional planning included the large opposed lateral fields with 2 or 3 weight ratio at the target lateral （2F-2D） and the unilateral field with mixture of 6 MV photon and electron beams （X＋E）.The 3D techniques included 3DCRT,MSRT and IMRT.Their dose distributions were calculated and compared for 8 patients treated in our center.Different beam arrangements were used for 3D techniques.In each case,the dose of PTV was prescribed to 60 Gy.All plans were compared using dose-volume histogram data.The conformity index （CI） and heterogeneity index （HI） of dose were used to evaluate the dose coverage of the target volume.Dose sparing of brain stem,spinal cord and the contra lateral parotid was also compared.To compare IMRT and MSRT,the timing of planning and radiation delivery was recorded.Results：Compared to conventional planning,the 3DCRT,MSRT and IMRT plans produced adequate target coverage,and the CI showed 3DCRT plans （0.78） produced poorer target coverage than MSRT （0.81） and IMRT （0.85）.MRST and IMRT plans showed a significant reduction in maximum dose to the spinal cord,brainstem and the contra lateral parotid,compared to the conventional plans,while the 3DCRT plan did not show significant sparing of these structures.MSRT and IMRT plans produced better dose coverage among all the techniques.The efficacy of beam delivery comparing between two modulated planning showed MSRT was better.Conclusion：For postoperative irradiation of parotid cancer,3D planning techniques generated better target dose-coverage,without compromising the dose-sparing advantages of important structures.A satisfactory dose distribution can be obtained using MSRT and such a simple technique may be suitable for replacing IMRT.