探讨调强放疗计划中并行器官腮腺的优化方法

Study of Intensity -modulated Radiotherapy Planning Optimization Method in the Parallel Organs of Parotid Gland

目的：在鼻咽癌调强计划设计中,尝试克服物理约束的局限性,通过改变腮腺的优化条件,使腮腺受照量达到RTOG规定的要求且既不影响靶区剂量。方法：对12例已实施调强放疗的鼻咽癌患者的腮腺进行全部（包括被靶区包绕的深叶腮腺组织）和部分（指靶区外的腮腺组织）勾画,在30%、50%和75%腮腺体积处设置目标剂量和不同权重,对优化计算过的靶区和腮腺所产生的剂量分布,通过结构评估和DVH直方图,定量分析腮腺受照剂量及对靶区的影响。结果：同样的优化条件对部分腮腺体积和全部腮腺优化时,部分腮腺体积优化的D50、MD均大于按全部体积优化的结果。对全部腮腺按不同权重优化得出的结果显示,各靶区98%的体积基本达到98%的处方剂量,但在腮腺优化权重增加到2倍时,CTV2的剂量会降低2%左右,靶区外热点会转移至上颌骨处,靶区适形度略差。但可以使得腮腺MD≤26 Gy;而把权重增加到1.2和1.6倍优化时,都可以使腮腺D50〈28 Gy,MD≤30 Gy,V20都大于70%以上。结论：要按全部腮腺体积优化,加大无重叠区腮腺的剂量权重1.2～1.6倍左右,既可保证靶区剂量符合要求又可使得腮腺D50≤28 Gy（符合RTOG一个标准）,MD≤30 Gy。

In nasopharyngeal carcinoma （NPC） IMRT plan design,to try to overcome the physical constraints and limitations,by changingthe optimum conditions of the parotid gland,parotid amount reached RTOG requirements and does not affect the dose of the target area. Methods： 12 cases has been the implementation of intensity-modulated radiontherapy in patiens with NPC ,The parotid gland contoured are all （including the target zone around the deep lobe ofparotid gland tissue） and part （parotid gland outside target volume）. Set target dose and different weights in 30%,50% and 75% with the parotid gland volume .After optimiztion and calculation,by structural assessment and DVH to target zone and the parotid gland dose distributions. Quantitative analysis dose ofparotid gland and influence to the target area. Results： The same optimization conditions on the part of the parotid gland volume and total parotidectomy optimization,part of the parotid gland volume optimization for D50, MD were greater than at full volume optimization results. Show to the total parotidectomy optimization in different weight optimization results,the target region 98% volume reached 98% of the prescribed dose,but in the parotid gland to optimize the weights to increase 2 times, dose of the CTV2 will be reduced about 2%. Heatof the target area will be transferred to maxilla,target conmail slightly worse.But parotid MD≤26 Gy.When the weight increased to 1.2 and 1.6 times to optimize,parotid D50〈28 Gy,MD≤30 Gy, V20≥70%. Conclusions： Optimization should be based on the whole parotid organ.With a weight of 1.2 or 1.6 times set to the non-overlapping area, the target volumes receive acceptable dose coverage,and the parotid D50 meet one of the RTOG requirements： ≤28 Gy,but MD≤30 Gy.