鼻咽癌后程三维适形与传统放疗剂量对比分析

目的比较鼻咽癌后程三维适形(3-dimensionalconformalradiotherapy,3DCRT)和传统放疗(2-dimensionalradiotherapy,2DRT)在靶区和周边重要器官的不同剂量分布并探究3DCRT的潜在优势.方法比较和分析5例鼻咽癌7野后程3DCRT和其相应的2DRT在各靶区和重要器官的剂量体积直方图(dosevolumehistogram,DVH)的各项指标值.结果与2DRT相比,3DCRTPTV的Dmean从92.7%提高至96.1%;剂量不均匀度(DI)从84.1%降至59.3%;90%等剂量线适形指数(CI)从0.32提高到0.51;但两者PTV接受90%处方剂量的体积均小于90%;在颈动脉鞘区,3DCRT的Dmean提高了5%但Dmax达117.2%.3DCRT和2DRT相比,串行器官如视神经、脑干和颞叶的Dmax分别为:33.5%和104.3%,11.7%和26.4%,97.6%和103.2%;但在晶体、眼球和下颌骨则分别为:16.1%和2.8%,21.3%和8.7%,115.3%和104.2%.在并行器官的Dmean,颞颌关节:68.5%和93.3%;耳蜗:58.5%和69.0%;而腮腺则为59.8%和43.3%。结论与传统放疗相比,鼻咽癌后程3DCRT降低了视神经、脑干、颞叶、颞颌关节和耳蜗的剂量,但却增加了晶体、眼球、下颌骨和腮腺的剂量.3DCRT使靶区剂量的适形性分布有所改善,潜在可能使颈动脉鞘区受累的鼻咽癌患者受益.但靶区剂量覆盖仍显不足,通过调强放疗有望达到更理想的剂量分布.

The Dosimetric Comparison of 3D Conformal Boost with Traditional 2D Radiotherapy for Carcinoma of the Nasopharynx

Objective This study was designed to compare the dosimetric effects of the 3D conformal boost and the traditional radiotherapy for both targets coverage and critical organs sparing in localized nasopharyngeal cancer(NPC),and hence to explore the potential therapeutic advantage of the 3DCRT over 2DRT.Methods 5 cases of localized NPC patients previously treated with boost 3DCRT were compared with their respective traditional 2DRT plans.The DVHs were evaluated and compared for both target coverage and critical organ sparing.Results Compared with that in the 2DRT plans,the D_ mean of the PTV in the 3DCRT plans increased from 92.7% to 96.1%,the dose imhomogeneity decreased from 84.1% to 59.3%,the 90% isodose conformity index improved from 0.32 to 0.51,the V90 was less than 90% for both 3DCRT and 2DRT plans.The D_ mean of the 3DCRT plans in the carotid area had a 5% increase but with their D_ max reached at 117%.The D_ max of the serial organs as optic nerve,brain stem and temporal lobe had a versus of 3DCRT to 2DRT as 33.5% Vs 104.3%,11.7% Vs 26.4% and 97.6% Vs 103.2% respectively,however,16.1% Vs 2.8%,21.3% Vs 8.7% and 115.3% Vs 104.2% for lens,eyeballs and mandible accordingly.The D_ mean in parallel organs as temporomandibular joints and cochleae were 68.5% Vs 93.3% and 58.5% Vs 69% favored in 3DCRT plans,but the D_ mean of the parotids increased from 43.3% to 59.8%.Conclusion Compared with 2DRT,the 3DCRT had a mixed effects in normal tissue sparing with dose decreases in the optic nerve,brain stem,temporal lobe,temporo-mandibular joints and cochlea and dose increases in lens,eyeballs,mandible and parotids.The NPC patients with carotid area involved may potentially benefit from 3DCRT with high dose concentrated in this area.The dose conformity of the PTV was improved but the general coverage was not enough.Intensity modulated radiotherapy will be a future pursuit to get ideal target coverage and more decreased normal tissue dose.