鼻咽癌束流调强放疗的腮腺保护剂量学研究

Dosimetry of parotid glands in IMRT plan of nasopharyngeal carcinoma

目的探讨不同鼻咽癌束流调强放疗计划对腮腺剂量分布的影响。方法在相同的剂量要求和限制下,比较鼻咽癌常规束流调强放射治疗计划与仅保护一侧腮腺时或腮腺扩大计划靶区（加2或3mm边缘）时的束流调强放射治疗计划。结果仅保护一侧腮腺的调强计划与常规计划比较,PTV70在靶区覆盖情况、均匀指数和适形指数方面均相似。PTV59.4的最小剂量大于常规计划（P〈0.01）,D95也得到提高（P〈0.01）。两个计划需保护的腮腺D50%VOL和Dmean相似。扩大腮腺计划靶区（加2或3mm边缘）的调强计划与常规计划比较：PTV70在靶区覆盖情况、均匀指数和适形指数方面均相似。然而从常规计划到腮腺加2mm边缘的调强计划再到加3mm边缘的调强计划,PTV59.4的Dmin和Dmean有下降的趋势,而脑干和脊髓的受量有增加的趋势。结论调强计划中腮腺保护困难时,可仅做保护一侧腮腺的束流调强放疗计划;估计腮腺可能产生明显的位置变化时,可考虑加大腮腺的计划靶区,以保证治疗过程腮腺始终能得到较好的保护。

Objective To evaluate the effect of different intensity-modulated radiation therapy （IMRT） plan on the dosimetry of parotid in patients with nasopharyngeal carcinoma. Methods Under the same constraints and objections, the IMRT plan of nasopharyngeal carcinoma with sparing unilateral parotid and the IMRT plan added plan tumor volume （PTV） margin for parotid gland was investigated. Results Between conventional IMRT plan and the IMRT plan spared unilateral parotid, their target coverage, homogeneity index and conformal index of PTV70 is similar. On PTV60, D min in the plan of sparing one parotid gland was more than that in normal IMRT plan （ P 〈 0.01 ）, D95 in the plan of sparing one parotid gland have improved （ P 〈 0.01 ）, Compared with normal IMRT plan, D50%VOL and D of parotid gland were similar between the two plans. Between conventional IMRT plan and the IMRT plan added 2 or 3 mm margin for parotid gland, their target coverage, homogeneity index and conformal index of PTV70 is similar. Dmin, D mcan and D95 of PTV60 have decreased tendency from normal IMRT plan to 2 mm margin plan to 3 mm margin plan. Dmax of brainstem and spine cord have increased tendency from normal IMRT plan to 2 mm margin plan to 3 mm margin plan. Conclusions The IMRT plan of nasopharyngeal carcinoma with sparing unilateral parotid may be adopted not to protect both two parotids, while PTV margin for parotid added as parotid move.