鼻咽癌调强放疗腮腺功能变化与放射剂量、体积的关系

目的研究调强放射治疗对鼻咽癌患者腮腺功能的保护作用及腮腺功能变化与剂量-体积的关系。方法2002年8月至2004年12月,48例接受调强放射治疗的鼻咽癌患者,分别在治疗前、治疗结束时及治疗后3个月检测腮腺99mTc清除率测定其分泌指数(EI)和摄取指数(UI),并结合腮腺的剂量体积直方图(DVH)进行分析。结果健侧和患侧腮腺平均剂量分别为(22．8±4．5)Gy和(31．9±4．1)Gy。全组患者口干症状轻微。健侧腮腺EI值放疗前为0．35±0．25,放疗结束时为0．31±0．24,放疗后3个月为0．33±0．22,其UI值在3个时间点分别为7．12±3．56、5．81±2．25和5．72±2．81,差异无统计学意义。患侧腮腺EI和UI放疗前分别为0．36±0．27和8．02±3．89,放疗结束时分别为0．21±0．16和4．87±2．45,放疗结束时比放疗前均有下降,差异均有统计学意义(均P<0．05)。DVH结果:放疗结束时EI在腮腺平均剂量<26 Gy组和≥26 Gy组,差异有统计学意义(P=0．009);V25(受照剂量<25 Gy的腮腺体积)≥50％和V25<50％者比较,EI下降差异有统计学意义(P<0．01)。两种情况UI下降差异无统计学意义(P>0．05)。结论腮腺剂量低于26 Gy对腮腺功能保护有阈值效应,腮腺的功能保护存在剂量、体积阈值,在靶区剂量不受影响同时,尽可能减少腮腺照射容积及其剂量,有助于保护患者放疗后的腮腺功能。

The relationship between the parotid glands function and the dose-volume effect in nasopharyngeal carcinoma patients with intensity-modulated radiation therapy

OBJECTIVE: To study the preservation of parotid glands function and relationship between parotid glands function and dose-volume histogram (DVH) in nasopharyngeal carcinoma (NPC) patients treated by intensity modulated radiation therapy (IMRT). METHODS: From August 2002 to December 2004, the excretion index (EI) and uptake index (UI) of parotids in 48 NPC patients underwent radical IMRT was examined by ECT at the beginning, the end of and the 3 months after radiotherapy. The relationship between parotid function (EI and UI) and DVH were analyzed. RESULTS: The mean doses to the contralateral parotid and ipsilateral parotid were 22.8 +/- 4.5 Gy and 31.9 +/- 4.1 Gy, respectively. The symptom of xerostomia was mild at the end of radiotherapy. ECT showed EI of contralateral parotid were 0.35 +/- 0.25, 0.31 +/- 0.24 and 0.33 +/- 0.22 at the beginning, the end of and 3 months after radiotherapy (RT), respectively. UI were 7.12 +/- 3.56, 5.81 +/- 2.25 and 5.72 +/- 2.81 at the same intervals. This shows no statistical difference. The EI and UI of ipsilateral parotid at the completion of radiotherapy declined significantly (0.21 +/- 0.16 and 4.87 +/- 2.45, respectively) compared with those of pre-treatment (0.36 +/- 0.27 and 8.02 +/- 3.89, respectively) (P < 0.05). DVH showed: at the end of RT, the EI was significant difference between mean dose < 26 Gy and > or = 26 Gy group (P = 0.009) and decreased significantly in the group of V25 (the percentages of parotid volume irradiated with < 25 Gy) > or = 50% compared with the group of V25 < 50% (P < 0.01). The UIs were no significant difference in two groups (P > 0.05). CONCLUSION: 26 Gy is a threshold dose for the preservation of parotid glands function. There is also a threshold volume irradiated for the preservation of the parotid glands function. Based on the precondition of assuring significant dose to the target volume (PTV), we should reduce the irradiated volume and dose to parotid glands as possible as we can so as to preserve its function.