不同分期鼻咽癌IMRT解剖体积变化对剂量分布影响

目的 探讨不同分期的鼻咽癌IMRT解剖体积变化及其对剂量分布影响, 客观评价重新修改IMRT计划的必要性。方法 将24例初诊鼻咽癌放化疗患者根据鼻咽癌2008分期分为早中期组(12例)和局部晚期组(12例)。在放疗至第5周时重新进行CT扫描, 重新勾画靶区和OAR, 并计算原计划在新CT上的剂量分布结果。分析靶区和OAR解剖体积变化及剂量分布变化, 并行配对t检验和Spearman相关分析。结果 与放疗前比较, 早中期组放疗中颈部阳性淋巴结靶体积(GTV_nd)缩小相近(P=0.059), 鼻咽大体肿瘤体积(GTV_nx) 、高危临床靶体积(CTV₁)和腮腺体积均明显缩小(P=0.001、0.012、0.002、0.000);局部晚期组放疗中GTV_nx、GTV_nd、CTV₁和腮腺体积均较前明显缩小(P=0.000、0.000、0.003、0.003、0.000)。两组腮腺剂量放疗中均较放疗前升高(P=0.044、0.026、0.033、0.026和P=0.024、0.016、0.030、0.015), 局部晚期组还观察到GTV_nd剂量升高(P=0.029、0.049)。结论 局部晚期鼻咽癌患者推荐在放疗第5周重新CT扫描并重新制定IMRT计划, 以保证靶区剂量和保障腮腺安全剂量。

Influence of change in anatomical volume on dose distribution during intensity-modulated radiotherapy for different stages of nasopharyngeal carcinoma

Objective To explore the change in anatomical volume during intensity-modulated radiotherapy (IMRT) for different stages of nasopharyngeal carcinoma (NPC) and its influence on dose distribution, and to assess the necessity to modify the IMRT plan. Methods Twenty-four patients with newly diagnosed NPC who received IMRT and chemotherapy were enrolled in the study, and were divided into early-intermediate group (12 cases) and locally advanced group (12 cases) according to the 2008 staging system for NPC. Each patient had a repeated CT scan at week 5 of radiotherapy, and target volume and organs at risk (OAR) were contoured. The dose distribution of the original plan shown on CT was calculated. Changes in target volume, OAR anatomical volume, and dose distribution were analyzed, and paired t-test and Spearman correlation analysis were performed. Results In the early-intermediate group, gross target volume of neck positive lymph nodes (GTV_nd) was reduced during radiotherapy (P=0.059), and gross target volume of nasopharynx (GTV_nx), high-risk clinical target volume (CTV₁), and parotid volume were reduced significantly during radiotherapy (P=0.001, 0.012, 0.002, and 0.000, respectively). In locally advanced group, GTV_nx, GTV_nd, CTV₁, and parotid volume were significantly reduced during IMRT (P=0.000, 0.000, 0.003, 0.003, and 0.000, respectively). Compared with the values before radiotherapy, the parotid dose increased significantly in the two groups during IMRT (P=0.044, 0.026, 0.033, and 0.026, respectively;P=0.024, 0.016, 0.030, and 0.015, respectively), and the increase in GTV_nd dose was observed in the locally advanced group (P=0.029 and 0.049). Conclusions It is recommended to perform another CT scan for patients with locally advanced NPC at week 5 of radiotherapy and formulate a new IMRT plan to maintain target volume dose and guarantee a safe parotid dose.