更新后的IVa区淋巴结勾画对鼻咽癌甲状腺剂量及甲状腺功能减退风险的影响

文献信息

中文摘要

目的： 2024年和2025年国际共识指南重新定义了鼻咽癌（NPC）选择性淋巴结照射区IVa区的前界。本研究旨在通过量化该解剖学改进对甲状腺和喉部剂量的影响，并将这些剂量降低转化为临床可解释的正常组织并发症概率（NTCP）估计，首次对该解剖学改进进行剂量学验证。
方法与材料： 选取30例接受螺旋断层放疗的NPC患者，以代表下颈部淋巴结受累的全谱。为每例患者生成2个针对不同淋巴结临床靶区（CTVn）定义的比较治疗计划：（1）基于2018年指南的CTVn，将IVa区前界定义为胸锁乳突肌前缘；（2）基于2024/2025年指南的CTVn，将该边界移至舌骨下带状肌后缘。在保持靶区覆盖等效的前提下，优化计划以最小化甲状腺和喉部剂量。采用配对分析比较剂量学参数以及甲状腺功能减退和喉水肿的NTCP。
结果： 更新后的CTVn勾画显著降低了甲状腺平均剂量，从48.5 Gy降至44.8 Gy（P < .001），并将接受≥50 Gy的甲状腺体积从59.9%降至46.3%（P < .001）。喉部平均剂量从25.9 Gy降至21.7 Gy（P < .001）。甲状腺功能减退的NTCP从43.9%降至34.9%（P < .001），对应20.5%的相对风险降低。靶区覆盖和其他危及器官的剂量在计划间保持相当。
结论： 采用2024/2025年国际共识指南进行IVa区勾画，在不影响靶区覆盖的情况下显著降低了甲状腺和喉部的辐射剂量。这转化为原发性甲状腺功能减退风险的临床有意义降低，支持广泛实施这些指南以改善NPC患者的生存结局。

英文摘要

PURPOSE: The 2024 and 2025 international consensus guidelines redefined the anterior border of the level IVa elective nodal volume for nasopharyngeal carcinoma (NPC). This study aimed to provide the first dosimetric validation of this anatomic refinement by quantifying its impact on thyroid and larynx doses and translating these reductions into clinically interpretable normal tissue complication probability (NTCP) estimates.
METHODS AND MATERIALS: Thirty patients with NPC treated with helical tomotherapy were selected to represent a full spectrum of lower cervical nodal involvement. For each patient, 2 comparative treatment plans for different nodal clinical target volume (CTVn) definitions were generated: (1) CTVn based on 2018 guidelines, defining the level IVa anterior border at the anterior edge of the sternocleidomastoid muscle; and (2) CTVn based on 2024/2025 guidelines, shifting this border to the posterior edge of the infrahyoid ribbon muscles. Plans were optimized to minimize thyroid and larynx doses while maintaining equivalent target coverage. Dosimetric parameters and NTCP for hypothyroidism and laryngeal edema were compared using paired analyses.
RESULTS: The updated CTVn delineation significantly reduced thyroid mean dose from 48.5 Gy to 44.8 Gy (P < .001) and thyroid volume receiving ≥50 Gy from 59.9% to 46.3% (P < .001). Larynx mean dose decreased from 25.9 Gy to 21.7 Gy (P < .001). The NTCP for hypothyroidism was reduced from 43.9% to 34.9% (P < .001), corresponding to a 20.5% relative risk reduction. Target coverage and doses to other organs at risk remained comparable between plans.
CONCLUSIONS: Adopting the updated 2024/2025 international consensus guidelines for level IVa delineation significantly reduces radiation dose to the thyroid and larynx without compromising target coverage. This translates into a clinically meaningful reduction in the risk of primary hypothyroidism, supporting the widespread implementation of these guidelines to improve survivorship outcomes in patients with NPC.