Department of Clinical Oncology, Queen Elizabeth Hospital, Hong Kong, China.
Department of Clinical Oncology, Gleneagles Hong Kong Hospital, Hong Kong, China.
Med Dosim. 2021;46(1):39-44. doi: 10.1016/j.meddos.2020.07.002. Epub 2020 Aug 4.
Radiation-induced hypoglossal nerve palsy is an infrequent but debilitating late complication after definitive radiotherapy for head and neck cancers. D1cc < 74 Gy (equivalent dose in 2 Gy fractions, EQD2) has been proposed as a potential dose constraint that limits 8-year palsy risk to < 5%. This study sets to perform detailed dosimetric assessments on the applicability of this novel dose constraint in advanced nasopharyngeal carcinoma (NPC).
This is a retrospective single-institution dosimetry study. NPC radiotherapy plans were identified from an institutional database, with an aim to select 10 eligible cases. Bilateral hypoglossal nerves were retrospectively contoured following a standard atlas. Cases with either one, or both, hypoglossal nerves D1cc exceeded 74 Gy EQD2 were included. Dosimetry of hypoglossal nerves, planning target volumes (PTV) and normal structures before and after application of the new hypoglossal nerve constraint were compared and analyzed.
Ten NPC cases were replanned. All hypoglossal nerve contours overlapped with high-dose PTV, predominantly at regions of gross nodal diseases. D1cc in 15 out of 20 hypoglossal nerves exceeded 74G y EQD2 at initial plans. All nerves fulfilled the pre-specified constraint of 74Gy EQD2 after re-plan. Median hypoglossal nerve D1cc reduced from 74.8Gy (range, 74.1 to 77.4Gy) to 73.5Gy (range, 72.4 to 74.0Gy) (p < 0.001), corresponded to a projected reduction in 8-year palsy risk from 5%-14% to 3%-5%. PTV V100 was maintained above 95% in all cases. Dose increments in near-maximum (D2) and decrements in near-minimum (D98) were < 1 Gy. Safety dosimetric parameters of standard head and neck organs-at-risk showed no significant changes.
Hypoglossal nerve D1cc < 74 Gy EQD2 is a dosimetrically feasible constraint in definitive radiotherapy for NPC. Tumor target coverage and normal organ dosimetry were not compromised with its usage. Its routine application should be considered in definitive radiotherapy for head and neck cancers.
放射性舌下神经麻痹是头颈部癌症根治性放疗后一种罕见但使人虚弱的迟发性并发症。已有研究提出 D1cc<74Gy（等效剂量 2Gy 分数，EQD2）作为潜在的剂量限制，可将 8 年麻痹风险限制在<5%。本研究旨在对头颈部癌症根治性放疗中应用这一新剂量限制的适用性进行详细的剂量评估。
这是一项回顾性单机构剂量学研究。从机构数据库中确定了鼻咽癌（NPC）放疗计划，目的是选择 10 例符合条件的病例。双侧舌下神经根据标准图谱进行回顾性勾画。如果一侧或两侧舌下神经 D1cc 超过 74Gy EQD2，则纳入研究。比较并分析了新的舌下神经限制前后舌下神经、计划靶区（PTV）和正常结构的剂量学。
10 例 NPC 病例重新计划。所有舌下神经轮廓均与高剂量 PTV 重叠，主要位于大体淋巴结疾病区域。在初始计划中，20 条舌下神经中有 15 条 D1cc 超过 74Gy EQD2。所有神经在重新计划后均满足预先规定的 74Gy EQD2 限制。中位舌下神经 D1cc 从 74.8Gy（范围：74.1-77.4Gy）降至 73.5Gy（范围：72.4-74.0Gy）（p<0.001），预计 8 年麻痹风险从 5%-14%降至 3%-5%。所有病例 PTV V100 均保持在 95%以上。近最大剂量（D2）的剂量增加和近最小剂量（D98）的剂量减少均<1Gy。标准头颈部危及器官的安全剂量学参数无显著变化。
D1cc<74Gy EQD2 是 NPC 根治性放疗中一种具有可操作性的剂量限制。使用该限制后，肿瘤靶区覆盖和正常器官剂量学未受影响。在头颈部癌症的根治性放疗中应常规考虑其应用。
