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Overlap-adapted Subvolume Prescription to Reduce Temporal Lobe Injury Risk in T4 Nasopharyngeal Carcinoma: A
Huadong Liao1, Jing Wang2, Yongzheng Lai1
1Department of Radiation Oncology, Jiangxi Cancer Hospital and Institute, Second Affiliated Hospital of Nanchang Medical College, Nanchang, Jiangxi, China; NHC Key Laboratory of Personalized Diagnosis and Treatment for Nasopharyngeal Carcinoma, Jiangxi Cancer Hospital, Second Affiliated Hospital of Nanchang Medical College, Nanchang, Jiangxi, China; Jiangxi Medical College, Nanchang University, Nanchang, China.
Purpose:
Radiation-induced temporal lobe injury (RTLI) remains a major late toxicity in T4 nasopharyngeal carcinoma (NPC) because primary target volumes frequently overlap the temporal lobe planning risk volume (PRV), limiting near-maximum dose constraints. This study evaluated the long-term safety and efficacy of an overlap-adapted subvolume prescription strategy.
Materials And Methods:
This non-randomized, single-institution, prospective observational cohort study with a contemporaneous comparator (ClinicalTrials.gov identifier: XXXX) enrolled patients with T4N0-3M0 NPC treated between 2018 and 2022 who had planning target volume (PTV)-temporal lobe PRV overlap ≥ 0.1 cm3. The modified delineation and planning (MD) approach subdivided the primary tumor PTV (PTVnx) into a non-overlap subvolume (PTVsv1, prescribed 70 Gy) and an overlapping subvolume (PTVsv2, prescribed 66 Gy) using simultaneous integrated boost. The standard delineation and planning (SD) approach prescribed a uniform 70 Gy to the entire PTVnx.
Results:
Among 361 patients (MD, n = 104; SD, n = 257), the 5-year cumulative incidence of RTLI was significantly lower in the MD group (23.2% versus 36.2%; P = 0.019). Multivariable analysis revealed that MD was independently associated with reduced RTLI risk (hazard ratio = 0.56; 95% confidence interval: 0.34-0.94; P = 0.029). No significant differences were found in 5-year local relapse-free survival (92.3% versus 89.6%; P = 0.577) or overall survival (84.7% versus 84.4%; P = 0.896). No marginal recurrences were confined to PTVsv2. After lobe-level propensity-score matching (205 lobes per group), MD achieved significantly lower temporal-lobe Dmax and D1cc (both P < 0.001) without differences in V40-V60 and a borderline reduction in V65 (P = 0.053).
Conclusions:
An overlap-adapted subvolume prescription strategy (66 Gy to PTVsv2) significantly reduced the incidence of radiographic RTLI while preserving long-term tumor control in anatomically constrained T4 NPC. The reduction in symptomatic RTLI was numerical but did not reach statistical significance and warrants further validation.
