3519 - ICRU 83-Informed Dose Layering to Reduce Temporal Lobe Injury Risk in T4 Nasopharyngeal Carcinoma: A Prospective Cohort Study with a Contemporaneous Comparator
Presenter(s)
H. Liao1,2, J. Wang2, and Y. Lai1,2; 1Jiangxi Medical College, Nanchang University, Nanchang, China, 2Department of Radiation Oncology, Jiangxi Cancer Hospital, Second Affiliated Hospital of Nanchang Medical College, Nanchang, China
Purpose/Objective(s): Radiation-induced temporal lobe injury (RTLI) remains a major late toxicity in patients with T4 nasopharyngeal carcinoma (NPC), as primary target volumes frequently overlap the temporal lobe planning risk volume (PRV), thereby limiting achievable near-maximum dose constraints. This study evaluated the long-term safety and effectiveness of an International Commission on Radiation Units and Measurements (ICRU) Report 83–informed “dose-layering” strategy.
Materials/Methods: This non-randomized, single-institution, prospective observational cohort study with a contemporaneous comparator (ClinicalTrials.gov identifier: NCT03539250) 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 dose 70 Gy) and an overlapping subvolume (PTVsv2, prescribed dose 66 Gy) delivered using a simultaneous integrated boost technique. The standard delineation and planning (SD) approach prescribed 70 Gy to the entire PTVnx without overlap-specific subvolumes.
Results: A total of 361 patients were analyzed (MD, n = 104; SD, n = 257). The 5-year cumulative incidence of RTLI was significantly lower in the MD group than in the SD group (23.2% versus 36.2%; P = 0.019). Multivariable analysis revealed that the MD approach was associated with reduced risk of RTLI (hazard ratio = 0.56; 95% confidence interval: 0.34–0.94; P = 0.029). No significant differences were observed between MD and SD groups 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 for dosimetry (205 versus 205 temporal lobes), the MD approach achieved significantly lower temporal lobe maximum dose and dose to the hottest 1 cm3 (both P < 0.001), with no differences in the volume receiving V40–V60 and a borderline reduction in the volume receiving V65 (P = 0.053).
Conclusion: An overlap-specific ICRU Report 83–informed dose layering (66 Gy to PTVsv2) significantly reduced the incidence of RTLI while preserving long-term tumor control in anatomically constrained T4 NPC.