1179 - Elective Nodal Irradiation to 44 Gy with Sequential IMRT Boost in HPV-Positive Oropharyngeal Squamous Cell Carcinoma

Purpose/Objective(s):

Human papillomavirus–positive (HPV+) oropharyngeal squamous cell carcinoma (OPSCC) carries an excellent prognosis after definitive chemoradiotherapy. Many current treatment schemas allow elective nodal doses up to 56 Gy, but data evaluating outcomes at lower doses in large, uniformly treated cohorts are limited. We assessed elective nodal failure (ENF) in patients treated with 44 Gy elective coverage followed by sequential boost to determine whether this lower dose maintains oncologic control.

Materials/Methods:

We retrospectively analyzed patients with non-metastatic (T0–4, N0–3) HPV+ OPSCC treated with definitive intensity-modulated radiotherapy (IMRT) at a single institution between 2010 and 2023. Elective nodal regions received 44 Gy (range 40–46 Gy), followed by a sequential boost to 70 Gy to the primary tumor and involved lymph nodes. The majority of patients received concurrent cisplatin-based chemotherapy. Patients were excluded if they received induction chemotherapy, neck dissection, intermediate-dose nodal volumes, or had metastatic disease at presentation.

The primary endpoint was ENF, defined as recurrence within the 44 Gy elective nodal volume. Secondary endpoints included local, regional, and locoregional control, distant metastasis–free survival (DMFS), progression-free survival (PFS), and overall survival (OS). Time-to-event outcomes were calculated from radiotherapy start using Kaplan–Meier methods.

Results:

A total of 312 patients met inclusion criteria. Median follow-up was 77 months. ENF occurred in less than 1% of patients (n=2); one isolated recurrence and one with synchronous regional gross nodal recurrence. The overwhelming majority of locoregional failures occurred within the 70 Gy target volumes rather than within electively treated nodal regions. The incidence of ENF was too low to identify contributing factors. Three- and five-year outcomes, including freedom from ENF, local control, locoregional control, DMFS, PFS, and OS, are summarized in the table below.

Conclusion:

Elective nodal irradiation to 44 Gy in HPV+ OPSCC was associated with very low ENF rate and excellent locoregional control, DMFS, PFS, and OS. Most locoregional recurrences occurred within the high-dose (70 Gy) target volumes encompassing the primary tumor and involved lymph nodes, rather than electively treated regions. These single-institution data demonstrate the oncologic safety of de-escalating elective nodal dose to 44 Gy, with isolated ENF rates comparable to or better than those reported with higher doses. These findings support reduced elective nodal dosing in HPV+ OPSCC patients and justify prospective evaluation of doses =44 Gy.

	3-years	5-years
Freedom from ENF	99.6%	99.1%
Local Control	96.7%	96.3%
Locoregional Control	93.1%	91.8%
DMFS	91.1%	89.4%
OS	89.9%	85.4%
PFS	84.5%	79.4%