Proposals for the Delineation of Neck Clinical Target Volume Specific to Oral Squamous Cell Cancer Based on Lymph Node Distribution

Abstract

To establish the regional lymph node (LN) distribution probability map and draw the neck clinical target volume specific to oral squamous cell cancer (OSCC). A total of 293 patients with pathologically proven OSCC were enrolled from Jan 2014 to Jun 2022. The patients were divided into two groups according to the ≤1 cm or>1 cm of minimal distance from the lesion's edge to the midline of body. The center point of the LNs with a minimal axial diameter of ≥10 mm was marked on a single treatment planning computed tomography scan. The neck LN levels I to X were based on 2013 updated international consensus guidelines. LN distribution probability maps were established. The relationships between the LN distribution and consensus guidelines were analyzed to propose modifications for clinical target volume boundaries specific to OSCC. A total of 1033 LNs were marked. Compared with the >1 cm group, The ≤1 cm group has following feature tendencies: strong addiction to smoking and drinking, predilection for tongue and oral floor cancer, larger primary lesion with mainly infiltrative growth pattern, more frequent extra-nodal extension with mainly contralateral LNs. For the ≤1cm group, the distribution probability of LNs was: ipsilateral II (42.67%), ipsilateral Ib (17.35%), contralateral II (11.18%), ipsilateral III (8.74%), contralateral Ib (7.46%), Ia (6.43%). The other group was: ipsilateral Ib (43.14%), ipsilateral II (37.64%), contralateral Ib (4.31%), ipsilateral III (3.92%), contralateral II (3.53%), Ia (0.78%). Accordingly, the proposals for the delineation of neck clinical target volume were: 1. the inferior boundary of level Ia extends until the level of the thyroid cartilage plate; 2. the upper boundary of level Ib descends to the level of the mandibular angle, and the inner posterior boundary only includes the lateral and posterior margin of the submandibular gland within 5mm; 3. the upper boundary of level II changes to the transverse process of the second cervical vertebra, and the posterior boundary retracts to the posterior edge of the levator scapula. 4. the anterior inner border of level IVa contains only the internal jugular arteriovenous sheath. This is the first description of LN topographic spread patterns for OSCC. Optimization of CTV delineation is helpful to improve the treatment outcome and reduce adverse events.