Parotid Node Metastases in Locally Advanced Nasopharyngeal and Oropharyngeal Cancer: Implications for Radiotherapy Target Volume Delineation

Terence M. Williams MD, PhD; Jeffrey M. Vainshtein, MD; Matthew E. Spector, MD; Douglas B. Chepeha, MD; Matthew Stenmark, MD; Avraham Eisbruch, MD
Published: Monday, Oct 05, 2015

Expert’s Perspective

Andy Trotti, MD
Andy Trotti, MD
Professor and Senior Member
Department of Radiation Oncology
Moffitt Cancer Center

Williams and Eisbruch have addressed an uncommon clinical scenario in the setting of bulky jugulodigastric adenopathy. Their observation of parotid lymph node failures prompted a review of their experience and of the literature. They have thoroughly considered a number of factors including anatomic and physiologic considerations initially described by Million and Rouvier. The absolute number of parotid failures is small in any series, calling into question our ability to accurately estimate clinical risk. However, by invoking classic anatomic literature combined with lymphatic physiology the authors have constructed a strong argument for covering parotid lymph node stations as a potential site of failure in bulky neck disease.

The presence of adenopathy causing retrograde flow into otherwise low risk sites has long been a fundamental tenet of the rationale for nodal station risk and associated need for treatment. Nonetheless, the decision to cover parotid lymph node stations should not be taken lightly since it may significantly increase the risk of severe xerostomia and associated changes in quality of life.

It is fitting that these observations and suggested policies come from perhaps the most senior and well respected pioneer of three-dimensional and intensity modulated radiotherapy (IMRT). Eisbruch and colleagues thus extend and continue to refine our knowledge base, further advancing the art and science of radiotherapy.

Abstract

Purpose

To determine the frequency and clinical characteristics of parotid gland metastasis (PGM) from nasopharyngeal cancer (NPC) and oropharyngeal cancer (OPC) and define criteria for elective inclusion of parotidean nodes in the radiotherapy clinical target volume (CTV).

Methods and Materials

All cases of NPC and stage III/IV OPC referred for radiotherapy at our institution between 2003 and 2011 were reviewed. Incidence and risk factors for PGM at presentation and at time of failure were analyzed. A literature review of PGM incidence in head and neck squamous cell carcinoma was performed.

Results

Of 52 NPC and 231 OPC patients, two (3.8%) NPC patients and 4 (1.9%) patients presented with PGM. All PGMs were located ipsilateral to the primary tumors in patients with bulky, ipsilateral level II and multilevel ipsilateral lymph node involvement of aggregate size greater than 6 cm in diameter. Similar rates and characteristics were found in the literature after an extensive search.

Conclusions

The ipsilateral parotidean nodes may be at risk of metastatic involvement when bulky ipsilateral level II metastases and multilevel nodal disease are co-existent, possibly due to retrograde lymphatic drainage. Inclusion of the ipsilateral parotid gland in the CTV should be considered in such cases.

Introduction

The most common oral complication and cause for reductions of quality of life (QOL) after head and neck radiation is salivary gland dysfunction and xerostomia.1,2 Parotid gland-sparing intensity-modulated radiation therapy (IMRT) techniques have become standard of care in an attempt to prevent salivary flow dysfunction and xerostomia. IMRT has facilitated parotid-sparing by virtue of enabling steep dose gradients between normal tissue and clinical target volumes (CTV) in close apposition. Indeed, the use of IMRT has increased dramatically in the United States.3 Furthermore, in comparisons between IMRT and conventional radiation for head and neck cancer (HNC), no significant increases in the rate of locoregional relapse have been found with the use of IMRT.4-6


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