A 72-year-old man with a 10-year history of chronic sun exposure and actinic keratosis presents with a 2.5 cm nodular lesion on his left ear with central ulceration. Biopsy reveals poorly differentiated squamous cell carcinoma with perineural invasion. Examination reveals no palpable cervical lymph nodes. CT scan of the head and neck shows no distant metastasis. What is the most appropriate next step in management?