• Histologically or cytologically confirmed diagnosis of advanced loco regional squamous cell carcinoma of the nasopharynx (AJCC v8 Stage II IV); oropharynx (AJCC v8 Stage I III for HPV+ cancer, excluding T1 2N0; AJCC v8 Stage III IV for Human papillomavirus (HPV) negative cancer); larynx (AJCC v8 Stage III to IV); or hypopharynx (AJCC v8 Stage III to IV), scheduled to undergo chemoradiation. Patients with squamous cell carcinoma of the head and neck from an unknown primary site with involved nodes (N1 to 3) also qualify.

• Scheduled to received definitive RT with concurrent platinum based chemotherapy at Stanford

• Eastern Cooperative Oncology Group (ECOG) performance status (PS) 0 to 1

• Must be able to swallow d limonene gelcaps at the time of enrollment.

• Adequate hepatic function within 2 weeks prior to registration defined as follows: Bilirubin ≤ 2 mg/dL; aspartate aminotransferase (AST) or alanine aminotransferase (ALT) \< 3 times the upper limit of normal

• Adequate hematologic function within 2 weeks prior to registration defined as follows:

‣ Absolute neutrophil count (ANC): ≥ 1,500/mm3

⁃ Platelets: ≥ 100,000/mm3

⁃ Hemoglobin: ≥ 8.0 g/dL (Note: The use of transfusion or other intervention to achieve Hgb ≥ 8.0 g/dL is acceptable).

• Adequate renal function defined as follows:

∙ Serum creatinine ≤ 1.5 mg/dL within 2 weeks prior to registration or creatinine clearance (CC) ≥ 50 mL/min within 2 weeks prior to registration determined by 24 hour collection or estimated by Cockcroft Gault formula:

∙ CCr male = \[(140 - age) x (wt in kg)\] \[(Serum Cr mg/dL) x (72)\] CCr female = 0.85 x (CrCl male)

• Negative serum pregnancy test within 2 weeks prior to registration and agreement to use a birth control method during the entire duration of d limonene treatment for women of childbearing potential

• Ability to understand and the willingness to sign a written informed consent document