Long-Term Outcomes Following Definitive or Adjuvant Proton Radiotherapy for Adenoid Cystic Carcinoma.

Area of Science:

• Oncology
• Radiation Oncology
• Head and Neck Surgery

Background:

• Adenoid cystic carcinoma (ACC) is a rare head and neck malignancy with limited outcomes data.
• Treatment for ACC presents challenges and risks, necessitating studies on long-term results.

Purpose of the Study:

• To report long-term outcomes of patients with head and neck ACC treated with proton therapy (PT).
• To evaluate the efficacy and toxicity of PT in managing ACC.

Main Methods:

• A prospective registry of 56 patients with de novo, nonmetastatic ACC treated with PT (definitive or adjuvant) from 2007-2021.
• Median primary site dose of 72.6 Gy (RBE), with concurrent chemotherapy and nodal radiation administered in select cases.

Main Results:

• 5-year survival rates: LRC 88%, DFS 85%, CSS 89%, OS 89%.
• Intracranial extension and gross residual tumor were associated with lower local-regional control (LRC).
• 5-year cumulative incidence of grade ≥3 toxicity was 15%.

Conclusions:

• Proton therapy demonstrates excellent disease control for head and neck ACC with acceptable toxicity.
• T4 disease, intracranial involvement, and residual disease post-biopsy/subtotal resection are poor prognostic indicators for PT outcomes.