Postoperative Intensity-Modulated Proton Therapy for Head and Neck Adenoid Cystic Carcinoma

Emma Holliday,Jack Phan,X Ronald Zhu,David I Rosenthal,William H Morrison,Adam S Garden,Steven J Frank,Merrill S Kies,Ehab Hanna,G Brandon Gunn,Xiaodong Zhang,Onita Bhattasali

doi:10.14338/ijpt-15-00032.1

Abstract

Postoperative radiation therapy can improve control for adenoid cystic carcinoma (ACC) of the head and neck; however, delivering adequate dose to the tumor bed must be balanced with limiting dose to nearby critical organs. Intensity-modulated proton therapy (IMPT) may help improve the therapeutic ratio, though concerns exist regarding tissue heterogeneity and other sources of uncertainty in several head and neck subsites. We report control and toxicity outcomes for patients with ACC of the head and neck treated at a single institution with postoperative IMPT and robust planning and analysis. Sixteen patients with head and neck ACC treated with postoperative IMPT were identified. Intensity-modulated proton therapy was delivered by using multifield optimization. Robust planning and analysis were performed. The median dose was 60 (range, 60 to 70) Gy (RBE) (Gy [relative biological effectiveness]). Adjuvant IMPT was given with (N = 12) or without (N = 4) platinum-based chemotherapy. Tumor control outcomes were recorded from the medical record, and acute and chronic toxicities were graded weekly during treatment and upon follow-up per Common Terminology Criteria for Adverse Events, version 4.0 (CTCAE v4). Median follow-up is 24.9 (range, 9.2 to 40.2) months. One patient developed local and distant recurrence and subsequently died. The remaining 15 patients are alive without evidence of disease. Four patients experienced acute grade 3 toxicities: dermatitis (N = 3) and oral mucositis (N = 1). One patient developed a chronic grade 4 optic nerve disorder. There were no grade 5 toxicities. Intensity-modulated proton therapy is a feasible option for patients with ACC of the head and neck in the postoperative setting. Robust treatment planning and plan analysis can be performed such that uncertainties and tissue heterogeneities do not appear to limit safe and effective IMPT delivery. Safety and efficacy appear comparable to those of other types of radiation therapy, but further follow-up of clinical outcomes is needed.

Highlights

Postoperative radiation therapy (RT) has been shown to improve control rates for adenoid cystic carcinoma (ACC) of the head and neck, compared to surgery alone, with the greatest advantage conferred to patients with positive margins or more advanced stage disease [1, 2]
Our results demonstrate that patients with ACC of the head and neck treated with postoperative multiple-field optimization (MFO)-intensity-modulated proton therapy (IMPT) at a large, tertiary referral center have excellent local control outcomes at 2 years as well as high freedom from significant toxicity
Despite the challenging location of these tumors, often in areas of tissue heterogeneity and in close proximity to critical structures, robust treatment planning and plan analysis methods can result in high levels of confidence, such that setup and range uncertainties do not affect our ability to effectively deliver a curative dose to the target volume while keeping doses to organs at risk (OARs) within tolerance

Summary

Introduction

Postoperative radiation therapy (RT) has been shown to improve control rates for adenoid cystic carcinoma (ACC) of the head and neck, compared to surgery alone, with the greatest advantage conferred to patients with positive margins or more advanced stage disease [1, 2]. Proton radiation therapy has more recently been implemented in head and neck ACC as adjuvant treatment with promising outcomes [5, 6]. Optimization techniques for active scanning treatment plans include single-field optimization and multiple-field optimization (MFO) [8]. Single-field optimization involves optimizing the spot intensities for each beam individually, while MFO optimizes the intensities of all beams simultaneously to balance the doses to targets and organs at risk (OARs), based on stated objectives [9]. Active scanning with MFO is often referred to as intensity-modulated proton therapy (IMPT) because the intensity of the proton beam can be varied from spot to spot to deliver the desired dose in the target volume after adding the contributions of all treatment fields. IMPT is different from intensitymodulated radiation therapy (IMRT) in that the energy as well as the intensity can be varied

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Discussion

Conclusion