Predicted Secondary Malignancies following Proton versus Photon Radiation for Oropharyngeal Cancers

Abstract

Purpose There has been a recent epidemic of human papillomavirus (HPV)–positive oropharyngeal cancer, accounting for 70% to 80% of diagnosed cases. These patients have an overall favorable prognosis and are typically treated with a combination of surgery, chemotherapy, and radiation. Because these patients live longer, they are at risk of secondary malignant neoplasms (SMNs) associated with radiation therapy. Therefore, we assessed the predicted risk of SMNs after adjuvant radiation therapy with intensity-modulated proton therapy (IMPT) compared with intensity modulated photon radiation therapy (IMRT) in patients with HPV- positive oropharyngeal cancers after complete resection. Materials and Methods Thirteen consecutive patients with HPV-positive oropharyngeal cancers treated with postoperative radiation alone were selected. All patients were treated with pencil beam scanning IMPT to a total dose of 60 Gy in 2 Gy fractions. The IMRT plans were generated for clinical backup and were used for comparative purposes. The SMN risk was calculated based on an organ equivalent dose model for the linear-exponential dose-response curve. Results Median age of the patient cohort was 63 years (range, 47-73 years). There was no difference in target coverage between IMPT and IMRT plans. We noted significant reductions in mean mandible, contralateral parotid, lung and skin organ equivalent doses with IMPT compared with IMRT plans (P < .001). Additionally, a significant decrease in the risk of SMNs with IMPT was observed for all the evaluated organs. Per our analysis, for patients with oropharyngeal cancers diagnosed at a national median age of 54 years with an average life expectancy of 27 years (per national Social Security data), 4 excess SMNs per 100 patients could be avoided by treating them with IMPT versus IMRT. Conclusions Treatment with IMPT can achieve comparable target dose coverage while significantly reducing the dose to healthy organs, which can lead to fewer predicted SMNs compared with IMRT.

Current Status and Future Directions of Proton Therapy for Head and Neck Carcinoma

“…The recent study by Jain et al focused on the predicted risk of SPM in a cohort of patients with HPV-positive OPC subjected to transoral robotic surgery (TORS) and selective neck dissection followed by adjuvant IMPT [ 36 ]. Both IMPT and IMRT plans were generated for each patient, and previously reported models of organ-specific radiation-induced cancer incidence were used to address the aim of the study.…”

Proton Beam Radiation Therapy for Oropharyngeal Squamous Cell Carcinoma

“…Jain et al [ 40 ] reported on 13 patients with HPV-positive OPSCC treated with TORS and postoperative IMPT, treating bilateral fields to 60 Gy in 30 fractions at the University of Pennsylvania. When compared with IMRT, IMPT resulted in significant reductions in the mean doses to the mandible, contralateral parotid, lung, and skin organ equivalent doses ( P < .001).…”

Proton Therapy for Squamous Cell Carcinoma of the Head and Neck: Early Clinical Experience and Current Challenges

“…Furthermore, young age, favorable prognosis, and previous irradiation in the head and neck region were other important factors that led to the clinicians’ preference for PT [ 18 ]. It is generally accepted that PT is a preferred treatment option for pediatric HNC patients, due to the advantage of low dose spread in tissue, with a potential reduction in secondary malignancies [ 66 ].…”