Predicted Secondary Malignancies following Proton versus Photon Radiation for Oropharyngeal Cancers.

Varsha Jain,Shannon O'Reilly,Peyton Irmen,Liyong Lin,Alexander Lin,Jennifer H Vogel

doi:10.14338/ijpt-19-00076.1

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.

Highlights

The general trends in the epidemiology of head and neck cancers in United States have dramatically changed in the recent decades [1]
They are managed with a multimodality treatment approach comprising surgery, radiation and chemotherapy and have significantly better overall survival and failure-free survival compared with human papillomavirus (HPV)- negative oropharyngeal cancers as well as cancers arising in other head and neck subsites [4]
We evaluate the predicted excess absolute risk of secondary malignant neoplasms (SMNs) after adjuvant radiation with intensity-modulated proton therapy (IMPT) compared with intensity modulated photon radiation therapy (IMRT) for patients with HPV-positive oropharyngeal cancer with an organ equivalent dose (OED) model for the linear-exponential dose-response curve

Summary

Introduction

The general trends in the epidemiology of head and neck cancers in United States have dramatically changed in the recent decades [1]. Unlike most head and neck cancers, they tend to occur in young- to middle-aged, white men (40-59 years) of higher socioeconomic status, who are typically nonsmokers and nondrinkers [3] They are managed with a multimodality treatment approach comprising surgery, radiation and chemotherapy and have significantly better overall survival and failure-free survival compared with HPV- negative oropharyngeal cancers as well as cancers arising in other head and neck subsites [4]. Given their favorable prognosis and typical absence of high risk lifestyle behaviors (tobacco, alcohol), these patients live longer and are at an increased risk of secondary malignant neoplasms (SMNs) related to their initial cancer treatment. Radiation-induced SMNs typically occur in tissues adjacent to the target tumor volume but may be associated with exposure to low doses of scatter and leakage radiation outside of the primary treatment field [5]

Methods

Results

Conclusion