Proton therapy for skull base chordomas in the pediatric and adolescent patient

Abstract

Radiation therapy for skull base tumors requires knowledge, skill, and experience by the radiation oncologist. Tumors often require high target dosages, which can conflict with the competing goals of normal organ dose limitation for risk reduction of long-term functional impairments and anatomic disfigurement in the surviving children and adolescents. Protons are well suited to meet those challenges, specifically by employing active scanning technology. Chordomas represent the most challenging histology. Postoperative or definitive proton therapy with target doses ranging between 72-76-80GyRBE for small to large tumor volumes, respectively, has resulted in local control rates similar to the adult patient cohort. Due to the rarity of the disease no prospective randomized data are available, but comparison with published data using alternative conformal and/or stereotactic photon modalities strongly indicates a more favorable outcome using protons. Considering the anatomically close proximity of tumors to critical normal structures in the skull base, high target dosages require also relatively high normal tissue dose constraints compared to general radiation oncology practices. Likely due to favorable dose-volume effects of protons, i.e., its sharp dose fall-off within defined organs, the rates of severe adverse events appear acceptable. This chapter reviews the principles and practice of proton therapy for skull base chordomas.