Conformal proton radiation therapy of the posterior fossa: a study comparing protons with three-dimensional planned photons in limiting dose to auditory structures

Abstract

Purpose: Conventional radiation therapy for pediatric posterior fossa tumors can cause sequelae such as hearing loss and impairments in language and learning. Modern three-dimensional (3D) treatment techniques have improved dose conformity to the posterior fossa. This report compares the normal tissue dose-sparing capabilities of proton radiation therapy (PRT) with 3D conformal photon plans. Methods and Materials: Nine children underwent previous PRT for primary CNS malignancies. Using original planning CT scans, the posterior fossa, inner and middle ear, and temporal lobes were delineated. Three-dimensional treatment plans were generated for protons and photons. Normal tissue exposures were calculated by averaging mean doses received and by analysis of dose–volume histogram. Results: The 95% isodose encompassed the posterior fossa in all plans. Normal structures received markedly less radiation from PRT plans than from 3D photon plans. The cochlea received an average mean of 25 ± 4% of the prescribed dose from PRT, and 75 ± 6% from photons. Forty percent of temporal lobe volume was completely excluded using protons; with photons 90% of the temporal lobe received 31% of the dose. Conclusion: PRT resulted in increased dose sparing of normal structures analyzed. Posterior fossa conformity of 3D photons came at the expense of increasing amounts of normal tissue receiving low to moderate doses.