Dosimetric comparison of three-dimensional conformal proton radiotherapy, intensity-modulated proton therapy, and intensity-modulated radiotherapy for treatment of pediatric craniopharyngiomas

Purpose: Cranial irradiation in pediatric patients is associated with serious long-term adverse effects. We sought to determine whether both three-dimensional conformal proton radiotherapy (3D-PRT) and intensity-modulated proton therapy (IMPT) compared with intensity-modulated radiotherapy (IMRT) decrease integral dose to brain areas known to harbor neuronal stem cells, major blood vessels, and other normal brain structures for pediatric patients with craniopharyngiomas. Methods and Materials: IMRT, forward planned, passive scattering proton, and IMPT plans were generated and optimized for 10 pediatric patients. The dose was 50.4 Gy (or cobalt Gy equivalent) delivered in 28 fractions with the requirement for planning target volume (PTV) coverage of 95% or better. Integral dose data were calculated from differential dose-volume histograms. Results: The PTV target coverage was adequate for all modalities. IMRT and IMPT yielded the most conformal plans in comparison to 3D-PRT. Compared with IMRT, 3D-PRT and IMPT plans had a relative reduction of integral dose to the hippocampus (3D-PRT, 20.4; IMPT, 51.3%), dentate gyrus (27.3, 75.0%), and subventricular zone (4.5, 57.8%). Vascular organs at risk also had reduced integral dose with the use of proton therapy (anterior cerebral arteries, 33.3, 100.0%; middle cerebral arteries, 25.9%, 100%; anterior communicating arteries, 30.8, 41.7%; and carotid arteries, 51.5, 77.6). Relative reduction of integral dose to the infratentorial brain (190.7, 109.7%), supratentorial brain without PTV (9.6, 26.8%), brainstem (45.6, 22.4%), and whole brain without PTV (19.4, 34.4%) were recorded with the use of proton therapy. (Differences were significant based on Friedman's test with Bonferroni-Dunn correction, α = 0.05) Conclusions: The current study found that proton therapy was able to avoid excess integral radiation dose to a variety of normal structures at all dose levels while maintaining equal target coverage. Future studies will examine the clinical benefits of these dosimetric advantages.