Optimizing radiotherapy of orbital and paraorbital tumors: Intensity-modulated X-ray reams vs. intensity-modulated proton beams

Purpose: This study presents a dosimetric optimization effort aiming to com pare intensity-modulated (IM) X-rays and IM protons in 4 different orbital and paraorbital tumors, These are most challenging targets for standard rad iotherapy due to their close relationship with the eyes and related structu res, Methods and Materials: A primary orbital lymphoma, an optic nerve meningiom a, a sphenoidal ridge meningioma protruding into the orbit, and a pediatric parameningeal paraorbital rhabdomyosarcoma were selected for the purpose o f this study, Planning target volumes (PTVs) and organs at risk (OAR) were defined in each patient CT data set for each tumor site, IRI X-ray and IM p roton three-dimensional treatment plans were implemented. The following tot al tumor doses were prescribed: 30 Gy for the orbital lymphoma, 54 Gy for b oth meningiomas, and 50.4 Gy for the rhabdomyosarcoma case, Dose-volume his tograms (DVHs) were obtained for all targets and OAR with both treatment te chniques, DVHs mere used to predict normal tissue complication probabilitie s (NTCPs) for the OAR in the vicinity of the tumor, Results: The PTV coverage was optimal and equally homogeneous with both IRI X-rags and LR I proton plans in the 4 tumor sites. DVHs for most OAR were better with IM proton beams especially in the low- to mid-dose range region , The integral nontarget dose was lower with IR I protons in every case (fa ctor ranging from 1.5 to 1.9), However, predicted NTCPs (for severe late ef fects) were equally low for both treatment techniques in every tumor site. Conclusion: Although IRI proton plans optimally decreased the dose to the O AR in all tumor sites, both optimized X-ray and proton beams equally succee ded to reduce severe-toxicity prediction risks to less than 5% while optima lly treating the PTV. (C) 2000 Elsevier Science Inc.