Comparative planning study for proton radiotherapy of benign brain tumors

Purpose: A comparative study of different systems for proton-based radiotherapy was conducted. Material and Methods: The Paul Scherrer Institute method for spot scanning was compared with the systems for passive scattering from the Helax-TMS and the Varian Eclipse. Twelve cases of "benign" brain tumors were considered (meningiomas, neurinomas, and hypophyseal adenomas). Organs at risk included chiasm, brainstem, eyes and optic nerves as well as the not otherwise specified healthy brain tissue in view of long-term toxicity. Results: The results showed that high target coverage was achievable (V-90 > 98% for all systems). Plans designed with the spot-scanning technique presented the minimum involvement of healthy tissue (e.g., the lowest maximum significant dose to healthy brain [25.6 Gy] or the lowest conformity index [CI95 = 1.3], between 38% and 46% lower than for the other techniques). Conclusion: In this study, no definitive indication of superiority of any technique can be drawn but spot scanning can better conform dose distributions and minimize the irradiation of healthy volumes at medium to Low dose Levels, a factor of interest when tong Life expectancy is considered.