Joint Optimization of Photon–Carbon Ion Treatments for Glioblastoma

PurposeCarbon ions are radiobiologically more effective than photons and beneficial for treating radioresistant gross tumor volumes (GTV). However, owing to a reduced fractionation effect, they may be disadvantageous infiltrative tumors, in which healthy tissue inside the clinical target volume (CTV) must protected through fractionation. This work addresses question: What is ideal combined photon–carbon ion fluence distribution tumors given specific fraction allocation between carbon ions?Methods MaterialsWe present method simultaneously optimize sequentially delivered intensity modulated photon (IMRT) (CIRT) treatments based on cumulative biological incorporating both variable relative effect of within linear quadratic model. The demonstrated 6 glioblastoma patients comparison with current standard independently optimized CIRT–IMRT plans.ResultsCompared reference plan, joint optimization strategies yield inhomogeneous dose distributions that cumulatively deliver homogeneous distribution. In optimal distributions, CTV mostly by restricted GTV variations depending size location. Improvements conformity high-dose regions reflected mean EQD2 reduction 3.29 ± 1.22 Gy fall-off margin around CTV. Carbon higher doses center GTV, contributions increased at interfaces critical structures. results 8.3 2.28 Gy, brain stem abuts volumes.ConclusionsWe have developed biophysical model treatments. For patient cases, we show our approach targeted application (1) reduces normal tissues volume, can only fractionation; (2) boosts central reduce integral dose. Joint IMRT–CIRT enable exploration new spectrum plans better address physical radiobiological treatment planning challenges. ions? We plans. Compared volumes.