%0 Journal Article
%A Bennan, Amit Ben Antony
%A Unkelbach, Jan
%A Wahl, Niklas
%A Salome, Patrick
%A Bangert, Mark
%T Joint optimization of photon - carbon ion treatments for Glioblastoma.
%J International journal of radiation oncology, biology, physics
%V 111
%N 2
%@ 0360-3016
%C Amsterdam [u.a.]
%I Elsevier Science
%M DKFZ-2021-01203
%P 559-572
%D 2021
%Z #EA:E040#LA:E040#/2021 Oct 1;111(2):559-572
%X Carbon ions are radiobiologically more effective than photons and are beneficial for treating radioresistant gross tumour volumes (GTV). However, due to a reduced fractionation effect, they may be disadvantageous for treating infiltrative tumours, where healthy tissue inside the clinical target volume (CTV) must be protected through fractionation. This work addresses the question: what is the ideal combined photon-carbon ion fluence distribution for treating infiltrative tumours given a specific fraction allocation between photons and carbon ions?We present a method to simultaneously optimize sequentially delivered intensity modulated photon (IMRT) and carbon ion (CIRT) treatments based on cumulative biological effect, incorporating both the variable RBE of carbon ions and the fractionation effect within the linear quadratic model. The method is demonstrated for six Glioblastoma patients in comparison to current clinical standard of independently optimized CIRT - IMRT plans.Compared to the reference plan, joint optimization strategies yield inhomogeneous photon and carbon ion dose distributions that cumulatively deliver a homogeneous biological effect distribution. In the optimal distributions, the dose to CTV is mostly delivered by photons while carbon ions are restricted to the GTV with variations depending on tumour size and location. Improvements in conformity of high dose regions are reflected by a mean EQD2 reduction of 3.29 ± 1.22 Gy in a dose fall-off margin around the CTV. Carbon ions may deliver higher doses to the center of the GTV, while photon contributions are increased at interfaces with CTV and critical structures. This results in a mean EQD2 reduction of 8.3 ± 2.28 Gy, where the brainstem abuts the target volumes.We have developed a biophysical model to optimize combined photon-carbon ion treatments. For six glioblastoma patient cases, we show that our approach results in a more targeted application of carbon ions that (1) reduces dose in normal tissues within the target volume which can only be protected through fractionation (2) boosts central target volume regions in order to reduce integral dose. Joint optimization of IMRT - CIRT treatments enable the exploration of a new spectrum of plans that can better address physical and radiobiological treatment planning challenges.
%F PUB:(DE-HGF)16
%9 Journal Article
%$ pmid:34058258
%R 10.1016/j.ijrobp.2021.05.126
%U https://inrepo02.dkfz.de/record/169036