Room: Track 1
We introduce a novel multi-ion particle therapy (MIT) treatment modality where combining two or more particle beams (proton [p], helium ions [He] and/or carbon ions [C]) affords enhanced biophysical features such as constant RBE/physical dose and improved LET uniformity within the target volume, as well as reduced dose to surrounding normal tissues.
The PRECISE (PaRticle thErapy using single and Combined Ion optimization StratEgies) treatment planning system was established for MIT optimization and assessment based on the GPU-accelerated dose engine FRoG (Fast dose Recalculation on GPU). Combined ion-beam with constant RBE (CICR) treatment plans using C and p (CICR[C-p]) as well as C and He (CICR[C-He]) were generated and examined using the local effect model and microdosimetric kinetic model. Dosimetric and biological validation studies using pin-point ionization chambers and in vitro clonogenic assay with a glioma cell line (GL261), respectively, were performed in both homogenous and heterogeneous settings using an anthropomorphic head-phantom. Furthermore, patient case studies were conducted for CICR against conventional planning techniques using a single ion species.
CICR(C-p) and CICR(C-He) treatments yielded increased treatment stability and more homogenous biophysical distributions compared to conventional particle treatments, with an increased RBE of ~1.5 compared to protons and reduced LET/RBE gradients at the distal-end compared to carbon ions. Measured physical dose and mean target RBE were within ~3% and ~1% against prediction, respectively, for CICR plan irradiations. Reduced dose-averaged LET, RBE and physical dose variability in the target was observed for CICR plans compared to single ion modalities.
In this work, we demonstrate that by combining ions, more biophysically robust and conformal treatment plans can be delivered. Moreover, we performed the first biological and dosimetric verification of MIT treatments.