Abstract
PurposeTo evaluate the clinical potential of spot-scanning hadron arc (SHArc) therapy with a heavy-ion gantry.Methods and MaterialsA series of in silico studies was conducted via treatment plan optimization in FRoG and the RayStation TPS to compare SHArc therapy against reference plans using conventional techniques with single, parallel-opposed, and 3-field configurations for 3 clinical particle beams (protons [p], helium [4He], and carbon [12C] ions). Tests were performed on water-equivalent cylindrical phantoms for simple targets and clinical-like scenarios with an organ-at-risk in proximity of the target. Effective dose and dose-averaged linear energy transfer (LETD) distributions for SHArc were evaluated against conventional planning techniques applying the modified microdosimetric kinetic model for considering bio-effect with (α/β)x = 2 Gy. A model for hypoxia-induced tumor radio-resistance was developed for particle therapy with dependence on oxygen concentration and particle species/energy (Zeff/β)2 to investigate the impact on effective dose.ResultsSHArc plans exhibited similar target coverage with unique treatment attributes and distributions compared with conventional planning, with carbon ions demonstrating the greatest potential for tumor control and normal tissue sparing among the arc techniques. All SHArc plans exhibited a low-dose bath outside the target volume with a reduced maximum dose in normal tissues compared with single, parallel-opposed, and 3-field configuration plans. Moreover, favorable LETD distributions were made possible using the SHArc approach, with maximum LETD in the r = 5 mm tumor core (~8 keVμm-1, ~30 keVμm-1, and ~150 keVμm-1 for p,4He, and 12C ions, respectively) and reductions of high-LET regions in normal tissues and organs-at-risk compared with static treatment beam delivery.ConclusionSHArc therapy offers potential treatment benefits such as increased normal tissue sparing. Without explicit consideration of oxygen concentration during treatment planning and optimization, SHArc-C may mitigate tumor hypoxia-induced loss of efficacy. Findings justify further development of robust SHArc treatment planning toward potential clinical translation.
Highlights
The growing prevalence of proton gantry systems using raster-scanning technology is facilitating the development and widespread use of sophisticated approaches to targeting and treating deep-seated tumors, such as intensity modulated particle therapy (IMPT).[1,2] the root concepts date back to the 1990s,3 clinical interest in proton arc techniques is on the rise, offering high-dose reductions in adjacent healthy tissues in the form of a low-dose bath compared with multifield IMPT
Two complete sets of IMPT and scanning hadron arc (SHArc) optimizations were performed for the following scenarios: Case A: Simple phantom study with target and normal tissue optimization criteria Case B: Clinical-like setting with planning target volume (PTV), organ at risk (OAR), and normal tissue optimization criteria
Among the SHArc treatments, helium and carbon ions exhibited the greatest normal tissue sparing, as demonstrated in the line profiles and dose volume histogram (DVH), with entrance dose values increasing from ~0.3 GyRBE to ~0.5 GyRBE from the entrance to 10 mm radially away from the target boundary
Summary
The growing prevalence of proton gantry systems using raster-scanning technology is facilitating the development and widespread use of sophisticated approaches to targeting and treating deep-seated tumors, such as intensity modulated particle therapy (IMPT).[1,2] the root concepts date back to the 1990s,3 clinical interest in proton arc techniques is on the rise, offering high-dose reductions in adjacent healthy tissues in the form of a low-dose bath compared with multifield IMPT. Several key parameters related to biophysical implications of arc therapy with particle beams remain unknown or undefined
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