Biological Dose Optimization for Particle Arc Therapy Using Helium and Carbon Ions

Abstract

Purpose: To present biological dose optimization for particle arc therapy using helium and carbon ions.

Methods and materials: Treatment planning and optimization procedures were developed for spot-scanning hadron arc (SHArc) delivery using the RayStation treatment planning system and FRoG dose engine. The SHArc optimization algorithm is applicable for charged particle beams and determines angle dependencies for spot and energy selection with three main initiatives: (i) achieve standard clinical optimization goals and constraints for target and organs at risk (OARs), (ii) target dose robustness, and (iii) increase linear energy transfer (LET) in the target volume. Three patient cases previously treated at the Heidelberg Ion-beam Therapy Center (HIT) were selected for evaluation of conventional versus arc delivery for the two clinical particle beams (helium [⁴He] and carbon [¹²C] ions): glioblastoma, prostate adenocarcinoma, and skull-base chordoma. Biological dose and dose-averaged LET (LET_d) distributions for SHArc were evaluated against conventional planning techniques (volumetric modulated arc therapy [VMAT] and 2-field intensity modulated particle therapy) applying the modified microdosimetric kinetic model with (α/β)_x = 2 Gy. Clinical viability and deliverability were assessed via evaluation of plan quality, robustness, and irradiation time.

Results: For all investigated patient cases, SHArc treatment optimizations met planning goals and constraints for target coverage and OARs, exhibiting acceptable target coverage and reduced normal tissue volumes, with effective dose >10-GyRBE compared with conventional 2F planning. For carbon ions, LET_d was increased in the target volume from ∼40-60 to ∼80-140 keV/µm for SHArc compared with conventional treatments. Favorable LET_d distributions were possible with the SHArc approach, with maximum LET_d in clinical target volume/gross tumor volume and potential reductions of high-LET regions in normal tissues and OARs. Compared with VMAT, SHArc affords substantial reductions in normal tissue dose (40%-70%).

Conclusions: SHArc therapy offers potential treatment benefits such as increased normal tissue sparing from higher doses >10-GyRBE, enhanced target LET_d, and potential reduction in high-LET components in OARs. Findings justify further development of robust SHArc treatment planning toward potential clinical translation.