Implementation of spot scanning dose optimization and dose calculation for helium ions in Hyperion

Area of Science:

• Medical Physics
• Radiation Oncology
• Particle Therapy

Background:

• Helium ions (4He) offer potential advantages over protons in particle beam therapy due to superior physical dose distribution.
• Accurate dose calculation and biological modeling are crucial for assessing the clinical utility of novel particle therapies.

Purpose of the Study:

• To develop and integrate a dose calculation module incorporating relative biological effectiveness (RBE) for helium ions into the Hyperion treatment planning system.
• To compare the efficacy and safety of helium ion beam therapy with proton therapy through treatment planning studies.

Main Methods:

• An empirical, depth-dependent "zonal" RBE model for helium ions was developed, with RBE values ranging from 1.0 in the plateau to 2.8 at the Bragg peak.
• The RBE model was also applied to protons (max RBE 1.6) and integrated into the Hyperion system alongside a pencil beam algorithm.
• Treatment plans for four different tumor sites were generated using both physical dose calculation and biological modeling for helium ions and protons, and validated against Monte Carlo simulations.

Main Results:

• The Hyperion implementation showed excellent agreement with Monte Carlo simulations (γ mean < 0.3).
• Helium ion plans demonstrated comparable target volume coverage to proton plans, with a slight increase observed for helium ions.
• Helium ion therapy resulted in generally reduced doses to organs at risk (OARs), with some reductions exceeding 30%, particularly when biological effects were considered.

Conclusions:

• The developed biological helium ion model represents a preliminary approach aligned with existing biological data.
• Helium ion therapy shows a potential advantage in minimizing dose to surrounding tissues and OARs.
• Further biological experiments and extensive treatment planning studies are required to fully elucidate the benefits of helium ion beam therapy.