Short-lived radioactive ⁸Li and ⁸He ions for hadrontherapy: a simulation study

Abstract Purpose. Although charged particle therapy (CPT) for cancer treatment has grown these past years, the use of protons and carbon ions for therapy remains debated compared to x-ray therapy. While a biological advantage of protons is not clearly demonstrated, therapy using carbon ions is often pointed out for its high cost. Furthermore, the nuclear interactions undergone by carbons inside the patient are responsible for an additional dose delivered after the Bragg peak, which deteriorates the ballistic advantage of CPT. Therefore, a renewed interest for lighter ions with higher biological efficiency than protons was recently observed. In this context, helium and lithium ions represent a good compromise between protons and carbons, as they exhibit a higher linear energy transfer (LET) than protons in the Bragg peak and can be accelerated by cyclotrons. The possibility of accelerating radioactive 8Li, decaying in 2 α-particles, and 8He, decaying in 8Li by β − decay, is particularly interesting. Methods. This work aims to assess the interest of the use of 8Li and 8He ions for therapy by Monte Carlo simulations carried out with Geant4. Results. It was calculated that the 8Li and 8He decay results in an increase of the LET of almost a factor 2 in the Bragg peak compared to stable 7Li and 4He. This results also in a higher dose deposited in the Bragg peak without an increase of the dose in the plateau region. It was also shown that both 8He and 8Li can have a potential interest for prompt-gamma monitoring techniques. Finally, the feasibility of accelerating facilities delivering 8Li and 8He was also discussed. Conclusion. In this study, we demonstrate that both 8Li and 8He have interesting properties for therapy. Indeed, simulations predict that 8Li and 8He are a good compromise between proton and 12C, both in terms of LET and dose.