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

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 Li-8, decaying in 2 alpha-particles, and He-8, decaying in Li-8 by beta (-) decay, is particularly interesting. Methods. This work aims to assess the interest of the use of Li-8 and He-8 ions for therapy by Monte Carlo simulations carried out with Geant4. Results. It was calculated that the Li-8 and He-8 decay results in an increase of the LET of almost a factor 2 in the Bragg peak compared to stable Li-7 and He-4. 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 He-8 and Li-8 can have a potential interest for prompt-gamma monitoring techniques. Finally, the feasibility of accelerating facilities delivering Li-8 and He-8 was also discussed. Conclusion. In this study, we demonstrate that both Li-8 and He-8 have interesting properties for therapy. Indeed, simulations predict that Li-8 and He-8 are a good compromise between proton and C-12, both in terms of LET and dose.