O ye of little faith.
The Study: For those who have never read from the Book of Hall, carbon ions have the theoretical advantage of minimizing risk of treatment-induced cancer due to less integral doses and less neutron production than that seen with photons or even protons. And for ye of little faith, we do say “theoretical” because the number of years (since 1994) and patients (~20K) comprising carbon outcomes aren’t ripe for much real-world proof. To maximize post-treatment life-years, where else should you turn but prostate cancer treated in Japan, i.e. the first nation to offer carbon ion therapy. This large retrospective cohort analysis took ~1.5K men treated with carbon ions for localized prostate cancer at a single center in Japan and propensity-matched them with men treated with surgery (n=~6K) or photon therapy (n=~2K) in a Japanese registry. The cumulative incidences of second primary cancer at ten years were 16% after carbon, 19% after surgery, and 24% after photons. This all produced hazard ratios of 0.8 with favorable compatibility intervals when comparing carbon to either photons or even surgery (maybe the air hit it?) via propensity score-matching taking into account age, calendar year and endocrine therapy.
Bottom Line: Notwithstanding its dependence on registry data, carbon ions may turn out to confer the lowest risk of second cancer of any local treatment for prostate cancer. | Mohamad, Lancet Oncol 2019