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Top Line: It’s a rare twitter scroll that doesn’t include some iteration of a photon versus proton debate.
The Study: It usually comes down to theoretical advantages on the one hand and lack of hard data on the other. To be fair, detecting differences in long term toxicity takes a long time. Here we have a large retrospective comparison of clinical outcomes within 90 days of treatment with photons (n=1092) versus protons (n=391) concurrent with chemo for any locally-advanced cancer treated at UPenn from 2011-2016. As expected, there was a significantly lower integral dose with protons (hello, theory) and no difference in disease outcomes. Intriguingly, on propensity score matched analysis, there was indeed a statistically lower rate of grade 2+ (HR 0.78) and especially of grade 3+ (HR 0.31) toxicities after proton therapy. What’s more, there was half the risk of performance status decline (HR 0.51). As an accompanying editorial points out, despite the pristine methodology of the authors, there remain unaccounted selection biases including healthcare literacy and even cancer type—for example, only 10% of those in the proton arm were treated for head and neck cancers compared to 36% of the photon arm. They close with a practical call for enrollment on phase 3 trials, a goal that would made much more feasible by the support of the payers who call for them.
TBL: Retrospective clinical data suggests proton therapy confers lower risk of toxicity with equal efficacy compared to photon therapy, but ultimately we (and by we, we mean insurers) will need phase 3 data. | Baumann, JAMA Oncol 2019