Proton vs. Photon Therapy for Patients With Lung Cancer
By: Joseph Fanelli
Posted: Thursday, March 8, 2018
The results of a study published in the Journal of Clinical Oncology suggest that proton therapy does not result in decreased toxicity compared with intensity-modulated (photon) radiotherapy (IMRT) in the treatment of patients with non–small cell lung cancer (NSCLC). The findings of this study, led by Zhongxing Liao, MD, of the MD Anderson Cancer Center, challenges assumptions that proton therapy delivers more focused radiation with less exposure to healthy tissue.
“Personally, as a radiation oncologist, I would not recommend proton therapy for NSCLC outside a clinical trial setting until a clinical benefit is demonstrated in a prospective randomized study,” concluded Feng-Ming Kong, MD, PhD, of the Indiana University Simon Cancer Center in Indianapolis, in an accompanying editorial.
In this randomized study—the first to directly compare proton versus photon therapy in patients with NSCLC—149 patients with inoperable lung cancer were assigned to either IMRT (n = 92) or passive scattering proton therapy (n = 57). For doses of 5 to 10 Gy (relative biologic effectiveness, RBE), proton therapy did expose less lung tissue to radiation compared with IMRT. However, at doses of 20 Gy (RBE) or higher, proton therapy exposed more lung tissue. Furthermore, proton therapy exposed less heart tissue at all dose levels between 5 and 80 Gy (RBE).
For patients receiving proton therapy, researchers found no benefit in grade ≥ 3 radiation pneumonitis or local failure compared with IMRT. At 1 year of therapy, the proton therapy cohort had a 10.5% rate of radiation pneumonitis, whereas the IMRT group had a 6.5% rate.