A new study, published in the Journal of Clinical Oncology , showed that proton therapy is not superior in reducing serious lung toxicity compared with intensity-modulated (photon) radiotherapy ( IMRT ).

This finding "challenges the assumption on the part of many that protons would certainly be superior and emphasizes the importance of evidence-based medicine and randomized trials," comments Feng-Ming (Spring) Kong, from the Indiana University School of Medicine, Indianapolis.

The randomized trial, led by University of Texas MD Anderson Cancer Center involved 149 patients with inoperable NSCLC. A total of 92 patients received IMRT and 57 received proton therapy. The trial set out to determine whether proton therapy would reduce lung toxicity compared with IMRT. The endpoint was grade 3 or greater radiation pneumonitis (RP).

The proton therapy group had a 10.5% rate of grade 3 or greater RP at 1 year compared with only 6.5% in the IMRT group (P = .537), despite a significant reduction in low-dose volume in the dosimetric histograms for the proton therapy group, as the editorialist points out.

However, two patients receiving IMRT had grade 5 RP vs none with grade 4 or 5 RP in the proton therapy group, the authors point out. In addition, "the magnitude of improvement in RP was greater and statistically more meaning in the PSPT [proton therapy] arm," they commented.

The other endpoint of the trial was the local failure, which also did not differ between the two treatment groups: The local failure rate at 1 year was 10.9% after IMRT and 10.5% after proton therapy (P = 1.0).

Proton therapy exposed less lung tissue at doses of 5 to 10 Gy, but more lung tissue was exposed to doses greater than 20 Gy. The mean radiation dose to the heart was significantly reduced only with proton therapy (P = .002). The median overall survival was similar for the two groups: 29.5 months for the IMRT group vs 26.1 months for the proton therapy group (P = .297).

The authors conclude that they found no benefit in grade 3 or greater RP or local failure after proton therapy, presumably because proton therapy was not associated with improved lung dose-volume indices.

The results of the current study suggest "dismal future" for proton therapy in locally advanced NSCLC, Dr. Kong writes in the editorial, but these negative results "can not exclude the potential benefit of proton therapy in other clinical situations, such as for pediatric patients . "

"With decreased costs, improved delivery systems, decreased doses to normal tissues including immune system, and improved understanding of biology, proton therapy may be proven to be cost-effective cancer treatment of specific diseases in specific settings," she concludes.