Passive Scattering Proton Therapy vs Intensity-Modulated Photon Radiotherapy for Locally Advanced NSCLC
In a study reported in the Journal of Clinical Oncology, Liao et al found that passive scattering proton radiotherapy (PSPT) improved heart—but not lung—radiation dose-volume indices vs intensity-modulated photon radiotherapy (IMRT) in patients with advanced non–small cell lung cancer (NSCLC) receiving concurrent chemotherapy. PSPT was not associated with improved rates of radiation pneumonitis or local failure.
Study Details
In the trial, 149 patients with stage IIB to IIIB NSCLC (or stage IV NSCLC with a single brain metastasis, or recurrent lung or mediastinal disease after surgery) who were candidates for concurrent chemoradiation treated at The University of Texas MD Anderson Cancer Center or Massachusetts General Hospital were randomized to receive PSPT (n = 57) or IMRT (n = 92). The trial used adaptive randomization, in which real-time assessment of accumulated outcome data is used to detect differences between arms and adjust the ratio of patient allocation; thus, more patients are allocated to the better treatment plan if a difference is observed, with the allocation ratio approaching 1:1 in the absence of any difference. The primary endpoints were grade ≥ 3 radiation pneumonitis and local failure.
Radiation Exposure
The study assessed measurements based on the concept of relative biologic effectiveness (RBE), which is the ratio of biologic effectiveness of one type of ionizing radiation relative to another, given the same amount of absorbed energy. Overall, there were no differences between groups in mean dose in Gy(RBE)—ie, the absorbed Gy dose multiplied by the RBE factor for protons—in the lung (P = .818) or esophagus (P = .717). PSPT exposed less lung tissue to radiation doses of 5 to 10 Gy(RBE), more lung tissue to ≥ 20 Gy(RBE), and less heart tissue at all dose levels from 5 to 80 Gy(RBE) (P = .002).
For the PSPT vs IMRT groups, 1-year rates of grade ≥ 3 radiation pneumonitis were 10.5% vs 6.5% (P = .537) and local failure rates were 10.5% vs 10.9% (P = 1.0). Exploratory analysis comparing 12-month combined radiation pneumonitis and local failure rates for patients enrolled before vs after the trial midpoint showed improvements with later enrollment in both the PSPT group (31.0% vs 13.1%, P = .027) and the IMRT group (21.1% vs 18.2%, P = .047).
The investigators concluded, “PSPT did not improve dose-volume indices for lung, but did for heart. No benefit was noted in [radiation pneumonitis] or [local failure] after PSPT. Improvements in both endpoints were observed over the course of the trial.”
The study was supported by National Cancer Institute grants.
Zhongxing Liao, MD, of the Department of Radiation Oncology at The University of Texas MD Anderson Cancer Center, is the corresponding author for the Journal of Clinical Oncology article.
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