Passive scattering proton therapy (PSPT) does not reduce radiation exposure or the incidence of radiation pneumonitis (RP) and local failure (LF) in lung tissue compared with intensity-modulated (photon) radiotherapy (IMRT), according to a study published in the Journal of Clinical Oncology.1

Chemoradiation therapy is the standard of care for non–small cell lung cancer (NSCLC), but can lead to radiation-induced toxicities such as RP. PSPT may reduce radiation exposure to target tissue.

For this study, researchers developed IMRT and PSPT treatment plans for 149 patients with NSCLC eligible for concurrent chemotherapy and radiation therapy. Patients were randomly assigned to radiation if both plans met the same pre-specified dose-volume constraints for at-risk organs at the same tumor dose. Ninety-two and 57 patients were assigned to receive IMRT and PSPT, respectively.

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The median follow-up times for IMRT were 24.1 and 36.4 months for all patients and for patients alive at time of analysis, respectively; corresponding follow-up durations for PSPT were 25.7 months and 48.8 months.

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PSPT exposed less lung tissue at doses of 5 to 10 Gy (relative biologic effectiveness [RBE]), but exposed more lung tissue at greater than 20 Gy (RBE).

PSPT significantly reduced radiation exposure to the heart (P < .002), but no differences were observed between PSPT and IMRT for the lung or esophagus.

At year 1, the overall RP rates were 6.5% and 10.5% for IMRT and PSPT, respectively (P = .537). Two patients in the IMRT arm developed grade 5 RP compared with no patients in the PSPT arm.

Median overall survival was 29.5 months for patients who underwent IMRT and 26.1 months for patients who received PSPT.

The authors concluded that “PSPT significantly reduced heart exposure in terms of both radiation dose and heart volume, and its influence on cardiac toxicity and overall survival is under active investigation.”


  1. Liao Z, Lee JJ, Komaki R, et al. Bayesian adaptive randomization trial of passive scattering proton therapy and intensity-modulated photon radiotherapy for locally advanced non-small-cell lung cancer. J Clin Oncol. 2018 Jan 2. doi: 10.1200/JCO.2017.74.0720 [Epub ahead of print]