Diffusion Capacity of the Lungs Following Passive-Scattering Proton Therapy and Intensity-Modulated Photon Radiation Therapy for Locally Advanced Non–small Cell Lung Cancer

Abstract

Proton therapy exposes smaller volumes of normal lung tissue to radiation dose when compared to photon based therapies and is therefore hypothesized to result in reduced pulmonary toxicity. In this study, we report results of pulmonary function tests (PFTs) in patients with inoperable non-small-cell lung cancer (NSCLC) treated with passively scattered proton therapy (PSPT) vs intensity-modulated (photon) radiotherapy (IMRT). An institutional randomized trial of patients with inoperable NSCLC (stage IIB-IIIB, stage IV with a single brain metastasis, or recurrent lung or mediastinal disease after surgery) randomized to PSPT or IMRT, both with concurrent chemotherapy, has been completed and primary outcomes are in editorial review. Pre and post treatment percent predicted hemoglobin normalized, diffusion capacity of the lungs for carbon monoxide (DLCO) values were obtained up to 12 months after the completion of treatment. Values were grouped in two month intervals up to 1 year. Paired t-test was used to compare baseline to maximum change at any time point. Wilcoxon signed-rank test was used to compare paired pre and post treatment values from baseline to each time point, while two sample t-test was used to compare change in DLCO between the two treatment groups. Pretreatment DLCO did not differ between treatment groups (70.7 IMRT vs 69.2 PSPT; p= .63). There was no difference in the maximum change in DLCO between IMRT and PSPT (-7.0% vs -6.2%; p= .74). At 0-2 months post-treatment, there was a significant reduction in DLCO from baseline for patients treated with IMRT (Mean -5.5%, Median -3%; n=57, p=.002) but not for patients treated with PSPT (Mean -2.5%, Median -2.5%; n=34 p=0.27). At 4-6 months there was a significant drop in DLCO from baseline for both treatment groups (IMRT: Mean -2.5%, Median -5%; n=31, p=0.009; PSPT: Mean -9.1%, Median -7%, n=14, p=0.04), but there was no significant difference in the change in DLCO between treatment groups (p=0.6). While DLCO values significantly decreased following treatment for all patients, there was no significant difference in the maximum change in DLCO between patients treated with PSPT or IMRT. A significant reduction in DLCO was seen for patients treated with IMRT at 0-2 months, while patients treated with PSPT did not experience a significant reduction in DLCO until 4-6 months after treatment.