Purpose: We sought to compare the symptomatic radiation pneumonitis (RP) in lung cancer patients treated with helical tomotherapy (HT) versus intensity-modulated radiotherapy (IMRT), and examine the predictive value of circulating lymphocyte subsets affecting the occurrence of RP.
Patients and Methods: Circulating lymphocyte subsets, clinical characteristics, dosimetric parameters and pulmonary function were collected from 130 lung cancer patients treated with HT (n = 53) or IMRT (n = 77) from 2016 through 2020. Symptomatic RP was compared between groups. Binary logistic regression was used to identify predictors of RP.
Results: The IMRT group had larger planning target volume (319.9 vs 240.8 cc, P = 0.041); more ECOG performance status 0– 1 (96.1% vs 79.2%, P = 0.002); more stage III–IV disease (94.8% vs 37.6%, P = 0.028); and more combined systemic therapy (85.7% vs 69.8%, P = 0.022). Grade ≥ 2 RP were comparable between IMRT and HT groups (16.9% vs 15.1%, P = 0.785). For stage III–IV disease, IMRT was associated with lower lung V10 (31.9% vs 35.8%, P = 0.047) and lower incidence of grade 5 RP (0% vs 9.1%, P = 0.018). All lymphocyte subsets reduced after radiotherapy. The decrease degree of total T cell count and CD4⁺ T cell count were larger after IMRT than HT (P = 0.043, P = 0.021). In univariate analysis, the smoking status, lower baseline FEV1, and higher total T cell count, higher CD8⁺ T cell count, lower total B cell count, lower CD4⁺/CD8⁺ ratio after radiotherapy were associated with the development of grade ≥ 2 RP. The higher CD8⁺T cell count after radiotherapy was the only risk factor associated with grade ≥ 2 RP in multivariable analysis (OR 1.003; 95% CI: 1.000– 1.005; P = 0.044).
Conclusion: IMRT was associated with lower lung V10 and less grade 5 RP than HT for stage III–IV lung cancer. Higher CD8⁺ T cell count after radiotherapy was associated with an increased risk of RP. HT may better preserve total T cell and CD4⁺ T cell than IMRT.
Keywords: radiation pneumonitis, lung cancer, helical tomotherapy, intensity-modulated radiotherapy, circulating lymphocyte