ESTRO 2024 - Abstract Book

S1698

Clinical - Lung

ESTRO 2024

Purpose/Objective:

Radiation pneumonitis (RP) is a major side effect of radiotherapy for locally advanced lung cancer, and IMRT has been shown to reduce lung doses and the incidence of RP above G3. In addition, prophylactic administration of clarithromycin (CAM) at low-dose long-term may reduce the incidence of RP associated with stereotactic body radiotherapy (SBRT) for early-stage lung cancer, as reported from Japan. Low-dose long-term therapy with CAM is a relatively inexpensive and safe antibiotic to use in the treatment of many upper and lower respiratory chronic inflammatory conditions. Radiation pneumonitis is thought to occur in an immune-induced fashion. The inhibitory effects of macrolide antimicrobials, such as on neutrophil migration capacity, may reduce the development of radiation pneumonia. The aim of this study was to evaluate the association between lung dose and low-dose long term CAM administration with the development of radiation pneumonitis associated with IMRT for lung cancer.

Material/Methods:

Eighty-nine patients who underwent definitive IMRT for locally advanced lung cancer between July 2019 and December 2021 were included and evaluated retrospectively. The median total and daily doses were 60 Gy and 2 Gy, respectively. Median lung V20 and lung V5 doses were 17.8% and 39.6%, respectively; 39 (44%) patients received low-dose long-term CAM for more than one month after the start of IMRT (median 3.0 months). The association between the development of radiation pneumonitis and lung dose parameters and low-dose long-term CAM administration was assessed. Eight patients with comorbid interstitial pneumonia were excluded from the study.

Results:

Radiation pneumonitis Grade 2 was identified in 6 (6.7%) and Grade 3 in 4 (4.5%) cases, occurring 2-90 days (median 38) after the end of IMRT; the median lung V20 and V5 of a total of 10 cases with radiation pneumonitis of Grade 2 or higher were 25.0% and 47.9% respectively. The median lung V20 and V5 values for a total of 10 patients who developed radiation pneumonitis of Grade 2 or higher were 25.0% and 47.9%, respectively, significantly higher than those of 17.5% and 38.6% in non-affected (Grade 0-Grade 1) patients (p=0.0225 and p=0.0489, Mann- Whitney U test). The incidence of radiation pneumonitis Grade 2 or higher in patients treated with low-doses long-term CAM was 2.6% (1/39 patients), which was significantly lower than the 18.0% (9/50 patients) in non-treated patients (p=0.0383, Fisher's exact test). No significant differences in lung dose parameters (lung V20 and V5) were found between the CAM-treated and non-treated groups.

Conclusion:

The incidence of radiation pneumonitis of Grade 2 or higher may be reduced by lower lung doses and low-doses long-term CAM.

Keywords: radiation pneumonitis, lung cancer, clarithromycin