118P High dose chemo-radio-immunotherapy for NSCLC III: ESR/ATS thresholds for DLCO correlate with radiation dosimetry and predict pneumonitis

Durvalumab following chemoradiotherapy for non-small cell lung cancer (NSCLC) UICC stage III has become the standard of care in the past few years. With this treatment approach 5-year overall survival has risen to 50% for PD/PDL-1-positive patients. Therefore pulmonary function (PF) after treatment is of high importance in long term survivors. In this respect carbon monoxide diffusing capacity (DLCO), which represents the alveolar compartment, was found to be a suitable measure for residual pulmonary capacity. The aim of the current analysis was to correlate pre-treatment DLCO with the occurrence of pneumonitis and to model DLCO decline after therapy to the total radiation dose within a defined lung volume. Eighty-five patients with histologically confirmed NSCLC III treated between 2015/10 and 2020/10 were eligible for this study. Patients received two cycles of platinum-based induction chemotherapy followed by high dose radiotherapy and Durvalumab maintenance for one year. The clinical endpoints were based on the thresholds published by the European Respiratory Society. Pre-treatment DLCO of 60% was correlated to the incidence of pneumonitis and DLCO decline of 10% within three months after treatment was related to radiation dose. Patients with a pre-treatment DLCO below 60% had a higher probability for pneumonitis grade 2 or higher (N = 71, one-sided Pearson correlation coefficient –0.183, p-value 0.063), which became significant in the subgroup of patients without Durvalumab (N = 40, one-sided Pearson correlation coefficient –0.306, p-value 0.027). The decline in DLCO > 10% after the end of radiotherapy depended on the size of the lung volume receiving 45% to 65% (V65%–45%) of the total radiation dose (one-sided Pearson correlation coefficient = 0.264, p-value = 0.019). The current analysis revealed that DLCO is a predictor for clinically relevant pneumonitis and a monitoring tool for post-treatment lung function as it correlates with radiation dose. This underlines the importance of peri-treatment lung function testing.