1181P - The impact of dosimetric parameters on pneumonitis in patients with stage III non-small cell lung cancer during maintenance treatment with durvalumab after chemoradiotherapy

Background

Standard treatment for stage III non-small cell lung cancer has changed remarkably with maintenance durvalumab after concurrent chemoradiotherapy (Ch-RT). The addition of check-point inhibitor after lung radiotherapy raises the concern of increased lung toxicity, especially pneumonitis.

Methods

We retrospectively analysed data of stage III NSCLC patients who were treated with durvalumab after radical chemoradiotherapy from December 2017 and completed treatment until December 2020. The prescribed dose ranged from 54 Gy to 66 Gy in 2 Gy daily fractions. Treatment was planned with Three-Dimensional Conformal Radiotherapy or Volumetric Modulated Arc Therapy. Daily cone-beam CT was used for set-up correction. Besides baseline characteristics of patients’ demographics, progression free survival and overall survival, we also collected planning target volume (PTV), lung volume receiving at least 20 Gy (V₂₀) and mean lung dose (MLD). We determined the potential influence of dosimetric parameters on the treatment outcome and occurrence of pneumonitis.

Results

Eighty-five patients were included in the analysis. Most of them were male (70.6 %) in stage IIIB (56.5 %) with squamous cell carcinoma (58.8 %). The majority of patients were treated with induction ChT (96.5 %), and 63.5 % received concurrent ChT. The median RT dose was 60 Gy. Median V₂₀ was 27.2 % (range 7.0 % -35.6 %), median MLD 15.7 Gy (range 4.0 Gy – 20.2 Gy) and median PTV 416.6 cm³ (range 172.3 cm³ – 1282.6 cm³). Altogether, pneumonitis was observed in 15 (17.6 %) patients, in 1 patient grade (G) 1, in 10 G2 and in 4 G3. Durvalumab treatment was completed early due to pneumonitis in 12 patients (14.1 %). There was no association between PTV volume and the incidence or severity of pneumonitis. In addition, higher V20 and higher MLD did not predict increased rate of pneumonitis. Survival endpoints were not affected according to difference in V₂₀, MLD or PTV. Patients in higher stages had lager PTV (p=0.013), but no impact of the PTV volume on local progression was observed.

Conclusions

The incidence and severity of pneumonitis during the treatment with durvalumab after ChT in our cohort were not affected by PTV volume, V20 or MLD.

Clinical trial identification

Editorial acknowledgement

Legal entity responsible for the study

M. Vrankar.

Funding

Has not received any funding.

Disclosure

All authors have declared no conflicts of interest.