The safety of combined immunotherapy and thoracic radiation therapy (iRT) has been understudied. We evaluated toxicities in patients receiving iRT from 3 single-institutional phase 1/2 trials.

Clinical/treatment characteristics and toxicities (per the Common Toxicity Criteria for Adverse Events, version 4.0) were extracted. For purposes of this analysis, groupings were made into (1) patients receiving immunotherapy plus stereotactic body radiation therapy (50 Gy/4 fractions or 60 Gy/10 fractions), (2) immunotherapy plus 45 Gy/15 fractions, and (3) twice-daily chemoimmunoradiotherapy (45 Gy in twice-daily fractions).

None of the 60 patients undergoing immunotherapy plus stereotactic body radiation therapy (50 Gy, n = 49; 60 Gy, n = 11) experienced grade ≥4 events. There were 34 instances of any grade 3 event (in 15 total patients), with 9 pulmonary specific grade 3 events (in 4 patients). In the patients receiving 45 Gy/15 fractions (small cell lung cancers, n = 26; non-small cell lung cancers, n = 27), there were 2 grade 4 events (in the same patient), along with 17 grade 3 toxicities experienced by 10 total patients (2 pulmonary specific). Lastly, in the twice-daily cohort (n = 22), there were 5 grade 4 events (3 of which occurred in 1 patient) and 16 grade 3 toxicities occurring in 8 total patients (half of which were hematologic).

Administration of combined iRT is safe in the short term. Toxicities did not appreciably associate with demographics or dosimetry.