Toxicity and time lapse between immunotherapy and stereotactic radiotherapy of brain metastases

Purpose. - Stereotactic radiotherapy (SRT) is the standard treatment for brain metastases of non-small-cell lung cancer (NSCLC) and melanoma, mostly in combination with immunotherapy. The objective was to retrospectively evaluate the influence of the time-lapse between immunotherapy and stereotactic radiotherapy on toxicity. Patients and methods. - From 2016 to 2019, 59 patients treated with SRT for 103 brain metastases of NSCLC (60%) and melanoma (40%) in combination with concomitant immunotherapy (<= 30 days) were included. The prescribed dose was 20 Gy/1f or 33 Gy/3f at the isocentre and 14 Gy or 23.1 Gy (70%) respectively at the PTV envelope (PTV = GTV + 2 mm). The mean tumour diameter was 14 mm (4-52 mm). The immunotherapies used were anti-PD1 and anti-PDL1 . The 103 metastases were classified into 3 groups according to the time-lapse between instatement of immunotherapy and instatement of SRT for the patient concerned: 7 (7%) in group A (<= 7 days), 38 (37%) in group B (7 to 14 days) and 58 (56%) in group C (14 to 30 days). Results. - The mean follow-up was 10.1 months. The median overall survival was 11.5 months for NSCLC and 12.5 months for melanoma. The percentage of local control (LC) at one year was 65.1% (93.6% for NSCLC and 26.5% for melanoma). The time-lapse between immunotherapy and SRT was not a significant predictor of LC (P = 0.86), while the histology was (P < 0.001). The proportion of grade >= 3 toxicities was 5.1%, and that of radionecrosis was 9.7% (among these patients, 80% were non-symptomatic): 0%, 13.1% and 8.6% for groups A, B and C respectively. The time-lapse between immunotherapy and SRT was not a significant predictor of toxicity. Only tumour volume was a significant predictive factor (P = 0.03). Conclusion. - The time lapse between immunotherapy and SRT does not influence brain toxicity. The tumour volume remains the main factor. (C) 2021 Published by Elsevier Masson SAS on behalf of Societe francaise de radiotherapie oncologique (SFRO).

Automated summary

The study found that the time lapse between immunotherapy and stereotactic radiotherapy does not affect brain toxicity, with tumor volume being the main predictive factor.