Complications after late (delayed) stereotactic radiosurgery boost in patients with non-small cell lung and breast cancer

The purpose of the work is the assessment of the functional state and the main complications af-ter the delayed boost, depending on the level of doses used and the number of irradiated metastases. In 30 patients with non-small cell lung cancer (n=11) and breast cancer (n=19) with metastatic brain lesion after the end of WBRT, in the long term a boost (SRS) was performed. The prescribed dose for the late boost ranged from 10 to 22 Gy with a median of 15 Gy. Irradiation for single-fraction was performed in 26 patients (86.7%), for 2 fractions – in 2 patients (6.7%), for 3 fractions – in 2 patients (6.7%), respectively. As of December 2021, 26 of 30 patients (86.7%) died, only 53.3% from progression in the central nervous system, from complications 0%. Local progression (growth in the boost zone) was noted in 7 patients (23.3%), distant progression (the appearance of new metastasis or carcinomatosis) – in 56.7%. Often, patients had a combined lesion. Increasing the dose with a delayed boost of ≥15 Gy did not affect the functional state of patients after 12 (p=0.767), 24 (p=0.820), and 36 months (p=1.0) after WBRT. The late boost did not lead to a significant increase in cognitive impairment (p=0.437), despite the larger number of ra-diosurgical targets and the high dose level compared to the standard boost. There were no significant differences (p=0.935) in the frequency of radionecrosis in groups with a boost dose of ≥15 Gy and <15 Gy (p=0.935); this complication was recorded in 6 out of 24 (23.1%) and 1 out of 4 (25%) patients. At an average dose level ≥20 Gy, the probability of developing radionecrosis was higher (p=0.002). The volume of the tumor mass (Vbust) did not affect the formation of radionecrosis in the future (p=0.213), there was no significance for such predictors as the maximum transverse size of metastasis (p=0.991), the number of metastases (p=0.224) and target (im-mune) therapy (p=0.289). The median overall survival in patients with developed radionecrosis was 38.6 months (95% Cl: 25.5-51.7), in its absence – only 21.5 months (p=0.015). Late boost can be used for multiple (from 4 to 10) metastatic brain lesions or oligometastases that do not meet the criteria for radiosurgical treatment in size. In general, this treatment program is safe, the functional status of patients remains at a fairly high level. Even with the development of radionecrosis, the quality of life and overall survival rates do not decrease.