The effect of low-dose radiation spillage during stereotactic radiosurgery for brain metastases on the development of de novo metastases

• Published in: Clinical and translational radiation oncology 2021-05, Vol.28, p.79-84
• Main Authors: Paul, Shiby, Ohri, Nitin, Velten, Christian, Brodin, Patrik, Mynampati, Dinesh, Tomé, Wolfgang, Mao, Serena P.H., Kabarriti, Rafi, Garg, Madhur, Fox, Jana
• Format: Article
• Language: English
• ISSN: 2405-6308; 2405-6308
• DOI: 10.1016/j.ctro.2021.03.003

•165 new brain lesions in 38 patients who had prior SRS for brain metastases.•73% primary lung cancer patients.•Lower incidence of new lesions with increasing dose received by the region from prior SRS.•Accounting for discrepancies in both volume of the brain and follow-up period, regions that received doses of 4 Gy or more from previous SRS had 3 or fewer new lesions compared to 17 new lesions per 100 cm3 brain per year in regions that received 1 Gy or less. Stereotactic radiosurgery (SRS) for metastatic disease to the brain is associated with higher in-brain failures compared to whole brain radiation therapy (WBRT). Here we investigated the relationship between low-dose fall off during SRS and location of new brain lesions. One hundred sixty-seven patients treated with single fraction or fractionated SRS for intact or resected brain metastases at our institution from January 2016 to June 2018 were reviewed. Patients with imaging findings of new brain metastases after the initial SRS were included. Patients with WBRT before SRS were excluded. MRI scans for repeat treatments were fused with initial SRS plan. New lesions were outlined on the initial SRS planning CT. The mean dose that the site of new lesions received from initial SRS was tabulated. Thirty-eight patients met inclusion criteria. 165 new lesions were evaluated. There was a lower propensity to develop new brain lesions with increasing dose received by the regions from prior SRS, with 66%, 34%, 19%, 13%, 6%, 5%, 2% and 1% of new lesions appearing in regions that received less than 1 Gy, greater than or equal to 1, 2, 3, 4, 5, 6, and 7 Gy, respectively. Higher doses are received by smaller brain volumes during SRS. After accounting for volume, 14, 14, 11, 7, 2, 2, 1 and 1 new lesions appeared per 100 cm3 of brain in regions that received doses of less than 1 Gy, greater than or equal to 1, 2, 3, 4, 5, 6, and 7 Gy, respectively, from prior SRS. We identified low dose spillage during SRS to be associated with lower incidence of new brain metastases. Validation in larger dataset or prospective study of the combination of SRS with low dose WBRT would be crucial in order to establish causality of these findings.