Impact of PTV margin reduction (2 mm to 0 mm) on pseudoprogression in stereotactic radiotherapy of solitary brain metastases

Abstract Purpose To determine the influence of PTV-margin (0 mm versus 2 mm) on the incidence of pseudoprogression (PP) and local tumour control (LC) in patients treated with stereotactic radiotherapy (SRT) for solitary brain metastases. Methods Patients were treated on Novalis LINAC. Three dose schedules were used depending on the PTV-size. The PTV-margin was 2-mm prior to 2015 and 0-mm thereafter. MRI-scans were made every three months including a perfusion MRI-scan when pseudoprogression was suspected. We examined the relation of pseudoprogression and local control with the size of PTV-margin. Besides this, the association of dose-volume data of the whole brain (minus GTV) and pseudoprogression was investigated. Results 121 patients were analyzed (2-mm margin in 84 patients; 0-mm margin in 37 patients). There was no difference in GTV (7.6 cc versus 9.1 cc p = 0.2). At 24 months there was no difference in incidence of pseudoprogression (49% and versus 33%, p = 0.5) and local control in the 2-mm and 0-mm group (82% and versus 79%, p = 1.0). The size of PTV-margin was not associated with PP. Both margin and volume of brain receiving 12 Gy (V12) were not associated with pseudoprogression in patients treated with single fraction. Conclusions PTV-margin reduction did not reduce the incidence of pseudoprogression in LINAC-based-SRT for single brain metastases. We did not find a significant association of GTV-PTV margin or V12Gy with the incidence of pseudoprogression in solitary metastases treated with a single fraction. LC rates were similar, indicating margin reduction seems to be safe.