Keywords:
CNS, MR, Radiation therapy / Oncology, Cancer
Authors:
M. D. Shanker, H. Foley, S. Crowley, E. Thomson, C. Bradhurst, M. Huo, V. Atkinson, M. Foote, M. Pinkham; Woolloongabba, QLD/AU
DOI:
10.26044/ranzcr2021/R-0020
Methods and materials
A retrospective single-institution analysis was performed of patients who received single-fraction Cobalt-based SRS for melanoma brain metastases from January 2016 to June 2019. Predictive factors relating to patient characteristics, tumor factors, SRS dose, volume and systemic therapy treatment factors such type (CTLA-4, PD-1 and/or BRAF/MEK inhibitors) and timing of treatment were collected. Response assessment was characterised radiologically using MRI on pre-contrast 3-dimensional (3D) T1 and post-contrast 3D T1-Gadolinium sequences with 1-1.5mm isotropic resolution as per ‘Standardized Brain Tumor Imaging Protocol’ (BTIP) guidelines (1). Lesion volume (cc) and diameter (cm) for each treated lesion was measured using Leksell GammaPlan® treatment planning software (Version 10, Elekta™, Stockholm, Sweden) and AGFA Impax (Version 6, Agfa-Gevaert N.V.™, Mortsel, Belgium) at each imaging interval. Treatment volume of each lesion was delineated on a T1-weighted Gadolinium contrast enhanced MRI at baseline and at each follow-up scan. Cubic spline interpolation was used to impute missing data across time intervals and standardised to 3-monthly intervals.
The primary outcome was relative volumetric change in T1-contrast enhancement at 3, 6, 9, 12- and 15-months relative to baseline. A repeated measures ANOVA was used to assess for differences in mean volumetric change between interpolated 3-month intervals.
Continuous variable characteristics were assessed using the Shapiro-Wilk test for deviations from normality and then divided categorically into equivalent quartiles for categorical analysis if appropriate. Univariate and multivariate logistic regression analyses were performed using the Wald χ2 test with respective odds ratios reported. Kaplan Meier curves were generated for time to progression of disease and cumulative incidence function plots were generated for time to best response after SRS excluding patients who ultimately progressed locally at time of last follow-up. The log-rank test was used to test for differences between groups. . was utilized for statistical significance in univariate analyses to signify inclusion in the final multivariate cox proportionate model and a p<0.05 was used for significance in the multivariate analysis (MVA). A linear mixed multivariate regression analysis was performed to assess the relationship between explanatory variables and volumetric change with a two-tailed significance of α=0.05. All statistical analysis was performed on SAS (Statistical Analytical Sciences Studio Release 3.7, SAS Institute INC, Cary, NC. USA).