ESTRO 2021 Abstract Book

S862

ESTRO 2021

Conclusion SRS represents a feasible and effective treatment option for patients with brain metastases from NSCLC. The SRS dose and the histology have a major impact on LC, while infratentorial involvement and the need for CST supportive therapy before SRS negatively affect LRC, PFS and, more importantly, OS. The addition of WBI improves LRC but not OS, confirming the actual trend in omitting extensive brain irradiation in this setting. Lastly, the intracranial tumor burden at the time of SRS affects OS. All these factors should be carefully evaluated to offer a tailored therapy to these patients. PO-1033 Molecular profile and early MRI changes after chemoradiation in high grade diffuse astrocytoma R. Basu Achari 1 , L. Goyal 1 , S. Chakraborty 1 , M. Arunsingh 1 , B. Arun 2 , S. Das 3 , T. Bhattacharyya 1 , I. Mallick 1 , S. Chatterjee 1 , J. Chatterjee 4 , S. Dhara 4 , N. Ghosh 5 , J. Mukhopadhyay 3 1 Tata Medical Center, Radiation Oncology, Kolkata, India; 2 Tata Medical Center, Medical Physics, Kolkata, India; 3 Indian Institute of Technology, Computer Science, Kharagpur, India; 4 Indian Institute of Technology, School of Medical Science and Technology, Kharagpur, India; 5 Indian Institute of Technology, Electrical Engineering, Kharagpur, India Purpose or Objective To determine the association between integrated molecular profile and early volumetric changes on MRI after adjuvant chemoradiation in high grade diffuse astrocytoma. Materials and Methods Records of 109 patients (94 glioblastoma,15 anaplastic astrocytoma) treated from 2017-20 were evaluated retrospectively after consent waiver. RANO was used for response assessment. Thresholding based semi- automated segmentation with manual correction in Eclipse was done on pre- and post-chemoradiotherapy T1 contrast, T2-FLAIR and T2w MRI. Volume and T1c:T2 FLAIR changes were recorded. Multivariable analysis using linear regression was used to determine association between volume changes and independent variables IDH status, MGMT methylation, TP53 and TERT promoter mutation. Results Eighty-nine (81.7%) IDH-wild, MGMT methylated (22.9%), TERT mutated (53.2%) and TP53 mutations seen in 22.9%. Table 1 shows volume and ratio changes. In univariate analysis IDH wild-type and TERT mutation had increased post-chemoradiation FLAIR (p<0.01 and p= 0.01) and T2 (p<0.01 and p = 0.05) volumes. MGMT and TP53 mutation lacked association. In multivariate analysis only IDH wild-type tumors were associated with FLAIR volume increase (p=0.05) and T1C:FLAIR ratio (p=0.02) decrease.

Table 1 Parameter

Median change (ml) IQR Mean (CI)

T1c

4.0

12.4 2.2(-2.1, 6.5)

T2

-9.3

60.9 -30.5 (-45.0, -15.9)

FLAIR

-3.5

61.9 -23.9 (-38.8, -8.9)