ESTRO 2023 - Abstract Book

S929

Digital Posters

ESTRO 2023

We extracted all the BM patients who underwent SRS without surgery or whole-brain radiotherapy from our institutional disease database from 2016–2021. The exclusion criteria are as follows: Single BM, leptomeningeal disease, and Karnofsky Performance Status (KPS)<60. The raw dataset was divided into two groups according to the number of BMs (BM 2–10 vs BM>10). Given the small population of BM>10 patients who underwent SRS and the different baseline characteristics of the two groups, we performed a propensity score matching to create the 2:1 matched dataset. The non-inferiority comparison between the two groups required a minimum of 237 patients to achieve >70% power in the matched dataset. The non inferiority margin was considered the adjusted hazard ratio (HR) of 1.3: non-inferiority would be established if the upper limit of the one-sided 95% CI for the difference in mortality was less than the margin at an α level of 0.10. We used multivariable logistic regression to estimate the propensity score for survival outcome on the following covariates: number of BM, GPA, KPS, age, ECM, cancer type, EGFR/ALK mutation, PD-L1, and systemic regimens. Overall survival (OS) and intracranial progression-free survival (PFS) were calculated in the raw and matched datasets using the Log-rank test, and survival curves were constructed using the Kaplan-Meier method. Univariate and multivariate Cox proportional hazards analyses were used to examine factors associated with increased risk of death and BM progression. All statistical analyses were performed using R software version 3.6.1. Statistical significance was set at P<0.05, and all tests were one-sided. Results Of all the 1042 patients assessed for eligibility, 434 were analyzed (BM 2–10: n = 324, BM>10: n = 110). The estimated propensity score was matched 2:1 without replacement (BM 2–10: n = 160, BM>10: n = 80). In the matched dataset, the median OS was 16.5 months in the BM 2–10 group and 20.0 months in the BM>10 group (P = 0.76). The adjusted HR ratio was 0.76 [95% CI: 0.53–1.1], and the upper limit of 95% CI was within the non-inferiority margin of 1.3. Although the median PFS in the BM 2–10 group was better than that of the BM>10 group in the raw dataset, the difference in the matched dataset was not significantly different (5.6 months vs 4.6 months, P = 0.56). The number of BM was not associated with OS and PFS after controlling for significant covariables in a multivariable model: better KPS score, female, ECM absent, cancer type (breast cancer or lung adenocarcinoma), PDL1 positive (50–100%), and use of targeted therapy were independently associated with better OS. Better KPS score, female, and lung adenocarcinoma were independently associated with better PFS. Conclusion The results of this study suggest that SRS for patients with >10 BM may be non-inferior in OS to patients with 2–10 BM. Purpose or Objective Small-cell lung cancer (SCLC) is an aggressive type of cancer associated with poor prognosis due to rapid growth and early distant metastasis, especially brain metastasis. Patients with limited stage (LS) achieve a median survival of 18 months and a 5-year survival rate of 15%. Several studies have shown prophylactic cranial irradiation (PCI) to be an independent prognostic factor. Hippocampal sparing (HS) PCI 25 Gy/10 fractions has minimum impact on neuro-cognitive function while Whole Brain RT (WBRT) 30Gy/10 fractions has maximum impact. Materials and Methods In this cohort study 10 LS-SCLC patients were administered HS-PCI with IMRT, and same number of patients received WBRT during January to April 2020. Baseline neuro-cognitive function was measured before administering radiation and final neuro-cognitive function was measured after median follow up of 18 months. Neuro-cognitive function was assessed by Montreal Cognitive Assessment (MoCA). Results At the end of 18 months, 7 patients are alive in HS-PCI group and 6 in WBRT group with minor deterioration of neuro cognitive function score compared to baseline measurement. For HS-PCI and WBRT groups mean pre-treatment MoCA score are 27/30 and 26/30. Mean post-treatment MoCA score for the groups are 25/30 and 23/30 respectively. Conclusion Both HS-PCI and WBRT are effective in LS-SCLC for preventing brain metastasis in long term. WBRT affects neuro-cognitive function more than HS-PCI. Hippocampal sparing as well as lower radiation dose in HS-PCI could be the major factors for this outcome. PO-1161 Neuro-cognitive effect of whole brain versus hippocampal sparing prophylactic irradiation in LS-SCLC S. Acharya 1,2 1 Assam Cancer Care Foundation, Radiation Oncology, Lakhimpur, India; 2 PAY-W Clinic, Oncology, Nayagarh, India

Poster (Digital): Haematology

PO-1162 Whole Lymph Node Area Delineation with Deep Learning Model for Total Marrow/Lymphoid Irradiation

H.S. choi 1 , H. Kang 1 , J.H. Chang 1 , B. Jang 1

1 Seoul National University Hospital, Department of Radiation Oncology, Seoul, Korea Republic of

Purpose or Objective Total body irradiation (TBI) has been performed for conditioning before hematopoietic stem cell transplantation. However, TBI can be related to diverse adverse events including radiation pneumonitis and cataract. Efforts to reduce these events include the total marrow irradiation (TMI) and total marrow and lymphoid irradiation (TMLI). Compared to TMI, TMLI requires more target delineations with lymph nodes which can be labor-intensive and time-consuming. However, with the