S2598
Radiobiology - Radiobiological modelling
ESTRO 2026
Category: Radiobiology: Radiobiological modelling
keV/ μ m), with median LETd values of 6.6 keV/ μ m (M1T2) and 7.1 keV/ μ m (M1T1).Logistic regression models including Dph as a predictor provided statistically significant improvements over the null models (M1T2: Δχ² = 7.52, p = .006; M1T1: Δχ² = 9.47, p = .002). The individual coefficients indicated that Dph at M1T2 (Odds Ratio [OR] = 1.154, p = .025) and M1T1 (OR = 1.221, p = .012) were significant predictors of vasculopathy.
Mini-Oral 296
High-LET dose linked to vasculopathy in children with craniopharyngioma treated by proton beam radiotherapy Thomas E Merchant 1 , Vadim P Moskvin 1 , Fakhriddin Pirlepesov 1 , Chris Melendez-Suchi 1 , Chris J Beltran 2 1 Department of Radiation Oncology, St. Jude Children's Research Hospital, Memphis, USA. 2 Department of Radiation Oncology, Mayo Clinic, Jacksonville, USA Purpose/Objective: Vasculopathy is a common and potentially serious complication following proton radiotherapy in pediatric patients with brain tumors. The underlying factors contributing to its development remain poorly understood. This study investigated the roles of radiation dose and linear energy transfer (LET) in the development of vasculopathy, using a field-by-field analytical approach. Material/Methods:
Conclusion: High-LET radiation dose, rather than LET alone, is a key predictor of post-treatment vasculopathy. Careful attention to high-LET dose at critical vascular locations may reduce the incidence of vasculopathy. References: 1. Souris K, Lee JA, Sterpin E. Fast multipurpose Monte Carlo simulation for proton therapy using multi- and many-core CPU architectures. Med Phys. 2016;43(4):1700-12. Keywords: proton beam therapy, LETd, vasculopathy
Digital Poster 1592
Defining the optimal BED thresholds for achieving textbook oncologic outcomes with SRS for small brain metastases Sreenija Yarlagadda 1 , Yanjia Zhang 2 , Ranjini Tolakanahalli 1,3 , D Jay J. Wieczorek 1,3 , Yongsook C. Lee 1,3 , Tatiana Bejarano 1,3 , Eyub Akdemir 1 , Robert A. Herrera 1 , Haley R. Appel 1 , Matthew D. Hall 1,3 , Robert H. Press 1,3 , Evan D. Bander 4,3 , Michael W. McDermott 4,3 , Alonso N. Gutierrez 1,3 , Minesh P. Mehta 1,3 , Rupesh Kotecha 1,3 1 Department of Radiation Oncology, Miami Cancer Institute, Baptist Health South Florida, Miami, USA. 2 TD – Artificial Intelligence and Machine Learning, Baptist Health South Florida, Miami, USA. 3 Department of Oncological Sciences, Herbert Wertheim College of Medicine, Florida International University, Miami, USA. 4 Department of Neurosurgery, Miami Neuroscience Institute, Baptist Health South Florida, Miami, USA Purpose/Objective: Textbook oncologic outcome (TOO) is a composite quality measure reflecting the best expected or “textbook” outcome. In stereotactic radiosurgery (SRS), we define it as the composite absence of local failure (LF) and radiation necrosis (RN). In the current study, we evaluated optimal biologically effective dose (BED) thresholds to achieve favorable TOO following SRS to small (£ 2cm in max diameter) brain metastases (SBM). Material/Methods: A retrospective review of patients with intact SBM treated with single-fraction SRS (20-24 Gy) between January 2017 and July 2022 was conducted. Each lesion was followed from the date of SRS to date of LF, RN, or last follow-up. Tumor BED with an alpha-beta ratio of 10 Gy (BED10)was computed using linear-quadratic cubic (LQC) model to account for high-dose per fraction. Lesions were stratified
Pediatric craniopharyngioma patients treated with parallel-opposed proton radiotherapy were grouped based on MR angiography findings indicating the presence (n = 30) or absence (n = 29) of post- treatment vascular changes (vasculopathy). In both groups, 26 patients were treated from the left side first and were included in the analysis. Median time to vasculopathy diagnosis was 12.4 months.To assess dose and LET, 5 mm diameter spherical regions of interest ("detectors") were positioned at key locations within the cerebral vascular system (see Figure 1). Physical dose (Dph) and dose-weighted LET (LETd) distributions were calculated using the MCSquare Monte Carlo simulation code [1]. For each patient, the mean Dph and LETd from each field were obtained across the detectors for analysis. Logistic regression was performed to evaluate the association between Dph and the likelihood of developing vasculopathy. Results: Distinct differences were observed between the vasculopathy and non-vasculopathy groups at the M1T2 and M1T1 detectors, which correspond to the right and left middle cerebral arteries, respectively (see Figure 2). Both detectors were positioned at the distal edge of their respective radiation fields. In the non- vasculopathy group, both detectors received lower physical doses (Dph) (median 0.256 Gy [M1T2], 0.137 Gy [M1T1]) across a broad range of LET values (2–9 keV/ μ m), with median dose-weighted LET (LETd) values of 7.2 keV/ μ m (M1T2) and 7.6 keV/ μ m (M1T1). In contrast, the vasculopathy group received higher Dph (median 2.68 Gy [M1T2], 4.73 Gy [M1T1]) within a narrower LET range (6–9
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