ESTRO meets Asia 2024 - Abstract Book

S61

Interdisciplinary – Brachytherapy

ESTRO meets Asia 2024

4 McGill University Health Centre, McGill University, Montréal, Canada. 5 Department of Radiation Oncology, Brigham and Women's Hospital/Dana-Farber Cancer Institute, Harvard University, USA

Purpose/Objective:

Drug-eluting stents are the first line of therapy for in-stent restenosis 1 and intravascular brachytherapy (IVBT) is the next step for patients with failed drug-eluting stents 2 . Current clinical dosimetry for IVBT is water-based, such that the absorbed dose in the target volume, which is 2 mm from the source center, is calculated by assuming that heterogeneities present in patient’s artery, such as the fibrotic and calcified plaques, metallic stents, and off-centered guidewire are all water with unit mass density 3 . We have previously developed a Monte Carlo based dosimetry software, RapidBrachyIVBT, to calculate dose on optical coherence tomography images (OCT), accounting for these heterogeneities. This study examines scenarios when off centered guidewires present during irradiation are facing away from or towards calcified plaques and when multiple guidewires are used in cases where the source train passes through a bifurcation of blood vessels. Simulations were performed with RapidBrachyIVBT, based on the Geant4 10.02.p02 toolkit 4-6 , which includes the Novoste Beta-Cath 3.5F IVBT device with a 90 Sr 90 Y source train 7 . This study included five patients undergoing coronary IVBT treated for recurrent in-stent restenosis at Brigham and Women’s Hospital in Boston, Massachusetts, USA. OCT images were used to compare absorbed dose calculations considering all heterogeneities compared to water. Patient 1 had one guidewire facing away from calcification, Patients 2 and 3 had multiple guidewires present during irradiation, and Patients 4 and 5 had guidewires facing towards calcification. Segmentation of the patient's arteries comprised of the lumen, fibrotic plaque, calcified plaque, tunica media, and stents. The source train was assumed to be at the image origin, in the position of the OCT imaging device, and positions of the guidewire(s) positions were also segmented at the exact positions during imaging. Simulations were performed on the Digital Research Alliance of Canada Cedar supercomputing cluster using 200 million histories to yield less than 1% average uncertainty on the target volume absorbed dose. The absorbed dose was scored along a 42 mm length, including stents, the source train, and a 2 mm margin in rectangular voxels of 0.1 x 0.1 x 1.0 mm 3 . The prescribed dose to the target volume was 23 Gy. The percentage difference between dose calculated in water and in patient-specific materials and geometry as well as the dose homogeneity index, the maximum to minimum dose ratio in the target volume, were calculated. Material/Methods:

Results:

The percentage dose differences in the entire lesion and target volume, as well as homogeneity indices are summarized in Table 1 for the patients included in our study.