ESTRO 2024 - Abstract Book

S3606

Physics - Dose prediction, optimisation and applications of photon and electron planning

ESTRO 2024

Cureus [Internet]. 2022 Mar 28 [cited 2022 Aug 17]; Available from: https://www.cureus.com/articles/89073-a dosimetric-study-comparing-3d-crt-vs-imrt-vs-vmat-in-left-sided-breast-cancer-patients-after-mastectomy-at-a tertiary-care-centre-in-eastern-india

2) Yu PC, Wu CJ, Nien HH, Lui LT, Shaw S, Tsai YL. Tangent-based volumetric modulated arc therapy for advanced left breast cancer. Radiat Oncol. 2018 Dec;13(1):236.

3) Jeulink M, Dahele M, Meijnen P, Slotman BJ, Verbakel WFAR. Is there a preferred IMRT technique for left-breast irradiation? J Appl Clin Med Phys. 2015 May;16(3):197–205.

4) Fogliata A, Seppälä J, Reggiori G, Lobefalo F, Palumbo V, De Rose F, et al. Dosimetric trade-offs in breast treatment with VMAT technique. Br J Radiol. 2017 Feb;90(1070):20160701.

5) Pasler M, Lutterbach J, Björnsgard M, Reichmann U, Bartelt S, Georg D. VMAT techniques for lymph node positive left sided breast cancer. Z Für Med Phys. 2015 Jun;25(2):104–11.

1813

Digital Poster

Impact of lesion asymmetry on radiosurgery: Proposing an innovative asymmetry index

Lara Caglayan, Dr. Patrick Eich, Davide Scafa, Dr. Christina Leitzen, Dr. Shari Wiegreffe, Dr. Andrea Glasmacher, Fabian Kugel, Prof. Dr. Eleni Gkika, Younèss Nour

University Hospital Bonn, Radiation Oncology, Bonn, Germany

Purpose/Objective:

The asymmetry of a lesion plays a crucial role in determining the degree of conformity in dose distribution in radiation therapy and radiosurgery [1]. Accurate assessment of lesion asymmetry is essential for the development of optimal treatment planning. This study presents a novel, easy-to-determine asymmetry coefficient and evaluates its effectiveness in comparison with other common asymmetry parameters. Our goal is to demonstrate the potential benefits of the proposed index for clinical practice, especially due to its ease of determination.

Material/Methods:

A total of 78 brain metastases (BM) from 20 patients were analyzed. The planning target volumes (PTV) ranged up to 4.3 cm³ and none of the BM were in proximity to critical organs at risk. The BM were divided into four categories according to their size: up to 1 cm³, 1 to 2 cm³, 2 to 3 cm³, and over 3 cm³. The TrueBeam STx System was utilized for treatment delivery with separate plans for multiple metastases. Two different techniques were employed in this study: Volumetric Modulated Arc Therapy (VMAT) and Dynamic Conformal Arc (DCA). For each individual lesion, a radiation plan was created with one arc and three equidistant half-arcs. Both the VMAT and DCA plans utilized the same field arrangement, collimator angle, and aperture opening. The radiation planning was performed using a 6 MV energy beam in FFF (flattening filter-free) mode [2]. Dose calculations were performed using the Analytical Anisotropic Algorithm (AAA) with a calculation grid of 0.125 cm. In order to evaluate dose distribution outside the lesions and conformity, the Conformity Index (CI) according to RTOG [3] and the Dose Spillage Index (DSI) [4] were used. In the treatment plans, it was ensured that 99.5% of the PTV received 100% of