ESTRO 2024 - Abstract Book

S4302

Physics - Intra-fraction motion management and real-time adaptive radiotherapy

ESTRO 2024

2017

Digital Poster

Cardiorespiratory-gated cardiac proton radiotherapy using a novel ultrasound guidance system

Keith Cengel 1 , Saskia Camps 2 , Michele M Kim 3 , Sarah Hagan 1 , Alexander Kalinin 2 , Tara Oster 1 , Eric Diffenderfer 1 , Adriano Garonna 2 , Cory Tschabrunn 4 1 University of Pennsylvania, Radiation Oncology, Philadelphia, USA. 2 EBAMed SA, N/A, Geneva, Switzerland. 3 University of Pennsylvania, Radiaiton Oncology, Philadelphia, USA. 4 University of Pennsylvania, Medicine, Philadelphia, USA

Purpose/Objective:

Cardiac radioablation is as a promising noninvasive treatment for patients with refractory ventricular tachycardia. To account for cardiorespiratory motion using current treatment planning and delivery techniques, the target cardiac substrate volume is expanded by 2-4 fold in the final PTV. Thus, novel techniques to improve motion management are needed [1]. Gating the treatment beam for both respiratory and cardiac motion would provide a valuable tool to reduce the target volume and increase healthy tissue sparing [2-3]. Moreover, as we develop new, intra-fraction motion sensitive proton technologies such as FLASH and proton arc radiotherapy, real-time motion management strategies take on a enhanced potential clinical significance for applications outside cardiac targeting. With the aim to prove feasibility of EBAMed´s novel image guided radiotherapy and cardiorespiratory motion gating, cardiac radioablation was performed on a porcine model. Using a novel adaptation of γ-H2AX tissue staining techniques [4] we have been able to localize a radiation beam in large animal tissue to assess targeting accuracy within a defined field. Three Yorkshire swine (Animal 1-3) underwent surgical implantation of three or four metal fiducial markers on the anterior lateral left ventricular wall, which is an anatomical location representative of a ventricular tachycardia target (Fig. 1). Following recovery, animals underwent 4D (cardiac- and respiratory-binned) contrast Computed Tomography (CT) scans and transthoracic echocardiography. Treatment planning was performed to deliver 25 Gy of stereotactic body radiation therapy with protons (Fig. 1) was based on an end expiratory phase of the respiratory-binned 4D-CT (animals 1, 3) or an and expiratory breath hold CT (animal 2). The target is located at the center of the fiducial markers and consists of 1-2 spots in 1-2 energy layers with a beam direction that is perpendicular to the target tissue surface. Approximately 4-7 days following simulation, the animals were aligned using Cone Beam Computed Tomography (CBCT) and irradiated with an IBA ProteusPlus therapy machine using EBAmed image guided gating. Image guidance and heart motion gating was based on electrocardiogram (ECG), ultrasound imaging and optical tracking [5-6]. The gating windows were selected to correspond to the end-exhale phase (respiration) and between end of T-wave and beginning of P-wave (heartbeat) to minimize residual heart motion. The response times to gating commands were characterized prior to treatment and taken into account while delivering the gated radiation. Following irradiation, the animals were euthanized, and the heart was excised. Using the fiducials as a guide, the tissue was divided into a 1-1.5 cm grid pattern and these tissue sections were flash frozen in OCT at the ~1 hour post irradiation timepoint to maximize γ -H2AX signal intensity. Immunohistochemistry using γ-H2AX with Hoechst nuclear counterstaining was Material/Methods: