ESTRO 2024 - Abstract Book

S1169

Clinical - Haematology

ESTRO 2024

Carme Auñon Sanz 1,2,3 , Ingrid Romera-Martínez 4,2 , Diego Jurado-Bruggeman 4,2 , Arantxa Eraso Urien 1,2,3 , Rafel Fuentes Raspall 1,2,3 1 Institut Català d’Oncologia, Radiation Oncology, Girona, Spain. 2 Institut d’Investigació Biomèdica de Girona Dr. Josep Trueta, IDIBGI, Girona, Spain. 3 University of Girona, UdG, Girona, Spain. 4 Institut Català d’Oncologia, Medical Physics and Radiation Protection, Girona, Spain

Purpose/Objective:

Radiation therapy (RT) is an important treatment for localized gastric lymphoma. Particularly Mucosa-Associated Lymphoid Tissue (MALT) lymphomas failing to Helicobacter pylori treatment and some selected B cell lymphomas. Treatment reproducibility is a challenging issue due to daily changes in position and size of the stomach.

We tested a protocol aiming at improving treatment delivery and accuracy for this group of patients.

Material/Methods:

Between 2014 to 2021, 7 consecutive patients (6 MALT lymphoma, 1 Diffuse large B cell lymphoma (DLBCL)) were treated under the following conditions. Planning Computed Tomography (CT) images were obtained on an empty stomach after 20 cm 3 of water, 10 minutes before the acquisition, to contrast the stomach wall as shown in Figure 1A. Iodine intravenous contrast was also used. CTV was delineated following the guidelines (1). A margin of 1.5 cm was applied isotropically to PTV. Treatment dose was 30 to 40.5 Gy, fractions of 1.5 Gy daily.

The same stomach filling protocol was repeated through all treatment sessions adding 8 mg of ondansetron orally. Of the whole group we have obtained cone beam CT (CBCT) images daily of 5 patients as shown Figure 1B.

Mean reproducibility values (µ), systematic (Σ) and random (σ) errors, and margin CTV -PTV for vertical (vrt), longitudinal (lng) and lateral (lat) axis were calculated.

Results:

Seven patients (5 females and 2 males) with a median age of 55 (range 39 – 69) were treated with the tested protocol. The protocol allowed us to identify the stomach on both CT and CBCT images easily.

The mean reproducibility value, systematic and random errors for all axes on CBCT registrations are shown in Figure 2. The calculated CTV margin to PTV according to van Herk (2) is also presented.