ESTRO 2024 - Abstract Book

S1876

Clinical - Mixed sites, palliation

ESTRO 2024

Keywords: SABR, Stereotactic, Oligometastasis

References:

1. NHS Clinical Commissioning Policy Stereotactic ablative radiotherapy (SABR) for patients with metachronous extracranial oligometastatic cancer (all ages) (URN: 1908) Publication date: March 2020 Version number: 1.0

1005

Poster Discussion

Gradient-based alternative to Lattice radiotherapy for the treatment of bulky tumours

Diana Guevara Barrera 1 , Silvia Rodriguez Villalba 1 , Jose Pérez-Calatayud 2,3 , Francisco Blazquez Molina 2 , Maria J Pérez Calatayud 4 , Manuel Santos Ortega 1 1 Hospital Clínica Benidorm, Radiation Oncology, Benidorm, Spain. 2 Hospital Clínica Benidorm, Radiophysics, Benidorm, Spain. 3 Hospital Universitario y Politécnico La Fe, Radiophysics, Valencia, Spain. 4 Hospital Universitario y Politécnico La Fe, Radiation Oncology, Valencia, Spain

Purpose/Objective:

Spatially Fractionated Radiation Therapy (SFRT) has been in use since the early 1900’s, initially as GRID therapy, and later as it’s 3D evolution, Lattice Radiotherapy (LRT), in which, geometrically spaced spherical volumes of high doses are placed inside of the tumour, with surrounding lower dose areas (“valleys”), that allow for Organs at Risk (OAR) to be spared. SFRT has been mainly used in bulky tumors and palliative concept. In it, the intentional heterogeneity in intratumoral dose distribution conditions biological changes, cell death in areas of ablative dose and preservation of the tumor microenvironment and vascularization in areas of lower dose, which promote immunomodulation and “bystander” effects, which increase the tumor response. The technique presented in this work represents a particular approach in tumors, in which the lattice geometry presents difficulties for its implementation. In it we use decreasing dose volumes, from first volume of maximum tumor activity, defined from the PET, which receives an ablative dose, establishing decreasing dose gradients in a stepwise manner, to end in a conventional dose on a PTV volume, standard for the tumor in question. This dose distribution is administered on the first day of treatment to subsequently complement it with conventional fractionation. The purpose of this work is to describe this gradient based technique and our preliminary clinical results.

Material/Methods:

Nineteen patients were treated in our centre between November 2021 and August 2023. All patients had a simulation CT scan with couch immobilization. GTV, and one (in smaller tumours), or two internal concentric volumes were contoured, to indicate the areas that should receive a higher dose, using PET CT imaging when available to target areas with the most metabolic activity. A geometric PTV of 0.5-1cm was applied to the GTV. No CTV was contoured. Two radiation therapy plans were created; one for the inhomogeneous treatment session,