ESTRO 2024 - Abstract Book

S3524

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

ESTRO 2024

4 Lehmann J, Hussein M, Barry MA, Siva S, Moore A, Chu M, Díez P, Eaton DJ, Harwood J, Lonski P, Claridge Mackonis E, Meehan C, Patel R, Ray X, Shaw M, Shepherd J, Smyth G, Standen TS, Subramanian B, Greer PB, Clark CH. SEAFARER - A new concept for validating radiotherapy patient specific QA for clinical trials and clinical practice. Radiother Oncol. 2022 Jun;171:121-128. doi: 10.1016/j.radonc.2022.04.019.

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Dosimetric Comparision of VMAT and HyperArc Techniques for Multiple Brain Metastasis

Emine Burcin Ispir 1 , Oznur Senkesen 2 , Zeynep Ozen 3 , Irem Aydın 1 , Evrim Tezcanlı 3 , Sedenay Oskeroğlu 1 , Ufuk Abacıoğlu 2 1 Acibadem Atasehir Hospital, Radiation Oncology Department, Istanbul, Turkey. 2 Acibadem Mehmet Ali Aydınlar University, Radiation Oncology Department, Istanbul, Turkey. 3 Acibadem Altunizade Hospital, Radiation Oncology Department, Istanbul, Turkey

Purpose/Objective:

The purpose of this study was to compare the dosimetric aspects of volumetric modulated arc therapy (VMAT) and HyperArc (HA) planning techniques for more than 10 brain metastases with a single isocenter.

Material/Methods:

The study included ten patients with multiple brain metastases (mean 15, range 10-23) treated in our clinic. VMAT plans were created using single isocenter non-coplanar fields. We registered computed tomography (CT) images with 1-mm slice thickness utilized in treatment planning to 1 or more magnetic resonance (MR) image sets using rigid registration. Each target was delineated by the radiation oncologist using high-resolution structure settings in the contouring workspace in the Eclipse planning system. For lesions larger than 10 mm, gross tumor volume (GTV) was assumed equal to the planning target volume (PTV), while GTV was added 1 mm to create PTV for lesions smaller than 10 mm. The prescribed dose was 20-30 Gy for a 98% volume of the target structures for multiple metastases cases in three-five fractions. The HA treatment plans were retrospectively created for each patient using the HyperArc TM system with the TrueBeam Stx. Prior to HA plan optimization, the virtual Encompass (QFix, Avondale, PA, USA) mask was added to the patient CT images. In the HA technique, the optimization process was not manually intervened at any stage. The HA plans that automatically position the isocenter at the center of selected target structures were generated using Eclipse version 16.1, whereas the prior platform on which VMAT plans were created utilized Eclipse version 13.6. The dosimetric parameters were compared in terms of target volume (homogeneity index [HI]; conformity index [CI]; gradient index [GI]) and sparing of organs at risk (OARs).

Results:

The study found that HA and VMAT plans exhibited similar PTV and GTV dose coverage. There was no significant difference in CI and GI for VMAT and HA plans, while the study found a significant difference in HI in favor of HA plans. With the HA technique, the volume of brain minus PTV receiving 10 Gy was reduced by 36%, compared to the VMAT technique. A significant difference was found between the maximum dose values of the brain,