ESTRO 2023 - Abstract Book

S1643

Digital Posters

ESTRO 2023

PO-1897 Dosimetric impact of cardiac motions for CyberKnife stereotactic arrythmia radioablation

J. Bellec 1 , L. Lemaire 2 , L. Rigal 2 , R. Martins 2 , R. De Crevoisier 3 , A. Simon 2

1 Centre Eugene Marquis, Department of Medical Physics, RENNES, France; 2 Univ Rennes, CHU Rennes, CLCC Eugene Marquis, Inserm, LTSI , UMR 1099, Rennes, France; 3 Univ Rennes, CHU Rennes, CLCC Eugene Marquis, Inserm, LTSI , UMR1099, Rennes, France Purpose or Objective To evaluate the ability of proactive beam delivery synchronization of CyberKnife in presence of cardiorespiratory motions. Materials and Methods A Quasar respiratory motion phantom (ModusQA Inc) containing a homogeneous moving film cassette insert with a virtual CTV and 3 fiducial markers was placed on a Quasar respiratory motion platform (ModusQA Inc) for simulating different combinations of cardiac (Cx) and respiratory (Ry) motion amplitudes with x ranging from 0 to 15 mm and y ranging from 5 to 15 mm. Treatment plans were optimized in Precision v3.2 (Accuray Inc.) treatment planning system (TPS) and delivered on a CyberKnife M6 equipped with an Incise2 MLC (Accuray Inc.). For each cardiorespiratory combination, two PTV were designed: a PTV equal to the CTV (PTV=CTV) and a PTV encompassing the whole cardiac excursion of the CTV (PTV=ITV_card). All treatment plans were optimized to ensure an optimal conformality of the prescription isodose line to the PTV (new conformality index = 1.1), and were delivered using the Synchrony respiratory tracking system (Accuray Inc). Delivered dose distribution was measured with EBT-XD Gafchromic film (Ashland Inc) which was placed into the film cassette insert. For PTV=CTV, the measured dose was compared to the calculated TPS dose in the film plane by performing a gamma index analysis at 3%/1.5 mm criteria. Evaluation of target coverage (TC) which was defined as the proportion of CTV encompassed within the prescription isodose line level on the film plane were evaluated for both PTV=CTV and PTV=ITV_card. Additionally, the Synchrony model generated during treatment plan delivery was compared to the effective motion of the CTV. Results Gamma passing rate and TC are reported in Table 1 and Table 2, respectively. When using PTV=CTV, the mean gamma pass rate over the evaluated respiratory motion amplitudes was 97.9%, 95.5%, 69.9% and 37.7% for C0, C5, C10 and C15 respectively; and mean TC over the evaluated respiratory motion amplitudes was 99.5%, 99.2%, 97.1% and 83.0% for C0, C5, C10 and C15 respectively. When using PTV=ITV_card, TC was systematically higher than 99% in any combinations. For all cardiorespiratory motions, the CTV motion modelled by the Synchrony tracking system during beams delivery was consistent with only the respiratory component of CTV motion.