ESTRO 2023 - Abstract Book

S1499

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ESTRO 2023

Tab.1: dose rescaling factors.

Conclusion The O4D and OSL film allow fast-in-time acquisitions in contrast to EBT3 films. The O4D has the lowest krescale and 1 σ and can be used for 3D dose measurement. On the other side, the OSL system has the highest resolution (0.1mm) followed by EBT3s (0.175mm) and can be used for mm-target s after the development of an accurate calibration. The three detectors, when used for high dose PSQA, showed an agreement score >91%.

PO-1778 Validation study for multiple mets radiosurgery using RTsafe Encephalon3D gel dosimetry

A.H. Mroue 1 , A. Saplaouras 1 , H. El-Shaer 2 , R. Slade-Carter 1 , M. Younes 1 , V. Mahalwar 1 , P. Laycock 1 , G. Kataitzakis 3

1 GenesisCare, Medical Physics, Oxford, United Kingdom; 2 GenesisCare, Medical Physics, Oxfrod, United Kingdom; 3 RTsafe, Medical Physics, Athens, Greece Purpose or Objective Accurate delivery is crucial in radiosurgery and is challenging in multiple Mets treatments, especially for small lesions distant from the isocentre (see figure 1 below). The aim of this study is to validate and measure the accuracy of dose delivery on Elekta’s Versa-HD equipped with the ExacTrac Dynamic (ET-D) imaging system. The measurements were evaluated using gel dosimetry.

Figure1: Demonstration of positions and sizes of PTVs

Materials and Methods The treatment plan was produced for the RTsafe Encephalon3D head phantom CT data set filled with gel using our BrainLab's Elements (EL) TPS, also an initial T2 sequence MR-imaging was performed using our 1.5T MR-scanner. The plan was delivered according to our clinical workflow for both systems. The single isocentre plan treated 6 spherical PTVs (the maximum distance between PTVs is 10cm) and was optimized using the MultipleMets module. Table 1 lists the diameter d (cm), the volume V (cc), the distance D (cm) from the geometric center, and the conformity and gradient indices for a prescription of 8 Gy to the 70% isodose line (IDL). The plan used 5 couch angles with 10 arcs with a PTV coverage range of 99-99.1% for all Mets. After initial setup, corrections were applied at each couch angle using the ET-D imaging system. The irradiated phantom was MR scanned within 48hrs of irradiation time in order to reconstruct the dose cube using a set of T2 sequences on the same MR scanner. The estimated dose matrices were registered rigidly with the CT sim scan. To compare the geometric accuracy of the irradiations, we estimate the offset (mm) between the geometric centers of the planned and delivered 100% IDL.