Performances evaluation of a PET/CT device for treatments virtual simulation in radiotherapy

Abstract

Introduction The Big Bore PET/CT is the model which offers the widest opening of tunnel (a diameter of 85 cm) due to the absence of external septa. The use of bulky restraint systems like those used in radiotherapy is possible. Therefore the Big Bore is presented like the PET/CT dedicated to virtual simulation of radiation treatment. Few studies have been conducted on performances evaluation of the PET/CT Big Bore. Besides, none bears to pay particular attention to the absence of external septa. The purpose of this study is to compare the Big Bore performances to the standard model TF 16, used as a reference in this work, to assess the impact of the tunnel enlargement on the quantification and the target volumes definition in radiotherapy. Meanwhile, this study offers to carry out new tests, more specific to the characteristics of the PET/CT Big Bore. Material and methods The Big Bore is composed of 28336 crystals of 4 × 4 × 22 mm 3 Cerium doped Lutetium Yttrium Orthosilicate (LYSO) spread over 44 rings of 90 cm diameter. Wide bore opening is 85 cm. The axial (〚FOV〛_ax) and transverse (〚FOV〛_tr) fields of view axial are 18 cm and more than 67.6 cm, respectively. It doesn't have any septa and can operate in 3-dimensional (3D) mode. The coincident window width is 3.8 ns. The energy is greater than 440 keV. The electronic system allows using the Time Of Flight (TOF). The CT scanner is the Brillance 16 slice. In comparison, PET/CT Gemini TF 16 has same characteristics except a wide bore opening of 70 cm because of presence of external septa of 7.5 cm. The performances of both PET/CT are evaluated using ‘‘classical” experiments found in literature: the NEMA NU 2-2007 Protocol, measurement of intrinsic radioactivity from LYSO and evaluation of temporal and energy resolutions. The original experiment, created for this work, consists on assessment of an external radioactivity source influence, over multiple distances, on the image quality of test phantom. Results The preliminary results of the first experiment underline that the absence of external septa has an influence on the image quality. Carrying out other experiments would permit to characterize the phenomenon in depth. Conclusion This study proposes the performances evaluation of the Big Bore. Results of the different experiments are being processed and will be presented.