Image-mode performance characterisation of a positron emission tomography subsystem designed for Biology-guided radiotherapy (BgRT)

Abstract

Objectives: In this study, we characterize the imaging-mode performance of the positron emission tomography (PET) subsystem of the RefleXion X1 machine using the NEMA NU-2 2018 standard. Methods: The X1 machine consists of two symmetrically opposing 900 arcs of PET detectors incorporated into the architecture of a ring-gantry linear accelerator rotating up to 60 RPM. PET emissions from a tumor are detected by the PET detectors and used to guide the delivery of radiation beam. Imaging performance of the PET subsystem on X1 machine was evaluated based on1 sensitivity of the PET detectors,2 spatial resolution,3 count-loss performance,4 Image quality, and daily system performance check. Results: PET subsystem sensitivity was measured as 0.183 and 0.161 cps/kBq at the center and off-center positions, respectively. Spatial resolution: average FWHM values of 4.3, 5.1, and 6.7 mm for the point sources at 1, 10, and 20 cm off center, respectively were recorded. For count loss, max NECR: 2.63 kcps, max true coincidence rate: 5.56 kcps, and scatter fraction: 39.8%. The 10 mm sphere was not visible. Image-quality contrast values were: 29.6%, 64.9%, 66.5%, 81.8%, 81.2%, and background variability: 14.8%, 12.4%, 10.3%, 8.8%, 8.3%, for the 13, 17, 22, 28, 37 mm sphere sizes, respectively. Conclusions: When operating in an imaging mode, the spatial resolution and image contrast of the X1 PET subsystem were comparable to those of typical diagnostic imaging systems for large spheres, while the sensitivity and count rate were lower due to the significantly smaller PET detector area in the X1 system. Clinical efficacy when used in BgRT remains to be validated. Advances in knowledge: This is the first performance evaluation of the PET subsystem on the novel BgRT machine. The dual arcs rotating PET subsystem on RefleXion X1 machine performance is comparable to those of the typical diagnostic PET system based on the spatial resolution and image contrast for larger spheres.

First-Year Experience of Stereotactic Body Radiation Therapy/Intensity Modulated Radiation Therapy Treatment Using a Novel Biology-Guided Radiation Therapy Machine

“… 1 , 2 The X1 system consists of an 85 cm O-ring gantry linear accelerator (linac) rotating at 60 rpm, a fan-beam kilovoltage computed tomography (kVCT) for image guidance of intensity modulated radiation therapy (IMRT) and stereotactic body radiation therapy (SBRT), and PET for real-time tumor tracking for biology-guided radiation therapy (BgRT). 3 The linac consists of a 6 MV flattening filter-free photon beam, a binary multileaf collimator (MLC) with 64 leaves, and 2 pairs of jaws located above and below the MLCs. The width of an MLC leaf is 6.25 mm at isocenter (85 cm from the source).…”

Commissioning of a novel PET‐Linac for biology‐guided radiotherapy (BgRT)

“…The beam commissioning of the RefleXion X1 for intensity-modulated radiotherapy (IMRT)/stereotactic body radiotherapy (SBRT) was evaluated by Han et al 8 and the small field measurements and Monte Carlo simulations were performed by Shi et al 9 The treatment planning system was evaluated previously for IMRT and SBRT 10,11 and for BgRT. 12 The PET system characterization, calibration and quality assurance of RefleXion X1 was previously reported by Hu et al 13 where NEMA NU2-2018 standards were used to assess the PET image sensitivity, spatial resolution, scatter, count normalization, and image quality, in addition to the results of the daily PET quality assurance results. The PET subsystem sensitivity for X1 was measured at 0.183 and 0.161 cps/kBq at the center and off -center positions, respectively.…”

Evaluation of fan-beam kilovoltage computed tomography image quality on a novel biological-guided radiotherapy platform

“…A recently designed radiotherapy platform has incorporated an on-board kV fan-beam CT (kVCT) and Positron Emission Tomography (PET) system into a ring-shaped gantry that can provide both anatomical and functional images [8] . A few studies on this novel radiotherapy platform have been reported regarding the initial machine commissioning [9] , the characteristics of the PET imaging system performance [10] , treatment planning experiences [11] , [12] as well as a detailed clinical workflow for using this system for biology-guided radiotherapy [13] . However, the imaging performance of the kVCT system has not been investigated.…”