Room: Track 1
Purpose: Electronic portal imaging devices (EPIDs) lend themselves to beams-eye view clinical applications, such as tumor tracking, but are limited by low contrast and detective quantum efficiency (DQE). We characterize a novel EPID prototype utilizing multiple layers and investigate its suitability for clinical use.
Methods: A prototype multilayer imager (MLI) was constructed utilizing four conventional EPID layers, each consisting of a copper plate, Gd2O2S:Tb (GOS) phosphor scintillator, and amorphous silicon flat panel array detector. We measured the detector’s response to a 6MV photon beam with regards to modulation transfer function, noise power spectrum, DQE, contrast-to-noise ratio (CNR), signal-to-noise ratio (SNR), and dose response linearity. Measured values were compared between the MLI’s top layer only (analogous to Halcyon’s EPID), all four layers of the MLI, and a standard Varian AS-1200. Pre-clinical imaging was done on an anthropomorphic phantom using actual patient VMAT fields. Acquired images were used to assess the detector’s CNR, SNR and spatial resolution in a clinical environment. Patient data acquired in a pilot clinical study assessed image quality improvements. Images obtained from spine and liver patient treatment deliveries were analyzed to verify expected CNR/SNR improvements.
Results: The MLI has a DQE(0) of 9.7%, almost 6 times the reference AS-1200 detector. Improved noise performance largely drives the increase. Resolution of the 4-layer configuration was similar to single-layer. In the clinical data, the CNR/SNR of the 4-layer configuration was twice that of the single-layer images, and three times greater than the reference imager, as expected from the phantom experiments.
Conclusion: A novel MLI was characterized and tested under preclinical conditions prior to clinical translation. The MLI substantially improved DQE and CNR performance while maintaining resolution. Pilot patient data were analyzed, confirming improved CNR/SNR during clinical acquisition. Clinical applications are anticipated to include accurate soft tissue tracking and high-quality, low-dose MV-CBCT.
Funding Support, Disclosures, and Conflict of Interest: NIH/NCI R01CA188446
Electronic Portal Imaging, Megavoltage Imaging