The PSM used in the Barnes publication is based upon a simplified version of the Greer Used PSM‐corrected EPID imaging as an absolute measure of wide field beam symmetry as a means of photon beam angle steering. Both the Yaddanapudi and Cai studies were based upon an adaptation of the Boriano method The focus of that study was to demonstrate that PSM‐corrected EPID imaging could provide consistent profiles for matched linacs. The study of Cai et al.Īlso looked at QA applications of PSM‐corrected EPID images. This study also suggested that the method could be used for beam symmetry evaluation, although no assessment of symmetry was presented. The study used changes in the flatness of the beam profile as measured using PSM‐corrected EPID imaging as a measure of beam energy. Utilized PSM‐corrected EPID images for linac acceptance testing purposes. Three studies have been published which examined the utilization of PSM‐corrected EPID images for linac QA purposes. The PSM is analogous to the array‐type calibrations used in commercial 2D‐array detectors to correct for response differences between individual detectors. Who named this new calibration procedure the pixel‐sensitivity‐map (PSM). Such a calibration procedure was first attempted by Greer As such, the flood‐field correction represents a major current limiting factor to the use of EPID for dosimetry and QA applications.īecause of the problems associated with the EPID flood‐field calibration for QA applications a number of authors have attempted to develop alternate EPID calibration procedures where the non‐uniformity of the imager response is corrected without disturbing the non‐uniformity of the incident beam. However, correcting out the non‐uniformities introduced by the beam is problematic for many linac and patient quality assurance (QA) applications because the beam non‐uniformities (i.e., profile shape) are the information required for investigation. This is standardly achieved via the flood‐field calibration procedure. As such, correcting out the non‐uniformities introduced by the beam and those introduced by the EPID panel itself are required. For such applications, the image non‐uniformities caused by the patient anatomy in the beam are of interest. Go through the portal and proceed to the disassembly area.The amorphous silicon (aSi) electronic portal imaging device (EPID) was designed for patient positioning applications. Put the same portal from the roof to the wall facing the door. Use the second Faith Plate to get on the Light Bridge. Place the other portal on the roof, so that it's in front of the Faith Plate. Use the Aerial Faith Plate.įollow the Light Bridge and fire a portal on the end panel. Put the other portal on the panels just above the Goo. Place a portal on the panels near the ceiling where the Light Bridge ends. Go to the checkpoint and to the next room. Proceed to go through the portal and to the area with the Safety Cube receptacle. Walk to your portal, turn around, and place a portal on the panels near the ceiling.

Shoot a portal on the panels where the Light Bridge ends after going through the portal. Go through the portal under the Edgeless Safety Cube dispenser.Įnter through the portal and use the switch. Contents Mechanicsįire a portal on the wall next to you and to the 3rd panel to the right of the Switch next to the Hard Light Bridge.

The second room is the first Co-op chamber that requires the use of a vertical Light Bridge and in addition use the Faith Plate at the same time. Get the Edgeless Safety Cube by using the Light Bridge and then use the same Light Bridge to reach the exit. The first room is pretty straight forward.

Pixel 3 portal 2 images