Daily Morning QA Guide

This will be a guide on how to perform the daily QA for the Elekta Synergy machine, though some steps may apply for other machines.

Place a bubble level on the gantry, and set the gantry such that the bubble indicates the appropriate level for 90°. Position another bubble level on the gantry to check for the collimator, and set the collimator such that the bubble indicates the appropriate level for 0°. Leveling the collimator may unlevel the gantry, thus, adjust the gantry and collimator in combination to find the sweet spot where both become appropriately leveled. With the collimator at the mechanical angle of 0°, rotate the gantry back to its mechanical 0° position as well.

The steps mentioned previously would be the exact procedure to perform before beginning to test for variables. However, if the gantry and collimator angle indicators typically differ minimally from the actual, omitting the leveling and using only the indicators may be sufficient. Additionally, when aligning a phantom to the isocenter, it should be done by using the crosshairs of the light field and the front pointer. However, if the room lasers typically differ minimally from the mechanical isocenter, aligning a phantom using only the room lasers may be sufficient.

Place the Daily QA 3 phantom on the table, and align its crosshairs with the crosshairs of the light field. Set the front pointer to 100 CM SSD, and raise the couch until the surface of the phantom barely comes into contact with the tip of the front pointer. Check the ODI and the room lasers that they are both within tolerance (distance indicator (ODI) @ iso for non-IMRT, IMRT, and SRS/SBRT: 2 mm, 2 mm, and 2 mm); (laser localization for non-IMRT, IMRT, and SRS/SBRT: 2 mm, 1.5 mm, and 1 mm). Set the field size to 20 x 20 CM, and check that the light field matches with the etchings of the phantom (collimator size indicator for non-IMRT, IMRT, SRS/SBRT: 2 mm, 2 mm, and 1 mm).

Perform an output verification for photon energies of 6 MV and 18 MV daily, and electron energies of 6 MeV, 9 MeV, 12 MeV, 15 MeV, and 20 MeV weekly (x-ray output constancy (all energies): 3%); (electron output constancy (except for machines with unique e-monitoring requiring daily): 3%). Check that the beam on indicator and radiation monitor are functional as the outputs are checked for (beam on indicator: functional); (audiovisual monitor(s): functional). Additionally, open the vault door while the beam is on to check that the beam shuts off (door interlock (beam off): functional). As the vault door closes, create a motion within the range of the door’s proximity and/or pressure sensors to check that the door reopens (door closing safety: functional). Check that the treatment couch can be seen and that sounds within the treatment room can be heard from console via the audiovisual system (audiovisual monitor(s): functional). Though stereotactic interlocks are not checked for the Elekta Synergy, check to see that interlocks clear such as when the correct stereotactic applicator is placed correctly in the tray (stereotactic interlocks (lockout): functional).

Remove the Daily QA 3 phantom, and mode up a field with a picket fence MLC pattern. Deliver this beam to the EPID imager, and visually look for deviations (qualitative test (i.e., matched segments, aka “picket fence”: visual inspection for discernible deviations such as an increase in interleaf transmission). Mode up a field with a wedge, and check that there are no interlocks (morning check-out run for one angle for universal: functional).

Re-enter the room, and gently depress the cover on the EPID, imaging detector, and source housing to check that machine interlocks are functional (collisional interlocks for non-SRS/SBRT and SRS/SBRT: functional and functional).

Place the Winston Lux-Quality Assurance (WL-QA) cube on the table, and align the smaller, offset crosshairs to the isocenter by using the crosshairs of the light field. An alignment by this method will result in measurements that are independent of the room lasers. Acquire an AP and a lateral MV image, and perform a 2D/2D match via the imaging software. Check that the couch shifts are within tolerance compared to the known offsets (positioning/repositioning for non-SRS/SBRT and SRS/SBRT : ≤ 2 mm and ≤ 1 mm). Allow the imaging software to perform the couch shifts to reposition the WL-QA cube. If desired, reenter the room to confirm that the central crosshairs of the WL-QA cube are in alignment with the crosshairs of the light field. Take another AP MV image, and see that the center of the sphere in the WL-QA cube agrees with the isocenter defined by the graticule of the imaging software (imaging and treatment coordinate coincidence (single gantry angle) for non-SRS/SBRT and SRS/SBRT : ≤ 2 mm and ≤ 1 mm). Repeat the following procedure for planar kV and CBCT imaging.

Related Content:

Basic IMRT QA/Portal Dosimetry Guide
Electron Cutout Calibration Walkthrough
Monthly Mechanical QA Guide
Machine Specification Guide