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Appendix III.

Simulator’s monthly check

Date: __

The simulator must be in default position (gantry at 0°, collimator and couch at 0°, 10 x 10 cm2 field sizes, 100 cm FAD and SSD) for the examination. Lead collimators are set 52 cm x 52 cm. Settings on mechanical scale.

1. Set SAD=100 cm!

Check the 100 cm SAD sign on the gantry, if it is consistent with the value measurable from the reference point given on the cover (usually a focus sign must be on the outside cover of the X-ray tube). Metal ruler or metal tape measure should be used for this measurement. (It cannot be measured on Siemens simulators)

2. Check of the optical distance indicator (range-finder) by using the mechanical pointer

The integrity of the mechanical front pointer set must be checked visually before using. A minimal curvature can be accepted.

Is mechanical pointer all right? YES/NO

For the examination the immobilization device of the pointer should be sliced on block tray.

Place the graph paper on the couch in default simulator position (10 x 10 cm2 field and main planes marked on it). If it is possible (It is not possible by Siemens simulators) the 80 cm pointer should be used first. Set the couch just to touch the pointer. Turn on the optical distance indicator, and read the result. If it is not accurate, the couch height must be changed until the optical range finder shows the right value. Than replace the mechanical pointer, calculate the difference. The method must be repeated at SAD=110 cm and at least SAD=100 cm as well. The values of in room monitors are shown in the table. If SAD=80 cm can’t be set, then use the SAD=120 cm instead. Tolerance values are ±2 mm. (An example is given below)

3. Couch isocentre

Settings are the same as above. Fix graph paper on the couch marking the field center. Initial values: SAD=100 cm, couch angle=0°, set on mechanical scale! Set the crosswires to coincide with the fields axis on the graph paper, and read the couch angle written on readout. The couch should be rotated at 270°, and at 90° by the mechanical scale and the difference between the crosswires and the cross on graph paper should be noticed. Notice the in room monitor value as well. (Comment: The position of the crosswires does not change, only the couch should be moved.)

4. Collimator symmetry and isocentre position

Set the gentry angle 90°, than set the collimator angle at 0° by using a spirit level. Set SAD=100 cm at MedTec IAD-1 tool and set the crosswires to cover the crosses of the tool to sign principal planes. Instead of this a 30 x 30 x 20 cm3, Plexiglas box with opened bottom can be used as well. Graph paper (with symmetry axis, marked principal planes and field size, e.g. 10 x 10 cm2 on it) are fixed on the sides of the plexi box. (“Patient phantom”)
Write the digital values of collimator angle in the table. This must be repeated at 90°, 180° and 270° collimator angle as well. Tolerance values are ± 1mm and ±1°.

Set the gantry to 0°again, use spirit level! Set the collimator to 0° based on digital readout. Set the crosswires to cover the crosses of the tool to sign principal planes! Notice the differences of the above two crosses at 0°, 90°, 180° and 270° angles.

5. The mechanical check of gantry’s isocentre

The examination can be performed by MedTec IAD-1 tool, or a 4 cm edge cube. In case of MedTec tool SAD=100 should be set, in case of cube SAD=98 cm should be set. The collimator angle should be 0°. To set the SAD use mechanical pointer, the gantry should be set at 0° by spirit level! The crosswires should cover the cross of the testing tool! Notice the gantry angle on the mechanical and digital scale! Repeat the measurements at 90°, 180°, 270° gantry angle and keep rotated further till 180°! To set the angle use spirit-level! In addition to this, measure the difference between the two crosses at 90° and 270° gantry angle.

6. Examination of the laser settings

Set the gantry at 0° angle by spirit level! The crosswires should cover the cross on the 4 cm edge cube!

Checks of the settings at isocentre

Rotate the gantry by e.g. 90° to check the laser on ceiling! To check the side and sagittal lasers rotate the gantry to default position! Tolerance value is ± 1 mm.
The same examination can be performed by MedTec IAD-1 tool as well. The plate with signs must be rotated in suitable direction.

Control of the settings on the patient

Use the “Patient phantom”! The cross marking on phantom should be coincide with crosswires. The coincidence of crosses and lasers can be checked. Tolerance values are ±1 mm.
By using the MedTec IAD-1 tool: after setting the above the plate with the markers it should be in a suitable direction. By moving to left and right by 15 cm and up and down (in case of Siemens simulator only down) the laser cross should coincide with the cross of the tool within tolerance values.

7. Isocentre of the gantry on fluoroscopy system

Set the optical distance indicator to 100 cm on the surface of the MedTec IAD-1 and the crosswires should be covered with the sign of the principal plane of the tool. From the shielded place expose two 70 kV/400 mAs to warm the simulator up, than use the fluoroscopy system! Move the couch that the shadows of the crosswires coincide with the centre of field. Set the plate of the tool to upright carefully, set the gantry angle at 90°, and move the couch up and down to have no difference between the shadow of crosswires and the cross of the tool. The cross is in the isocentre determined by source. Set the gantry to 270° and 180° (rotate the plate with it), the shadow of crosswires should remain in the centre of the field of the examination tool. Tolerance value is ± 2 mm. After examination gantry should be set at 0° angle. The examination can be performed by using the 4 cm edge cube as well, if every cross has a steel pellet in itself. The SAD must be 98 cm by using cube, everything else is the same.

8. Laser alignment

The examination can be performed by using the 4 cm edge cube and MedTec IAD-1 tool as well. Tolerance value is ± 1 mm.

9. Optical field examination

Set the simulator at “default position”! The 5, 10, 20 and 30 cm fields can be examined with the graph paper in appropriate size. The field size should be set on the digital readout. The adjusted and optical field sizes must be within ± 2 mm.

Field defining wires

Comments: The notation can be different depending on the manufacturer. The DICOM uses the scale of IEC. Some data:

Lead plates

Set the gantry at 90° angle, SAD should be 100 cm. The examination tool should be the MedTec IAD-1 or the above mentioned box standing on its edge. The crosswires should cover the cross of the examination tool. The tolerance value is ± 2 mm in case of 5, 10 and 20 cm quadratic fields.

10. Field lighting

The examination should be performed by maximum field size. A blank paper is enough for the qualitative examination, but naturally graph paper can be used as well. The maximal field size based on digital readout (by Siemens simulator) is 5,20.0 cm x 5,20.0 cm ± 0.2 cm.

Notes, comment, round of the duties (enough space)


Closing comments

According to Appendix I. hard copy is needed at monthly QA check. If the machine is equipped with appropriate software (and it is on the network), than the image of the image intensifier can be sent, stored, evaluated or printed. For the more rigorous annual tests film should always be used. Appendix III. must be completed with the right instruction. The QA of image intensifier chain is discussed in the suitable chapter.

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