Field QA Tool

Correct alignment of the light field with the radiation field is vital for reliable treatment setup.  Using the X-Lite, the check is performed with more convenience than ever, using no film, no cables and no connectors.

The X-Lite is a fluorescent plate for visualizing the accelerator radiation field directly on the treatment table.  The plate is activated by ionizing radiation, producing a green fluorescence which is clearly visible and lasts for a few minutes after the radiation ceases to allow sufficient time to examine the coincidence of radiation field to the collimated light field.  The 23 x 23 cm active area is permanently marked with 5 x 5, 10 x 10, 15 x 15 and 20 x 20 field scales in centimeters.

A protective orange filter prevents undesired activation of the phosphor by the light field from the gantry head or by ambient lighting.  Irradiation photons and electrons penetrate the filter to activate the phosphor within the plate.

Using the X-Lite is easy, and alignment checks can become a part of the daily QA routine.  With the filter in place, the light field is collimated to the scale on the X-Lite.  Any build-up material is added on top of the plate and the exposure is made.  Upon irradiation, the light filter is removed and the fluorescence of the X-Lite is checked for radiation field alignment.  It is not necessary to wait for the afterglow to fade between irradiations, since the contrast is high as long as the following dose is the same or higher.

The radiation beam should coincide with the light field to within ±2mm on each side at the normal SSD.

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